Harnessing rice husk-derived phytochemicals for eco-friendly synthesis of^ CdO/ZnO heterostructures for solar photocatalytic water treatment

A CdO/ZnO nanocomposite was successfully synthesized through a green and eco-friendly route using rice husk extract as a biogenic reducing and stabilizing agent. Structural, crystallographic, morphological, and optical analyses confirmed the successful formation of the heterostructure. The phytochemicals present in the extract facilitated the complexation of Cd2+ and Zn2+ ions, promoting controlled nanoparticle growth and stabilization. TEM-based particle size distribution analysis revealed average particle sizes of approximately 26 nm for CdO, 75 nm for ZnO, and 50 nm for the CdO/ZnO nanocomposite. Optical studies demonstrated dual absorption edges with band-gap energies ranging from 2.93–2.85 and 1.40–1.23 eV, indicating enhanced light-harvesting capability. The CdO/ZnO nanocomposite achieved 98% degradation of malachite green (MG) under direct solar irradiation within 80 min, outperforming the individual oxides. Scavenger experiments identified photogenerated holes (h+) and hydroxyl radicals (•OH) as the dominant reactive species. These findings highlight the potential of rice husk-derived CdO/ZnO nanocomposites for sustainable solar-driven wastewater treatment.