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Application of Covalent Organic Frameworks in Adsorptive Removal of Divalent Mercury from Water

Shiyu Li , Yongguang Yin , Jianbo Shi , Guibin Jiang

Progress in Chemistry ›› 2022, Vol. 34 ›› Issue (5) : 1017 -1025.

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Progress in Chemistry ›› 2022, Vol. 34 ›› Issue (5) : 1017-1025 DOI: 10.7536/PC210918
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Application of Covalent Organic Frameworks in Adsorptive Removal of Divalent Mercury from Water
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Abstract

With the rapid development of modern industry, large amounts of mercury-containing compounds are discharged into the aqueous environment through various ways. Developing advanced technology for divalent mercury ion (Hg2+) removal from water is critical to reduce health risks and ensure ecological safety. As one of the effective water treatment technologies, the adsorptive removal of Hg2+ from aqueous solution has been concerned, and the key to make a breakthrough is to design adsorption materials with excellent performance. In recent years, covalent organic frameworks (COFs) have been widely used in the environmental remediation because of their high specific surface area, ordered porous structure and facile surface functionalization. Herein, the latest applications of COFs in adsorptive removal of Hg2+ from water are reviewed. The structure design, functionalized synthesis, Hg2+ adsorption behavior, reaction mechanism, affecting factors and potential to expand to large-scale applications of COFs are also discussed. Eventually, the future opportunities and development directions for COFs in Hg2+ removal are prospected.

Contents

1 Introduction

2 The structure and topology design of COFs

3 Functionalized synthesis of COFs

3.1 Bottom-up method

3.2 Post-synthesis modification

3.3 Physical blending method

4 Adsorption of Hg2+from aqueous solution by COFs

4.1 Adsorption isotherm

4.2 Adsorption kinetics

4.3 Mechanism of interaction between COFs and Hg2+

4.4 Influence of coexisting metal ions and pH value

4.5 Fluorescence characteristics of COFs during adsorption

5 Conclusions and perspectives

Graphical abstract

Keywords

covalent organic frameworks / mercury / functionalized synthesis / water treatment / adsorption

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Shiyu Li, Yongguang Yin, Jianbo Shi, Guibin Jiang. Application of Covalent Organic Frameworks in Adsorptive Removal of Divalent Mercury from Water. Progress in Chemistry, 2022, 34(5): 1017-1025 DOI:10.7536/PC210918

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1 Introduction

Heavy metal pollution is one of the important environmental problems facing mankind because of its high toxicity, bioaccumulation and persistence[1⇓~3]. As a widespread heavy metal in nature, mercury is liquid at room temperature and has high toxicity. It can volatilize into the atmosphere and transport over long distances, causing global pollution and health risks[4]. The Minamata disease incident in Japan in the mid-20th century made people deeply aware of the serious harm of mercury pollution[5]. As a global environmental problem, the emission of mercury has attracted more and more attention from the international community. The World Health Organization (WHO) lists mercury as one of the "top ten chemicals of significant public health concern."[6]. On August 16, 2017, the Minamata Convention on Mercury, jointly signed by 128 countries, came into force, marking a new stage of global cooperation to reduce mercury pollution[7]. At the same time, many countries have introduced laws and regulations against mercury emissions in order to reduce the environmental pollution and human health risks caused by mercury emissions[8,9].
Most of the earth's mercury is stored in metal-rich mineral deposits and fossil fuels, where it is released into the environment along with natural and anthropogenic activities, resulting in its ubiquity in various environmental media[10]. According to the Global Mercury Assessment 2018 of the United Nations Environment Programme (UNEP), the total atmospheric Mercury emissions from anthropogenic sources in 2015 were about 2220 tons, an increase of 20% compared with 2010[11]. In addition, mercury contaminates aquatic and terrestrial ecosystems through direct wastewater discharge, landfills, and atmospheric deposition[12]. Because mercury does not decompose or disappear in the environment, these new anthropogenic emissions will circulate in the biosphere and persist for a long time with the total amount of historical legacies[13].
As a medium that human beings must contact in daily production and life, water is an important "sink" of anthropogenic mercury emissions. Mercury can exist in many forms in the environment, such as elemental mercury, inorganic mercury and organic mercury, while in the water phase, divalent mercury ion (Hg2+) is the most common form of mercury[14]. Long-term exposure to low concentrations of Hg2+ can cause kidney and liver organ damage, and once it is transformed into organic forms by microorganisms or certain environmental conditions, such as methylmercury (MeHg), it will have higher bioaccumulation and toxicity, resulting in more serious health hazards[15,16][17][18⇓⇓~21]. Therefore, it is of great significance to develop pollution control technologies for Hg2+ in water bodies to reduce their water environment and health risks.
Similar to other heavy metal ions, Hg2+ in water cannot be degraded and are usually treated by isolation or conversion to low toxicity forms[22]. Due to the complex composition of environmental water, conventional water treatment technologies such as chemical precipitation, coagulation, electrolysis and reduction are difficult to remove mercury efficiently[23]. In order to control the discharge of mercury-containing wastewater and ensure the quality and safety of surface water, a variety of technologies have been developed to remove Hg2+ from water, such as ion exchange, adsorption, membrane separation, electrochemical treatment (electro-alloying, electro-deposition, electro-adsorption) and bioremediation[24][25][26][27⇓~29][30]. However, most of the methods still have some problems, and most of them are in the laboratory testing stage. Among them, the adsorption method has a considerable development space because of its low cost, no external energy and simple operation, and is expected to be a large-scale practical application of mercury removal technology.
For the adsorption removal of pollutants, the construction of efficient adsorbents is usually the key link[31]. At present, a series of new materials have been designed and synthesized for mercury pollution control in aquatic environment, especially Covalent organic frameworks (COFs) with high specific surface area, good chemical stability, fluorescence properties, adjustable pore size and ligands containing specific groups[25,32⇓ ~34][35]. Since its first report in 2005, this ordered porous crystalline material formed by reversible covalent polymerization has gradually become a research hotspot, and its adsorption capacity, selectivity and removal efficiency have been significantly improved compared with traditional materials[36,37]. In addition, other important characteristics of COFs materials such as water stability, regeneration methods, reusability, and mass preparation methods have been rapidly developed and applied to the removal of Hg2+ in real water environmental samples (lake water, mercury-containing sludge, etc.)[38][39,40].
In order to control mercury pollution and health risks in water and explore the broad potential of COFs as multifunctional materials in the field of environmental remediation, this paper summarizes the research progress of new COFs in the adsorption and removal of mercury ions in water in recent years. The structural characteristics of the materials, the environmental remediation-oriented functional synthesis strategy, and the adsorption behavior, reaction mechanism and adsorption process of COFs for Hg2+ in water were mainly discussed, and the challenges faced by industrial application and possible development directions in the future were also put forward.

