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Preparation, Stabilization and Applications of Nano-Zero-Valent Iron Composites in Water Treatment

Yan Xu , Chungang Yuan

Progress in Chemistry ›› 2022, Vol. 34 ›› Issue (3) : 717 -742.

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Progress in Chemistry ›› 2022, Vol. 34 ›› Issue (3) : 717-742 DOI: 10.7536/PC210232
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Preparation, Stabilization and Applications of Nano-Zero-Valent Iron Composites in Water Treatment
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Abstract

Nano zero-valent iron (nZVI/Fe0) has attracted tremendous attentions for its excellent catalytic activities and economic applicability. However, tendency to agglomeration and instability normally limit its practical applications. In recent years, a series nZVI composites and/or stabilizers have been fabricated to address the above-mentioned issues with great promotion in preparations, substrates and applications. This review summarized and discussed the related studies on loading methods, stabilizing approaches and aqueous environmental applications in recent five years. The comprehensive reviews and prospects about nZVI composites are discussed from three main aspects: (1) the support frames including polymers, clays, carbons and metal oxides; (2) the new achievements of bimetal/multimetals, surface coating and vulcanizationfor composite stability; (3) the removal of heavy metals and organic pollutants through adsorption, reduction, complexation, co-precipitation, electrochemical reaction, (quasi) Fenton oxidation and other processes, and treatment promotion by the introduction of light, heat, electricity, ultrasound, and microwave.

Contents

1 Introduction

2 Composites of nano zerovalent iron

2.1 Organic polymer carriers

2.2 Inorganic mineral carriers

2.3 Carbon material carriers

2.4 Metallicoxide carriers

2.5 Comparisions of various carriers

3 Stabilization of nano zero valent iron particles

3.1 Vulcanization

3.2 Binary or multi-elements metal nanoparticles

3.3 Surface coating

3.4 Stabilizers contrast

4 Applications

4.1 Removal of metal ions

4.2 Removal of organic pollutants

5 Conclusion and prospects

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Keywords

nano-zero-valent iron / modification / water treatment / composite materials

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Yan Xu, Chungang Yuan. Preparation, Stabilization and Applications of Nano-Zero-Valent Iron Composites in Water Treatment. Progress in Chemistry, 2022, 34(3): 717-742 DOI:10.7536/PC210232

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1 Introduction

Nanoscale zero-valent iron (nZVI) has potential advantages in wastewater treatment and groundwater remediation due to its comparable activity, high specific surface area and economic applicability to precious platinum-based catalysts. Pilot projects have been carried out in Taiwan, Ontario, Canada and Florida, USA. Some cases are briefly summarized in Table 1[1⇓~3][4][5][6]. In general, nZVI can efficiently remove heavy metals, endocrine disruptors, chlorinated organic compounds, polycyclic aromatic hydrocarbons and nutrients in water through adsorption, reduction, complexation, precipitation and Fenton-like oxidation processes to improve water pollution[7][8][9][10][11,12].
However, the surface oxide layer is inevitably formed during the preparation and storage of nanoscale zero-valent iron, which causes a "hysteresis effect" in the early stage of pollutant removal[13]. In the reaction process, the excessive corrosion products will cover the active sites, and the insulating products such as lepidocrocite will block the electron transfer, and eventually promote the passivation of zero-valent iron[14]. Due to the influence of nanometer effect and self-magnetism, nZVI molecules have high Van der Waals force and attractive force, so they are easy to aggregate and the surface activity is reduced[15]. After the reaction, the residual ultrafine powder is difficult to be completely recovered, the excited ROS can promote lipid peroxidation, and the nZVI penetrating the cell membrane can cause the loss of cell structure and function, and has potential toxicity[16][17].
In order to improve the application of nZVI, it is necessary to optimize the dispersion and recycling of nZVI, and the dispersion and recycling of nanoscale zero-valent iron can be solved to a certain extent by compounding different frameworks[19][18⇓⇓~21]. The polymer supports improve the dispersion of particles by increasing the steric hindrance effect. Chemical bonding, Van der Waals force and electrostatic interaction are the main ways to achieve particle loading[18]. Clay minerals are usually used as carrier materials because of their low cost, good stability, strong ion exchange performance and adsorption capacity[19]. The carbon material, especially the biochar material, can disperse the nano zero-valent iron and retain the pore structure of the carbon material[20]; The self-reactivity of the oxide support can be further improved after the nano zero-valent iron is loaded and doped[21].
Surface sulfurization, metal doping and surface coating are all effective ways to improve the stability and dispersibility of particles. Surface sulfidation is the formation of iron sulfide on the surface of nZVI by introducing sulfiding agent, and the sulfur component can promote the electron transfer of Fe0 to the catalytic target. The surface hydrophobicity of the nano zero-valent iron after vulcanization is increased, the affinity of the nano zero-valent iron to hydrophobic organic pollutants in the water body is increased, and the selectivity and the reaction activity are improved; Sulfidation can also reduce the reaction between Fe0 and water, inhibit the release of hydrogen, and make the electrons generated easier to transfer to pollutants[22]. Metal doping can accelerate the electron transfer and promote the reaction. The metal with higher activity than iron mainly acts as electron donor to slow down the oxidation of nZVI; Noble metals with low activity, such as palladium (Pd), platinum (Pt) and gold (Au), are mainly used as hydrogen acceptors to accelerate the reductive degradation of pollutants. Precious metals are mostly in the form of active metal hydrides in the reaction, and diatomic dissociation reactions can occur[23]. After coating the surface of nanoscale zero-valent iron, the surface charge of the particles changes, the electrostatic attraction decreases, and the agglomeration behavior decreases[24]. Surfactants, negatively charged polymers and biopolymers have been widely used as coating materials.In recent years, biopolymers have been studied extensively and deeply, which are often bonded to the surface of nZVI through carboxyl, hydroxyl, amino and other functional groups, and have high stability and biocompatibility[25,26].
In the past five years, some progress has been made in the preparation, stabilization methods and environmental applications of nanoscale zero-valent iron composites.In this paper, these research results are summarized and reviewed to provide a reference for the preparation, stabilization methods and practical applications of nanoscale zero-valent iron composites.

2 Preparation of nanoscale zero-valent iron composites

Nanometer zero-valent iron particles are easy to agglomerate under the action of nanometer effect and self-magnetism. In the past five years, organic polymers, inorganic minerals, carbon materials and metal oxides have been fully studied as nano-zero-valent iron carriers.

2.1 Organic polymer carrier

Organic carriers can be divided into two types: monomeric and polymeric. Monomers include synthetic polymer materials (such as polyaniline, polyacrylonitrile, etc.) And natural polymer materials (starch, humus, etc.)[29][30][31][32]. The zero-valent iron nanoparticles can be loaded on different carriers by two methods of in-situ preparation and post-loading. Nanoparticles are combined with the carrier through Van der Waals force, electrostatic attraction, hydrogen bonding and chemical bonding. Monomer carriers are mostly presented in the form of membrane materials, and some of them exist in the form of rigid materials (such as carboxylated cellulose nanocrystals)[33]. Cation exchange resins, polymeric anion exchangers, MOF, COF are also used as carriers[34][35][36][37]. In addition, electrospinning technology can also realize the in-situ synthesis of sponge-like zero-valent iron on three-dimensional nanofiber networks, which provides a new idea for the research and development of materials and the application of nano-zero-valent iron in the future[38].
The polymer obtained by crosslinking a plurality of organic polymers can be further used as a carrier to prepare the nano zero-valent iron composite material, so that the carrier is derived to have excellent performance which the monomer does not have. Aft that PAA and the PVA are crosslinked, the water-soluble carry has water resistance, and the ferric ions are complexed and reduce with the carboxyl of the PAA, so that the nano zero-valent iron particles are stably loaded on the carrier, and high surface area volume ratio, high porosity and good reusability are maintained[39]. pH-responsive poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) membranes were successfully prepared by asymmetric polymerization. In addition, layer-by-layer coating and grafting techniques were also successfully used to prepare nanoscale zero-valent iron composites[40][41][42]. In addition to the above synthetic polymers, some commercial materials such as filter paper can also be used as substrate materials and achieve better results[43]. Table 2 lists the methods and effects of preparing composite materials with polymer as the carrier in recent years. The nZVI is mainly deposited on the surface of the polymer or in the pore/fiber structure after chemical reduction, so as to realize the dispersion of nZVI load and improve the comprehensive performance of the material while retaining the advantages of the carrier material.
The preparation of single-component polymer carriers is usually relatively simple, but sometimes the stabilization effect of nano-zero-valent iron particles is difficult to achieve expectations, and the application is limited. Multi-component polymer carriers will consume more solvents in the preparation process, which will have a certain degree of impact on the environment after volatilization. Composite materials that can take into account both environmental impact and application effect are the current research focus.

