Multi-function adsorbent-photocatalyst MXene-TiO composites for removal of enrofloxacin antibiotic from water.

MXenes, a new family of two-dimensional transition metal carbides or nitrides, have attracted tremendous attention for various applications due to their unique properties such as good electrical conductivity, hydrophilicity, and ion intercalability. In this work, TiC MXene, or MX, is converted to MX-TiO composites using a simple and rapid microwave hydrothermal treatment in HCl/NaCl mixture solution that induces formation of fine TiO particles on the MX parent structure and imparts photocatalytic activity to the resulting MX-TiO composites. The composites were used for enrofloxacin (ENR), a frequently found contaminating antibiotic, removal from water. The relative amount of the MX and TiO can be controlled by controlling the hydrothermal temperature resulting in composites with tunable adsorption/photocatalytic properties. NaCl addition was found to play important role as composites synthesized without NaCl could not adsorb enrofloxacin well. Adding NaCl into the hydrothermal treatment causes sodium ions to be simultaneously intercalated into the composite structure, improving ENR adsorption greatly from 1 to 6 mg ENR/g composite. It also slows down the MX to TiO conversion leading to a smaller and more uniform distribution of TiO particles on the structure. MX-TiO/NaCl composites, which have sodium intercalated in their structures, showed both higher ENR adsorption and photocatalytic activity than composites without NaCl despite the latter having higher TiO content. Adsorbed ENR on the composites can be efficiently degraded by free radicals generated from the photoexcited TiO particles, leading to high photocatalytic degradation efficiency. This demonstrates the synergetic effect between adsorption and photocatalytic degradation of the synthesized compounds.