Photochemical Water Oxidation in a Buffered Tris(2,2′-bipyridyl)ruthenium–Persulfate System Using Iron(III)-Modified Potassium Manganese Oxides as Catalysts

Study of manganese oxides for electrocatalytic and photocatalytic oxidation of water is an active area of research. The starting material in this study is a high-surface-area disordered birnessite-like material with K + in the interlayers (KMnOx). Upon ion-exchange with Fe 3+ , the disordered layer structure collapses (Fe(IE)MnOx), and the surface area is slightly increased. Structural analysis of the Fe(IE)MnOx included examination of its morphology, crystal structure, vibrational spectra, and manganese oxidation states. Using the Ru(bpy) 3 2+ -persulfate system, the dissolved and headspace oxygen upon visible light photolysis with highly dispersed Fe(IE)MnOx was measured. The photocatalytic activity for O 2 evolution of the Fe(IE)MnOx was three times better than KMnOx, with the highest rate being 9.3 mmol O 2 mol Mn -1 s -1 . The improvement of the photocatalytic activity was proposed to arise from the increased disorder and interaction of Fe 3+ with the MnO 6 octahedra. As a benchmark, colloidal IrO 2 was a better photocatalyst by a factor of ∼75 over Fe(IE)MnOx.