Optical band gap engineering of phosphotungstic acid upon hybridization with hexamine-nickel and -cobalt for solar/visible light photocatalysis: a combined experimental and theoretical approach

Two new organic hybrids of phosphotungstic acid (PTA) were prepared by means of hexamine complexes of nickel and cobalt. The effects of complexes were studied on the photocatalytic activity of PTA. The hybrids were characterized by elemental analyses, FTIR, powder XRD and TGA. The optical band gaps of phosphotungstate-hexamine-nickel and phosphotungstate-hexamine-cobalt were estimated from the diffuse reflectance spectra using the Tauc plots. Dye adsorption and photocatalytic properties of hybrids were tested by decolorizing of model dye solutions methylene blue, rhodamine B and methyl orange. Band gap engineering of the hybrids was investigated using the quantum chemical calculations based on density functional theory through variation in the composition. Theoretical analysis demonstrates how the band gap of these hybrids can be adjusted with variation in their composition. The scavengers were used to suggest photodegradation mechanism. The degradation advanced through the excitation of hybrid by light, followed the oxidation of dye by superoxide radicals.