Efficient magnetic hybrid ZnO-based photocatalysts for visible-light-driven removal of toxic cyanobacteria blooms and cyanotoxins

Abstract

A hybrid magnetic-ZnO-based photocatalyst platform is designed for the efficient and simultaneous sunlight-driven photoremoval of cyanobacteria and mineralization of cyanotoxins (anatoxin-A). The photocatalyst killing ability was evaluated against two types of microalgae with different morphology and toxicity, Spirulina platensis paracas and Anabaena flos-aquae. The hybrid photocatalyst Ni@ZnO@ZnS-Spirulina was synthetized by means of a multistep process using Spirulina as biotemplate. The effects of reactor geometry, magnetic actuation, and concordant architecture on photokilling ability were tested. Moreover, the prepared photocatalysts were demonstrated to be effective for the anatoxin-A degradation under artificial sunlight. In the interest of reducing waste content and optimizing resources, photocatalyst recycling after their useful lifetime has ended is proposed through the fabrication of microalgal biofuel-pellets. This inexpensive circular process involves multi-functional algae-based photocatalysts applied to the simultaneous destruction of algae blooms and cyanotoxins and then recycled to close the circle through cultivating biotemplates.