Green construction of N-ZnO/g-C3N4 heterojunction for boosting spatial charge separation in photocatalytic CO2 reduction and ciprofloxacin oxidation

N-ZnO/g-C₃N₄ (MZC) composites with varying N-ZnO contents were fabricated by a green grinding strategy aimed at constructing an S-scheme heterojunction with enhanced visible-light catalytic performance. The characterizations and properties of these photocatalysts, along with the reaction mechanism, were investigated in detail. Especially, the transfer direction of photoexcited electrons in the MZC was commendably determined by X-ray photoelectron spectroscopy (XPS) analysis. The results demonstrated that the MZC presented superior performances in the reduction of CO₂ and the degradation of ciprofloxacin compared with single components. Therein, the MZC-20 achieved the best photocatalytic degradation efficiency of 99.7% within 50 min, with its rate constant being 29.08- and 10.09-fold compared with bare N-ZnO and g-C₃N₄, respectively. Additionally, the CO yield of the optimized MZC-20 was 1.451 μmol·g⁻¹·h⁻¹ in the absence of sacrificial agent and was 2.93 times that of pristine g-C₃N₄. The boosted catalytic performance of the MZC composite stemmed chiefly from the formed S-scheme heterojunction and the enhanced light harvesting, resulting in the effective separation and utilization of free carriers. The present work affords a way of resolving the limited performance for g-C₃N₄, as well as offers some insights into designing fresh S-scheme composites with widespread applications in renewable energy production and environmental cleaning.