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

• Published in: Applied surface science 2019-10, Vol.490, p.469-480
• Main Authors: Székely, István, Baia, Monica, Magyari, Klára, Boga, Bíborka, Pap, Zsolt
• Format: Article
• Language: English
• Subjects: Heterogeneous photocatalysis; pH adjustment; Surface defects; Ternary composites; Titania; Tungsten trioxide
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2019.06.036

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. •The pH adjustment-based synthesis enhanced the degradation of MO and OA.•The crystallinity of the samples decreased as the pH value increased.•The two tungsten trioxides' presence in the composites was synergic.•The existence of W5+ was evidenced by Raman spectroscopy.•The activity was directly dependent on the presence of surface defects (W5+).