2 Structure and Topology Design of COFs

The structure of materials plays a vital role in their physical and chemical properties. Functional COFs materials containing specific groups can be constructed by selecting appropriate symmetrical organic monomers through specific reversible condensation reactions[41]. Generally, the synthesis steps are as follows: (1) design the target topology and decompose it into basic geometric units according to the symmetrical nodes and geometric shapes; (2) finding equivalent monomer molecules and then expanding them into topological structures by using linkers; (3) The plane structure is extended in space to form a highly ordered network structure[37].
By adjusting the monomer type, the topological structure of the material can be predicted and controlled, and different dimensional COFs materials with high crystallinity, good structural order and rich pores can be precisely synthesized (Fig. 1)[42]. For two-dimensional (2D) COFs, a variety of topologies, such as hcb (honeycomb), sql (square), kgm (triangle/hexagon), hxl (hexagon) and kgd (diamond), can be constructed by combining symmetric monomers with different geometric shapes, such as line (C2), triangle (C3), quadrilateral (C4) or hexagon (C6)[43][44][45][46][37]. However, reports on the structure of three-dimensional (3D) COFs are relatively limited, and their monomer modules must contain Td (tetrahedrons) or orthogonal geometric units. According to different combination modes, the formed spatial network structures are named dia, bor, pts, ctn, etc[47][48][49][50].
In order to ensure the high order and stability of the material structure, a variety of chemical bonds are used to extend the connection monomer, and these different types of chemical bonds greatly affect the physical and chemical properties of the material. For example, COFs with boron-oxygen six-membered rings and boronic ester bonds have high crystallinity and exhibit fluorescence characteristics, but they are difficult to exist stably in aqueous solution due to the electron-deficient characteristics of boron atoms[37]. The imine bond (C = N) is more stable than the boron-oxygen bond (B — O), and the COFs formed by the imine bond have better chemical stability, but the crystallinity is reduced due to the poor reversibility of the condensation reaction, and the nitrogen atom also causes the dissipation of excitation energy through photoinduced electron transfer (PET), resulting in the poor luminescence of most materials[51]. Compared with the above B/N-containing bonds, the substituted olefinic (C = C) COFs developed by Jiang et al. Integrate chemical stability and fluorescence properties by virtue of the π-conjugated skeleton[52]. At the same time, COFs containing cyclic phenazine and triazine units and non-substituted olefin bonds (— CH = CH —) have also been designed and synthesized, which can maintain high porosity and crystallinity after long-term immersion in aqueous solution or strong acid/base[53,54].
For the adsorption and removal of Hg2+ in water, most of the current studies focus on 2D-COFs, whose two-dimensional topological atomic layers are stacked with each other through π-π interaction to produce a layered structure. Generally, the possible interlayer stacking modes are AA stacking or AB stacking, the former does not shift from layer to layer, while the latter has a systematic interlayer shift of a certain angle[55]. It is found that the AA stacking contributes to the formation of one-dimensional ordered channels, and the high specific surface area and appropriate pore size promote the full contact between specific active groups and Hg to improve the removal efficiency[56][57]. Compared with 2D-COFs, 3D-COFs with interpenetrating configuration can have higher specific surface area, but there are still few studies due to the limitation of monomer configuration.

3 Functional Synthesis of COFs

The function of COFs can be precisely regulated by a variety of organic monomers through specific topological design and a variety of reversible reactions. The preparation methods of COFs have been widely reported, including solvothermal, ionothermal, mechanochemical, microwave heating and interfacial polymerization[37][54][58][59][60]. In order to realize the application of COFs in the field of environmental remediation, high specific surface area and highly ordered porous structure are needed, and the introduction of functional groups to enrich the surface active sites is equally important. Based on this, three strategies, bottom-up, post-modification and physical blending, were established for the synthesis of functionalized COFs adsorbents (Fig. 2)[50].

