Z-Scheme CoPi/Ag₃PO₄ via Microwave Irradiation for Photodegradation of Rhodamine B

Abstract

The widespread use of synthetic dyes in the textile industry has led to severe water pollution, as most dyes are not firmly bound to fabrics and are released into aquatic ecosystems. Unchecked release of untreated dye-bearing effluents critically risks environmental quality and human health. Photocatalytic degradation is considered one of the best and most eco-friendly methods employed to degrade dye pollutants from wastewater. In the present study, a Z-scheme photocatalyst, cobalt phosphate (CoPi) and silver phosphate (Ag₃PO₄), abbreviated as CoPi/Ag₃PO₄, was synthesized by a microwave irradiation method for the photodegradation of Rhodamine B (RhB) dye under visible light. The as-synthesized photocatalysts were characterized by field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), and UV-visible diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic activity was evaluated using a dosage of 0.375 g/L of catalyst in irradiation for 60 minutes. The 5% CoPi/Ag₃PO₄ showed the highest degradation efficiency at 96%, followed by 10% CoPi/Ag₃PO₄ (92%), Ag₃PO₄ alone (87%), 1% CoPi/Ag₃PO₄ (82%), 15% CoPi/Ag₃PO₄ (73%), and CoPi alone (71%). The enhanced activity of 5% CoPi/Ag₃PO₄ was explained in terms of the homogeneous distribution of the Co and P elements on Ag₃PO₄ and the reduced band gap, which favors better absorption and separation of light. Further studies on the effect of different operating conditions, including initial pH, RhB concentration, and catalyst dosage, were conducted. The optimal degradation was achieved at pH 9, 10 mg/L of RhB, and a catalyst dosage of 0.375 g/L. Scavenger experiments indicated that photogenerated holes (h⁺) were the major contributors to the mechanism of degradation. Finally, microwave-assisted CoPi/Ag₃PO₄ synthesis is a simple and efficient route to produce visible-light-responsive photocatalysts. Doping CoPi significantly enhanced the photocatalytic activity of Ag₃PO₄, and the composite is a promising material for the degradation of dye-contaminated wastewater