Synergistic effects of single/multi-walls carbon nanotubes in TiO2 and process optimization using response surface methodology for photo-catalytic H2 evolution

Abstract

Nobel metals free MW/SW supported TiO2 nanocatalysts were prepared via wet impregnation assisted sol-gel method and tested for photocatalytic H2 evolution. The photoactivity of TiO2 mediated by MW/SW was considerably improved due to superior charges separation. More importantly, hydrogen production depends on wall numbers such as multiwall or single wall carbon nanotubes, works as electrons acceptor and promoted charges separation. The maximum H2 evolution rate of 11,060 ppm h-1g-cat-1 was achieved over MW/TiO2/SW, 1.24 folds higher than SW/TiO2 and 1.42 times higher than MW/TiO2 composites. This improved productivity was due to synergistic effects between SW/MW, which greatly promoted charge carriers separations and enables absorption of visible light. Besides, more H2 production with SW/TiO2 compared to MW/TiO2 was due to more trapping of electrons by single wall than using multi-walls. The activity of composite further enhanced with methanol as hole-scavenger, higher in order of methanol > ethanol > propanol due to presence of α-hydrogen atoms bonded with C-atoms. Response surface methodology (RSM) approach of full factorial design applied to investigate significance and influence of reaction time, loading of catalyst and methanol-water concentration on H2 yield. The interaction between parameters reveals that catalyst loading has more influence on H2 evolution compared to other factors. Therefore, this study provides a new approach for noble-metals free synthesis of composite with enhanced visible light H2 evolution and optimization of parameters for maximum photo-catalytic H2 production.