3.1 Bottom-up method

The bottom-up method, also known as the direct modification method, refers to the direct synthesis of functionalized COFs materials by selecting functional or modified monomers at the starting point of synthesis, and the specific groups can be evenly distributed in the skeleton structure[42]. At the beginning of the design of the organic framework, the selection of symmetrical monomers with different lengths will change the pore size. For example, Fang et al. Used 1,3,5-tris (4-aminobiphenyl) benzene (TABPB) as a monomer instead of Tris (4-aminophenyl) amine (TAPA) to condense with pyromellitic dianhydride (PMDA) to obtain COFs with larger pore size[61]. At the same time, the same shape monomer modified by different functional groups can not only adjust the type of reversible reaction, but also some free groups can be further utilized in the subsequent synthesis to endow the material with other characteristics[57,62]. Therefore, COFs synthesized by bottom-up method have greater functionalization space and expansion possibility. However, the type and ratio of monomers will have a certain impact on the crystallinity and porosity of COFs, and the reaction conditions need to be optimized to ensure good stability and compatibility during the synthesis process[63].

3.2 Post-modification method

The post-modification strategy refers to the first synthesis of basic units with modifiable groups, and then further chemical modification of COFs by covalent or coordination bond connection with these free groups on the organic framework as reaction sites. Groups such as — OH, — CN, — C = C — and — C ≡ C — can be converted into functional groups with different functions through esterification and "click" reactions[57][64,65]. The introduction of these hydrophilic/hydrophobic, acid/basic or N, S-containing groups can greatly change the pore structure, hydrophobicity, surface charge distribution and affinity with the target pollutants of the material[66]. Compared with the bottom-up method, the post-modification method can directionally realize the target functionalization of the material while ensuring better stability. In addition to the grafting reaction, chemical reactions such as functional group isomerization or unsaturated bond conversion have also been used for the structural modification of COFs, which overcomes the problem of limited types of post-modification reactions to some extent[67].

3.3 Physical blending method

Since Dinca et al. Introduced functional molecular groups into the framework pores of COFs by solution immersion to improve the charge conduction of materials, physical blending has been widely explored as a relatively simple and practical modification strategy[68]. Due to the advantages of integrating different materials and introducing other physicochemical properties that COFs do not have, a variety of functional materials have been used to blend with COFs to form hybrid materials, such as metal/metal oxides, carbon materials (graphene/graphene oxides, carbon nanotubes) and metal-organic frameworks (MOFs)[69][70][71][72]. Based on the perspective of adsorption and removal of pollutants, the combination of COFs and magnetic materials (such as Fe3O4) can improve their separation ability, and the combination of COFs and graphene can improve their stability in water, thereby enhancing their adsorption performance[73][70]. In order to increase the practical application value, COFs powder can be embedded into crosslinked polymers to prepare films, and grafted on modified substrates to reduce the amount of COFs materials[74][60]. Although many composites containing COFs have been reported, their preparation methods are still relatively simple.

4 Adsorption of Hg2+ by COFs in water

In the existing water treatment technology, the coagulation method needs to add chemicals[3]; The chemical precipitation method needs secondary treatment[23]; The ion exchange method faces the problems of frequent system regeneration and maintenance[24]; The operation and management of bioremediation are difficult[30]; The membrane module of membrane separation technology is easy to be polluted[26]. The adsorption method has relatively low cost and simple operation, and can improve the adsorption performance of specific pollutants by constructing adsorption materials with high selectivity and adsorption capacity, so that it has great development potential and practical application value (Table 1)[25]. Relying on various advantages brought by structural characteristics, researchers have developed a series of COFs materials to adsorb and remove Hg2+ in water, such as COF-LZU8, TAPB-BMTTPA-COF, COF-S-SH, TPB-DMTP-COF-SH, TFPPy-CHYD, MSCTF-1, NOP-28, TpODH and SCTN-1, which show excellent removal effect compared with traditional materials (Table 2)[75][56][57][66][76][77][78][79][39]. The main reasons are as follows: (1) The highly ordered microporous/mesoporous framework is beneficial to the diffusion of adsorbates and the exposure of active sites, which improves the mass transfer efficiency; (2) Precisely adjustable pore size can increase the adsorption selectivity for pollutant ions; (3) The functionalized pore wall has more abundant surface active groups, which are adsorbed and combined with the target pollutants by strong affinity.

4.1 Adsorption isotherm

As one of the main indicators to measure the performance of adsorption materials, the maximum adsorption capacity can be obtained by fitting the adsorption isotherm. On the basis of previous research (TPB-DMTP-COF), Jiang et al. Used a bottom-up strategy to replace the methoxy group in the monomer with methylthio group, which effectively increased the sulfur content in the material while obtaining high-density stacked 2D-COFs[56]. The TAPB-BMTTPA-COF has high stability, crystallinity and porosity, and uses the strong combination of sulfur-containing groups in the organic skeleton and Hg to adsorb Hg2+ in water with a capacity of 734 mg/G, and the removal rate of the TAPB-BMTTPA-COF can remain above 90% after being reused for 6 times. In addition, the post-modification method has also been used to synthesize COFs materials containing sulfur groups. Thiol groups can be grafted onto vinyl-functionalized COFs by thiol-ene "click" reaction, thus achieving an ultra-high adsorption capacity for Hg2+ (1350 mg/G for COF-S-SH and 4395 mg/G for TPB-DMTP-COF-SH) and good stability (the removal rate is higher than 95% after four cycles)[57,66]. At the same time, most of the COFs have porous structures, and their adsorption isotherms can be well matched with the Langmuir model, indicating that the adsorption process of Hg2+ is mainly a monolayer adsorption on the surface of COFs[56].

