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

Abstract

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 TiOC bands determining the transfer direction of photo-excited hot charge carriers. The surface radical species including OH and O2− 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 and O2− radicals, being beneficial to the fundamental NH3 oxidation reaction. Furthermore, the remaining electrons were transferred to the surface of TiO2 via TiOC bonds, thus promoting the transformation of Ti4+ → TiO2-η 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.