Photodegradation of indigo carmine over a (BiO)2CO3@ZnCo2O4 heterojunction: experimental and DFT insights

Abstract

This work effectively synthesized the novel heterojunction (BiO)₂CO₃@ZnCo₂O₄ using precipitation and co-precipitation methods facilitated by microwave and ultrasonic techniques. The crystal structure and morphology of the synthesized samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and energy-dispersive spectroscopy (EDS) mapping, respectively. The photodegradation effectiveness of the heterojunction was evaluated by degrading the indigo carmine dye under visible light. The research findings demonstrated that the combination of (BiO)₂CO₃ and ZnCo₂O₄ at a mass ratio of 12% exhibited the most significant IC decomposition capability, attaining a photocatalytic efficiency of 98.6% after 60 minutes in darkness and 100 minutes of light exposure. The most appropriate approach was to establish a first-order kinetic model for the indigo carmine degrading process of (BiO)₂CO₃@ZnCo₂O₄. The Z-scheme mechanism was more relevant than the conventional type-II heterojunction, whereby O₂˙⁻ and ˙OH were the primary contributors to the photocatalytic process. The stable heterostructure (BiO)₂CO₃@ZnCo₂O₄ has advanced the method for effective heterojunction photocatalysis. DFT–Fukui analysis shows that the indigo carmine molecule donates electrons, acting as a nucleophile, and TD-DFT calculations using B3LYP/6-311G(d,p) in aqueous solution produce a HOMO–LUMO gap for IC that aligns more closely with experimental data than previous results.