Exploring the synthesis and application of ZnO-, TiO₂-, CuO-ZnO- and CuO-TiO₂‑carbon sphere (CSs) nanocomposites for the photocatalytic degradation of methylene blue (MB) dye and ciprofloxacin (CIP) antibiotic under ultraviolet (UV) irradiation

Current studies on carbon-metal oxide nanocomposites typically use risky synthetic procedures and concentrate on single photocatalysts, minimising comparative performance and structure-activity relationships. In this study, four nanocomposites made with plant extract from Commelina benghalensis (ZnO-, TiO₂-, CuO-ZnO-, and CuO-TiO₂‑carbon spheres) are compared. When it came to the degradation of ciprofloxacin (CIP) and methylene blue (MB) dye in wastewater, the C. benghalensis -mediated 20/80 ZnO‑carbon sphere nanocomposites (ZnO-CSs) performed better than the others. By surpassing plant-derived ZnO nanoparticles and other CS-based nanocomposites, the 20/80 ZnO-CSs nanocomposite demonstrated degradation efficiencies of 85 % under UV irradiation, with a 0.36 min −1 rate constant for MB and 56 % CIP removal under optimal conditions (pH 5, 90 mg catalyst, 5 mg/L pollutant). As electron reservoirs, carbon spheres increase active surface area (21.95 m 2 /g vs. 11.07 m 2 /g for ZnO) and decrease charge recombination (EPR verified oxygen vacancies, g ≈ 2.1011). The primary reactive species identified by scavenger experiments were electrons (e − ) and hydroxyl radicals (•OH), yielding kinetics similar to those of other carbon-ZnO systems reported in the literature. The nanocomposite demonstrated its exceptional reusability by maintaining over 70 % efficiency over four cycles. To assess mineralisation the total organic carbon (TOC), chemical oxidation demand COD, the Average Oxidation State (AOS) and Carbon Oxidation State (COS) were all measured in this study. The result showed the COD (10.25 mg/L) and TOC (3.00 mg/L) with an AOS of +4.1 and COS of −1.23 For MB. While reporting, COD (9.67 mg/L) and TOC (3.08 mg/L) with an AOS of +3.62 and COS of +0.71 For CIP. The study offers a crucial comparison framework for selecting the optimal semiconductor‑carbon combinations for advanced wastewater treatment, and these results highlight the 20/80 ZnO-CSs as a scalable, solar-active photocatalyst. • Novel green microwave synthesis of ZnO‑carbon spheres. • Carbon spheres serve as electron reservoirs for ZnO. • Enhanced photocatalytic degradation of organic pollutants. • Excellent reusability over multiple catalytic cycles.