A new visible driven nanocomposite including Ti-substituted polyoxometalate/TiO_2: synthesis, characterization, photodegradation of azo dye process optimization by RSM and specific removal rate calculations

摘要

A new visible driven photocatalyst K7Ti2W10PO40/TiO2 (KPW/TiO2) with various KPW contents (2, 11 and 20 wt%) was successfully synthesized through a modified sol-gel-hydrothermal method. The structural properties of the prepared nanocomposite were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, photoluminescence spectroscopy and diffuse reflectance spectra (DRS). From the results obtained, the 11-KPW/TiO2 showed the highest photocatalytic activity. Photoluminescence analysis for all synthesized samples showed that the 11-KPW/TiO2 had the lowest intensity and recombination rate of photogenerated electron and holes. Tauc plots of the photocatalysts show that the presence of KPW in the x-KPW/TiO2 nanocomposites reduced the band gap of nanocomposites, but the change in the amount of KPW have not a specific effect on the band gap reduction. It seems that the change in the loading of the KPW is effective on the amount of recombination of electron-hole. The absorption edge of the modified TiO2 showed a red shift into the visible light range. Mott-Schottky plots show a positive slope as expected for n-type semiconductor. The prepared photocatalysts were examined for degradation of DR16 under visible light irradiation. The performance of the photocatalyst was analyzed and modeled by response surface methodology. Optimum conditions were DR16 conc. of 20mg/L, reaction time 4h, initial pH (3) and polyoxometalate loading 11 wt%. In order to assess the treatment capacity of the nanophotocatalyst, specific removal rate for the DR16 at all operating conditions were calculated.