Application of a binary ZnO/WO3 nanocomposite supported on carbon-covered alumina for the visible-light-driven photocatalytic degradation of azo dyes

The graphical abstract illustrates the photocatalytic degradation of azo dyes under visible-light irradiation using a b inary zinc oxide/tungsten trioxide (ZnO/WO₃) nanocomposite supported on carbon-covered alumina. Chemical structures of azo dyes are depicted to represent the target pollutants. A series of binary ZnO/WO3 (ZW) nanocomposites supported on carbon-covered alumina (CCA) was synthesised via a simple sol-gel method. The materials were characterized via X-ray diffraction (XRD), Fourier-transform infrared (FTIR), Brunauer-Emmett-Teller (BET), scanning/transmission electron microscopy (SEM/TEM), energy-dispersive X-ray (EDX), photoluminescence (PL), and ultraviolet-visible diffuse reflectance (UV–Vis DRS) spectroscopies. Compared with pure ZnO, the ZW/CCA composites exhibited a reduced bandgap and enhanced visible light absorption. The photocatalytic performance was evaluated using direct red 80 (DR80) and Congo red (CR) as model pollutants. The ternary ZW/CCA (1:2) composite achieved complete degradation of DR80 within 135 min and 60% degradation of CR within 180 min under visible light. Chemical oxygen demand analysis confirmed substantial mineralisation of the dyes. The enhanced activity was attributed to synergistic effects at the ZnO/WO3–CCA interfaces, improved surface area, and efficient separation of photo-induced charge carriers. The catalyst retained 98% of its photocatalytic activity after five reuse cycles, confirming its stability and reusability. This study highlights the potential of ZW/CCA nanocomposites as efficient, recyclable photocatalysts for sustainable wastewater treatment.