Enhanced photocatalytic removal of methyl orange dye employing SiO2/Mn2O3 based nanocatalyst under visible light.

Surface water contamination by dye pollutants is a global environmental concern. The treatment of effluent from textile waste using metal oxide-based photocatalysts is a widely employed approach owing to its efficacy and simplicity. Herein, the synthesis and fabrication of novel visible radiation receptive manganese oxide and mesoporous silica nanocomposites (Mn 2 O 3 /SiO 2) is described. Surface morphology of nanocomposites using scanning electron microscopy (SEM) displayed spherical shaped agglomerated structure. The chemical composition of nanocomposites was examined by using energy dispersive x-ray (EDX) analysis respectively indicating the presence of respective elements. Structural analysis was carried out by using XRD spectroscopy, while optical properties were evaluated by employing UV–visible spectroscopy. The photocatalytic activity of pure Mn 2 O 3 and SiO 2 nanoparticles as well as their nanocomposites with two different ratios Mn 2 O 3 /SiO 2 (1:3) and Mn 2 O 3 /SiO 2 (3:1) were evaluated by using methyl orange (MO) as a model dye. The band gap energy of Mn 2 O 3 /SiO 2 (1:3) and Mn 2 O 3 /SiO 2 (3:1) nanocomposite was 2.39 eV and 1.69 eV respectively. The nanocomposites exhibited improved photocatalytic efficiency as compared to pure nanoparticles as a function of pH and mixing ratio. For instance, at pH 7.0, Mn 2 O 3 /SiO 2 (1:3) nanocomposite has depicted maximum degradation efficiency of 68 % for degradation of MO as compared to Mn 3 O 4 /SiO 2 (3:1) nanocomposite, Mn 3 O 4 and SiO 2 nanoparticles. However, at pH 2.0 Mn 2 O 3 /SiO 2 (3:1) nanocomposite had shown maximum degradation efficiency of 99 % as compared to Mn 2 O 3 /SiO 2 (1:3), Mn 2 O 3 and SiO 2 nanoparticles. The degradation reaction followed pseudo first order kinetics. At pH 7.0, the rate constant values of nanocomposites i.e. Mn 2 O 3 /SiO 2 (1:3) and Mn 2 O 3 /SiO 2 (3:1) comes out to be 4.68 × 10−3 min−1 and 2.49 × 10−3 min−1 respectively. At pH 2.0, the rate constant values calculated for Mn 2 O 3 /SiO 2 (1:3) nanocomposite and Mn 2 O 3 /SiO 2 (3:1) nanocomposite was 4.91 × 10−3 min−1 and 1.24 × 10−2 min−1 respectively. The easy fabrication of these nanocomposites coupled with facile tuning of their properties make them suitable contenders for efficient dye degradation in wastewater treatment. [ABSTRACT FROM AUTHOR]