The objective of this work was to analyze the effect of carbon support on the activity and selectivity of N-doped TiO2 nanoparticles. Thus, N-doped TiO2 and two types of composites, N-doped TiO2/CNT and N-doped TiO2/rGO, were prepared by a new environmentally friendly one-pot method. CNT and rGO were used as supports, triethylamine and urea as N doping agents, and titanium (IV) tetraisopropoxide and ethanol as Ti precursor and hydrolysis agent, respectively. The as-prepared photocatalysts exhibited enhanced photocatalytic performance compared to TiO2 P25 commercial catalyst during the photoreduction of CO2 with water vapor. It was imputed to the synergistic effect of N doping (reduction of semiconductor band gap energy) and carbon support (enlarging e--h+ recombination time). The activity and selectivity of catalysts varied depending on the investigated material. Thus, whereas N-doped TiO2 nanoparticles led to a gaseous mixture, where CH4 formed the majority compared to CO, N-doped TiO2/CNT and N-doped TiO2/rGO composites almost exclusively generated CO. Regarding the activity of the catalysts, the highest production rates of CO (8 µmol/gTiO2/h) and CH4 (4 µmol/gTiO2/h) were achieved with composite N1/TiO2/rGO and N1/TiO2 nanoparticles, respectively, where superscript represents the ratio mg N/g TiO2. These rates are four times and almost forty times higher than the CO and CH4 production rates observed with commercial TiO2 P25.
Keywords: carbon dioxide conversion; carbon nanotubes; nitrogen doping; reduced graphene oxide; titania.