Insight into the defective sites of TiO2/sepiolite composite on formaldehyde removal and H2 evolution

Abstract

TiO2/sepiolite composites (T–S–R) with different contents of Ti3+ and oxygen vacancy were successfully prepared through 0D/1D structural assembly and thermal treatment under various atmospheres (R = Air, O2, N2, Ar and H2). The content of Ti3+ and oxygen vacancy was confirmed through electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), which exhibited significant effect on the photocatalytic formaldehyde (HCHO) removal and H2 evolution. The T–S–Ar composite exhibited much higher formaldehyde degradation efficiency (91.8% within 90 min) and H2 production performance (1974.8 μmol/h/g) than other samples under simulated solar light. According to the material characterizations and DFT calculations, the improved photocatalytic activity could be ascribed to the synergistic effect between natural sepiolite and TiO2. Besides, the generation of mid-gap levels induced by the appropriate content of Ti3+ and oxygen vacancy led to the larger specific surface area, smaller nano-sized TiO2 and higher photogenerated carriers’ separation efficiency. Furthermore, it was found that higher content of oxygen vacancies would act as the recombination centers for electron–hole pairs, thereby greatly reducing the photocatalytic performance. Notably, our study provides a promising candidate for effectively addressing the air pollution (e.g. HCHO removal) and energy issues (e.g. H2 production) based on the defect engineering and mineral support technology.