Efficient degradation of naphthenic acids in water using a sustainable engineered biochar/ZnO composite under simulated solar light.

[Display omitted] • BC/ZnO composites were successfully synthesized from wood wastes. • The BC/30 %ZnO composite showed enhanced photocatalytic performance than pure ZnO. • The composite presented good reusability and stability after 4 cycles of use. • First study applied BC/ZnO composite for NAs mixture photocatalytic degradation. • Over 95 % of NAs in mixture were degraded by BC/30 %ZnO after 6 h solar irradiation. Naphthenic acids (NAs) present in oil sands process water (OSPW) have brought increasing environmental concerns due to their potential risk to aquatic and mammalian species. In this study, sustainable biochar zinc oxide (BC/ZnO) composites were synthesized using wood waste with different ZnO content and applied under simulated solar light for the photocatalytic degradation of different NAs for the first time. The best experimental conditions were determined as 0.5 g/L BC/30%ZnO and 4 h of simulated solar irradiation time, achieving 93.7 % degradation of cyclohexanecarboxylic acid (CHA) following the pseudo-first order kinetics. BC, with a porous structure and roughened surface, acted as an excellent platform for ZnO particles and an electron reservoir to inhibit the recombination of photogenerated electron-hole pairs. Hydroxyl radicals (•OH) were identified to play the dominant role in CHA degradation, and the enhanced photocatalytic performance of the BC/30%ZnO composite was proved by more •OH species detected compared to synthesized ZnO. The composite showed good reusability and stability after 4 successive cycles of use, still achieving 92.9 % degradation of CHA. Moreover, this is the first study applying BC/30%ZnO composite for the simultaneous degradation of a complex mixture of eight NAs with significantly different chemical structures. The competition kinetics were observed among different NAs in the mixture, resulted in over 95 % degradation of total NAs after 6 h treatment. By applying wood waste-based BC/ZnO composite with excellent photocatalytic performance in combination with solar light as green energy source, this research highlights a promising sustainable approach for real OSPW remediation. [ABSTRACT FROM AUTHOR]