4.2 Adsorption kinetics

Advanced adsorption materials not only need to have a high adsorption capacity for Hg2+, but also need to have a fast kinetic process[57]. Yu et al. Synthesized melamine and diphenyl sulfide into NOP-28 covalent triazine ring polymer in one pot by using Friedel-Crafts reaction, and obtained the adsorption capacity of 658 mg/G, and at the same time, it could adsorb and remove more than 90% of the Hg2+(1~25 mg/L) in water within 5 min. If it was extended to 10 min, the removal rate could be further improved (99.9%)[78]. On this basis, Bhaumik et al. Synthesized triazine ring-containing polymer nanospheres SCTN-1 by ionothermal method. By introducing high-density thioether groups into the monomer, it can reduce the Hg2+ of 5 mg/L to less than 1.6 μg/L within 5 min (lower than the WHO limit of 2 μg/L for mercury in drinking water), achieve a removal rate of 99.99% and show an ultra-fast kinetic process, and the removal rate is still higher than 95% after 7 cycles[39]. The adsorption distribution constant (Kd) is often used to evaluate the affinity of adsorbents with metal ions, and the Kd of SCTN-1 is 1.89×108mL/g, which is higher than that of commercial adsorption materials such as resin ( (5~10)×105mL/g) and silane chelating fiber (3.0×105~3.8×106mL/g)[25]. The kinetic processes of COF-S-SH and TPB-DMTP-COF-SH mentioned above are also relatively fast, and their Kd are as high as 2.3×109 and 3.23×109mL/g, respectively. In addition, almost all of the reported Hg2+ adsorption data of COFs could be well fitted by the pseudo-second-order kinetic equation.

4.3 Mechanism of interaction with Hg2+.

According to Lewis acid-base theory, Hg and S belong to soft acid and soft base respectively, and they have strong coordination binding ability[80]. The functionalized COFs reported so far are mainly based on the strong binding interaction between Hg and S, by introducing sulfur-containing groups such as thiols and thioethers to construct surface active sites on the organic framework or pore wall, and then adsorb and remove trace Hg2+ in water[65][75]. The main reason for the different adsorption effects of COFs is the difference in the structure (pore size and topology) and sulfur-containing groups (type, content and spatial arrangement) of COFs caused by the regulation of reaction monomers and synthesis paths. In addition, other adsorption mechanisms such as electrostatic interaction, coordination of electron-rich atoms and formation of amalgam have also been reported[79][82]. However, COFs constructed based on the above mechanism are still not comparable to COFs functionalized with sulfur-containing groups in terms of adsorption capacity and removal efficiency.

4.4 Effect of coexisting metal ions and pH

Whether it is industrial/domestic wastewater discharged by human beings or natural surface water in natural environment, its composition is often not single, but exists in a complex form of multiple mixtures. Especially for industrial wastewater, the water quality conditions are relatively harsh, and most of them are the mixed discharge of a variety of toxic and harmful metal pollutants under extreme pH[83,84]. For practical purposes, the constructed COFs should not only have good chemical stability and high adsorption removal efficiency over a wide pH range, but also have certain selectivity for Hg2+ as required (Table 3).
COFs materials that adsorb Hg2+ are mainly based on the interaction between Hg and S in the HSAB theory, and sulfur-containing groups such as mercaptan, thioether and methylthio can strongly coordinate with soft acid metal ions[66][77][56]. The study found that,It is used to treat Na+, K+, Ca2+,Mg2+, Mn2+, Fe3+ and Al3+ have almost no adsorption effect.It is less effective for Co2+, Ni2+, Zn2+, U Sn2+ U N Cr3+, which belong to junctional acids. While for the three soft acid or boundary acid metal ions of Cd2+, Pb2+ and Cu2+, different COFs showed differential binding ability, e.g., TAPB-BMTTPA-COF showed greater than 99% removal of both Hg2+ and Pb2+[56]. TpODH has almost no adsorption effect on Pb2+, but it can effectively remove Hg2+ and Cu2+ at the same time. It mainly uses the coordination of electron-rich N and O atoms with Hg and Cu to achieve the adsorption effect by electrostatic interaction[79]. Therefore, the introduction of chalcogen groups into COFs should also take into account the potential effects of nitrogen-containing groups and organic frameworks on the surface charge arrangement.
Because COFs are condensed by reversible reactions, they usually maintain good crystallinity over a wide pH range. However, when the pH is as low as 2 ~ 3, the adsorption effect of the material on Hg2+ in water will be inhibited to a certain extent, mainly due to two reasons: (1) the protonation effect of the groups containing S and N and the organic framework due to the high concentration of H+, resulting in the failure of the active sites[39]; (2) a large amount of H+ is adsorbed on the surface of the material, so that the Zeta potential of the material is positive, and a certain electrostatic repulsion force exists between the H+ and the Hg2+, so that the mutual combination is hindered[40]. In addition, too high pH (> 10) is not conducive to the adsorption reaction. At this time, Hg2+ is often combined with OH- and exists in various forms, such as HgOH+ and Hg(OH)2, and OH- in water will compete with functional groups for coordination[85,86]. Because of the weak binding force between these complexes and active groups, the adsorption effect will be reduced.

