Photocatalytic study of TiO2 thin films modified with Anderson-type polyoxometalates (Cr, Co and Ni): Experimental and DFT study

In this work, three Anderson-type polyoxomolybdates (POMs) with general formula (NH4)6-n[XMo6O24H6]- 6+n where X = Co3+, Cr3+, and Ni2+ were deposited on TiO2 thin films Furthermore, the methylene blue (MB) dye adsorption capacity and photocatalytic degradation were studied. Morphological results show that the POMs/TiO2 films have a more heterogeneous surface in terms of particle size and distribution than bare TiO2 films. Optical characterization indicated that the CrMo6/TiO2 material had the lowest band gap energy with a value of 2.8 eV. The adsorption results show that the maximum percentage of MB adsorption was 37 % for NiMo6/TiO2 while bare TiO2 has only 9.2 %. The MB adsorption on POMs-TiO2 was modeled using and the Freundlich model showed the best fit in all studied films for MB removal. The MB photodegradation values shows this tendency 12 % for bare TiO2, 55 % for NiMo6/TiO2, 73 % for NiMo6/TiO2 and, 83 % for CrMo6/ TiO2. Finally, DFT calculations were performed to characterize the geometry and electronic structure of the all compounds studied in this work, with the aim to explain the observed experimental results.