Metal doped titanate photo catalysts for the mineralization of congo red under visible irradiation
Strontium titanate catalysts and titania were synthesized by the sol–gel method. 1 mol% nickel/ruthenium was doped on the strontium titanate catalyst to shift its optical response to the visible region. UV-diffuse reflectance spectral analysis confirms the red shift with the band gap of 1.9 eV and 2.13 eV for the Ni and Ru doped strontium titanate catalysts, respectively. The catalysts were characterized using various instrumental techniques such as X-ray diffraction (XRD), UV-diffuse reflectance spectroscopy (UV-DRS), BET surface area analysis, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Transmission Electron Microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of bare TiO2, bare strontium titanate and metal doped strontium titanate catalysts were evaluated towards the decolourisation/degradation of congo red under UV, visible and solar irradiation and monitored by a UV-visible spectrophotometer and TOC analyser. Among the catalysts nickel doped strontium titanate completely decolourised CR in the shortest reaction time (300 min), and hence it was subjected to decolourise textile effluent. It was found to be very effective in the degradation of textile effluent as it showed a significant reduction in the TOC. Kinetic studies indicate that the degradation of congo red followed pseudo first order kinetics. The recycling test confirmed that the most active nickel doped strontium titanate catalyst is highly photostable.