π complexation techniques show the advantages of low energy consumption, high efficiency, and reproducibility, etc. Thus, the π complexation techniques have been widely used in the fields of fuel desulfurization, olefin/paraffin separation, and CO separation from gas mixtures. Adsorbents are the key factors to the π complexation techniques. This review focuses on the synthesis methods and application efficiency of the π complexation adsorbents, and summarizes some important advances both at home and abroad. In general, the universal methods to synthesize the π complexation adsorbents are introduction of transition metal ions (Cu(Ⅰ), Ag(Ⅰ), and Pd(Ⅱ), etc.) into the supports with high surface areas. So far, methods on preparation of π complexation adsorbents based on inorganic molecular sieves have been very detailed, including ion exchange, impregnation method, solid-state grinding, and space confining etc. In this respect, researchers have carried out a large amount of studies. Moreover, the adsorbents show high efficiency. Recently, researchers devote to preparation of π complexation adsorbents based on metal-organic frameworks (MOFs), including undecorated and decorated MOFs. This route has good prospects in research and application fields. In addition, this review summarizes the advantages and disadvantages of several π complexation adsorbents, and gives prospects for the future development trends.

Contents
1 Introduction
2 Preparation of π complexation adsorbents based on inorganic molecular sieves
2.1 Ion exchange method
2.2 Impregnation method
2.3 Solid-state grinding method
2.4 Space confining method
3 Preparation of π complexation adsorbents based on metal-organic frameworks (MOFs)
3.1 In situ π complexation adsorption sites
3.2 Construction of π complexation adsorption sites
4 Preparation of π complexation adsorbents based on other porous materials
5 Chemical theories of π complexation adsorption
6 Other applications of complexation effect
7 Conclusion and outlook