2.2 Inorganic mineral carrier

Natural minerals can be used to disperse nanoscale zero-valent iron particles, and clay minerals are the most studied species in natural minerals. Clay minerals mainly include kaolin, montmorillonite, hydrated mica, vermiculite, chlorite and so on, which are hydrous aluminosilicate minerals with layered structure and abundant reserves, and have the characteristics of green, non-toxic and low price. Different kinds of clay minerals have slightly different crystal structures, morphologies and physical properties, and their chemical compositions are also different.They are usually dominated by SiO2 and Al2O3, and contain other metal oxides such as Fe and Mg. In general, clay minerals have strong adsorption and ion exchange capacity, and show good adsorption performance for various types of pollutants in water. Some clay minerals, such as montmorillonite and vermiculite, belong to swell-shrink minerals and can be replaced by isomorphous minerals, which have high cation exchange capacity. Montmorillonite has a multilayer structure, which has been widely studied in the field of water remediation due to its large specific surface area and well-developed mass transfer channels. The interlayer gap of 2 ~ 8 8 Å can provide good retention sites for iron ions, which is conducive to the dispersion of Fe0 nanoparticles in the preparation process[44]. Monodisperse nanoscale zero-valent iron can significantly improve its reduction activity to pollutants, and inorganic minerals as dispersed carriers can also protect nanoscale zero-valent iron from being occupied by dissolved organic matter (NOM) in water, thus weakening the inhibition of NOM activity[44]. The main mineral component of bentonite is montmorillonite, which is a 2:1 layered silicate clay mineral with low price and abundant reserves. It is a very promising nano-material carrier. Its high specific surface area and unique interstitial structure provide abundant binding sites for nano-zero-valent iron particles[45]. However, since the nanoscale zero-valent iron cannot be tightly combined with the inorganic mineral carrier material, the dispersed nanoscale zero-valent iron cannot be sufficiently stabilized only by the single mechanical support of the layered inorganic mineral, which may lead to shedding or re-agglomeration[46]. In recent years, lignin has attracted the attention of researchers due to its excellent physical and chemical properties, including good thermal stability, excellent oxidation resistance, good stiffness and unique three-dimensional network structure. The composite material is constructed by loading the nano zero-valent iron on the bentonite after the organosolv lignin is modified, so that the advantages of the lignin and the bentonite can be exerted; the organosolv lignin is used as a stabilizer of the nano zero-valent iron, and the bentonite is used as a carrier material to exert a synergistic effect[46]. Lignin-modified nanoscale zero-valent iron loaded on bentonite can significantly improve the adsorption and reduction capacity of the material for Cr (Ⅵ), and the reduction process of Cr (Ⅵ) to Cr (Ⅲ) is beneficial to the production of Fe-Cr co-precipitation, thus realizing the removal and reduction of Cr[46]. Clay minerals such as vermiculite and kaolinite have been used as carriers of nanoscale zero-valent iron[47][48,49]. In the past five years, the research on montmorillonite (stone), clay and bentonite has become more concentrated[44,50][51][45]. Another kind of clay mineral is attapulgite, which is a kind of water-bearing Mg-rich aluminosilicate clay mineral with chain-layered structure and channel structure. Attapulgite is negatively charged and has surface hydrophilicity. Ding et al. loaded nano zero-valent iron particles on attapulgite (ATP) carrier, and nano zero-valent iron was uniformly dispersed on the surface of attapulgite. The original regular orientation and bundle fiber morphology of ATP did not change significantly, but increased the dispersion of nZVI, thereby increasing the possibility of contact between pollutants and active sites[52]. Even if the surface of nZVI is slightly oxidized, its dispersion and reactivity will not be greatly improved. The cost of clay minerals is low, the surface area is very large, and the adsorption capacity brought by porous structure is very considerable, which provides a high possibility for particle attachment. Its low price has a certain attraction in in-situ remediation of water bodies. Because it is difficult to exist stably in water for a long time, the recovery of nano-zero-valent iron after release is extremely difficult, and the impact on the surrounding aquatic organisms is inevitable.
In addition to the above clay minerals, zeolite, as a low-cost and easily available porous material, has the advantages of large pore volume, large specific surface area and easy surface modification, and can also be used as a carrier material for nano-zero-valent iron[53,54]. The main component of natural zeolite is sodium aluminosilicate, which has a framework structure, contains exchangeable cation pores and cavities, and is a natural porous material with good adsorption, ion exchange and catalytic capacity. In addition, pumice is a porous, lightweight, glassy volcanic extrusive rock, which is also used as a dispersion carrier for nano-zero-valent iron[55]. On the basis of adopting the carrier to disperse the nanometer zero-valent iron, the pollutant removal effect of the composite material can be improved by an external magnetic field strengthening technology[54]. Table 3 lists the main methods and effects of loading nZVI with clay minerals as the carrier in recent years. The composite material is still prepared by the loading method after chemical reduction. The inorganic mineral/nZVI composite material is prepared quickly and efficiently by immersing the carrier material in iron salt solution for saturated adsorption and in-situ reduction.

2.3 Carbon material carrier

Due to its large specific surface area and rich and controllable pore structure, carbon materials have unique advantages when used as nano-zero-valent iron particle carriers. Carbon powder, activated carbon fiber, activated carbon, biochar, graphene oxide, carbon nanotubes, etc. Have been reported. Table 4 summarizes the paths and effects of traditional carbon material carriers in dispersing and stabilizing nZVI[56][57][58][59,60][61][62]. The nano zero-valent iron is load into that pore structure of the carbon material through the processes of chelation, deposition and the like, so that the nano zero-valent iron can not fall off or coat particle like a fibrous membrane material, and is difficult to play a role; Even if deposited in the deep structure of carbon materials, a large number of pores can adsorb and transport pollutant components to active sites to complete the catalytic and adsorption removal of pollutants. In general, after the catalytic reaction is completed on the surface of the support material, the degradation products will return to the solution from the pore structure, and therefore, usually will not cause deactivation of the active sites of the catalyst. Due to the good performance of carbon materials, porous carbon materials have also been used as dispersion carriers and slow-release materials of nano-zero-valent iron to avoid the aggregation of nanoparticles to the greatest extent and make the particles play a lasting role. Generally, the strength and stability of high-temperature co-assembly of iron-based materials and carbon materials are higher than that of loading or pyrolysis bonding after carbonization, which is also confirmed by the research of Wu et al. The team used phenolic resin as a template and citrate as an iron chelating agent to co-assemble with nZVI. The obtained iron-containing polymer was annealed at 600 ℃ for 3 H with nitrogen to obtain mesoporous carbon/nano zero-valent iron (MCFe) products. The synthesis process is shown in Figure 1[63][64]. In the MCFe prepared by chelating co-assembly and carbothermal reduction, the average size of nanoscale zero-valent iron particles is 12 nm and uniformly dispersed in the mesoporous carbon framework.The oxygen permeated into the pore structure produces Fe2O3·FeO thin oxide layer on the surface of nanoscale zero-valent iron particles. In addition, the nanoscale zero-valent iron particles can also serve as a catalyst for the formation of graphitic carbon structures, and finally form a unique structure in which the nanoscale graphite layer wraps the iron oxide/nanoscale zero-valent iron particles and is embedded in the mesoporous carbon skeleton. The graphite layer and mesoporous carbon layer have certain reducibility, and the thin oxide layer avoids the contact between the inner core layer and oxygen to a certain extent, which effectively reduces the probability of electrochemical corrosion and chemical corrosion, so that the core layer has extremely high air stability, and the Fe0 of the core layer can be stable for more than 20 days. The carbon material has the advantages of light weight, high strength, high thermal and electrical conductivities, high temperature resistance and chemical corrosion resistance, large surface area which can effectively disperse iron nanoparticles and limit the agglomeration of the iron nanoparticles, and ultrafine particles embedded in the framework which can maintain long-acting stability and have obvious advantages in subsequent applications. The surface properties and electron distribution of carbon materials also play a positive role in electron shuttle and accumulation of pollutants, which can effectively promote the electron transfer of target pollutants and their intermediates in the process of adsorption, desorption and catalytic degradation.
On the basis of traditional carbon materials, biochar has made great progress in recent years. Biochar is produced by pyrolyzing biomass at high temperature under oxygen-limited conditions, which has superior reactivity and stability. Biochar has abundant surface functional groups and porous structure, which has great advantages in serving as a nano-zero-valent iron dispersion carrier.Oxidants such as H2O2, O3, KMnO4, HNO3 and the like are subjected to oxidation reaction on the surface of the biochar to introduce hydrophilic oxygen-containing functional groups such as CO, COOH, OH and the like, so that the adsorption capacity of the biochar to pollutants in a water body is further improved, and internal active components can play a role better[65]. Loading nanoscale zero-valent iron into biochar can significantly improve its crystallite size and dispersion, increase the efficiency of electron transfer with target pollutants, and improve the removal effect. At present, the preparation of three-dimensional nanoscale zero-valent iron/biochar composites has been realized, but the preparation of two-dimensional nanoscale zero-valent iron/biochar composites is more simple and mature[66]. The nanometer zero-valent iron/biochar composite material can be synthesized by co-pyrolysis, fractional precipitation, ball milling, carbothermal reduction, gasification and the like[67][68][68][69][70]; Woody plants, herbaceous plants, agricultural wastes, sludge, fungi and even old cartons can be used as raw materials for the preparation of biochar[71][72][73][74][75][76]. Cetyltrimethylammonium bromide, soluble bacterial beads, etc. Can be used as modifiers to improve the performance of materials[77][78]. Table 5 summarizes the synthesis and material properties of biochar/nZVI. Diversified synthesis routes, extensive material sources, and diverse modification methods make biochar materials an active research field in recent years. In addition, in addition to the preparation of amorphous biochar, the preparation and development of biochar membranes have also been carried out[79]. According to the research of Ahmed et al., the nZVI particles in the nZVI-fBC composite are effectively dispersed, and the surface of fBC is partially covered by nZVI particles, which is rough[80]. The iron content in the composite is 7. 8%, the particle size distribution is between 190. 1 nm (22. 1%) and 220. 2 nm (77. 9%), the nZVI accounts for 92% to 95%, and the rest is oxidized to FeOOH/Fe2O3/Fe3O4.

