Photocatalytic Reduction of CO(2) with N-Doped TiO(2)-Based Photocatalysts Obtained in One-Pot Supercritical Synthesis

The objective of this work was to analyze the effect of carbon support on the activity and selectivity of N-doped TiO(2) nanoparticles. Thus, N-doped TiO(2) and two types of composites, N-doped TiO(2)/CNT and N-doped TiO(2)/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 TiO(2) P25 commercial catalyst during the photoreduction of CO(2) 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 TiO(2) nanoparticles led to a gaseous mixture, where CH(4) formed the majority compared to CO, N-doped TiO(2)/CNT and N-doped TiO(2)/rGO composites almost exclusively generated CO. Regarding the activity of the catalysts, the highest production rates of CO (8 µmol/gTiO(2)/h) and CH(4) (4 µmol/gTiO(2)/h) were achieved with composite N(1)/TiO(2)/rGO and N(1)/TiO(2) nanoparticles, respectively, where superscript represents the ratio mg N/g TiO(2). These rates are four times and almost forty times higher than the CO and CH(4) production rates observed with commercial TiO(2) P25.