ZnO/rGO composite for photodegradation of Remazol Brilliant Blue R (RBBR) synthetic dye in Batik waste under UV irradiation

The synthetic dye Remazol Brilliant Blue R (RBBR), widely used in the Batik industry, was successfully degraded under UV irradiation using ZnO/rGO composite photocatalysts synthesized with reduced graphene oxide (rGO) derived from rice bran waste. Characterization was performed using X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) surface area analysis, and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic performance was evaluated for composites with varying rGO contents: ZR-0 (pure ZnO), ZR-1 (ZnO with 5 mg rGO), and ZR-2 (ZnO with 25 mg rGO). The ZR-1 composite exhibited the highest degradation efficiency of 78.95 % within 240 min, compared to 58.57 % for ZR-0 and 65.70 % for ZR-2. The corresponding pseudo-first-order rate constants were 0.0034 min −1 (ZR-1), 0.0065 min −1 (ZR-0), and 0.0048 min −1 (ZR-2). These results confirm that the addition of a moderate amount of rGO enhances the photocatalytic activity of ZnO, while excessive rGO may reduce UV light absorption due to surface coverage and recombination effects.