Sulfur-doped carbon/TiO2 composites for ethylene photo-oxidation. Enhanced performance by doping TiO2 phases with sulfur by mobile species inserted on the carbon support

The performance of carbon xerogel/TiO₂ composites in ethylene photo-oxidation was analyzed under dynamic conditions considering various parameters, namely sulfur doping, dry vs. humid conditions and type of radiation (ultraviolet, UV, vs. visible light, Vis). The catalysts were synthesized using an acid-catalyzed sol-gel process and characterized with complementary techniques, including SEM/EDX, XRD, XPS and physical adsorption of N₂ and CO₂, among others. The performance of samples in ethylene removal by adsorption and photo-oxidation under dynamic flow was discussed and related with their physicochemical properties and the experimental conditions. Although ethylene adsorption was hindered by doping and humidity, both factors were found to enhance photoactivity by promoting the formation of highly oxidant hydroxyl radicals (HO^•). The composites showed an improved catalytic performance compared to bare TiO₂, with sulfur improving the activity by approximately 8 %. The presence of the carbon material also enhanced the performance under Vis radiation by nearly 25 %. It was suggested that sulfur species could migrate from the carbon support to the TiO₂ nanoparticles during carbonization, forming Ti-O-S bonds. This finding constitutes a novel, cost-effective, sustainable and scalable method for the preparation of supported and doped TiO₂ nanocomposites.