The Role of Cotton Fibers in Mediating the Energy Band Structure of TiO 2 -BiFeO 3 Heterojunction in Cotton-TiO 2 -BiFeO 3 Composites for Its Photodegradation of Congo Red Dyes and Photoreduction of Cr(VI) Ions

TiO 2 -based heterojunctions loaded on organic templates (e.g., cotton fabrics) are found to have improved photocatalytic activities. However, the role of fibrous templates on their photocatalytic properties has hardly been investigated. In this paper, TiO 2 -BiFeO 3 heterojunction (TiO 2 -BFO) was immobilized on cotton fibers in hydrothermal process. The structures of both TiO 2 -BFO and cotton-TiO 2 -BFO composites (C-TiO 2 -BFO) were systematically characterized. Their photodegradation of Congo red (CR) dyes and photoreduction of Cr(VI) ions under visible lights were analyzed. Their active species were identified via trapping experiments and electron spin resonance spectra, and their energy band structures were examined via the density functional theory (DFT). Experimental results indicated that in comparison with the TiO 2 loaded cotton fibers (C-TiO 2 ), the superior photocatalytic properties of C-TiO 2 -BFO were attributed to its substitutional doping of C/O of cotton into BFO in the TiO 2 -BFO, which resulted in the narrowed band-gap, the strong light-harvesting capability, and the fast separation of photoinduced electron-hole pairs of C-TiO 2 -BFO. Importantly, DFT calculations testified that the energy band structure of TiO 2 -BFO could be mediated by constructing the built-in electric field between TiO 2 -BFO and cellulose cotton. The hole species were the dominant radicals in the C-TiO-BFO, while 1 O 2 species were the main radicals in the TiO-BFO in CR photodegradation process.