Semiconducting Properties of Ag₃PO₄ and Its Application to Rhodamine Degradation under Solar Light

Abstract

To assess its photocatalytic activity under visible light, Ag₃PO₄ nanopowder was prepared by precipitation of Ag₃PO₄ with Na₂HPO₄. The powder was identified by X-ray diffraction and characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, thermal analysis and diffuse reflectance spectroscopy. Ag₃PO₄ grains with sizes in the range (0.8–10 µm) were obtained. The optical gap, determined from the Kubelka–Munk function, is found to be 2.49 eV and the electrical conductivity is characteristic of a classical semiconductor with activation energy of 0.18 eV. The capacitance measurement indicates n type conductivity with a valence band (2.05), deriving from Ag⁺: 5s orbital, more anodic than the level O₂/${\text{O}}_{2}^{ \bullet }$. So, the compound was tested with success for the oxidation by ${\text{O}}_{2}^{ \bullet }$ radicals of the rhodamine B under solar light. The degradation obeys to a first order kinetic with a rate constant of 0.28 min⁻¹. Some peaks of Ag metal (~6%) appeared after the photocatalytic process and the optical gap shows red shift by 0.04 eV; such results are in contradiction with those reported by others.