Modulating the electronic structure of lanthanum manganite by Ruthenium doping for enhanced photocatalytic water oxidation
To the best of our knowledge this is the first report where in, ruthenium doped polycrystalline lanthanum manganite, LaMn1-xRuxO3 (x = 0.0-0.4), having high efficacy in oxygen production from water without the use of any sacrificial reagent or co-catalyst and as an efficient photocatalyst for dye degradation is reported. Ruthenium doping alters the crystal structure of the parent LaMnO3 (LMO) due to the induced chemical pressure of larger Ru4+ ion, which facilitates the bond angle of 1800 among Mn3+ – O – Mn4+ plane resulting in an easy extraction of photo-generated charge carrier population leading to the enhanced photocatalytic activity. Rietveld refinements reveal that the parent compound LMO crystallizes in rhombohedral phase, while with increase in doping concentration of ruthenium, the phase of the compounds changes from rhombohedral to cubic phase. Percentage of contribution of each phase has been estimated using the sixth-order polynomial and pseudo-Voigt function. Typically, all the compositions, LaMn1-xRuxO3 (x = 0.0-0.4) were prepared by conventional solid state route and studied for its photocatalytic activity. All the compositions were investigated by Powder X-ray diffraction (PXRD), UV-Visible diffuse reflectance spectroscopy (DRS), Fourier transformed infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. Structure - property correlation of the compound is presented based on Rietveld refinement combined with the experimental data. As prepared compounds show an efficient photocatalytic oxygen gas production from water without using any co-catalyst or sacrificial reagents. Among the five compositions, LaMn0.7Ru0.3O3 shows highest O2 production efficiency (4.73 mmol/g/h) with an apparent quantum yield (AQY) of 7.43 %. These ruthenium doped compositions also exhibit superior dye degradation properties, studied by taking the industrial dye, methyl orange (MO) as the model compound.