Direct Z-scheme-based novel cobalt nickel tungstate/graphitic carbon nitride composite: Enhanced photocatalytic degradation of organic pollutants and oxidation of benzyl alcohol

Abstract

Designing a photocatalyst with strong redox ability and broad absorption of visible light is challenging in the field of photocatalysis. In this study, a series of novel Z-scheme-based Co x Ni 1−x WO 4 /g-C 3 N 4 (x = 0, 0.2, 0.5, 0.8 and 1) photocatalysts are synthesized with a view to increasing their redox abilities and improve their photocatalytic activities under broad absorption of visible light. The physicochemical properties are investigated, and the data show that an intimate stable heterojunction is formed between the bimetallic tungstate (CoNiWO 4 ) and g-C 3 N 4 (g-CN). Bifunctional properties of the synthesized catalysts are assayed by studying the decomposition of rhodamine B (RhB), bisphenol A (BPA), and selective conversion of benzyl alcohol (BA) to benzaldehyde (BDA). The composite material containing 1:1 molar ratio of Co/Ni shows the highest activity towards the degradation of RhB (99.8%) and BPA (99.32%), and the conversion of BA to BDA (86.96%), each at 1 g/ L -dose. The well-matched band structure between CoNiWO 4 and g-CN facilitates the formation of a Z-scheme charge transfer path, which prolongs the life time of the photoinduced charge carriers with high redox power, thus enhancing the photocatalytic activity. An intensive study of the mechanism proves that the degradation is driven by the hydroxyl ( • OH) and superoxide ( • O 2 - ) radicals, indicating that CoNiWO 4 /g-CN follows the Z-scheme charge transfer pathway. The current study has shown the superior photocatalytic activity among all tungstate-based hybrid photocatalytic materials for the degradation of complex organic pollutants, and selective transformation of BA to BDA. The findings in this study provide a new direction to the development of an efficient direct Z-scheme Co-Ni bimetallic tungstate-based photocatalyst for several redox reactions, especially mineralization of recalcitrant aqueous organic compounds. • A novel direct Z-scheme-based CoNiWO 4 /g-CN heterojunction is synthesized. • Photocatalytic degradation of RhB and BPA, and oxidation of BA are investigated. • Material with 1:1 Co-Ni molar ratio shows the best photocatalytic activity. • • O 2 - and • OH are the main ROS in the photocatalytic degradation of aqueous pollutants. • A direct Z-scheme charge transfer mechanism over CoNiWO 4 /g-C 3 N 4 is proposed.