Photocatalytic Activity of La-Containing Mixed- Metal Oxides Derived from Layered Double Hydroxides to Degrade Methylene Blue in the Presence of H2O2

Abstract

AbstractPhotocatalytic degradation of polluted water by means of minerals, such as clays and oxides, which have surfaces that exhibit catalytic properties, has been suggested to be a useful new strategy to promote both organic and inorganic pollutant degradation. Nevertheless, much still remains to be studied about the capability of mixed metal oxides derived from lanthanum-containing layered double hydroxides to promote pollutant removal by means of photocatalytic degradation with the mineral surfaces. The objective of the present study was to investigate the synthesis of ternary MgAlLa mixed-metal oxides (MgAlLa-M) with various Mg/Al/La molar ratios through a hydrotalcite-like precursor route by co-precipitation of appropriate amounts of metal salts from homogeneous solution, followed by calcination at 600°C. The crystal structure, surface morphology, and optical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis diffuse reflectance spectroscopy (DRS). Analysis by XRD showed that MgO, La2O3, MgAl2O4, and La10Al4O21 phases coexisted in calcined samples as MgAlLa-M. The samples showed a small band gap of 3.11–3.35 eV according to DRS. The photocatalytic activities of the samples were evaluated by degradation of methylene blue (MB) under visible light irradiation. MgAlLa-M had better photocatalytic properties than hydrotalcite precursors, and the MgAlLa-0.5-M possessed the best photocatalytic activity. The photocatalytic degradation efficiency of MB dye with MgAlLa-0.5-M under visible light irradiation for 1 h was 99.89% in the presence of H2O2, which exceeded the binary MgAl-M (84.06%) under the same conditions. The high photocatalytic activity of the sample was attributed to the addition of La(III). In addition, the possible mechanism of photocatalytic degradation of MB by MgAlLa-M was discussed. The results showed that •O2– plays a major role in the MgAlLa-0.5-M/H2O2 system.