2.4 Metal oxide support

Nano-iron provides a new and feasible technical means for the treatment of water pollutants, especially refractory organic pollutants. Nano-scale zero-valent iron particles have large specific surface area and high surface activity, and their application scenarios are flexible. However, the practical application of nanoscale zero-valent iron in remediation of polluted water is limited due to the problems of agglomeration, instability and difficult separation. Organic polymers, natural minerals and carbon material carriers are introduced above, and metal oxide carriers are discussed below.
Metal oxides used as supports mainly include Al2O3, Co3O4, MnO2, TiO2, ZnO, etc[83][84][85][86][87]. Table 6 provides a summary of the loading of nZVI. Jain and Agarwal used Al2O3 as the carrier of nanoscale zero-valent iron, which can avoid the agglomeration of nanoscale zero-valent iron[83]. Alumina has good stability and porous structure, large specific surface area and high activity under various geological conditions.As a siderophore, alumina can play a synergistic role in the process of heavy metal removal.When it is first applied to the removal of arsenic from water, the effect is good, and the adsorption capacity can reach 15.50 mg·g-1, which provides a solution to the problem of low porosity of nanoparticle packed bed. Zhao et al. prepared Co3O4 mesoporous nanocages based on ZIF-67 structure to disperse and load nano zero-valent iron particles. The FeNPs@Co3O4 nanocage composite material has peroxidase-like characteristics, shows strong H2O2 affinity, and can catalyze tetramethylbenzidine color development. Based on this, a simple colorimetric biosensing method for the determination of glucose was established[84]. Qiu et al. Successfully prepared nano-zero-valent iron /MnO2 nanowire composite membrane by in-situ chemical deposition method and used it for the separation and removal of selenium in water.The composite membrane not only has high chemical activity and excellent reusability, but also has excellent mechanical properties and ideal loose structure, which can achieve a maximum selenium retention of 95. 62% and has a certain enrichment effect on selenium-containing wastewater[85]. The Fe0/MnO2 can capture selenium on the surface of the material through oxidation-reduction reaction, and finally can realize the separation of 94.62% of selenium, and has wide prospect in the recovery of selenium. Dong et al. prepared anatase TiO2 nanoscale zero-valent iron composite material with three-dimensional laminated structure by two-step hydrothermal synthesis and liquid phase deposition method. The three-dimensional material is composed of two two-dimensional TiO2 sheets with a thickness of about 30 nm, which has high charge and hole mobility and good visible light catalytic activity[86]. Similarly, the nano composite material loaded by nano zero-valent iron and ZnO also shows better visible light catalytic ability, and the doped nZVI can also generate impurity energy levels in the valence band and the conduction band of ZnO, so that the response of the material to a low-energy light source is improved, and the oxidative degradation of organic pollutants is realized in a wider wavelength range[87]. In addition to the above metal oxides, iron oxides are also used to disperse nanoscale zero-valent iron[87⇓~89]. The unique reverse spinel structure of the Fe3O4 enables the Fe-O bond to exist in both tetrahedron and octahedron, the stabilized nanometer zero-valent iron particles are uniformly attached to the surface of the Fe3O4 and have better dispersion and larger specific surface area, and the Fe2+ and the Fe3+ in the octahedron structure can exist at the same time, thereby providing a new way for electron transfer[88]. The Fe3O4 material has strong magnetism, and the magnetism of the material after the nanometer zero-valent iron is stabilized is further increased, so that the material is easier to separate through an external magnetic field, and convenience is provided for regeneration of the material. Jonoush et al. Prepared Fe0/Fe3O4 supported on nickel foam. The surface of three-dimensional nickel foam is flat, but there are microcavities inside, which are arranged in the form of honeycomb in the form of pentagons with different sizes and slightly concave centers[89]. After depositing Fe0, the smooth surface of the nickel foam becomes rough, and the whole surface is completely covered by the nano platy material; At first, the Fe3O4 was attached to the Fe0 in the form of sheet, and after a period of time, the Fe0 and Fe3O4 gradually became spherical. Among the two crystal forms of Fe2O3, α-Fe2O3 has a significant surface effect, which is more suitable for catalysts and is also selected as the support material of nano-zero-valent iron particles[21]. The Fe0@Fe2O3 has a core-shell structure, the nano zero-valent iron particles are coated by an outer iron oxide shell layer, iron ions are adsorbed, and the nano zero-valent iron particles are oxidized to iron oxides on the surface and accumulate continuously, so that the activity of the coated Fe0 is affected during long-term use. Dissimilatory iron-reducing bacteria (DIRB, Aeromonas hydrophila HS01) can realize the continuous reduction of iron oxide and the release of Fe2+, and maintain a high activity of the reaction system[21].

2.5 Comparison of advantages and disadvantages of different carriers

To some extent, the support of nZVI can solve the problems of dispersion and recovery. As shown in fig. 2, after the carrier is adsorbed and saturated in the precursor solution, it is reduced to the surface and internal pores of the carrier by means of borohydride, hydrogen, high temperature carbonization, etc., to complete the loading process. Different carriers have different effects in the particle loading process.
Organic polymer supports often have high specific surface area, low mass density, controllable pore structure, high physical and chemical stability and thermal stability, and nZVIs are often immobilized by pore constraints, intermolecular forces and chelation of functionalized ligands to improve their dispersion. In addition, the surface of organic polymer support usually contains abundant reaction sites, which can provide improvement space for subsequent modification and application. The reconstruction of support can be carried out by modifying single ligand, ligand module and its proportion, but the preparation process is relatively complex.
During the formation of clay minerals, the phenomenon of isomorphous substitution (that is, the central ions of the mineral lattice are replaced by cations with similar properties but lower valence) often makes the surface of clay minerals negatively charged, which has a strong adsorption effect due to surface action and ion exchange. Under different hydration conditions, the expansion properties of clay minerals are different, and the pore structure will change to different degrees, which may lead to the shedding of nZVI loaded, but their high porosity, high chemical stability, strong mechanical properties and low price are widely used as nZVI carriers.
In contrast, carbon materials have the advantages of good conductivity, controllable pore morphology, good stability, good toughness and easy modification, but the preparation of carriers needs to be carried out in high temperature environment, with high energy demand and certain environmental and cost pressures.
The stability of nZVI immobilized on metal oxide supports is often improved by anchoring effect, and the acidity, alkalinity and redox characteristics of the supports can play a unique advantage in the application process. When the carrier is magnetic, it can also be separated by an external magnetic field. However, the preparation and modification processes of the support are often complex, and there are still some problems in the control of surface properties, the modification of microstructure and the improvement of stability.

3 Stabilization of Nanoscale Zero-valent Iron Particles

Nanoscale zero-valent iron needs to maintain good stability and reduce oxidation in practical applications. Surface vulcanization, metal doping and surface coating are the most common methods to improve stability.

3.1 Vulcanization stabilization

Nanoscale zero-valent iron can be easily oxidized, resulting in reduced activity and shortened service life. Partial sulfidation of nanoscale zero-valent iron can slow down the reaction between nanoscale zero-valent iron and water (hydrogen production), and overcome the above problems to a large extent. At the same time, sulfurization can also improve the selectivity of pollutants in water. The preparation of the sulfurized nano zero-valent iron can adopt a one-step method for reducing iron ions in the presence of sulfur ions, that is, sodium borohydride and sodium dithionite solution are simultaneously added into Fe2+ or Fe3+ solution for reaction; Nanoscale zero-valent iron can also be prepared by a two-step process of first preparing nanoscale zero-valent iron followed by sulfurization, i.e., adding one form of sulfur (e.g., sodium sulfide, sodium dithionite, and thiosulfate) to a previously synthesized nanoscale zero-valence iron suspension. The research and application of preparing Fe0 and FexSy mixtures by one-step reaction are relatively few, while the research of vulcanized nanomaterials by two-step synthesis is relatively more[90]. Compared with the material obtained by a two-step method, the material obtained by the one-step synthesis method has better selectivity, reaction activity and longer service life, and S elements are distributed on the surfaces of the obtained Fe0 particles,The material prepared by the two-step method has a core-shell structure with an inner Fe0 core and an outer FeS shell, and the oxidation of the inner Fe0 can be delayed by consuming oxygen in the air through the FeS in the shell[22]. Recent studies show that the S/Fe ratio of the nanoscale iron sulfide synthesized by one-step sulfidation is higher than that of the product synthesized by two-step sulfidation, and the S on the surface of the nanoscale iron sulfide exists in the forms of S 2 -, S 2 2 - and S n 2 -, but mainly S 2 2 -[22]. A large amount of H2S gas is released in the one-step synthesis process, and the synthesized nano zero-valent iron and nano iron sulfide particles are doped to be difficult to realize the coating of FeS on the Fe0, and part of nano zero-valent iron particles are oxidized to reduce the reaction activity[21]. In the two-step method, the formation of the core-shell structure is ensured by the way of surface vulcanization after the synthesis of Fe0, the introduction of low dosage of S component can significantly reduce the emission of H2S gas, the excellent core-shell structure can simultaneously increase the specific surface area of particles, which is beneficial to the mass transfer of pollutants, and the synergy of FeS and Fe0 can further improve the application effect[90]. Sulfidation not only introduces sulfide and sulfate groups into the surface of zero-valent iron nanoparticles (both on the oxide shell and on the sheet structure), but also introduces sulfur into the core region of Fe0, which inhibits the electron transfer pathway between Fe0 and oxygen[91].
In addition, the ball milling method also plays an important role in the preparation of vulcanized nZVI. In the method, the particles are disintegrated under the action of stress such as impact, compression and the like, and the iron-containing particles with tiny particle size are further formed. After milling the mixture of pyrite and aluminum powder, the aluminum phase was separated by chemical leaching, and the particles with particle size less than 100 nm were prepared[92]. The ellipsoidal S-mZVI can be obtained by mixing and grinding the sulfur powder and the iron powder, and the sulfur corrodes the surface of the mZVI and forms a coating layer on the surface, weakens the chemical reaction between the H2O and the iron surface, and reduces the occurrence of a passivation reaction in an alkaline environment. When nZVI was applied to the degradation of trichloroethylene (TCE), the degradation rate reached 70% at pH = 9 within 24 H, and the degradation rate could still maintain a 0.03 h-1 at pH = 10, which broadened the pH application range of nZVI[93,94].