4.5 Fluorescence characteristics of COFs in adsorption process

Some COFs were found to have a change in fluorescence intensity during the adsorption of Hg2+ in water, and this fluorescence characteristic could be used for real-time detection of Hg2+ concentration (Table 4). For example, Wang et al. Synthesized COF-LZU8 by a bottom-up method, and the COF-LZU8 rich in thioether groups can not only adsorb and remove Hg2+, but also show a significant fluorescence quenching effect after adsorption by virtue of the electron transfer effect from the π-conjugated structure to the unoccupied orbital of Hg2+[75]. Although the adsorption capacity is limited (236 mg/G), COF-LZU8 can realize the simultaneous detection and removal of Hg2+ in water, thus improving its application value in the environmental field. On this basis, Qiu et al. Introduced flexible CHYD as a connecting unit to prepare TFPPy-CHYD, which could effectively regulate the aggregation quenching of fluorescence by interlayer π-π stacking, and the absolute quantum yield was increased to 13.6%, while the material also had a high adsorption capacity (758 mg/G). When contacted with Hg2+, TFPPy-CHYD produced photoinduced electron transfer effect (PET), resulting in fluorescence quenching[76]. To sum up, the advantages of COFs in simultaneous detection and removal of Hg2+ in water are mainly as follows: (1) The extended ordered π-conjugated framework can effectively improve the fluorescence intensity and become a signal transducer for the binding response between COFs and Hg2+; (2) a variety of functionalization strategies can introduce specific active groups into the organic framework to improve the selectivity of COFs for Hg2+; (3) The one-dimensional channels of the porous structure contribute to the sufficient contact between the Hg2+ and the functional groups. At present, there are still few reports on the simultaneous detection and adsorption removal of Hg2+ by COFs, and the main fluorescence quenching mechanisms are PET, ESIPT, AIQ, intramolecular charge transfer (ICT) and aggregation-induced luminescence (AIE)[76,87].

5 Conclusion and prospect

The performance of COFs for the adsorption of Hg2+ in water has been fully proved, and the maximum adsorption capacity of COFs can reach more than 4 times the mass of the adsorbent itself, and at the same time, it has a very fast kinetic process (2 min), and the adsorption effect is far superior to that of the existing commercial adsorbents[66]. However, in order to be applied in practical environments as soon as possible, COFs still need to solve a series of potential problems.For example, the synthesis steps are cumbersome and time-consuming, a large number of toxic organic reagents are consumed in the preparation and regeneration process, the cost of organic monomers is high, and it is difficult to achieve large-scale preparation, and most adsorbents only use Hg2+ aqueous solution for performance evaluation, which may lead to overestimation of adsorption effect. Based on this, some existing relevant examples and solutions will help COFs materials from the laboratory testing stage to practical industrial applications, mainly including the following three aspects.
(1) COFs materials mostly need to use organic monomers with high cost in synthesis, and the steps of modification are cumbersome, and organic solvents harmful to human body are needed. For example, before COF-LZU8 was polymerized by solvothermal method, the two monomers underwent one or three steps of modification[75]. Therefore, it is necessary to find alternative monomers with low cost and develop more green and simple synthetic routes. For example, Tong et al. Synthesized COF-SH containing thiol groups in one pot by using two monomers as precursors through Schiff base reaction, and achieved a high adsorption capacity (1283 mg/G). At the same time, the synthesis process of COF-SH is relatively simple, which is helpful for its promotion in practical application[40].
(2) Although COFs have achieved excellent adsorption capacity for Hg2+ in aqueous solution, their application in real aqueous environment needs to be explored. The low pH and complex composition of pollutants in industrial wastewater, and natural organic matter (NOM) commonly existing in natural water, can affect the adsorption process of Hg2+, which may weaken the performance of adsorbents[23]. Therefore, in addition to the use of Hg2+ aqueous solution to investigate the adsorption kinetics and adsorption isotherms of materials, the application of actual water samples is also particularly important. For example, Bhaumik et al. Used pond and Bay of Bengal water samples to prepare standard Hg2+ solutions to evaluate the effect of NOM on the adsorption performance of SCTN-1, and found that the Hg2+ removal efficiency was 99.9%,Kd and could reach 1.78×108mL/g[39]. To verify the application potential of COF-SH to actual wastewater, Tong et al. Used it to treat mercury-containing sludge from nonferrous metal smelting, and 75% of the Hg2+ extracted after acid washing could be removed within 5 min, proving that COF-SH can efficiently adsorb and remove Hg2+ even in wastewater with complex ions[40]. In addition, the influence of mercury species and forms should be considered when deducing the reaction mechanism of adsorption materials. Accurate identification of the occurrence of mercury in industrial/natural water bodies can help to design more effective adsorption materials.
(3) Most COFs can maintain their basic crystal structure in strong acid or alkali, and have better stability than other traditional materials. HCl solution is usually used to treat the COFs after adsorption of Hg2+, and the material after adsorption-desorption regeneration can be stably recycled for several times (the removal rate remains above 90%). However, these strong acids may be dangerous in practical applications, and their concentrations should be reduced or replaced by milder regeneration reagents in future studies. The use of chemicals can be avoided by using physical methods to desorb Hg. For example, the Ag NPs @ COF-LZU1 composite constructed by Qu et al. By physical blending method can be regenerated by thermal desorption method at 200 ℃ after adsorbing Hg2+, and the volatilized Hg vapor can be recovered by condensation method[82]. Based on the above discussion, the method of adsorbent regeneration should be further optimized to accelerate the industrial application of COFs.
The advantages of COFs, such as good chemical stability and high porosity, have attracted wide attention of researchers. Although the research on COFs is still in its infancy, its broad prospects in the field of environmental remediation are gradually developing. Taking advantage of the high affinity between sulfur and mercury, bottom-up and post-modification methods have been established for the synthesis of a series of sulfur-containing functional COFs, and the efficient adsorption removal of Hg2+ in water has been achieved. Its high specific surface area and highly ordered porous structure can promote mass transfer, which is beneficial for Hg2+ to fully contact with the active sites on the organic framework. However, the current understanding of the structure-activity relationship of adsorption materials (such as the synergistic effect between pore size and active groups) is not clear enough, and it needs to be further studied by means of theoretical calculation in the future. In addition, due to the rapid development of the application of COFs materials in the environmental field, the related ecological risk assessment needs to be carried out. With the more comprehensive and in-depth understanding of these materials, COFs are expected to play a more important role in water treatment technology, contributing to water environmental risk management and water ecological security.

