Structure and properties of vanadium-doped α-MnO2 and enhanced Pb2+ adsorption phenol/photocatalytic degradation

Vanadium (V)-doped cryptomelane was synthesized and characterized by powder X-ray diffraction, electron microscopy, N2 adsorption, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Vanadium doping does not change the basic crystal structure but slightly decreases the lattice parameters (a, b, c, β and cell volume) and increases the coherent scattering domain (CSD) sizes (16-19 nm). These V-doped cryptomelane materials are granular particles with increased specific surface areas (149-183 m2 g−1) and increased concentrations of hydroxyl groups on the surfaces with increasing V doping. Both V 2p3/2 spectra and V K-edge X-ray absorption near edge spectroscopy indicates that V exists in +5. Substitution of V5+ for Mn4+ in cryptomelane framework results in reduction in Mn average oxidation state and increase in bond lengths of Mn-O in [MnO6] unit, edge- and corner-sharing Mn-Mn(V) pairs. These V-doped materials have greatly increased adsorption capacities for Pb2+ (937-1146 mmol kg−1). Doping ∼1.4 wt.% V can significantly enhance cryptomelane optical absorption properties and thus photocatalytic degradation of phenol, i.e., with a TOC removal rate of ∼77%. These results can facilitate the modification and application of environmental friendly Mn oxide materials in pollution control and remediation.