P123 assisted sol-gel combustion synthesis of mesoporous strontium titanate nanomaterials for photocatalytic degradation of methylene blue

Abstract

We have reported the synthesis of strontium titanate (ST) nanomaterials via sol-gel combustion method in the presence and absence of pluronic P123 as a templating agent and citric acid as fuel at relatively high temperature. The presence of templating agent and fuel helps to generate mesoporosity in the materials resulting in mesoporous strontium titanate (MST). The materials are well characterized by various instrumental techniques. X-ray powder diffraction analysis has confirmed that both of the strontium titanate materials exhibited cubic perovskite structure. The FT-IR spectra has indicated that during high temperature calcination, carbonate species expelled out from the decomposition of the volatile impurities get adsorbed on the surface of titanate nanostructure, which is predominant in MST as indicated by the variation in the intensity of peak in between 1450 cm-1 –1470 cm-1. From diffuse reflectance spectra, the absorption edge of the MST is extended to visible regions and showed band gap energy of 3.14 eV compared to 3.21 eV for ST. The reduction in intensities of PL emission bands in MST compared to ST has indicated that slow electron-hole recombination takes place in this material compared to ST. The Transmission electron microscopic studies reveal the formation of spherical and cuboidal nanostructures with an average size of 55 and 38 nm for ST and MST material, respectively. From N2 sorption studies, the MST exhibit type IV adsorption isotherms with H3 type hysteresis loop indicated the formation of mesoporosity in this material whereas the ST indicated the formation of type II adsorption isotherms typical of nonporous materials. The elemental analysis of MST material is further confirmed from X-ray photoelectron spectroscopic analysis and confirm the formation of carbonate species on the surface of the materials. The photocatalytic activity of the materials is elucidated by the degradation of methylene blue under UV light irradiation and degradation followed first order kinetics with Langmuir-Hinshelwood adsorption pathways. The activity of MST material is found to be 5 times faster than ST at similar experimental conditions. The enhanced activity of the MST might be attributed to, lower band gap energy, presence of carbonate species, and lower electron-hole recombination in this material.