Sunlight assisted photocatalytic degradation using the RSM-CCD optimized sustainable photocatalyst synthesized from galvanic wastewater

•For the first time, galvanic wastewater is incorporated with g-C3N4 for the synthesis of a photocatalyst.•The photodegradation of a mixture of azo dyes (Tartrazine, Congo Red, Orange G, and Bismarck Brown R) was studied under sunlight.•RSM-CCD was utilized for optimizing the ratio of GWW to g-C3N4. In this study, a sustainable and highly efficient photocatalyst for the degradation of azo dyes using sunlight was engineered. For the first time, photocatalyst was prepared using galvanic wastewater (GWW) along with graphitic-carbon nitride (g-C3N4) by the sol-gel method. The ratio of GWW (1–5 mL) to g-C3N4 (0.1–0.5 g) was optimized to obtain the best photodegradation efficiency using Response Surface Methodology-Central Composite Design (RSM-CCD) model. A mixture of azo dyes (Tartrazine, Congo Red, Orange G, and Bismarck Brown R: 25 ppm each) was utilized to study the photodegradation under sunlight for 2 h. The optimum ratio of the photocatalyst was found to be 0.5 g g-C3N4 and 5 mL GWW which was used to photodegrade a mixture of azo dyes with an efficiency of 98.3% under sunlight. Characterization of the photocatalyst was performed using ICP-OES, UV-DRS, PL, GC-MS, TGA, XRD, XPS, FESEM, and FTIR to validate the optical performance and the anchoring of GWW on g-C3N4. [Display omitted]