Bias-Free Catalytic Photoelectrochemical Degradation of Congo Red Using a Boron–Iron Oxide Coated Electrode: A Green and Sustainable

The persistent discharge of azo dyes poses serious ecological and health problems due to their stability and resistance to conventional treatments. This study presents a novel, bias-free catalytic photoelectrochemical (catalytic PEC) system with photovoltaic cell-type assembly for visible light driven degradation of Congo red. Boron-iron oxide composite catalyst was immobilized on graphite electrode. The catalyst was synthesized through thermal treatment of boric acid and iron (II) sulphate, while the electrode was coated by sol–gel process followed by annealing. The SEM, FTIR, TGA, EDX, XRD, and CV analysis confirmed a thermally stable, redox-active, and heterogenous surface. The dual chamber PEC cell consists of anodic (Congo red solution) and cathodic (ascorbic acid solution) compartment, connected by salt-bridge, irradiated with light source, and operating without external bias. The system achieved optimum degradation efficiency of 79.8% and a pseudo-first order rate constant of 1.5966 min^‒1 in ideal conditions. The improved performance is attributed to the synergistic electron transfer between boron vacant orbital and the Fe²⁺/Fe³⁺ redox couple, facilitating effective generation of hydroxyl radicals. This first-of-its-kind approach demonstrate a cost effective, sustainable, and energy-autonomous strategy for azo dye degradation, offering a promising pathway for decentralized industrial wastewater treatment.