Photocatalytic degradation of single and binary dyes using activated HKUST-1 and its derived copper oxide

Organic dye contamination poses serious environmental and health concerns due to stability and poor biodegradability of common dyes like methylene blue (MB) and methyl orange (MO). In this work, HKUST-1 was synthesized and activated through two distinct routes i.e., heat treatment (HT) and solvent exchange using dichloromethane (DCM) to systematically investigate the influence of activation on structure, porosity, optical properties, and photocatalytic performance. Furthermore, HKUST-1 was thermally converted into a copper metal oxide (CMO) to evaluate the effect of MOF-to-oxide transformation on photocatalytic efficiency. Detailed characterization confirmed that activation method alters crystallinity, surface area, pore structure, and band gap, which in turn dictate photocatalytic behavior. Photocatalytic experiments were performed using an initial MB concentration of 10 mg/L and a catalyst dose of 0.25 g/L under simulated sunlight irradiation of 100 mW/cm². Photocatalytic degradation of MB was examined under acidic, neutral, and basic conditions, revealing superior activity under basic condition, with HT achieving ~ 99.04% degradation within 60 min. This is attributed to the enhanced generation of reactive hydroxyl radicals under alkaline conditions. Radical scavenger studies corroborated that hydroxyl radicals were the primary reactive species, supported by band edge positions obtained from electrochemical and optical analyses. The HKUST-1-derived oxide exhibited a significantly reduced band gap (~ 1.41 eV) and demonstrated markedly enhanced degradation kinetics across a wide pH range (2–12), achieving ~ 98.80% MB degradation within 30 min at pH 12. This enhancement is attributed to its narrower band gap, which promotes efficient visible-light absorption and charge carrier generation. Additionally, selective dyes and simultaneous degradation of a binary MB + MO dyes system were explored, revealing strong pH-dependent selectivity and deviations from classical pseudo-first order kinetics due to competitive adsorption effects. Overall, this study provides a comprehensive correlation between activation strategy, physicochemical properties, and photocatalytic performance, highlighting the potential of HKUST-1 and its derived oxide for efficient and tunable dye degradation in complex aqueous environments.