Highly reduced ecotoxicity of ZnO-based micro/nanostructures on aquatic biota: Influence of architecture, chemical composition, fixation, and photocatalytic efficiency

Abstract

Developing efficient sunlight photocatalysts with enhanced photocorrosion resistance and minimal eco-toxicological effects on aquatic biota is critical to combat water contamination. Here, the role of chem-ical composition, architecture, and fixation on the ecotoxicological effects on microalgae of different ZnO and ZnO@ZnS based water decontamination photocatalysts was analyzed in depth. In particular, the ecotoxicological effects of films, nanoparticles and biomimetic micro/nano-ferns were carefully as-sessed by correlating the algae's viability to the Zn(II) release, the photocatalyst-microalgae interac-tion, and the production of reactive oxygen species (ROS). The results showed a drastic improvement in algal viability for supported ZnO@ZnS core@shell micro/nanoferns, as their ecotoxicity after 96 h light exposure was significantly lower (3.7-10.0% viability loss) compared to the ZnO films (18.4-35.5% loss), ZnO micro/nanoferns (28.5-53.5% loss), ZnO nanoparticles (48.3-91.7% loss) or ZnO@ZnS nanoparticles (8.6-19.2% loss) for catalysts concentrations ranging from 25 mg L-1 to 400 mg L-1. In particular, the ZnO@ZnS micro/nanoferns with a concentration of 400 mg L-1 exhibited ex-cellent photocatalytic efficiency to mineralize a multi-pollutant solution (81.4±0.3% mineralization ef-ficiency after 210 min under UV-filtered visible light irradiation) and minimal photocorrosion (< 5% of photocatalyst dissolution after 96 h of UV-filtered visible light irradiation). Remarkably, the ZnO@ZnS micro/nanoferns showed lower loss of algal viability (9.8±1.1%) after 96 h of light exposure, with min-imal reduction in microalgal biomass (9.1±1.0%), as well as in the quantity of chlorophyll-a (9.5±1.0%), carotenoids (8.6±0.9%) and phycocyanin (5.6±0.6%). Altogether, the optimized ZnO@ZnS core@shell micro/nanoferns represent excellent ecofriendly photocatalysts for water reme-diation in complex media, as they combine enhanced sunlight remediation efficiency, minimal adverse effects on biological microorganisms, high reusability and easy recyclability.