Synthesis of silica materials containing cyclodextrin and their applications in wastewater treatment

Cyclodextrin-functionalized silica networks are advancedadsorbents for environmental applications. Silica-based adsorbents are low-cost and robust inorganic solids having large surface areas, high porosity, and excellent mechanical, physical, and chemical properties. They also possess wide possibilities of functionalization due to the silanol reactivity. Cyclodextrins are natural molecules obtained from the enzymatic degradation of starch. Theybelong to the family of cage moleculeshaving a hydrophobic cavity that can encapsulate other molecules. Cyclodextrin-functionalized silicas offer generally improved access to the binding sites because cyclodextrins are located on the external surface of the material. However, an uneven distribution of cyclodextrin molecules is often observed, and these materials havelow cyclodextrin loading, which can limit adsorption capacities. Nonetheless, for cyclodextrin-silica hybrid systems prepared through sol-gel or self-assembly process, cyclodextrin molecules are located within the framework of nanoporous silicas and, as a consequence, high cyclodextrin loadings, robust structures and higher surface area are observed. The application of cyclodextrin-based silica materials in solving environmental pollution problems has recently received a lot of attention due to their combined physical and chemical properties, resulting in strong binding affinities toward target chemical substances such as metal ions, dyes, pesticides, and drugs. This review reports the use of cyclodextrin-silica hybrid systems and cyclodextrin-functionalized silica used as adsorbents for the removal of inorganic and organic pollutants from aqueous solutions in solid-phase extraction and adsorption-oriented processes.