Nanostructured NiCo₂O₄/BiVO₄ Heterojunctions for Visible-Light\nPhotocatalytic H₂O‑to‑H₂O₂ Synchronized Organic\nPollutant Oxidation

Abstract

Photocatalytic\nH₂O₂ generation using unlimited\nsolar energy for in situ oxidation of organic pollutants in wastewater\nhas been environmentally attractive. Photocatalytic H₂O-to-H₂O_2(aq)reaction by BiVO₄, however, suffered\nfrom relatively low yields (e.g., 24 μM h^–1) under visible-light irradiation, mainly due to its high recombination\nrate of charge carriers. Herein, nanostructured NiCo₂O₄/BiVO₄ Z-scheme heterojunctions were prepared to\nincrease the oxygen reduction reaction for a higher H₂O₂ yield rate (than BiVO₄ by 16 times approximately).\nAdditionally, highly reactive superoxide (^•O₂^–) and hydroxyl (^•OH)\nradicals from the photocatalytic H₂O-to-H₂O₂ process enhanced oxidation of a representative organic pollutant\n(i.e., methylene blue) under visible-light irradiation. The photocatalytic\noxidation rate constant was as high as 2 × 10^–7 M^–1 s^–1. This visible-light\nphotocatalytic H₂O-to-H₂O₂ synchronized\noxidation of an organic pollutant by the nanostructured NiCo₂O₄/BiVO₄ heterojunctions demonstrates the possibility\nfor a potential energy self-sufficient organic wastewater treatment\nprocess.