Ultrafine MoOx clusters anchored on g-C3N4 with nitrogen/oxygen dual defects for synergistic efficient O2 activation and tetracycline photodegradation
Huidong Shen, Xinyu Zhan, Song Hong, Liang Xu, Chunming Yang, Alex W. Robertson, Leiduan Hao, Feng Fu, Zhenyu Sun
Abstract
Photocatalytic O 2 activation to generate reactive oxygen species is crucially important for purifying organic pollutants, yet remains a challenge due to poor adsorption of O 2 and low efficiency of electron transfer. Herein, we demonstrate that ultrafine MoO x clusters anchored on graphitic carbon nitride (g-C 3 N 4 ) with dual nitrogen/oxygen defects promote the photocatalytic activation of O 2 to generate·O 2 − for the degradation of tetracycline hydrochloride (TCH). A range of characterization techniques and density functional theory (DFT) calculations reveal that the introduction of the nitrogen/oxygen dual defects and MoO x clusters enhances the O 2 adsorption energy from −2.77 to −2.94 eV. We find that MoO x clusters with oxygen vacancies (Ov) and surface Ov-mediated Mo δ + (3 ≥ δ ≥ 2) possess unpaired localized electrons, which act as electron capture centers to transfer electrons to the MoO x clusters. These electrons can then transfer to the surface adsorbed O 2 , thus promoting the photocatalytic conversion of O 2 to ·O 2 − and, simultaneously, realizing the efficient separation of photogenerated electron–hole pairs. Our fully-optimized MoO x /g-C 3 N 4 catalyst with dual nitrogen/oxygen defects manifests outstanding photoactivities, achieving 79% degradation efficiency toward TCH within 120 min under visible light irradiation, representing nearly 7 times higher activity than pristine g-C 3 N 4 . Finally, based on the results of liquid chromatograph mass spectrometry and DFT calculations, the possible photocatalytic degradation pathways of TCH were proposed.