Synthesis Of TiO₂-based Composite Photocatalytic Fibers With Heterostructures And Their Photocatalytic Property

In the past few decades, advanced oxidation technology in the degradation of refractory organic pollutants has attracted the wide attention of the researchers. There is no doubt that environmental friendly photocatalytic oxidation technology has an attractive application prospect in this kind of oxidation technology. In this regard, TiO2 as a photocatalyst with stable chemical properties, non-toxity and harmless, high activity and low-cost, is considered to be the most ideal semiconductor photocatalyst. However, there are some disadvantages, such as insufficient visible light response, wide band gap and charge recombination, difficult to recovery and secondary pollution, etc. All these inherent disadvantages have become the bottleneck of TiO2 photocatalytic technology to practical.Guided by the theory of heterostructures, the synthesis of ZnO/TiO2, BiVO4/TiO2 and InVO4/TiO2 fibers were carried out via the subsequent hydrothermal method, respectively. The photocatalytic mechanism of the three composites was discussed. The major contents and results are summarized as follows:In the first part, mesoporous TiO2 fibers were synthesized on the basis of the modified sol-gel method and centrifugal spinning with tetrabutyl titanate (TBOT) as Ti sorce, ethyl acetoacetate (EAcAc) as chelating agent and tetrahydrofuran (THF) as solvent. With Zn(NO3)2-6H2O as the source of zinc and C6H12N4 as the structure of guide agent, ZnO/TiO2 fibers with controllable morphology and size are fabricated using hydrothermal method. ZnO/TiO2 fibers with different ZnO morphology and ratio were prepared through changing the concentration of ZnO seed solution. Compared with the in situ method, the preparation method is more favorable for the active component to exposure. The formation of the ZnO/TiO2 heterostructures and its complete crystal shape were demonstrated using a variety of characterization methods. Compared with the pure TiO2, the Ti2p of the 1:1 ZnO/TiO2 fiber had a red shift of 0.2 eV, showing that the addition of ZnO had changed the chemical environment around. At the same time, there is a small amount of oxygen vacancy and Ti3+. The introduction of ZnO made the absorption band edges of the fibers shift to red regon narrowing the forbidden band. And the excited charge carriers were inhibited. In the photocatalytic degradation of the X-3B aqueous solution,1:1 ZnO/TiO2 fiber was shown to be a kind of efficient composite photocatalyst.In the second section, the BiVO4/surface rough TiO2 fibers were fabricated via a mild hydrothermal method by using surface-modified Si-TiO2 as self-supporting substrate materials. The as-prepared fibers consisted of the needle-like or flower-like BiVO4 uniformly assembled on surface rough TiO2 fibers (RTF). Notably, several needle-like BiVO4 with lengths less than 1 μm and diameters ranging from 80 to 100 nm constructed a microflower by radiating from the center, which could be controlled by adjusting the concentration of the precursor. The incorporation of monoclinic BiVO4 in the composites was confirmed by XRD, SEM, PL and XPS. RTF was obtained through the dissolution of silicon in the surface of Si-TiO2 fibers (STF) by HF. The photocatalytic performance of the heterostructured fibers was investigated by the degradation of X-3B in aqueous solution under both ultraviolet and visible light irradiation. The 0.2BiVO4/RTF with mass ratio of 20% vanadate exhibited optimized photocatalytic activity compared with pure STF, BiVO4, 0.2BiVO4/STF and mechanically mixed 0.2BiVO4+RTF, which might be ascribed to synergistic effect of morphology and heterostructures. Moreover, such 0.2BiVO4/RTF composites were easy to separate from the treated wastewater and remained stable after ten irradiation cycles. It was proposed that electronic interactions at the interface of BiVO4/RTF heterostructures could effectively inhibit the charge recombination.In the third part, the band gap of mult-metal oxide InVO4 was 2.07 eV, which was an effectively visible light photocatalyst. The conduction band of InV04 is composed of the 3d V atomic orbital and atomic In 5s orbit, making the enhanced ability of electron migration. But pure InVO4 is susceptible to light corrosion and not easy to recycle. The InVO4/TiO2 fibers with efficient electrical transmission, suppressed charge carrier compound and broad-spectrum were prepared in this section. In composite fibers, the XRD characteristic peak position of InV04 offsetted in the direction of high angle, possibly because the compositing of InVO4 and RTF made the lattice squeeze smaller interplanar spacing. Maybe the incorporation of V5+ into the TiO2 crystal lattice also influenced each other to make the lattice distortion. SEM combined with EDX analysis can directly prove the formation of heterostructures between InV04 and RTF. At the same time, the FTIR analysis also showed the Ti-O in RTF was replaced with the In-0 in InV04 and forming Ti-O-In. The results of the photocatalytic performance evaluation showed that the 0.10 InVO4/RTF under visible light irradiation was optimal in the degradation of X-3B.