Tetraphenyl-porphyrin decorated anatase TiO2 catalysts for the visible-light photocatalytic oxidation of gaseous ammonia at room temperature

Tetraphenyl-porphyrin (1 wt% TPP) decorated anatase TiO2 catalysts were optimized by one-step solvothermal method and presented high-efficient photo-catalytic activity of ammonia oxidation under visible-light irradiation with above 98% removal efficiency at room temperature within 8 h. TPP modifiers were successfully loaded onto TiO2 surface via Ti-O-C bands determining the transfer direction of photo-excited hot charge carriers. The surface radical species including (OH)-O-center dot and O-center dot(2)- generated from H2O/-OH and surface oxygen species were fleeting and hyperactive for the photocatalytic degradation of ammonia. TPP gave an evident promotion via the stimulative reactions due to the contributions of H+ and gave VB holes (h(+)), which had strong oxidation power for the direct oxidation of -OH/H2O and adsorbed oxygen to generate (OH)-O-center dot and O-center dot(2)- radicals, being beneficial to the fundamental NH3 oxidation reaction. Furthermore, the remaining electrons were transferred to the surface of TiO2 via Ti-O-C bonds, thus promoting the transformation of Ti4+ -> TiO2-n to generate oxygen vacancy defects for the efficient oxidation of gaseous NH3 and adsorbed -NHx species during photocatalytic reaction. However, the thermodynamic stable NH4NO3 products were generated via the combination of NH4+ and -NO3 species that could exist on the catalyst surface stably, resulting in the decline of photocatalytic activity.