Effect of pH on the photocatalytic removal of silver ions by β-MnO2 particles

The presence of silver ions (Ag(I)) in wastewater has a detrimental effect on living organisms. Removal of soluble silver, especially at low concentrations, is challenging. This paper presents the use of beta-MnO2 particles as a photocatalyst to remove Ag(I) ions selectively from aqueous solution at various pH levels. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), field emission electron microscope (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron microscopy (XPS) were employed to determine the removal efficiency and to characterize the deposition of silver onto the surface of beta-MnO2 particles. The optimum pH for the removal of Ag(I) ions was at pH 4 with 99% removal efficiency under 1 h of visible light irradiation. This phenomenon can be attributed to the electrostatic attraction between beta-MnO2 particles and Ag(I) ions as well as the suppression of electron-hole recombination in the presence of H+ ions.