Improvement of photocatalytic activity of SnO2 nanoparticles co-doped by Ag and Cu for high degradation of azo dye

Semiconductor photocatalysis is an effective method for degrading toxic organic substances. Therefore, in this study, Ag and Cu co-doped SnO₂ nanoparticles (Ag–Cu/SnO₂ NPs) were synthesized via the coprecipitation method to degrade the azo dye Congo Red (CR). The crystal structure, optical properties, and surface morphology of the prepared materials were thoroughly analyzed by X-ray Diffraction (XRD), UV–vis Diffuse Reflectance Spectrophotometer (UV–vis DRS), Scanning Electron icroscopy (SEM) couple with Energy-Dispersive X-ray Spectroscopy (EDX) and Hight-Resolution Transmission Electron Microscopy (HRTEM). Ag–Cu/SnO₂ NPs had smaller particle sizes than pure SnO₂ NPs. Additionally, their absorption spectrum shifted to the visible light region in the UV–vis spectrum, with a band gap energy smaller than that of pure SnO₂. All Ag–Cu/SnO₂ samples exhibited significantly higher photocatalytic activity in degrading Congo Red dye compared to pure SnO₂ under visible light. Photodegradation of Congo Red by SnO₂ and Ag–Cu/SnO₂ follow pseudo-first-order kinetic model. The 1Ag1.5Cu/SnO₂ sample, containing 1.0% Ag and 1.5% Cu (w/w), achieved the highest Congo Red degradation efficiency with a rate of 0.0801 min⁻¹. The effects of photocatalyst dose, initial dye concentration, and solution pH on Congo Red dye degradation by 1Ag1.5Cu/SnO₂ NPs were thoroughly investigated. Furthermore, the 1Ag1.5Cu/SnO₂ catalyst exhibited excellent reusability, maintaining approximately 88.56% of its initial photocatalytic activity after five cycles.