3.2 Binary or multicomponent metal stabilization

The introduction of transition metals (such as Nb, Bi, Au) and amphoteric metals (such as Al, Zn, etc.) into the nanoscale zero-valent iron system can provide good passivation protection for nanoscale zero-valent iron particles. The research on three-metal components (Pd-Cu-Fe, Cu-Pd-Fe, etc.) provides a new idea for the stability of nanoscale zero-valence iron. The research on Fe/Ca/CaO is also quite effective. Table 7 briefly summarizes the relevant research results[95][96][75][97][98][99][99][100]. Studies have shown that the binary iron-based nanomaterials have higher reactivity and broader application prospects in pollutant treatment[96]. The Fe0 has a strong reduction potential, is an electron donor, and plays a role in reducing pollutants; The other metal has an oxidation potential (such as Au, Ag, Pd, Pt, and Ni) and serves as an electron acceptor to improve the reaction activity[96]. Taking zero-valent aluminum as an example, its potential is -1.66 eV, and the potential of nano-zero-valent iron is -0.44 eV. Therefore, Al has stronger reducibility than Fe, and can provide electrons for Fe. Generally, under neutral conditions, Al rapidly forms an oxide film in the environment, which hinders its further reaction. Similarly, when Al forms binary metal nanoparticles with other metals, the formation of oxide film on the surface of Al can be slowed down. Introducing Al to prepare Al-Fe binary metal nanoparticles can improve the reactivity of Fe0 nanoparticles, and nano zero-valent aluminum is considered as an electron donor to avoid the formation of iron hydroxide and iron oxide precipitates[97]. In contrast, Fe/Cu, Fe/Ni and Fe/Pd have been studied more in the past five years, and it has been reported that Fe/Ag bimetallic nanoparticles were synthesized in one step by using cypress leaf extract as reducing agent and coating agent[101][102⇓⇓~105][106][107]. Bimetallic system often reduces the oxidation rate of Fe0 and increases its stability time through the electrochemical reaction between two metals. For the system with the introduction of the metal without catalytic activity, the second metal generally plays a role in maintaining the continuous reduction reaction in the system, continuously reducing the Fe2+ in the system into Fe0 through a half-cell reaction, and maintaining the stable occurrence of the reaction; The H2 generated by the corrosion of the Fe0 in water can be adsorbed on the other hydrogen-absorbing material M to form a strong reducing substance M·H2, which has more excellent performance than the material without hydrogen absorption performance in the reduction and removal of pollutants. For the system introduced with catalytic active substances, the equivalent weight of the catalyst in the solution is maintained through the electron transfer between two metals, and the catalytic precursor continuously generates free radicals to realize the removal of pollutants. Taking the Fe-Cu bimetallic nanoparticles supported on carbon nanofibers (FeCu/CNF) prepared by Wang et al. As an example, the Fe-Cu bimetallic nanoparticles were formed by in-situ carbothermal reduction during the carbonization of PAN fibers, and the Fe-Cu nanoparticles were well dispersed[108]. The average diameter of the obtained carbon nanofibers is about 140 nm, and the fiber samples (Fe/CNF, FeCu/CNF, and Cu/CNF) are homogeneous and well dispersed. The Fe0 in CNF, FeCu/CNF, Cu/CNF and FeCu/C were 8, 15, 18 and 26 nm, respectively. The specific surface area, average pore diameter, and total pore volume of all the samples are similar, and they have similar porous structures. By integrating the characteristics of several metal nanoparticles, the metal properties of the composite nanoparticles are further improved to provide more active sites for subsequent reactions, and the synergistic effect of two or more components often shows more excellent effect than the catalytic activation of a single component. Under the same oxidation conditions, more active sites will share the oxidant equivalent and improve the comprehensive oxidation resistance of the material. However, the problem that metal particles are easy to aggregate still needs to be further solved, the introduction of precious metals will increase the cost of water treatment, and the toxicity mechanism of some precious metals is not yet clear.
Ball milling, liquid phase reduction, carbothermal reduction and green synthesis have been widely studied in the preparation of bimetallic materials. Ball milling is the balance of target fragmentation and recombination process, but the overall trend is dominated by fragmentation, which can prepare particles with high degree of metal disorder. The preparation of the Cu-C/Fe material is finally realized in an economical, effective and green manner through a mechanochemical process introduced without a solvent, the material can still maintain the high activity of 4-nitrophenol degradation after being stored in the open air for a week,Compared with the newly prepared particles, there is no significant reduction, and the air stability is significantly improved compared with most iron materials at this stage, but the efficiency is significantly reduced after two weeks of storage. The copper component in the material is used as an efficient nano-cathode, which can enhance the electron transfer between iron and 4-nitrophenol, while the carbon component protects the surface of iron and slows down the oxidation phenomenon. Through the electrochemical process and the extension of the active period, the active substance can rapidly reduce high-concentration nitrophenol in water without acid washing and activation process[109]. Ball milling can partially remove the oxide layer on the surface of nZVI and improve the reactivity, but the synthesized particles are inevitably agglomerated, and the particle size is generally large, so the introduced abrasive needs to be separated subsequently to avoid affecting the purity of nZVI composites.
Carbothermal reduction reduce precursors of iron oxide, iron salts and iron-containing compounds by means of heat energy and carbon-based material, and H2, CO and CO2 generated in that pyrolysis process of the carbon materials can exist as protective atmosphere[92]. The synthesized particles can be attached to the carbon skeleton under the intermolecular force and the chelation of some functional groups, which solves the problems of particle dispersion and oxidation to a certain extent.
Liquid phase reduction is one of the most commonly used methods to prepare nZVI at present, which uses the electrons released in the oxidation process of BH 4 - to reduce iron salt. This method can prepare uniform small particles with high purity, but there is a problem of boron residue, which will cause secondary pollution in application, and the production of low-purity H2 has the risk of explosion, so the preparation process often needs inert atmosphere protection.
Compared with other preparation methods, green synthesis has outstanding environmental benefits, and divalent or trivalent iron ions are often reduced to nZVI through plant extracts or animal rejection reactions. The preparation of plant extracts is complex, and the extraction of polyphenols and other materials takes a long time, which is less efficient than liquid phase reduction, and there may be a problem of incomplete reduction. The surface of the synthesized nZVI is often coated with biological macromolecules, which prolongs the activity of the particles, but reduces the reactivity to a certain extent[91,94,105]. Bacteria, fungi and other organisms have limited metabolic capacity, complex preparation mechanism, many uncontrollable factors and high cost, and there is no systematic study on tolerant strains[110].

3.3 Surface coating

The surface coating is mainly designed for the defects of nZVI, which are easy to agglomerate. By changing the surface charge distribution of nanoscale zero-valent iron particles, the stability of the particles is achieved by means of electrostatic effect and steric hindrance effect. Its adhesion, stability and secondary pollution are the main reference indicators. There are three kinds of surface coating materials: surfactant, surface negative charge polymer and biopolymer. The surfactant is adsorbed on the surface of the nano zero-valent iron particle through the hydrophobic tail group, and the aggregation is prevented by the repulsive force of the hydrophilic group; The hydroxide coating affects the migration characteristics of nZVI by changing the magnetic attraction. In order to solve the problem of electrostatic adsorption between nanomaterials and aquifer materials (often negatively charged at neutral pH), negative surface charge polymers were designed to increase the migration of materials in water by changing the electrical interaction (surface charge, electrostatic repulsion) and reach the action site more quickly and efficiently. The focus of biopolymer coating research is mainly on its environmental protection and low cytotoxicity, and its low cost and easy availability are also the main aspects. According to the nature of the coating, it can be divided into inorganic coating (silicon dioxide, aluminum hydroxide gel, magnesium hydroxide, etc.), organic coating (ethylene glycol, etc.), polymer coating (sodium alginate, artificial humic acid, polyvinyl pyrrolidone, polymaleic acid-co-olefin, etc), biopolymer (rhamnolipid, agarose, microbial extracellular polymer, etc).Table 8 follows the relevant research results at this stage[111][112][113][114][115][116][117][118][119][120][121]. Li et al. Used a two-step method to coat the surface of nano zero-valent iron particles with a silicon dioxide layer and a polydopamine layer, and the particles still had superparamagnetic properties and stability, and were easy to collect and recycle. The synthesis process is shown in Figure 3[122]. The SiO2 can effectively inhibit the ferromagnetism of the nZVI so as to prevent the nZVI from agglomerating, and the silanol groups on the surface of the nZV can be further functionalized to facilitate the adsorption and removal of pollutants. The thickness of the SiO2 layer in the Fe@SiO2 is 2-3 nm, and the coating of PDA is mainly a self-polymerization process of dopamine oxidation.Strong hydrogen bonds are formed between the hydroxyl groups on the surface of Fe@SiO2 and PDA, and the thickness of the PDA layer is 3-6 nm, which further weakens the chain-like aggregation of particles. Due to the multilayer structure, the nanoscale zero-valent iron particles have almost no chain-like aggregation structure or obvious oxidation phenomenon, and the size of the coated nanoscale zero-valent iron particles is less than 13 nm, and 80% of the particles are in the range of 6 to 11 nm. However, it should be noted that there is still a slight oxidation phenomenon (FeO, Fe2O3 and FeOOH) on the surface of Fe@SiO2@PDA, which may be due to the fact that the SiO2 shell is not partially coated or the micropores are opened.

3.4 Comparison of advantages and disadvantages of stabilization methods

The surface oxidation of nanoscale zero-valent iron particles can be slowed down and the stability can be enhanced through modification, and the commonly used modification ways are shown in Figure 4. The prepared nZVI can be directly placed in the modifier for surface modification, or the modifier can be introduced into the liquid phase of ferric salt for one-step reduction to prepare modified nZVI particles, or a mechanical ball milling method can be adopted. Surface vulcanization of particles can improve the reactivity and stability of particles to a certain extent, and enhance their selectivity to water pollutants. However, vulcanization inevitably produces H2S gas, which has the risk of secondary pollution. Additionally, sulfur modification may also increase particle size and pH sensitivity[124][125]. Metal doping alleviates nZVI oxidation by increasing active sites, and accelerates electron transfer by means of surface micro-battery reaction. However, metal doping may accelerate corrosion, and metal doping may also have environmental risks[126]. Surfactants attached to the surface of nZVI can increase the repulsive force between particles, reduce the dipole attraction and charge attraction between particles, and reduce the occurrence of particle agglomeration, but there may be problems such as blocking reaction channels, coating active sites and inhibiting electron transfer[127].

4 Application

In recent years, nanoscale zero-valent iron composites have been widely used in the removal of heavy metals and organic matter because of their large specific surface area, high reactivity and low biological toxicity, with obvious advantages and excellent results. At the same time, it is suitable for in-situ remediation of water body because of its high fluidity and convenient storage in water body[113][128,129]. The carrier or the modifier can adsorb and combine the carrier or the modifier through pore action, electrical action, reaction sites and the like, promote the occurrence of mass transfer reaction to a certain extent, and improve the application effect.

4.1 Removal of metal ions

The biological toxicity is not related to the total metal concentration in the solution, but mainly affected by the free (hydrated) metal ions. Heavy metals can be enriched through the food chain and eventually enter the human body.It produces chronic toxicity and can be removed efficiently through the catalysis, reduction, chelation and electrochemical action of nano zero-valent iron. Table 9 summarizes the research on its application in heavy metal removal.

4.1.1 As

Inorganic arsenic can accumulate in human tissues and combine with proteins, causing damage to the cardiovascular system and liver, and the toxicity of inorganic As (Ⅲ) and As (V) is higher than that of organic arsenic[130]. Under weakly acidic conditions, pentavalent arsenate is negatively charged and can be disposed of by adsorption, precipitation and membrane processes. The removal of trivalent arsenic is relatively difficult.When the pH value is lower than 9. 2, trivalent arsenic exists in the form of H3AsO3, and the bond between the molecule itself and the adsorbent is weak.Some traditional physical and chemical methods are limited in the treatment of uncharged H3AsO3, and the coexistence of heavy metal ions will also increase the removal difficulty of As (Ⅲ) in acidic wastewater. In the removal of As (Ⅲ), adsorption is the most important way, and new efficient adsorbents are the focus of research, and iron-based materials with wide sources, low price and environmental friendliness are widely studied. Nanoscale zero-valent iron (nZVI/Fe0) can be used for in-situ remediation of As (Ⅲ) -contaminated water due to its large surface area to volume ratio and high reactivity. The removal of As (Ⅲ) species by nZVI is usually achieved by physical and chemical adsorption.Under certain conditions, reactive oxygen species (ROS) can be induced to lead to the transformation of As (Ⅲ) to As (Ⅴ), and promote the adsorption reaction[131].

