Oxidation-Resistant Cyclodextrin-Encapsulated-MXene/Poly (N-isopropylacrylamide) composite hydrogel as a thermosensitive adsorbent for phenols

Abstract

Phenolic compounds are persistent organic pollutants that endanger the environment and human health. To reduce phenol contamination, an oxidation-resistant MXene/poly(N-isopropylacrylamide) (PNIPAM) hydrogel thermosensitive adsorbents was prepared, which displayed excellent adsorption properties, good mechanical properties, and no secondary pollution. By using the 2-cyanoethyltriethoxysilane (CTES) as a bridge, (6-tetraethylenepentamine-6-deoxy) -β-cyclodextrin (NH-β-CD) was grafted onto the MXene surface to obtain NH-β-CD encapsulated MXene (MXene-CTES-β-CD). We exploit this cyclodextrin encapsulation method to simultaneously improve the antioxidant properties and the number of active groups of MXene. A thermosensitive adsorbent was prepared by in-situ polymerization of MXene-CTES-β-CD incorporated into N-isopropylacrylamide (NIPAM) and polymerized to obtain cyclodextrin-encapsulated-MXene/PNIPAM (MXene-CTES-β-CD/PNIPAM) thermosensitive adsorbents. The hydrogel adsorbent exhibited excellent oxidation resistance and no significant changes were observed even after 500 h of swelling in water. It also has excellent mechanical properties and could return to their original states from strains of 95%. Compared with the maximum capacity of the MXene/PNIPAM and MXene-CTES-COOH/PNIPAM hydrogels of 141 and 136 mg·g−1, the adsorption capacity of the MXene-CTES-β-CD/PNIPAM hydrogel increased, and the effective adsorption of phenols with the maximum capacity of 162 mg·g−1 for 4-NP under room temperature conditions. The hydrogel still has a high removal rate of its initial value 82% after five adsorption–desorption cycles, and the entire desorption process could be completed in distilled water at 35 °C not produce secondary contamination. Therefore, MXene-CTES-β-CD/PNIPAM thermosensitive adsorbents with high adsorption capacity, oxidation resistance, and no secondary pollution, which reveals prospects for sewage disposal. It is believed that this work indicates a new way to improve the oxidation resistance of MXenes.