Ultrafine MoO x clusters anchored on g-C 3 N 4 with nitrogen/oxygen dual defects for synergistic efficient O 2 activation and tetracycline photodegradation

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.