Visible light-induced photocatalytic oxidation of gaseous ammonia on C surface-coated N-TiO2 catalyst: synthesis, properties and mechanism

This paper explores an eco-friendly and efficient photocatalytic oxidation (PCO) technology aimed at converting NH3 into N2, which holds considerable importance for environmental conservation and human well-being. Building upon previous investigations of N-TiO2 catalysts, the research group successfully synthesized an N-TiO2 catalyst featuring a carbon layer on its surface via mechanical mixing followed by calcination at 400 °C (denoted as C/N-TiO2(1), 1 represents the molar ratio of N and Ti). The analysis concentrated on the influence of C content on the PCO efficiency of NH3, revealing a peak performance correlated with increasing C levels. Notably, the C/N-TiO2(1) catalyst with 3.0 wt% C exhibited remarkable catalytic performance, achieving a conversion rate of 94 % and selectivity of 98 %. The enhancement of catalytic activity and selectivity is primarily attributed to the co-doping of C and N elements. Experimental results indicate that doping with N alone effectively suppresses the recombination of photogenerated carriers under visible light. Furthermore, the simultaneous doping of C and N significantly reduces the band gap energy of TiO2 (3.18 to 2.90 eV), thereby broadening its photoresponse range. Concurrently, more Ov (Oxygen vacancy) are formed under visible light irradiation, which enhances the PCO performance. More importantly, more acidic sites are introduced to improve the catalyst’s adsorption capacity for NH3. Additionally, the impact of various reaction components on the PCO capability of the 3.0 wt% C/N-TiO2(1) catalyst is examined further. The findings indicate that oxygen anion radicals produced from O2 play a critical role in facilitating NH3-PCO. However, the presence of CO2 and extra H2O could hinder the approach of NH3 molecules to the active sites and decrease the longevity of photogenerated ·OH, consequently reducing catalytic effectiveness. This research introduces fresh insights and optimization approaches for enhancing the activity, selectivity, and stability of catalysts.