Type-II Heterojunction CoWO ₄ /WO ₃ Nanocomposites for the Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants

This work reports the engineering of a visible-light-active type-II heterojunction CoWO4/WO3 nanocomposite via a hybrid hydrothermal and mechanical grinding method. Varying the hydrothermally produced CoWO4-to-WO3 weight ratio optimized the effective bandgap to 2.5 eV. Mechanical grinding generates intimate interfacial contact by dispersing nanosized CoWO4 (∼50 nm) over thinned monoclinic WO3 plates (∼100 nm), as confirmed by HR-TEM and FESEM. The optimized composite containing 42.85 wt % WO3 (CW3) exhibits a bandgap of 2.51 eV and a negative zeta potential (−26.9 mV), which enhances adsorption of cationic dyes. The composite shows an extended electron–hole recombination lifetime of 30.5 ns, which is 3–6× longer than that of pristine CoWO4 and WO3. Under visible-light irradiation (350 W, Xe lamp, λ > 420 nm filter), the composite achieves 98% degradation of methylene blue at pH 14 (40 min) and retains 80% efficiency after 10 reuse cycles. The composite degraded cationic methylene blue, methylene orange, rhodamine B, and some volatile organic chemicals (acetaldehyde) under visible-light energy sources. These results highlight the potential of CoWO4/WO3 heterojunctions for photocatalytic applications in environmental remediation.