Green Engineered CuO/SnO₂/HNT Composites: Illuminating the Photocatalytic Path for Organic Pollutant Remediation and Zebrafish Embryo Toxicity Evaluation

Photocatalysis stands out as a promising technique for treating organic contaminants, yet the quest for visible light active composite materials, crafted through cost-effective, eco-friendly, and uncomplicated processes, poses formidable challenges. Here, we introduce a successful endeavor, the synthesis of a CuO/SnO₂ (CS) composite via a microwave method, employing <i>Carissa edulis</i> fruit extract as a reducing as well as capping agent. Various loadings of CS-HNT composites were prepared by ultrasonically incorporating CS onto nanotubular halloysite (HNT) clay. Employing a suite of types of characterization, including XRD, XPS, FT-IR, FE-SEM, HR-TEM, ζ potential, UV-vis-DRS, TGA, BET, and EIS, we meticulously explored the morphology, structure, stability, surface area, electrochemical, and optical properties of the developed CS-HNT composites. HR-TEM observations unveiled the formation of a heterojunction between cubic CuO and spherical SnO₂ on the HNT clay surface. Optical and EIS analysis highlighted that the 20CS-HNT composite displayed significant absorption in the visible region, efficient electron-hole pair separation, and enhanced interfacial charge transport relative to other loadings. Photocatalytic evaluations and optimization studies revealed that the 20CS-HNT photocatalyst achieved notable removal efficiencies, eliminating 85% of Congo red (CR) and 80% of tetracycline (TC) within 90 min and 74% of ATZ in 3 h under visible light conditions. Scavenging investigations, the fluorescence probe method, and a NBT transformation study underscored the pivotal roles of hydroxyl and superoxide radicals in pollutant removal. The reusability trials highlighted the exceptional stability and recyclability of the photocatalyst, even after five cycles. In addition, zebrafish embryo toxicity tests revealed improved survival and hatching rates in photocatalyst-treated samples compared to those of controls. Moderate toxicity was observed in treated TC, while the treated CR sample showed non-lethal toxicity. In essence, this study unveils a straightforward and efficacious approach for developing photocatalysts for large-scale wastewater treatment. Furthermore, it proposes the adoption of safe clay-based bimetal oxide photocatalysts in diverse environmental applications.