Variation of pH and Composite Dosage on the Photocatalytic Activity of CuO/Epoxy Composites: An expanded review

This review consolidates current evidence on how solution pH and composite dosage (loading) govern the photocatalytic activity of CuO/epoxy composites for water treatment. Mechanistically, pH modulates surface charge relative to the CuO pHpzc (~8–9), pollutant speciation, band-edge alignment, and ROS pathways, while dosage shapes active-site density and the internal light field of pigmented epoxy films. Across supported CuO and polymer-immobilized oxides, the literature consistently shows best performance near neutral to slightly acidic pH (≈5–7), whereas very acidic or strongly alkaline media introduce instability, unfavorable adsorption, or enhanced recombination. Dosage exhibits a single-peak dependence: increasing loading improves rates up to an optimum, after which scattering/shading and aggregation lower the effective photon flux; practical ranges cluster around 0.3–1.0 g·L⁻¹ (slurry equivalents) or ~0.1–2 wt% for thin epoxy coatings when thickness and areal loading are reported. Comparative data from ZnO/epoxy under sunlight/visible irradiation confirm the same qualitative pH and loading trends, supporting transferable optimization rules. The review concludes with practical windows for lab screening and highlights the need for thickness-resolved optical/kinetic reporting and long-cycle stability testing in real effluents.