4.1.2 Se

Selenium is an essential micronutrient for human body, but excessive intake can lead to toxic effects. To date, selenium removal research has focused on solvent extraction, flotation, adsorption, ion exchange, and membrane separation. Solvent extraction and flotation are harmful to the environment in the process of selenium separation, the efficiency of adsorption and ion exchange is not high, the efficiency of membrane filtration is high, the operation is simple, and the energy consumption is ultra-low, which is one of the most effective methods for large-scale selenium separation. Zero-valent iron can reduce the oxidation state of selenium (selenite and selenate) to facilitate its adsorption removal, and selenium oxides can be precipitated from the solution in the form of elemental selenium under ideal conditions. The nZVI has the advantages of high separation efficiency, low release of selenium compounds after separation and controllable separation process in the selenium separation process, but the nZVI has low stability and high aggregation, so that the separation efficiency of the selenium is significantly reduced. In recent years, the membrane materials prepared by nanowires and nanofibers have been widely used for selenium removal. MnO2 nanowires, as a kind of one-dimensional materials, have shown excellent performance, which can withstand extreme environments such as acid and alkali, and have significant advantages as carrier materials. Qiu et al. chemically deposited nanoscale zero-valent iron particles on the surface of ultra-long MnO2 nanowires in situ for selenium separation[85]. The separation efficiency of Se (Ⅵ) was up to 95. 62% at pH 2 ~ 6. The separation efficiency of Se (Ⅵ) was still above 60% after three cycles, and the fiber material had good recoverability.

4.1.3 Pb

Lead ion (Pb2+), as one of the most toxic heavy metals, can inhibit hemoglobin and damage liver, kidney, reproductive system and central nervous system[132]. The maximum Pb2+ concentration limits in the World Health Organization (WHO), the United States Environmental Protection Agency (US EPA), and the Standards for Drinking Water Quality (GB 5749-85) are 0.010, 0.015, and 0.050 mg·L-1, respectively. The nZVI has a significant effect on the removal of Pb2+ by adsorption, reduction and co-precipitation, but the oxide film on the surface of nZVI affects its mass transfer and reduction to some extent. As the site of adsorption and coprecipitation reactions, the porous structure plays an important role in the capture of Pb2+, which makes it possible for nZVI to act as an adsorption material, provided that the problems of its agglomeration, surface corrosion and potential biological toxicity are effectively solved. Solid matrix support and immobilization of nZVI is a good way to solve this problem. Peng et al. firstly immobilized nZVI in carboxylated cellulose nanocrystals by in situ reduction, and the adsorption capacity could reach 653.59 mg·g-1 at 298.15 K[33]. In addition, surface modification is also an effective way to improve the removal efficiency of Pb2+. Humic acid (HA) is rich in oxygen-containing functional groups (phenolic hydroxyl, carbonyl, carboxyl, etc.), which can effectively promote the complexation with metal oxides and heavy metals, and has a certain ability to adsorb and remove heavy metals, and can be recycled by hydrochloric acid dissociation. Du et al. Used artificial humic acid (AHA) with abundant oxygen-containing functional groups (-OH and -COOH) as the modified material of nZVI, the maximum adsorption capacity was 649.0 mg·g-1, and the problem that HA could not be regenerated was solved[116].

4.1.4 Cr

Cr (Ⅵ) can induce a series of diseases such as digestive tract cancer and nervous system damage, and has carcinogenicity. Its high solubility and fluidity can easily lead to water pollution[133]. In contrast, the toxicity of Cr (Ⅲ) is lower, and it is an essential trace element for human. Therefore, the key to the removal of Cr (Ⅵ) is to reduce it to Cr (Ⅲ) and reduce its biological toxicity. Because of its small size, large surface area and high surface activity, nZVI has been widely studied as a reducing agent, but its chemical instability, low mechanical strength and strong aggregation tendency increase the cost of water treatment to a certain extent, thus limiting the scope of application. The loading and modification of nanoscale zero-valent iron provide a reliable solution for its popularization and application. Polyacrylonitrile (PAN) is used as a carrier material because of its hydrophilicity, high thermal stability and mechanical stability. Because its own functional groups have weak chelating effect on nZVI, its modification can reduce the secondary pollution to a certain extent.4-dihydroxy-L-phenylalanine (L-DOPA) can be grafted onto the surface of PAN membrane by hydroxyl and carboxyl groups, thus increasing the chelating ability of nZVI and improving the hydrophilicity of the membrane.Cr (Ⅵ) was reduced by Fe0 corrosion, including adsorption, reduction and coprecipitation.Strong acidic conditions are more favorable for Cr (Ⅵ) removal, and the removal process follows the pseudo-first-order kinetic model[30]. Aromatic polymer humus with loose spongy structure, large specific surface area and high surface energy is also one of the carrier materials, and the carboxyl, phenolic hydroxyl, ketone and other groups of the humus can enhance the binding stability of nZVI on the surface of the humus,Humic acid, the main component of the humic acid, played an effective synergistic role in chelating and adsorbing Cr (Ⅵ).The adsorption process was in good agreement with the Langmuir model, and followed the pseudo-first-order kinetics, with the maximum adsorption capacity of 40. 4 mg · G-1[32].

4.1.5 Other heavy metal ions

Adsorption, ion exchange, reduction and chemical precipitation are the main removal processes of heavy metals, and adsorption and complexation after free radical oxidation can realize the transformation and removal of low-valent heavy metals to high-valent heavy metals. In addition to the metal ions mentioned above, nanoscale zero-valent iron and its composite materials can also be used for the removal of Cu (II), U (VI), Sb (III), Sb (V) and other metal ions in water.
In industrial wastewater, Cu (Ⅱ) is usually present in stable chelate structure, which is difficult to be removed by conventional treatment technology, and coexisting anions can also cause interference. Theoretically, EDTA-Cu (II) will be replaced by Fe3+, and the free Cu2+ will be removed by precipitation, adsorption and reduction, and the removal efficiency largely depends on the reactivity of nZVI. 88.3% of EDTA-Cu (Ⅱ) was removed in 6 H by the polymer anion exchanger D201 with excellent mechanical strength and adjustable pore structure, and 97.2% of Cu was immobilized inside the D201-ZVI beads. Under the influence of Donnan membrane effect, the quaternary ammonium groups covalently bonded with the polymer matrix played an important role in the permeation of EDTA-Cu (Ⅱ) into the pores, thus fully activating the activity of nZVI[35].
Uranium usually exists in the form of soluble U (Ⅵ) and a small amount of U (Ⅳ) in the aquatic environment, and in the form of soluble complex in groundwater. Extraction, membrane separation, ion exchange, chemical precipitation and adsorption have been used to remove U (Ⅵ). It is an effective way to reduce soluble U (Ⅵ) to insoluble U (Ⅳ) and then separate it. Nanoscale zero-valent iron can be used as a rectification material for U (Ⅵ) to effectively reduce U (Ⅵ). The bimetallic oxide can play a synergistic role on the basis of maintaining the effect of a matrix, the density of active sites on the surface of the Fe-Ni bimetallic nanoparticles is high, Ni can effectively improve the adsorption capacity of nZVI on U (VI) while accelerating the removal speed,The high flexibility, high surface area, high conductivity and a large number of oxygen-containing functional groups of two-dimensional GO also show good U (Ⅵ) adsorption characteristics, and simplify the separation and recovery of the composite. GO/Fe-Ni has obvious advantages in field applications[102]. The technology of zero-valent iron permeable reactive barrier (PRB) has been successfully used to remove U (Ⅵ) in situ for many years, while surface passivation and agglomeration reduce the service life of PRB. Iron-based bimetallic materials can maintain the zero valence of iron by continuously providing electrons, exposing more sites to reduce U (Ⅵ), and Al can act as an electron donor while reducing the formation of iron hydroxide or oxide precipitates[97].
Sb (Ⅴ) and Sb (Ⅲ), namely Sb (OH) 6 - and Sb (OH) Sb(OH)3, are the main forms of antimony in water, and the toxicity of inorganic form is much higher than that of organic form. The existing form of antimony in water depends on pH value. In contrast, Sb (Ⅲ) is more stable and easier to remove, and reduction is an effective way to remediate Sb (Ⅴ) contaminated water. Because of its high surface energy and high adsorption capacity, nZVI is widely used as Sb (Ⅲ)/Sb (Ⅴ) adsorption material.Sludge biochar (SBC) is an ideal adsorbent for Sb (Ⅲ) due to its high stability and high porosity.When used as a carrier, it has obvious synergistic advantages with nZVI[74].

4.2 Removal of organic pollutants

Organic matter in water is often highly toxic, difficult to biodegrade, and can be transported for a long distance, so it is very harmful. The nZVI composite can be removed by adsorption, oxidation or reduction, reducing its environmental risk.

4.2.1 COCs

Chlorinated organic compounds mainly include chlorinated aromatic hydrocarbons, chlorinated aliphatic hydrocarbons and other chlorinated derivatives, which have strong biological toxicity and accumulation, and can be removed by physical, chemical and biological methods, but there are shortcomings. Physical methods, such as stripping, adsorption, extraction, etc., can only transfer chlorinated organic compounds but can not really remove them, with poor selectivity and competitive problems. Biological methods are divided into aerobic and anaerobic ways, but the problems of separation and domestication of efficient degradation strains have not been well solved. Chemical method is the most commonly used way at present, which can be divided into two ways: oxidation and reduction. Due to high equipment requirements, high operating costs and serious secondary pollution, incineration has been gradually replaced by Fenton oxidation, photocatalytic oxidation and ozone oxidation, which are widely studied because of their mild and controllable reaction conditions and little environmental impact, but the effect of advanced oxidation technology in the treatment of some polychlorinated organic compounds is poor[53,96]. The reduction pathway is mainly focused on electrocatalytic hydrogenolysis and nZVI reduction. The oxidation of zero-valent iron promotes the substitution of H+ for Cl- in the solution. The ferrous iron produced by the reaction also has a certain reduction effect on chlorine species, and the H2 produced by the electrochemical reaction can play a synergistic role in the dechlorination process[72,88,106]. In addition, the application of nanoscale zero-valent iron in the dechlorination reaction can avoid the problems of high cost of zinc, easy passivation of aluminum, low reducibility of copper and excessive hydrogen production of magnesium. It is also used for in-situ remediation of water bodies due to its advantages of small particle size, easy flow with water and relatively long residence time. Table 10 briefly summarizes them.

