Preparation And Photocatalytic Behavior Of Zn²⁺ Doped Tio₂ One-dimensional Nanomaterials

TiO₂ nanomaterials have board application prospects in many fields, such as photocatalytic degradation, dye sensitization, solar cells and water photolysis. However, their applications have been restricted due to wide band gap and low solar energy efficiency of TiO₂. In this paper, many efforts have been devoted to increase photocatalysis activity in visible light and practicality of TiO₂ nanomaterials through material modification and morphology changing.The TiO₂ nanopowders, its nanofibers and nanotubes, as well as Zn²⁺ doped TiO₂ nanofibers and nanotubes were prepared successfully. The morphology, structure and properties of the TiO₂ and Zn²⁺ doped TiO₂ nanomaterials were characterized by Termogravimetry-Differential Scanning Calorimetry (TG-DSC) analysis, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET specific surface areas analysis, multiangle ultrafine particle analyzer and Fourier transform infrared spectroscopy.For TiO₂ nanomaterials, combining DSC and XRD analyses, the anatase TiO₂ and the rutile TiO₂ were developed at temperatures about 400-450oC and 450-550oC respectively during calcination of the gel. The synthesized TiO₂ nanopowders had an uniform particle size distribution and an obvious agglomeration phenomenon with an average particle size of 30 nm and a specific surface area of about 40 m2/g. The diameters of the prepared TiO₂ nanofibers were decreased to 100-500 nm after calcinations for 4 h at temperatures of 400oC, 450oC, 500oC and 600oC, respectively.The TEM analyses results showed that the synthesized TiO₂ nanofibers were composed of small particles of 5-10 nm, and the specific surface area of the TiO₂ nanofibers was 70.81 m2/g after calcination at 400oC for 4 h. It is confirmed that Zn²⁺ has doped into TiO₂ lattice by XRD, SEM and EDS analyses for Zn²⁺ doped TiO₂ nanofibers. The temperatures, at which the peaks appeared in DSC curves, increased with the increase of doped Zn²⁺ concentration, but with small change. It indicated that doping Zn²⁺ can decrease phase developing temperature and phase transition temperature of TiO₂ nanofibers. The specific surface area was 64.77 m2/g for 0.52 at% Zn²⁺ doped TiO₂ nanofibers which were calcined at 400oC for 4 h. The TiO₂ nanotubes were prepared successfully by coaxial electrospinning, which had smooth tube surface, uniform tube diameter and wall thickness of about 50 nm after calcination at 400oC for 4 h.The structure of the anatase TiO₂ and the Zn²⁺ doped anatase TiO₂ were calculated based on density functional theory (DFT). The results confirm that the band gap of Zn²⁺ doped TiO₂ becomes smaller and its optical absorption edge has red shift, which benefits photocatalytic activity in visible light zone.The photocatalytic properties of the various TiO₂ nanomaterials were evaluated in UV light zone and visible light zone. The experiments results showed that the highest photodegradation rates for the various TiO₂ nanomaterials in methyl orange solution were 85% for TiO₂ nanopowders, 69% for nanofibers, 52% for Zn²⁺ doped TiO₂ nanofibers, and only 30% for TiO₂ nanotubers, respectively. It indicates that chemical modification and morphology changing for TiO₂ has little influence on photocatalytic properties in UV light zone. However, in visible light zone the highest photodegradation rates for the prepared various TiO₂ nanomaterials in methylene blue solution were 25% for TiO₂ nanopowders, 32% for nanofibers, 80% for TiO₂ nanotubers, 88% for Zn²⁺ doped TiO₂ nanofibers, and 92% for TiO₂ nanotubers, respectively. It shows that chemical modification and morphology changing for TiO₂ can improve the phtocatalytic properties in visible light zone. This provides a necessary theoretic foundation for TiO₂ nanomaterials in practice.