Synthesis of CQD-Decorated ZnO Nanoflowers for Efficient Photocatalytic Remediation of Organic Pollutants

Abstract

A heterostructured ZnO–Carbon Quantum Dot (CQD’s) nanocomposite was successfully synthesized with varying CQD’s loadings (5%, 10%, and 15%) to develop an efficient and reusable photocatalyst for environmental remediation. The composite exhibited a distinctive nanoflowerlike ZnO morphology uniformly decorated with CQD’s, forming a robust heterojunction that enhanced visible light absorption, promoted efficient charge separation, and facilitated easy catalyst recovery. Comprehensive material characterization using XRD, FTIR, XPS, BET, PL, UVDRS, FESEM, EDS, and HR-TEM confirmed its high crystallinity, surface area, and sunlight responsiveness. Photocatalytic performance evaluated under natural sunlight demonstrated an impressive 97.7% degradation of methylene blue within 60 minutes, following pseudo-first-order kinetics with a rate constant of 0.047 min⁻¹—over five times higher than commercial TiO₂-P25. The influence of operational parameters such as pH, light source, catalyst dosage, and reactive species was systematically assessed. The catalyst maintained high stability and reusability, retaining 85% efficiency after six cycles. LC-MS analysis revealed intermediate degradation products, while TOC and COD assessments confirmed substantial mineralization. Given the environmental persistence and toxicity of methylene blue, the ZnO-CQD composite presents a sustainable, solar-driven approach for treating dye-contaminated wastewater with high efficiency and recyclability.