4.2.2 Organic Dye

Dyeing, finishing, scouring and other processes in the textile industry will produce a large amount of dye wastewater, which will reduce light penetration after being discharged into the environmental water body, affecting the photosynthesis of aquatic organisms, and some dyes have carcinogenic risks. In the conventional treatment process, flocculation and homogeneous Fenton oxidation will produce sludge, which is difficult to be completely degraded by photochemical method, and electrochemical oxidation is expensive and time-consuming[43]. In recent years, nZVI composite materials have been used in the removal of acid dyes, basic dyes, reactive dyes, direct dyes and disperse dyes (Table 11). The damage to water can be reduced by destroying chromophoric groups and auxiliary pigments, which can be achieved by reduction and advanced oxidation. The active free radicals (such as · OH, SO4·-, Cl ·, 1O2, · O 2 -, etc.) produced by catalysis are the most studied pathways. The introduction of light, heat, electricity, ultrasound and microwave will increase the production of free radicals. Photon excitation can accelerate the production rate of active species such as · OH, · O 2 - and HO2·, reduce the recombination of photogenerated electron and hole pairs, and accelerate the interfacial mass transfer. The heat energy can accelerate the cracking of the oxidant, increase the generation rate of the strong oxidizing free radicals, and further shorten the reaction path under the condition that the activation energy is reduced, so that the reaction period is shorter; In the advanced electro-Fenton process, the anode of Fe loses electrons to promote the decomposition of H2O2 to generate hydroxyl radicals, and the cathode sustains the generation of H2O2 through electrons obtained by O2 and the like, and no additional oxidant is supplemented in a reaction system; Microwave radiation can weaken the chemical bond force, and the introduction of Fenton system can reduce the energy required for the rupture of chemical bonds such as — O = O —, and accelerate the occurrence of free radical reactions. Ultrasonic cavitation can accelerate the mass transfer, and the rupture of cavitation bubbles makes the pollutants on the surface of the catalyst constantly replaced, which improves the mass transfer and accelerates the reaction.

4.2.3 Other organic matter

In addition to chlorine-containing organics and dyes, nanoscale zero-valent iron is also widely used for the removal of nitro compounds, phenolic compounds, antibiotics, polycyclic aromatic hydrocarbons and other organics, and its efficient degradation can be achieved by adsorption, chemical reduction, photocatalytic oxidation, free radical oxidation and other ways (see Table 12).
Nitrobenzene has high hydrophobicity, toxicity and persistence, and the electron receiving characteristics of the nitro group make it impossible for traditional biological methods to treat wastewater with nitrobenzene concentration higher than the 100 mg·L-1.Due to the low cost, environmental friendliness and high reducibility of nZVI, the reduction of 3-dinitrobenzene by-product to aniline by nZVI can reduce its toxicity and enhance its degradability, which is beneficial to the subsequent biological treatment[71]. Nitrophenol (PNP) has excellent stability, high toxicity, three risks and is difficult to be degraded by microorganisms. Among the physical methods, adsorption is the most commonly used, but the cost of adsorbent regeneration is very high. The extraction method has poor effect on the treatment of high concentration wastewater, and the extractant itself has the risk of secondary pollution. The energy consumption of pyrolysis process is high, in contrast, advanced oxidation process and reduction method are more commonly used[87].
Trace bisphenol A (BPA) is toxic to the human body and the environment.Adsorption, advanced oxidation and biological treatment have been used for the degradation of BPA.In order to avoid the production of iron-containing sludge in the traditional Fenton system, nZVI has been introduced into the degradation system[45].
Tetrabromobisphenol A (TBBPA) has been widely recognized for its lipophilicity, bioaccumulation, persistence, and high toxicity. Nanoscale zero-valent iron (nZVI) has been widely studied due to its wide source, low price and good debromination ability. The dispersibility, the recyclability and the reaction activity of the particles can be remarkably improved through biomass loading and other metal doping, and the advantages are obvious[75]. In addition, the H2 produced during the nZVI reaction can be used as an electron donor to promote the growth of microorganisms, thus playing a synergistic role between nZVI and microorganisms in the degradation process[135].
Sulfamethoxazole (SMX) is a kind of antibiotics. Because of its resistance to microorganisms, it is easily adsorbed by sludge and difficult to be degraded. Coagulation and adsorption can only realize the transfer of SMX in the medium. Efficient and rapid degradation of SMX relies on chemical oxidation and advanced oxidation technologies, and Fenton oxidation with nZVI as catalyst is an effective way to remove SMX in water[98].
Tetracyclines (TCs) have been widely used worldwide as ideal antimicrobial agents, but they are difficult to degrade, have a long environmental half-life and pose a high health risk. There are many studies on the treatment of TCs wastewater by NZVI. Aluminum hydroxide gel (AHG) coated on the surface of NZVI can improve its dispersibility and oxidation resistance, and AHG itself also has a certain adsorption capacity[112].
Polycyclic aromatic hydrocarbons (PAH) are teratogenic, carcinogenic and mutagenic. Chemical transformation often produces harmful by-products, and biodegradation is difficult to play a role because of its stability. In contrast, adsorption is the most effective method, but the separation and recovery of adsorbents are extremely difficult. The superparamagnetic material which can be separated by an external magnetic field provides convenience for the separation and recovery of the adsorbent. The saturation magnetization of α-Fe can exceed that of 200 emu·g-1, so it has obvious advantages in magnetic separation. In order to make full use of nZVI, it is necessary to modify it properly to improve its stability and selectivity. The π-π stacking of polydopamine is beneficial to the improvement of nZVI performance and the adsorption and removal of pollutants[122].

5 Conclusion and prospect

Nanoscale zero-valent iron (ZVI) has been widely used in the remediation of environmental pollution and achieved good results due to its high catalytic activity, high reactivity and relative economic price advantage. Compared with other artificial metal nanomaterials, iron has low toxicity to aquatic organisms and little environmental impact. On the other hand, the further application of nanoscale zero-valent iron is limited due to its high reactivity and easy agglomeration and deactivation. In the past five years, the research on loading and stabilization methods of nanoscale zero-valent iron has generally developed in the direction of environmental friendliness, energy saving and consumption reduction, economy and practicality, and the application field has been expanded and the effect has been significantly improved. In this paper, a more comprehensive summary and appropriate outlook.
(1) Due to the influence of nano-effect, the direct introduction of nano-zero-valent iron into water will greatly reduce the performance due to agglomeration and loss, and the method of skeleton dispersion can effectively reduce the degree of agglomeration. The common loading framework materials include organic polymers, natural minerals, carbon materials and metal oxides. With regard to organic polymers, single-component and multi-component carriers have been extensively studied, involving membrane materials, crystal materials, natural polymers and resins. Natural minerals such as montmorillonite and bentonite can be used as carriers, but the loading is unstable and the recovery is difficult. Carbon material carriers such as carbon powder, carbon fibers, carbon nanotubes, graphene oxide and the like are also widely applied; Biochar materials prepared from plants, bacteria and wastes are also widely used. The acidity and alkalinity and redox characteristics of metal oxides can play a role in the practical application process, and there are many studies on single-component oxides.
(2) Zero-valent iron particles prepared by traditional methods have poor stability in the air and are prone to oxidation, which limits the promotion and application of nano-zero-valent iron. Therefore, the stability of nanoscale zero-valent iron is still a key factor for practical applications. Surface sulfidation, metal doping to construct multi-components (such as Ce, Mn, Co, etc.), and the introduction of coating materials are the stable means of more research at this stage. In addition, the mechanochemical method, ball milling, can also play an important role in the process of vulcanization modification, and the environmental friendliness is further improved compared with the chemical synthesis path. The properties of particles synthesized by different methods are different, such as energy consumption, economy, environmental friendliness and so on. The stability of coating materials depends to some extent on the coating degree of nZVI particles, and the adhesion and secondary pollution of coating materials should also be considered in the practical application process.
(3) In terms of application, heavy metals and organic compounds have achieved certain results. The most studied heavy metals are Cr, As, Se, Pb and so on, while organic pollutants are more extensive. The main mechanism of heavy metal removal is to reduce the occurrence of heavy metals in the water environment by converting them into low toxic forms and then enriching them from the water body. Mineralization into small molecules for direct removal of organics is the most ideal removal method. However, in the practical application process, the degradation of organic matter is difficult, and the removal process is accompanied by the production of various intermediates, some of which will remain in the reaction system in the form of final products, which need to be taken away by subsequent adsorption to achieve water purification. In terms of new materials, the development of materials with high visible light response, the extension of the recombination time of photogenerated electrons and holes, and the realization of efficient visible light catalysis are the research trends in the field of nano-zero-valent iron photocatalysis. In order to further improve the application effect, the coupling system of advanced oxidation process combined with light, heat, electricity, magnetic field, ultrasound, microwave and microbial metabolic process has been gradually paid attention to. The interaction between the energy field and the pollutant can supplement the energy required for the chemical fracture in the reaction process, reduce the activation energy of the reaction and accelerate the occurrence of the reaction; Microorganisms remove pollutants through their own metabolic processes, but the selection of reactive microorganisms is difficult, and the study of microbial metabolic processes and mechanisms needs to be further deepened.
To sum up, nanoscale zero-valent iron and its composites have good application prospects in water treatment, and the development of more green, stable and reusable zero-valent iron nanocomposites is an important demand in the future.

