Photocatalytic degradation of Congo red using RGO-modified MIL-125(Ti) under visible light

This study investigates the degradation of Congo red, a diazo-sulfonated dye, using reduced graphene oxide (RGO) modified MIL-125 (RGO-MIL) under visible light. The RGO-MIL photocatalyst was synthesized via a solvothermal method and characterized using Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and electrochemical measurements. A decrease in band gap from 3.45 eV to 2.90 eV, combined with improved charge transfer efficiency, confirmed the activation of RGO-MIL under visible light. A removal efficiency of 92.6 % was achieved, with a 4.8-fold increase in the degradation rate observed within 180 min of irradiation. Furthermore, the degradation mechanism of Congo red was elucidated through radical scavenging tests and X-ray photoelectron spectroscopy (XPS) analysis, conducted before and after degradation. The primary reactive species was identified as the hydroxyl radical (OH·), with secondary contributions from photogenerated holes and electrons. XPS analysis indicated that the amine and aromatic components of Congo red reacted with the photocatalyst, leading to the conversion of Congo red into smaller molecules and confirming the photocatalyst's stability. Additionally, the surface efficiency and apparent quantum yield (AQY) suggested that RGO-MIL is a promising photocatalyst for the degradation of Congo Red, outperforming other photocatalysts reported in the literature.