Clay-supported CuO nanoparticles: Synthesis, characterization, and photocatalytic activities for malachite green decolorization

Abstract

Highly porous, clay-supported nanomaterials have great potential to advance catalysis. In this study, we synthesized a clay-supported copper oxide nanocomposite (CuO NCPs) using the co-precipitation method, specifically designed for the photocatalytic decolorization of malachite green dye (MG). The copper oxide nanoparticles (CuO NPs ( 1 )) and clay-supported CuO NCPs ( 2 ) were characterized using UV-Vis, FTIR, XRD, BET, and SEM-EDX to investigate optical properties, molecular structure, crystal structure, surface area and pore size distribution, surface morphology, and elemental composition. Key quantitative results include: average crystallite sizes of 11.73 nm (CuO NPs) and 11.97 nm (CuO NCPs) by XRD; approximate band gap energies of 2.16 eV and 2.07 eV, respectively. The clay-supported CuO NCPs ( 2 ) achieved 89.67 ± 1.4% decolorization compared to 82.96 ± 1.8% for unsupported CuO NPs ( 1 ) under identical conditions, a modest but statistically significant improvement (p = 0.012) after 180 min under a 200 W tungsten lamp. Adsorption during dark equilibration accounted for 9.8% and 11.3% of total removal, respectively, confirming that photochemical processes dominate. We report decolorization (loss of chromophore) rather than complete mineralization; TOC analysis was not performed. Raw smectite clay exhibits a moderate BET surface area of 73.67 m 2 /g with a total pore volume of 0.156 cc/g and an average pore diameter of 8.47 nm, characteristic of mesoporous 2:1 layered aluminosilicates with interlayer and interparticle voids. Upon synthesis of unsupported CuO NPs (1), a significant reduction in surface area to 27.05 m 2 /g was observed, accompanied by a decrease in pore volume to 0.094 cc/g and an increase in average pore diameter to 13.90 nm. Notably, the clay-supported CuO NCPs (2) recovered a substantially higher surface area of 36.14 m 2 /g and pore volume of 0.132 cc/g compared to unsupported CuO, while maintaining a large average pore diameter of 14.61 nm. We acknowledge the absence of reusability studies and scavenger tests as limitations of this study. Overall, composite materials combining adsorption and photocatalysis exhibit promising properties for removing hazardous dyes from wastewater, as the clay support improves CuO NPs dispersion and increases accessible surface area. However, further optimization, mineralization studies (TOC/COD), and mechanistic studies are required before industrial application.