References

Publishing order | Descend order by publishing year | Descend order by cited within
[1]

Kim S J, Mahmood J, Kim C, Han G F, Kim S W, Jung S M, Zhu G M, de Yoreo J J, Kim G, Baek J B. J. Am. Chem. Soc., 2018, 140(5): 1737.
[2]

El-Temsah Y S, Joner E J. Chemosphere, 2012, 89(1): 76.
[3]

Kharisov B I, Dias H V R, Kharissova O V, Jime'nez-Pe'rez V M, Pe'rez B O, Flores B M. RSC Adv., 2012, 2: 9325.
[4]

Wei Y T, Wu S C, Chou C M, Che C H, Tsai S M, Lien H L. Water Res., 2010, 44(1): 131.
[5]

Kocur C M, Chowdhury A I, Sakulchaicharoen N, Boparai H K, Weber K P, Sharma P, Krol M M, Austrins L, Peace C, Sleep B E, O'Carroll D M. Environ. Sci. Technol., 2014, 48(5): 2862.
[6]

Quinn J, Geiger C, Clausen C, Brooks K, Coon C, O'Hara S, Krug T, Major D, Yoon W S, Gavaskar A, Holdsworth T. Environ. Sci. Technol., 2005, 39(5): 1309.
[7]

Newsome L, Morris K, Cleary A, Masters-Waage N K, Boothman C, Joshi N, Atherton N, Lloyd J R. J. Hazard. Mater., 2019, 364: 134.
[8]

Karim S, Bae S, Greenwood D, Hanna K, Singhal N. Water Res., 2017, 125: 32.
[9]

Xin J, Fan S F, Yuan M J, Wang X H, Zhang X J, Zheng X L. Sci. Total. Environ., 2020, 716: 137111.
[10]

Song Y, Fang G D, Zhu C Y, Zhu F X, Wu S, Chen N, Wu T L, Wang Y J, Gao J, Zhou D M. Chem. Eng. J., 2019, 355: 65.
[11]

Li X C, Huang L, Fang H W, He G J, Reible D, Wang C H. Sci. Total. Environ., 2019, 694: 133695.
[12]

Ruhl A S, Ünal N, Jekel M. Chem. Eng. J., 2012, 209: 401.
[13]

Guo X J, Yang Z, Liu H, Lv X F, Tu Q S, Ren Q D, Xia X H, Jing C Y. Sep. Purif. Technol., 2015, 146: 227.
[14]

Mu Y, Jia F L, Ai Z H, Zhang L Z. Environ. Sci.: Nano, 2017, 4(1): 27.
[15]

Chen L S, Yuan T J, Ni R, Yue Q Y, Gao B Y. Chem. Eng. J., 2019, 365: 183.
[16]

Zhou L J, Zhuang W Q, Wang X, Yu K, Yang S F, Xia S Q. Water Res., 2017, 111: 140.
[17]

Palombella S, Pirrone C, Rossi F, Armenia I, Cherubino M, Valdatta L, Raspanti M, Bernardini G, Gornati R. Nanomaterials, 2017, 7(8): 212.
[18]

Zhu F, Zheng Y M, Zhang B G, Dai Y R. J. Hazard. Mater., 2021, 401: 123608.
[19]

Frost R L, Xi Y F, He H P. J. Colloid Interface Sci., 2010, 341(1): 153.
[20]

Oh S Y, Seo Y D, Ryu K S, Park D J, Lee S H. Environ. Sci.: Processes Impacts, 2017, 19(5): 711.
[21]

Shi Z J, Shen W J, Yang K, Zheng N N, Jiang X F, Liu L M, Yang D D, Zhang L Z, Ai Z H, Xie B. Chem. Eng. J., 2019, 362: 63.
[22]

Xu J, Wang Y, Weng C, Bai W L, Jiao Y, Kaegi R, Lowry G V. Environ. Sci. Technol., 2019, 53(10): 5936.
[23]

He F, Zhao D Y. Environ. Sci. Technol., 2005, 39(9): 3314.
[24]

Tesh S J, Scott T B. Adv. Mater., 2014, 26(35): 6056.
[25]

Tang P F, Shen J, Hu Z D, Bai G L, Wang M, Peng B J, Shen R P, Linghu W S. J. Mol. Liq., 2016, 221: 497.
[26]

Borba P A A, Pinotti M, de Campos C E M, Pezzini B R, Stulzer H K. Carbohydr. Polym., 2016, 137: 350.
[27]

Mueller N C, Braun J, Bruns J, Černík M, Rissing P, Rickerby D, Nowack B. Environ. Sci. Pollut. Res., 2012, 19(2): 550.
[28]

Stefaniuk M, Oleszczuk P, Ok Y S. Chem. Eng. J., 2016, 287: 618.
[29]

Giri S, Bhaumik M, Das R, Gupta V K, Maity A. Appl. Catal. B Environ., 2017, 202: 207.
[30]

Liu P, Wang X Y, Ma J, Liu H L, Ning P. Chemosphere, 2019, 220: 1003.
[31]

Elkady M, Shokry H, El-Sharkawy A, El-Subruiti G, Hamad H. J. Mol. Liq., 2019, 294: 111628.
[32]

Fu R B, Zhang X, Xu Z, Guo X P, Bi D S, Zhang W. Sep. Purif. Technol., 2017, 174: 362.
[33]

Peng B X, Zhou R S, Chen Y, Tu S, Yin Y W, Ye L Y. Front. Chem. Sci. Eng., 2020, 14(6): 1006.
[34]

Chanthapon N, Sarkar S, Kidkhunthod P, Padungthon S. Chem. Eng. J., 2018, 331: 545.
[35]

Liu F, Shan C, Zhang X L, Zhang Y Y, Zhang W M, Pan B C. J. Hazard. Mater., 2017, 321: 290.
[36]

Xu L, Zhang D, Ma F Y, Zhang J R, Khayambashi A, Cai Y W, Chen L H, Xiao C L, Wang S A. ACS Appl. Mater. Interfaces, 2019, 11(24): 21619.
[37]

Liu X S, Xu H M, Wang L L, Qu Z, Yan N Q. Chem. Eng. J., 2020, 381: 122559.
[38]

Chen Y P, Yang L M, Chen J P, Zheng Y M. J. Hazard. Mater., 2019, 371: 576.
[39]

Ren J W, Yao M W, Woo Y C, Tijing L D, Kim J H, Shon H K. Compos. B Eng., 2019, 171: 339.
[40]

Mondal P, Purkait M K. J. Clean. Prod., 2018, 170: 1111.
[41]

K V G R, Argulwar S, Sudakaran S V, Pulimi M, Chandrasekaran N, Mukherjee A. Environ. Technol. Innov., 2018, 9: 122.
[42]

Wang X Y, Cong S, Ma J. Mater. Chem. Phys., 2017, 197: 215.
[43]

Yu P P, Yu H F, Sun Q S, Ma B M. Sci. Rep., 2019, 9: 11322.
[44]

Xu B D, Li D C, Qian T T, Jiang H. Chem. Eng. J., 2020, 387: 124063.
[45]

Bao T, Damtie M M, Hosseinzadeh A, Wei W, Jin J, Phong Vo H N, Ye J S, Liu Y W, Wang X F, Yu Z M, Chen Z J, Wu K, Frost R L, Ni B J. J. Environ. Manag., 2020, 260: 110105.
[46]

Chi Z X, Hao L, Dong H, Yu H, Liu H K, Wang Z, Yu H B. Chem. Eng. J., 2020, 382: 122789.
[47]

Zhao R R, Zhou Z M, Zhao X D, Jing G H. Chemosphere, 2019, 218: 458.
[48]

Li S Q, Yu C, Wu Z X, Cai X Q, Zha F S. Mater. Res. Express, 2020, 7(4): 045002.
[49]

Kakavandi B, Takdastan A, Pourfadakari S, Ahmadmoazzam M, Jorfi S. J. Taiwan Inst. Chem. Eng., 2019, 96: 329.
[50]

Kombaya-Touckia-Linin E M, Gaucel S, Sougrati M T, Khederlou K, Pen N, Stievano L, Gontard N, Guillard V. Chem. Eng. J., 2019, 357: 750.
[51]

Wang R, Jing G H, Zhou X B, Lv B H. J. Taiwan Inst. Chem. E., 2017, 18: 134.
[52]

Ding C X, Xiao S J, Lin Y J, Yu P, Zhong M E, Yang L H, Wang H, Su L, Liao C J, Zhou Y Y, Deng Y C, Gong D X. Chem. Eng. J., 2019, 360: 104.
[53]

Danish M, Gu X G, Lu S G, Naqvi M. Environ. Sci. Pollut. Res., 2016, 23(13): 13298.
[54]

Fu X Y, Zhang J, Zhao H D, Zhang S J, Nie T, Zhang Y T, Lu J F. Sep. Purif. Technol., 2020, 230: 115886.
[55]

Liu T Y, Yang Y L, Wang Z L, Sun Y Q. Chem. Eng. J., 2016, 288: 739.
[56]

Xu J, Liu X, Cao Z, Bai W L, Shi Q Y, Yang Y. J. Hazard. Mater., 2020, 384: 121253.
[57]

Ding X, Wang S Y, Shen W Q, Mu Y, Wang L, Chen H, Zhang L Z. Water Res., 2017, 112: 9.
[58]

He Q, Dai J L, Zhu L, Xiao K J, Yin Y R. J. Alloys Compd., 2016, 687: 326.
[59]

Lv Z M, Yang S M, Chen L, Alsaedi A, Hayat T, Chen C L. J. Environ. Sci., 2019, 76: 377.
[60]

Hu B W, Mei X, Li X, Hu J, Xu D, Ma J Y, Huang Y Y. J. Mol. Liq., 2017, 237: 1.
[61]

Lv X S, Qin X F, Wang K F, Peng Y Y, Wang P, Jiang G M. J. Hazard. Mater., 2019, 373: 176.
[62]

Yu H Q, Zhang T, Jing Z F, Xu J C, Qiu F X, Yang D Y, Yu L B. Chem. Eng. J., 2019, 205: 278.
[63]

Wang C, Kang J, Liang P, Zhang H Y, Sun H Q, Tadé M O, Wang S B. Environ. Sci.: Nano, 2017, 4(1): 170.
[64]

Wu Y W, Chen X T, Han Y, Yue D T, Cao X D, Zhao Y X, Qian X F. Environ. Sci. Technol., 2019, 53(15): 9081.
[65]

Liu W J, Jiang H, Yu H Q. Chem. Rev., 2015, 115(22): 12251.
[66]

Dai X H, Fan H X, Yi C Y, Dong B, Yuan S J. J. Mater. Chem. A, 2019, 7(12): 6849.
[67]

Liu L H, Liu X, Wang D Q, Lin H, Huang L. J. Clean. Prod., 2020, 257: 120562.
[68]

Lyu H H, Tang J C, Cui M K, Gao B, Shen B X. Chemosphere, 2020, 246: 125609.
[69]

Liang L P, Xue Y Y, Tian G L, Mao Q L, Lou Z X, Wu Q, Wang Q, Du J S, Meng X. RSC Adv., 2019, 9(45): 26136.
[70]

Trinh B S, Le P T K, Werner D, Phuong N H, Luu T L. Processes, 2019, 7(10): 660.
[71]

