A superhydrophobic covalent zeolitic imidazolate framework-polyhedral oligomeric silsesquioxane hybrid material as a highly efficient and reusable sorbent for organic solvents

Abstract

The deterioration of water bodies due to organic pollutants, arising from the discharge of industrial wastewater, requires the development of new functional materials such as superhydrophobic/superoleophilic materials for efficient water remediation. However, the large-scale practical applications of superhydrophobic materials are impeded by low surface energy fluorine compounds as one of the reactants in the synthesis of superhydrophobic materials, which has raised environmental issues due to their potential toxicity to humans. In addition to low surface energy, silicon-based compounds are eco-friendly and non-toxic and would be a better replacement for fluorine compounds to overcome these drawbacks. Accordingly, we have proposed a simple and fluorine-free strategy for constructing a superhydrophobic ZIF-POSS hybrid material through imine bond formation between the free aldehyde-functional group in zeolitic imidazolate frameworks (ZIF-90) and polyhedral oligomeric silsesquioxane containing amine groups (POSS-NH₂). Furthermore, the efficient incorporation of POSS-NH₂ into ZIF-90 is demonstrated by FT-IR, PXRD, thermogravimetric analyses, and ²⁹Si NMR and X-ray photoelectron spectroscopy. The resultant ZIF-POSS hybrid material displays an exceptionally high water contact angle of 157° and thus exhibits very high sorption selectivity and good absorbance for organic solvents from water. Consequently, ZIF-POSS@PDA@Sponge is successfully utilized for the removal of a series of organic solvents from water mixtures with a high separation efficiency of above 96% over 25 cycles of separation. More importantly, superhydrophobic ZIF-POSS and ZIF-POSS@PDA@Sponge exhibit excellent stability and durability under harsh chemical conditions which originate mainly from the mechanically and chemically inert POSS nanocage. Finally, this clearly suggests that the POSS supported zeolitic imidazolate framework (ZIF) might facilitate the rapid development of non-toxic superhydrophobic species for the excellent separation of organic solvents from water mixtures.