Enhancement of the visible light activity and stability of Ag₂CO₃ by formation of AgI/Ag₂CO₃ heterojunction

Highlights: • A novel AgI/Ag₂CO₃ heterojunction was prepared via coprecipitation process. • AgI/Ag₂CO₃ heterojunction increase e⁻/h⁺ pairs separation. • The production of ^• OH and O₂^{• −} radicals was promoted. • High photocatalytic activity and stability were obtained over AgI/Ag₂CO₃. - Abstract: An insurmountable problem for silver-based semiconductor photocatalysts is their poor stability. Here, at room temperature, AgI with different concentrations (5%, 10%, 20% and 30%) were coupled into Ag₂CO₃, producing a series of novel AgI/Ag₂CO₃ composite photocatalysts. The effects of AgI addition on the Ag₂CO₃ catalyst for photocatalytic degradation of methyl orange (MO) under visible light irradiation have been investigated. Some physicochemical technologies like N₂ physical adsorption/desorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were applied to characterize these products. Results show that the photocatalytic degradation activity of AgI/Ag₂CO₃ photocatalyst is much higher than that of pure AgI and Ag₂CO₃. With the optimal content of AgI (20 wt%), the AgI/Ag₂CO₃ exhibits the highest photocatalytic degradation efficiency. Its first order reaction rate constant (0.54 h⁻¹) is 20 times of that of AgI (0.026 h⁻¹) and 3.6 times of that of Ag₂CO₃ (0.15 h⁻¹). The characterizations and theory calculation show that AgI and Ag₂CO₃ have suitably matched band gap structures. The formation of AgI/Ag₂CO₃ heterojunction with intimate interface could effectively increase the separation efficiency of the e⁻/h⁺ pairs and promote the production of ^• OH and O₂^{• −} radicals, which brings about the fast degradation rate of the dye and an increase in photocatalytic stability