References

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

Fu F L, Wang Q. J. Environ. Manage., 2011, 92(3): 407.
[2]

Zou Y D, Wang X X, Khan A, Wang P Y, Liu Y H, Alsaedi A, Hayat T, Wang X K. Environ. Sci. Technol., 2016, 50(14): 7290.
[3]

Carolin C F, Kumar P S, Saravanan A, Joshiba G J, Naushad M. J. Environ. Chem. Eng., 2017, 5(3): 2782.
[4]

Gworek B, Dmuchowski W, Baczewska-Dᶏbrowska A H. Environ. Sci. Eur., 2020, 32: 128.
[5]

Balogh S J, Tsui M T, Blum J D, Matsuyama A, Woerndle G E, Yano S, Tada A. Environ. Sci. Technol., 2015, 49(9): 5399.
[6]

Wang L W, Hou D Y, Cao Y N, Ok Y S, Tack F M G, Rinklebe J, O'connor D. Environ. Int., 2020, 134: 105281.
[7]

Selin H, Keane S E, Wang S X, Selin N E, Davis K, Bally D. Ambio., 2018, 47(2): 198.
[8]

He J, Reddy G K, Thiel S W, Smirniotis P G, Pinto N G. Energ. Fuel., 2013, 27(8): 4832.
[9]

Ancora M P, Zhang L, Wang S X, Schreifels J J, Hao J M. Energy Policy., 2016, 88: 485.
[10]

Driscoll C T, Mason R P, Chan H M, Jacob D J, Pirrone N. Environ. Sci. Technol., 2013, 47(10): 4967.
[11]

UNEP, Global Mercury Assessment 2018, Geneva, Switzerland, 2019.
[12]

Liu M D, Du P, Yu C H, He Y P, Zhang H R, Sun X J, Lin H M, Luo Y, Xie H, Guo J M, Tong Y D, Zhang Q G, Chen L, Zhang W, Li X Q, Wang X J. Environ. Sci. Technol., 2018, 52(1): 124.
[13]

Streets D G, Horowitz H M, Lu Z F, Levin L, Thackray C P, Sunderland E M. Atmos. Environ., 2019, 201: 417.
[14]

Ni Chadhain S M, Schaefer J K, Crane S, Zylstra G J, Barkay T. Environ. Microbiol., 2006, 8(10): 1746.
[15]

Clifton J C. Pediatr. Clin. North Am., 2007, 54(2): 237.
[16]

Zahir F, Rizwi S J, Haq S K, Khan R H. Environ. Toxicol. Pharmacol., 2005, 20(2): 351.
[17]

Bravo A G, Cosio C, Amouroux D, Zopfi J, Chevalley P A, Spangenberg J E, Ungureanu V G, Dominik J. Water Res., 2014, 49: 391.
[18]

Kim K H, Kabir E, Jahan S A. J. Hazard. Mater., 2016, 306: 376.
[19]

Minoia C, Ronchi A, Pigatto P, Guzzi G. Crit. Rev. Toxicol., 2009, 39(7): 627.
[20]

Azevedo B F, Furieri L B, Pecanha F M, Wiggers G A, Vassallo P F, Simoes M R, Fiorim J, Batista P R D, Fioresi M, Rossoni L, Stefanon I, Alonso M J, Salaices M, Vassallo D V. J. Biomed. Biotechnol., 2012, 2012: 949048.
[21]

Colon-Rodriguez A, Hannon H E, Atchison W D. Neurotoxicology., 2017, 60: 308.
[22]

Luo J M, Fu K X, Yu D Y, Hristovski K D, Westerhoff P, Crittenden J C. ACS ES&T Engineering, 2021, 1(4): 623.
[23]

Vikrant K, Kim K H. Chem. Eng. J., 2019, 358: 264.
[24]

Xia M D, Chen Z X, Li Y, Li C H, Ahmad N M, Cheema W A, Zhu S M. RSC Adv., 2019, 9(36): 20941.
[25]

Ai K L, Ruan C P, Shen M X, Lu L H. Adv. Funct. Mater., 2016, 26(30): 5542.
[26]

