Green Engineered\nCuO/SnO<sub>2</sub>/HNT Composites:\nIlluminating the Photocatalytic Path for Organic Pollutant Remediation\nand Zebrafish Embryo Toxicity Evaluation

Photocatalysis stands out as a promising technique for\ntreating\norganic contaminants, yet the quest for visible light active composite\nmaterials, crafted through cost-effective, eco-friendly, and uncomplicated\nprocesses, poses formidable challenges. Here, we introduce a successful\nendeavor, the synthesis of a CuO/SnO<sub>2</sub> (CS) composite via\na microwave method, employing <i>Carissa edulis</i> fruit\nextract as a reducing as well as capping agent. Various loadings of\nCS-HNT composites were prepared by ultrasonically incorporating CS\nonto nanotubular halloysite (HNT) clay. Employing a suite of types\nof characterization, including XRD, XPS, FT-IR, FE-SEM, HR-TEM, ζ\npotential, UV–vis–DRS, TGA, BET, and EIS, we meticulously\nexplored the morphology, structure, stability, surface area, electrochemical,\nand optical properties of the developed CS-HNT composites. HR-TEM\nobservations unveiled the formation of a heterojunction between cubic\nCuO and spherical SnO<sub>2</sub> on the HNT clay surface. Optical\nand EIS analysis highlighted that the 20CS-HNT composite displayed\nsignificant absorption in the visible region, efficient electron–hole\npair separation, and enhanced interfacial charge transport relative\nto other loadings. Photocatalytic evaluations and optimization studies\nrevealed that the 20CS-HNT photocatalyst achieved notable removal\nefficiencies, eliminating 85% of Congo red (CR) and 80% of tetracycline\n(TC) within 90 min and 74% of ATZ in 3 h under visible light conditions.\nScavenging investigations, the fluorescence probe method, and a NBT\ntransformation study underscored the pivotal roles of hydroxyl and\nsuperoxide radicals in pollutant removal. The reusability trials highlighted\nthe exceptional stability and recyclability of the photocatalyst,\neven after five cycles. In addition, zebrafish embryo toxicity tests\nrevealed improved survival and hatching rates in photocatalyst-treated\nsamples compared to those of controls. Moderate toxicity was observed\nin treated TC, while the treated CR sample showed non-lethal toxicity.\nIn essence, this study unveils a straightforward and efficacious approach\nfor developing photocatalysts for large-scale wastewater treatment.\nFurthermore, it proposes the adoption of safe clay-based bimetal oxide\nphotocatalysts in diverse environmental applications.