Claus waste-derived TiO₂ coupled with UiO-66 for an S-scheme heterojunction with enhanced photocatalytic activity

This research investigates the decoration of UiO-66 with TiO₂ derived from recycling units of the gas refinery Claus process, using a solvothermal technique. Comprehensive materials characterization by XRD, FT-IR, TGA, FE-SEM, and BET confirmed the successful formation of a well-defined UiO-66/TiO₂ heterojunction, with TiO₂ nanoparticles uniformly distributed on the UiO-66 surface. The nanocomposite exhibited a reduced optical bandgap (2.92 eV) compared to pristine UiO-66 (3.97 eV) and TiO₂ (3.20 eV), as well as enhanced surface. The constructed UiO-66/CWT S-scheme heterojunction facilitates efficient charge separation via interfacial recombination of UiO-66 photogenerated electrons and CWT photogenerated holes, thereby improving photocatalytic efficiency. The resulting UiO-66/TiO₂ nanocomposite exhibited enhanced photocatalytic performance under visible light compared to pristine UiO-66 and TiO₂ particles. The optimal conditions for Rhodamine B (RhB) mineralization with the highest photocatalytic removal efficiency were determined by evaluating the effects of the Claus process waste (CWT) to UiO-66 weight ratio, pH, photocatalyst dose, initial dye concentration, and reaction temperature. Under optimal conditions, with a CWT to UiO-66 weight ratio of 2:1, a pH of 3, a photocatalyst dose of 500 mg/L, an initial dye concentration of 25 mg/L, and a temperature of 25 °C, the dye removal efficiency increased to 97.42%. In other words, the formation of the nanocomposite can improve charge carrier separation and enhance photocatalytic activity. Furthermore, the decolorization kinetics followed accurately the Langmuir-Hinshelwood (L-H) first-order model. In conclusion, high-purity TiO₂ was successfully produced using as-recycled TiO₂ sourced from the gas refinery Claus process, demonstrating the potential of converting low-grade TiO₂ from spent catalysts. The approach outlined here offers new perspectives on the value-added recycling of titanium resources in the Claus unit.