Bruno R, Mon M, Escamilla P, Ferrando-Soria J, Esposito E, Fuoco A, Monteleone M, Jansen J C, Elliani R, Tagarelli A, Armentano D, Pardo E. Adv. Funct. Mater., 2020, 31(6): 2008499.
[27]

Kim Y, Lin Z, Jeon I, Van Voorhis T, Swager T M. J. Am. Chem. Soc., 2018, 140(43): 14413.
[28]

Tunsu C, Wickman B. Nat. Commun., 2018, 9(1): 4876.
[29]

Candeago R, Kim K, Vapnik H, Cotty S, Aubin M, Berensmeier S, Kushima A, Su X. ACS Appl. Mater. Interfaces, 2020, 12(44): 49713.
[30]

Franco M W, Mendes L A, Windmöller C C, Moura K a F, Oliveira L G, Barbosa F R. Water Air Soil Pollut., 2018, 229(4): 127.
[31]

Luo J M, Yu D Y, Hristovski K D, Fu K X, Shen Y W, Westerhoff P, Crittenden J C. Environ. Sci. Technol., 2021, 55(8): 4287.
[32]

Ma L J, Wang Q, Islam S M, Liu Y C, Ma S L, Kanatzidis M G. J. Am. Chem. Soc., 2016, 138(8): 2858.
[33]

Fu K X, Liu X, Yu D Y, Luo J M, Wang Z W, Crittenden J C. Environ. Sci. Technol., 2020, 54(24): 16212.
[34]

Peng Y G, Huang H L, Zhang Y X, Kang C F, Chen S M, Song L, Liu D H, Zhong C L. Nat. Commun., 2018, 9(1): 187.
[35]

Xia Z J, Zhao Y S, Darling S B. Adv. Mater. Interfaces, 2020, 8(1): 2001507.
[36]

Huang N, Wang P, Jiang D L. Nat. Rev. Mater., 2016, 1: 10.
[37]

Diercks C S, Yaghi O M. Science, 2017, 355(6328): eaal1585.
[38]

Li J, Yang X D, Bai C Y, Tian Y, Li B, Zhang S, Yang X Y, Ding S D, Xia C Q, Tan X Y, Ma L J, Li S J. J. Colloid. Interface Sci., 2015, 437: 211.
[39]

Mondal S, Chatterjee S, Mondal S, Bhaumik A. ACS Sustain. Chem. Eng., 2019, 7(7): 7353.
[40]

Ma Z Y, Liu F Y, Liu N S, Liu W, Tong M P. J. Hazard. Mater., 2021, 405: 124190.
[41]

Kandambeth S, Dey K, Banerjee R. J. Am. Chem. Soc., 2019, 141(5): 1807.
[42]

Wang J L, Zhuang S T. Coord. Chem. Rev., 2019, 400: 213046.
[43]

Côté A P, Benin A I, Ockwig N W, O'keeffe M, Matzger A J, Yaghi O M. Science, 2005, 310(5751): 1166.
[44]

Ding X S, Guo J, Feng X, Honsho Y, Guo J D, Seki S, Maitarad P, Saeki A, Nagase S, Jiang D L. Angew. Chem. Int. Ed. Engl., 2011, 50(6): 1289.
[45]

Zhou T Y, Xu S Q, Wen Q, Pang Z F, Zhao X. J. Am. Chem. Soc., 2014, 136(45): 15885.
[46]

Dalapati S, Addicoat M, Jin S B, Sakurai T, Gao J, Xu H, Irle S, Seki S, Jiang D L. Nat. Commun., 2015, 6: 7786.
[47]

Uribe-Romo F J, Hunt J R, Furukawa H, Klöck C, O’keeffe M, Yaghi O M. J. Am. Chem. Soc., 2009, 131(13): 4570.
[48]

El-Kaderi H M, Hunt J R, Mendoza-Cortés J L, Côté A P, Taylor R E, O'keeffe M, Yaghi O M. Science, 2007, 316(5822): 268.
[49]

Lin G Q, Ding H M, Yuan D Q, Wang B S, Wang C. J. Am. Chem. Soc., 2016, 138(10): 3302.
[50]

Geng K Y, He T, Liu R Y, Dalapati S, Tan K T, Li Z P, Tao S S, Gong Y F, Jiang Q H, Jiang D L. Chem. Rev., 2020, 120(16): 8814.
[51]

Waller P J, Gandara F, Yaghi O M. Acc. Chem. Res., 2015, 48(12): 3053.
[52]

Jin E Q, Li J, Geng K Y, Jiang Q H, Xu H, Xu Q, Jiang D L. Nat. Commun., 2018, 9(1): 4143.
[53]

Lyu H, Diercks C S, Zhu C H, Yaghi O M. J. Am. Chem. Soc., 2019, 141(17): 6848.
[54]

Kuhn P, Antonietti M, Thomas A. Angew. Chem. Int. Ed. Engl., 2008, 47(18): 3450.
[55]

Mähringer A, Medina D D. Nat. Chem., 2020, 12: 985.
[56]

Huang N, Zhai L P, Xu H, Jiang D L. J. Am. Chem. Soc., 2017, 139(6): 2428.
[57]

Sun Q, Aguila B, Perman J, Earl L D, Abney C W, Cheng Y H, Wei H, Nguyen N, Wojtas L, Ma S Q. J. Am. Chem. Soc., 2017, 139(7): 2786.
[58]

