Nano surface engineering of Mn2O3 for potential light-harvesting application

Manganese oxides are well known applied materials including their use as efficient catalysts for various environmental applications. Multiple oxidation states and their change due to various experimental conditions are concluded to be responsible for their multifaceted functionality. Here we demonstrate that the interaction of a small organic ligand with one of the oxide varieties induces completely new optical properties and functionalities (photocatalysis). We have synthesized Mn2O3 microspheres via a hydrothermal route and characterized them using scanning electron microscopy (SEM), X-ray diffraction (XRD) and elemental mapping (EDAX). When the microspheres are allowed to interact with the biologically important small ligand citrate, nanometer-sized surface functionalized Mn2O3 (NPs) are formed. Raman and Fourier transformed infrared spectroscopy confirm the covalent attachment of the citrate ligand to the dangling bond of Mn at the material surface. While cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) analysis confirm multiple surface charge states after the citrate functionalization of the Mn2O3 NPs, new optical properties of the surface engineered nanomaterials in terms of absorption and emission emerge consequently. The engineered material offers a novel photocatalytic functionality to the model water contaminant methylene blue (MB). The effect of doping other metal ions including Fe3+ and Cu2+ on the optical and catalytic properties is also investigated. In order to prepare a prototype for potential environmental application of water decontamination, we have synthesized and duly functionalized the material on the extended surface of a stainless steel metal mesh (size 2 cm × 1.5 cm, pore size 150 μm × 200 μm). We demonstrate that the functionalized mesh always works as a "physical" filter of suspended particulates. However, it works as a "chemical" filter (photocatalyst) for the potential water soluble contaminant (MB) in the presence of solar light.