<italic>In situ</italic> FT-IR investigation on visible light photocatalytic NO oxidation mechanism with (BiO)<sub>2</sub>CO<sub>3</sub> and N-doped (BiO)<sub>2</sub>CO<sub>3</sub> hiararchical microspheres

Abstract

With the rapid development of industry, air pollution has become a focused issue worldwide. As one of the major air pollutants, nitric oxide (NO) would lead to serious atmospheric problems such as acid rain, haze, and photochemical smog. Photocatalysis, as a green and effective technology, has become one of the most promising technologies for solving air pollution problems. As one of the typical photocatalyst, (BiO)2CO3 consists of alternating layers of [Bi2O2]2+ and CO32− groups and has good optical absorption property, emerging as an attractive photocatalyst. In this work, (BiO)2CO3 and in situ N-doped (BiO)2CO3 hierarchical microspheres were fabricated by a one-pot hydrothermal method and applied to photocatalytic NO removal. The as-prepared samples were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and ESR. The photocatalytic NO oxidation process was monitored by in situ DRIFTS. The results indicated that the addition of urea has significant impact on (BiO)2CO3. The changed exposed facet influenced the morphological structure, band gap has narrowed and electronic-hole recombination rate of the as-prepared N doped (BiO)2CO3 has decreased. There are a lot of reports on photocatalytic NO oxidation, and the photocatalytic reaction mechanism for NO purification has been proposed for some photocatalysts with ·O2− and ·OH radicals as the main reactive species and nitrates as the final products. However, little is known about the reaction intermediates during photocatalysis. To reveal the reaction mechanism of photocatalytic NO oxidation, in situ DRIFTS investigation was applied to probe the reaction process. The photocatalytic NO oxidation mechanism was revealed based on the in situ DRIFTS and ESR results. With N doping, the reaction process and the free radicals which participated during the photocatalystic reaction process become different from the pure (BiO)2CO3 sample. For BOC, ·O2− is main active radical, but for NBOC, the active radical changed to ·OH. A new intermediate of NO+ was discovered during photocatalysis, which increased the efficiency of the reaction. Because of the N doping, the electronic structure of (BiO)2CO3 has been broken, which leads to the formation of more oxygen vacancy. The present work could provide new perspectives for advancing the photocatalysis efficiency, offer a new insight into the photocatalytic NO oxidation process and promote large-scale environmental applications of high-performance photocatalysts.