Biswal B P, Chandra S, Kandambeth S, Lukose B, Heine T, Banerjee R. J. Am. Chem. Soc., 2013, 135(14): 5328.
[59]

Kappe C O. Angew. Chem. Int. Ed. Engl., 2004, 43(46): 6250.
[60]

Wang C B, Li Z Y, Chen J X, Li Z, Yin Y H, Cao L, Zhong Y L, Wu H. J. Membrane Sci., 2017, 523: 273.
[61]

Fang Q R, Zhuang Z B, Gu S, Kaspar R B, Zheng J, Wang J H, Qiu S L, Yan Y S. Nat. Commun., 2014, 5: 4503.
[62]

Huang N, Krishna R, Jiang D L. J. Am. Chem. Soc., 2015, 137(22): 7079.
[63]

Yang Y J, Faheem M, Wang L L, Meng Q H, Sha H Y, Yang N, Yuan Y, Zhu G S. ACS Cent. Sci., 2018, 4(6): 748.
[64]

Lu Q Y, Ma Y C, Li H, Guan X Y, Yusran Y, Xue M, Fang Q R, Yan Y S, Qiu S L, Valtchev V. Angew. Chem. Int. Ed. Engl., 2018, 57(21): 6042.
[65]

Sun Q, Aguila B, Earl L D, Abney C W, Wojtas L, Thallapally P K, Ma S Q. Adv. Mater., 2018, 30(20): e1705479.
[66]

Merí-Bofí L, Royuela S, Zamora F, Ruiz-González M L, Segura J L, Muñoz-Olivas R, Mancheño M J. J. Mater. Chem. A., 2017, 5(34): 17973.
[67]

Waller P J, Lyle S J, Osborn Popp T M, Diercks C S, Reimer J A, Yaghi O M. J. Am. Chem. Soc., 2016, 138(48): 15519.
[68]

Bertrand G H, Michaelis V K, Ong T C, Griffin R G, Dinca M. Proc. Natl. Acad. Sci. U. S. A., 2013, 110(13): 4923.
[69]

Ding S Y, Gao J, Wang Q, Zhang Y, Song W G, Su C Y, Wang W. J. Am. Chem. Soc., 2011, 133(49): 19816.
[70]

Colson J W, Woll A R, Mukherjee A, Levendorf M P, Spitler E L, Shields V B, Spencer M G, Park J, Dichtel W R. Science., 2011, 332(6026): 228.
[71]

Yoo J T, Cho S J, Jung G Y, Kim S H, Choi K H, Kim J H, Lee C K, Kwak S K, Lee S Y. Nano Lett., 2016, 16(5): 3292.
[72]

Fu J R, Das S, Xing G L, Ben T, Valtchev V, Qiu S L. J. Am. Chem. Soc., 2016, 138(24): 7673.
[73]

Yao B J, Zhang X M, Li F, Li C, Dong Y B. ACS Appl. Nano Mater., 2020, 3(10): 10360.
[74]

Yuan S S, Li X, Zhu J Y, Zhang G, van Puyvelde P, van Der Bruggen B. Chem. Soc. Rev., 2019, 48(10): 2665.
[75]

Ding S Y, Dong M, Wang Y W, Chen Y T, Wang H Z, Su C Y, Wang W. J. Am. Chem. Soc., 2016, 138(9): 3031.
[76]

Cui W R, Jiang W, Zhang C R, Liang R P, Liu J, Qiu J D. ACS Sustain. Chem. Eng., 2019, 8(1): 445.
[77]

Yang Z L, Gu Y Y, Yuan B L, Tian Y M, Shang J, Tsang D C W, Liu M X, Gan L H, Mao S, Li L C. J. Hazard. Mater., 2021, 403: 123702.
[78]

Fu Y, Yu W G, Zhang W J, Huang Q, Yan J, Pan C Y, Yu G P. Polym. Chem., 2018, 9(30): 4125.
[79]

Li Y, Wang C, Ma S J, Zhang H Y, Ou J J, Wei Y M, Ye M L. ACS Appl. Mater. Interfaces, 2019, 11(12): 11706.
[80]

Wang Z Y, Mi B X. Environ. Sci. Technol., 2017, 51(15): 8229.
[81]

Huang L J, Shen R J, Liu R Q, Shuai Q. J. Hazard. Mater., 2020, 392: 122320.
[82]

Wang L L, Xu H M, Qiu Y X, Liu X S, Huang W J, Yan N Q, Qu Z. J. Hazard. Mater., 2020, 389: 121824.
[83]

Barakat M A. Arab. J. Chem., 2011, 4(4): 361.
[84]

Burakov A E, Galunin E V, Burakova I V, Kucherova A E, Agarwal S, Tkachev A G, Gupta V K. Ecotoxicol. Environ. Saf., 2018, 148: 702.
[85]

Lu X F, Ji W H, Yuan L, Yu S, Guo D S. Ind. Eng. Chem. Res., 2019, 58(38): 17660.
[86]

Li Y F, Hu T L, Chen R, Xiang R, Wang Q, Zeng Y F, He C Y. Chem. Eng. J., 2020, 398: 125566.
[87]

Yu Y X, Li G L, Liu J H, Yuan D Q. Chem. Eng. J., 2020, 401: 126139.

Funding

National Key Research and Development Program of China(2020YFA0907400)

National Natural Science Foundation of China(42025704)

CAS Interdisciplinary Innovation Team(JCTD-2018-04)

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