Green photooxidative degradation of reactive blue dye via ascorbic acid and its metal complexes: Kinetics, RSM optimization, and DFT validation

• Ascorbic acid (AA) achieved 96.9% degradation of Reactive Blue (RB) dye under visible light. • RSM-CCD optimized parameters for maximum dye degradation efficiency. • AA showed superior kinetics with a short half-life of 26.97 min. • DFT and LC-MS confirmed the degradation mechanism and by-product pathways. This work introduces a twin-track green photooxidative strategy for the visible-light-driven degradation of Reactive Blue (RB) dye, utilizing both a highly efficient metal-free system based on L -ascorbic acid and metal-based (Cu, Co, Al complexes) pathways. Among all photooxidative agents, AA exhibited the highest degradation efficiency (96.9%) within 120 min, suppressing Cu- AA ( C1 : 79.2%), Co- AA ( C2 : 75.6%), and Al- AA ( C3 : 43.3%). Low molar conductivity suggested covalent, non-electrolytic complex formation. Structural and spectral characterization of the Cu– AA complex ( C1 ) via FTIR evidenced strong metal-ligand interactions, while SEM revealed a porous, flake-like morphology conducive to charge separation and light harvesting. EDX validated elemental composition, and TGA demonstrated multi-step decomposition with thermal stability up to 150 °C. First-order kinetics correlated with the electronic properties of photooxidative agent AA, which exhibits a notably shorter half-life (t₁/₂ = 26.97 min) compared to C1 (87.74 min), underscoring its enhanced reactivity. Response Surface Methodology (RSM) was used to optimize operational conditions, and HPLC-MS analyses indicated progressive degradation and near-complete mineralization. Density Functional Theory (DFT) calculations supported the enhanced proton-donating and radical-generating capabilities of AA , elucidating its superior activity. This work highlights AA as a green, sustainable, and metal-free photooxidative agent with significant potential for eco-friendly wastewater treatment.