Solar-Assisted Synthesis of Poly(o-phenylenediamine)@Zinc Oxide Composites for Photocatalytic Cu(II) Ion Removal

Copper(II) ions in water sources pose serious environmental and health risks due to their toxicity and nonbiodegradability. Their persistent presence, primarily from industrial discharge, necessitates efficient and sustainable removal strategies. In response to this challenge, the present study focuses on developing a green and efficient approach for Cu(II) ion removal through solar-driven photocatalysis, employing solar-assisted synthesized poly(o-phenylenediamine) (POPD)@zinc oxide (ZnO) nanocomposites. POPD was selected for its strong visible light absorption (1.75 eV). At the same time, zinc oxide (ZnO) was selected for its excellent electron mobility and environmental compatibility, enabling the creation of a type-II heterojunction that enhances charge separation and suppresses electron–hole recombination. Thermodynamic studies confirmed the feasibility of Cu(II) reduction within the conduction band. The composites were characterized using FTIR, UV–vis DRS, XRD, SEM-EDX, and TGA. The chosen POPD/ZnO: 50/50 composite exhibited exceptional photocatalytic activity, achieving approximately 99% removal of Cu(II) ions under solar irradiation. A dosage of 2 g L^–1 effectively reduced 200 mg L^–1 of Cu(II) ions in the presence of 40 mM formic acid as a sacrificial agent. Kinetic studies favored the pseudo-first-order approach. This work presents a dual-functional, energy-efficient approach that harnesses solar energy for both material synthesis and environmental remediation, offering promising potential for real-world water treatment applications.