Highly Selective Photocatalytic Degradation of Organic Pollutants by ZnO@C Core–Shell Nanoparticles Via Superoxide Radical Pathway

Rapid industrialization and unlimited human activities have led to severe environmental challenges, particularly water contamination by persistent organic pollutants, posing serious risks to ecosystems and human health. Photocatalytic technology offers a sustainable remediation for pollutant degradation using solar energy. In this study, ultrathin carbon-encapsulated ZnO nanoparticles, ZnO@C are employed, as an efficient photocatalyst, using methylene blue and methyl orange as model pollutants. The carbon has a favorable band alignment with ZnO for efficient charge transfer. In fact, the optical absorption studies and finite-difference time-domain simulations establish an enhanced absorption and light-matter interaction upon thin uniform carbon encapsulation. Photoluminescence quenching (≈80%) indicates reduced electron-hole recombination, facilitated by defect-induced charge transfer from ZnO to carbon. Electron paramagnetic resonance measurements identify superoxide radicals (O₂•^-) as the dominant reactive species, driving a selective radical-mediated degradation pathway. Compared to pristine ZnO, the ZnO@C system exhibits over 60% higher degradation efficiency. Liquid chromatography-mass spectrometry analyses elucidate the sequential degradation pathway driven by O₂•^-. The ZnO@C demonstrates excellent photostability and reusability across multiple cycles, with a sixfold increase in kinetic rate constants over pristine ZnO. These improvements highlight the potential of ZnO@C core@shell nanostructures for sustainable environmental remediation.