Wei G L, Zhang J H, Luo J Q, Xue H J, Huang D Y, Cheng Z Y, Jiang X B. Front. Environ. Sci. Eng., 2019, 13(4): 61.
[72]

Liu G, Tang H R, Fan J J, Xie Z H, He T Y, Shi R, Liao B. Bioresour. Technol., 2019, 289: 121734.
[73]

Yang F, Zhang S S, Sun Y Q, Cheng K, Li J S, Tsang D C W. Bioresour. Technol., 2018, 265: 490.
[74]

Wei D N, Li B Y, Luo L, Zheng Y X, Huang L H, Zhang J C, Yang Y, Huang H L. J. Hazard. Mater., 2020, 391: 122057.
[75]

Kang N X, Zhu N W, Guo W Y, Shi C H, Wu P X, Wei X R. Chem. Eng. J., 2018, 334: 99.
[76]

Lian J J, Huang Y G, Chen B, Wang S S, Wang P, Niu S P, Liu Z L. Water Sci. Technol., 2018, 2017(3): 859.
[77]

Teng Z D, Shao W, Zhang K Y, Yu F L, Huo Y Q, Li M. J. Hazard. Mater., 2020, 384: 121505.
[78]

You N, Chen Y, Zhang Q X, Zhang Y, Meng Z, Fan H T. Sci. Total. Environ., 2020, 735: 139553.
[79]

Ahmed M B, Zhou J L, Ngo H H, Guo W S, Johir M A H, Sornalingam K, Belhaj D, Kallel M. Chem. Eng. J., 2017, 322: 571.
[80]

Xiang Y Y, Rene E R, Lun X X, Ma W F. Bioresour. Technol., 2020, 306: 123127.
[81]

Wei A L, Ma J, Chen J J, Zhang Y, Song J X, Yu X Y. Chem. Eng. J., 2018, 353: 595.
[82]

Su H J, Fang Z Q, Tsang P E, Zheng L C, Cheng W, Fang J Z, Zhao D Y. J. Hazard. Mater., 2016, 318: 533.
[83]

Jain A, Agarwal M. J. Water Process. Eng., 2017, 19: 51.
[84]

Zhao J, Dong W F, Zhang X D, Chai H X, Huang Y M. Sens. Actuat. B Chem., 2018, 263: 575.
[85]

Qiu Z W, Tian Q, Zhang T, Yang D Y, Qiu F X. Sep. Purif. Technol., 2020, 230: 115847.
[86]

Dong Y S, Meng F J. RSC Adv., 2020, 10(20): 11823.
[87]

Joshaghani M, Yazdani D, Zinatizadeh A A. J. Iran. Chem. Soc., 2017, 14(11): 2449.
[88]

Lv X F, Prastistho W, Yang Q, Tokoro C. Appl. Organomet. Chem., 2020, 34(5): 5592.
[89]

Jonoush Z A, Rezaee A, Ghaffarinejad A. J. Clean. Prod., 2020, 242: 118569.
[90]

Cao Z, Liu X, Xu J, Zhang J, Yang Y, Zhou J L, Xu X H, Lowry G V. Environ. Sci. Technol., 2017, 51(19): 11269.
[91]

Su Y M, Jassby D, Song S K, Zhou X F, Zhao H Y, Filip J, Petala E, Zhang Y L. Environ. Sci. Technol., 2018, 52(11): 6466.
[92]

Akhgar B N, Pourghahramani P. Int. J. Miner. Process., 2017, 164: 1.
[93]

Gu Y W, Wang B B, He F, Bradley M J, Tratnyek P G. Environ. Sci. Technol., 2017, 51(21): 12653.
[94]

Gu Y W, Gong L, Qi J L, Cai S C, Tu W X, He F. Water Res., 2019, 159: 233.
[95]

Culcu G, Iovan D A, Krogman J P, Wilding M J T, Bezpalko M W, Foxman B M, Thomas C M. J. Am. Chem. Soc., 2017, 139(28): 9627.
[96]

Gong J Y, Lee C S, Kim E J, Chang Y Y, Chang Y S. J. Hazard. Mater., 2016, 310: 135.
[97]

Xiang S H, Cheng W C, Nie X Q, Ding C C, Yi F C, Asiri A M, Marwani H M. J. Taiwan Inst. Chem. Eng., 2018, 85: 186.
[98]

Liu Y, Fan Q, Wang J L. J. Hazard. Mater., 2018, 342: 166.
[99]

Lubphoo Y, Chyan J M, Grisdanurak N, Liao C H. J. Taiwan Inst. Chem. Eng., 2016, 59: 285.
[100]

Lee S D, Mallampati S R, Lee B H. Environ. Sci. Pollut. Res., 2017, 24(21): 17769.
[101]

Zhu F, Ma S Y, Liu T, Deng X Q. J. Clean. Prod., 2018, 174: 184.
[102]

Zhang Q, Zhao D L, Ding Y, Chen Y, Li F F, Alsaedi A, Hayat T, Chen C L. J. Clean. Prod., 2019, 230: 1305.
[103]

Zhu F, Li L W, Ren W T, Deng X Q, Liu T. Environ. Pollut., 2017, 227: 444.
[104]

Zhu F, Wu Y Y, Liang Y K, Li H H, Liang W J. Chem. Eng. J., 2020, 389: 124276.
[105]

Zhu F, He S Y, Liu T. Ecotoxicol. Environ. Saf., 2018, 163: 544.
[106]

Shih Y H, Chen M Y, Su Y F, Tso C P. J. Hazard. Mater., 2016, 301: 416.
[107]

Taghizadeh S M, Berenjian A, Taghizadeh S, Ghasemi Y, Taherpour A, Sarmah A K, Ebrahiminezhad A. Ind. Crops Prod., 2019, 130: 230.
[108]

Wang J, Liu C, Li J S, Luo R, Hu X R, Sun X Y, Shen J Y, Han W Q, Wang L J. Appl. Catal. B Environ., 2017, 207: 316.
[109]

Cagnetta G, Huang J, Lomovskiy I O, Yu G. Environ. Technol., 2017, 38(22): 2916.
[110]

K V G R, Sudakaran S V,V Nancharaiah Y, P M, Chandrasekaran N, Mukherjee A. J. Environ. Chem. Eng., 2018, 6(2): 1683.
[111]

Wu M R, Ma Y W, Wan J Q, Wang Y, Guan Z Y, Yan Z C. J. Mater. Sci., 2019, 54(10): 7483.
[112]

Wang X Y, Zhang B B, Ma J, Ning P. J. Environ. Sci., 2020, 89: 194.
[113]

Hu Y B, Zhang M Y, Li X Y. Environ. Int., 2019, 133: 105249.
[114]

Ruiz-Torres C A, Araujo-Martínez R F, Martínez-Castañón G A, Morales-Sánchez J E, Guajardo-Pacheco J M, González-Hernández J, Lee T J, Shin H S, Hwang Y, Ruiz F. Chem. Eng. J., 2018, 336: 112.
[115]

Li Z H, Xu S Y, Xiao G H, Qian L M, Song Y. J. Environ. Manag., 2019, 244: 33.
[116]

Du Q, Li G X, Zhang S S, Song J P zhao Y, Yang F. J. Hazard. Mater., 2020, 383: 121170.
[117]

Tian H F, Liang Y, Yang D M, Sun Y F. Chemosphere, 2020, 239: 124807.
[118]

Kim H J, Leitch M, Naknakorn B, Tilton R D, Lowry G V. J. Hazard. Mater., 2017, 322: 136.
[119]

Xue W J, Peng Z W, Huang D L, Zeng G M, Wan J, Xu R, Cheng M, Zhang C, Jiang D N, Hu Z X. J. Hazard. Mater., 2018, 359: 290.
[120]

Luo F, Chen Z L, Megharaj M, Naidu R. Chem. Eng. J., 2016, 294: 290.
[121]

Zhou L, Li A, Ma F, Zhao H P, Deng F X, Pi S S, Tang A Q, Yang J X. Chem. Eng. J., 2020, 395: 125168.
[122]

Li J, Zhou Q X, Liu Y L, Lei M. Sci. Technol. Adv. Mat., 2017, 18: 3.
[123]

Dong H R, Ning Q, Li L, Wang Y Y, Wang B, Zhang L H, Tian R, Li R, Chen J, Xie Q Q. Sep. Purif. Technol., 2020, 230: 115869.
[124]

Rajajayavel S R C, Ghoshal S. Water Res., 2015, 78: 144.
[125]

Wang S C, Song Y D, SunY K. Environ. Technol. Innov., 2018, 11: 339.
[126]

Dong H R, Jiang Z, Deng J M, Zhang C, Cheng Y J, Hou K J, Zhang L H, Tang L, Zeng G M. Water Res., 2018, 129: 51.
[127]

Wang X Y, Yang J C, Zhu M P. J. Taiwan Inst. Chem. Eng., 2014, 45(3): 937.
[128]

Terzi K, Sikinioti-Lock A, Gkelios A, Tzavara D, Skouras A, Aggelopoulos C, Klepetsanis P, Antimisiaris S, Tsakiroglou C D. Colloids Surf. A Physicochem. Eng. Aspects, 2016, 506: 711.
[129]

Galdames A, Ruiz-Rubio L, Orueta M, Sánchez-Arzalluz M, Vilas-Vilela J L. Int J. Env. Res. Pub. He., 2020, 17(16): 5817.
[130]

Guan X H, Du J S, Meng X G, Sun Y K, Sun B, Hu Q H. J. Hazard. Mater., 2012, 215/216: 1.
[131]

FengH P, Tang L, Tang J, Zeng G M, Dong H R, Deng Y C, Wang L L, Liu Y N, Ren X Y, Zhou Y Y. Environ. Sci. Nano, 2018, 5: 1595.
[132]

MaY X, Kou Y L, Xing D, Jin P S, Shao W J, Li X, Du X Y, La P Q. J. Hazard. Mater., 2017, 340: 407.
[133]

Cumbal L, Greenleaf J, Leun D, Sen-Gupta A K. React. Funct. Polym., 2003, 54(1/3): 167.
[134]

Samarghandi M R, Dargahi A, Zolghadr Nasab H, Ghahramani E, Salehi S. Water Environ. Res., 2020, 92(8): 1173.
[135]

Peng X X, Wang Z N, Huang J F, Pittendrigh B R, Liu S W, Jia X S, Wong P K. Water Res., 2017, 122: 471.

Funding

National Natural Science Foundation of China(21777040)

Fundamental Research Funds for the Central Universities(2017ZZD07)

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