Adsorbent-to-photocatalyst: Recycling heavy metal cadmium by natural clay mineral for visible-light-driven photocatalytic antibacterial

High value-added recycling of hazardous substances emerges as one of the most promising directions in current society, which can simultaneously relieve the environmental burden and obtain useful products. Here, we propose a transformation strategy from adsorbent to photocatalyst by recycling heavy metal with natural clay mineral. Sepiolite is selected as an adsorbent for removing Cd2+ in wastewater due to its excellent adsorption properties in terms of high specific surface area and structural channels. Then, in-situ sulfidation of the adsorbed Cd2+ is carried out, transforming it into CdS/Sep photocatalyst, which exhibits efficient photocatalytic antibacterial activity for Escherichia coli with a sterilization efficiency of 98.8% within 2 h. The intense visible light absorption of CdS and the efficient separation of photogenerated carriers render the prominent antibacterial activity. The main reactive species including superoxide radicals and hydroxyl radicals produced by CdS/Sep under visible light irradiation are diffused into the solution and attack the bacteria surrounding the photocatalysts. This work not only develops new ideas for recycling heavy metals for fabrication of efficient photocatalysts, but also provides a reference for water purification based on cost-effective natural minerals.