Photocatalytic Degradation of Synozol Navy Blue Dye Using Ni-Ag Co-doped ZnO: Optimization, Mechanistic, Scavenging and Kinetics Studies.

Synozol Navy Blue poses severe ecological risks, necessitating advanced treatment approaches. Ni-Ag co-doped ZnO (Ni-Ag@ZnO) catalyst was synthesized via the sol-gel method and characterized using XRD, SEM-EDX, BET, UV-Vis, PL, and XPS. In contrast to previous research primarily focused on simple model dyes, this study demonstrates the effective degradation of Synozol Navy Blue, a highly resistant azo dye, utilizing Ni-Ag co-doped ZnO under visible light. Comprehensive characterization, including XPS analysis, offered valuable insights into the oxidation states and successful incorporation of Ni and Ag. Furthermore, scavenger studies, mineralization tests, and pH-dependent performance evaluations elucidated the mechanistic pathways and conditions that optimize photocatalytic activity. Ni-Ag doping reduced crystallite size from 35.4 to 29 nm and increased surface area from 1.89 to 2.54 m²/g, while narrowing the band gap from 3.42 to 3.28 eV. Photoluminescence confirmed reduced electron-hole recombination. Under optimized conditions of 75 mg/L dye concentration, 0.03 g/50 mL catalyst dosage, pH 2-, and 50-min contact time 10% Ni-Ag@ZnO doping ratio achieved 81% degradation efficiency under solar light irradiation, significantly outperforming pure ZnO. The process followed pseudo-first-order kinetics (k = 2 × 10⁻² min⁻¹) and attained 80% mineralization (TOC removal) in 60 min. Scavenging tests identified hydroxyl and superoxide radicals as the dominant reactive species, with IPA and BQ enhancing charge separation. These results establish 10% Ni-Ag@ZnO as a promising eco-friendly photocatalyst for wastewater remediation.