The effect of the pH adjustment upon the WO3-WO3·0.33H2O-TiO2 ternary composite systems' photocatalytic activity

In the present work novel, ternary semiconductor composites were prepared by applying the pH adjustment method (the WO₃ based components were obtained separately, while TiO₂ was a commercial one), where the pH was fine-tuned to 1, 4, 7 and 10. The composition of the prepared samples was in each case 76% commercial TiO₂ (Evonik Aeroxide P25), 12% monoclinic (WO₃) and 12% hexagonal partial hydrate (WO₃·0.33H₂O). All the composites showed improved UV light-driven photocatalytic activity compared to P25 in the degradation of methyl orange, oxalic acid and activity inhibition was observed in the case of phenol degradation. SEM micrographs and the XRD patterns of the samples proved that all three components were successfully integrated into the composite system. DRS spectra of the samples provided evidence concerning a mutual interaction of the composite components modifying their electronic structure, while the effect of the synthesis pH was also visible in the IR spectra. Raman Spectroscopy proved the presence of surface defects, manifested through the presence of (W⁵⁺ centers). Moreover, interesting correlations were found between several Raman peak intensity ratios (I₃₂₄/I₇₁₄; I₉₄₃/I₈₀₅) and the photoactivity pointing the importance of the W⁵⁺ centers and amorphous WO₃ formed under basic conditions.