Study On Synthesis By Self-assembly Method And Photocatalysis Of Nano-/Micro-TiO₂ Thin Films

As an important inorganic functional material, Titania (TiO₂) has many unique physical and chemical properties. This material is extensively used as a catalyst in purification of air and water, a pigment in making paints, an enamel, an antimicrobial and so on. TiO₂ powders are usually restricted by some performances in the application because they are easier to become inactive, to reunite and harder to be reclaimed in the photocatalytic process. But TiO₂ films can avoid these disadvantages.The aim of this thesis is to obtain TiO₂ /SiO₂ or TiO₂/glass films through combining the sol-gel technology and the layer-by-layer self-assembly method by using low-cost Titanium chloride (TiCl₄) or Titanyl sulfate (TiOSO₄) as the raw material and SiO₂ beads or glass slides as the raw carriers. In this research we have studied the modification to the composite with polyethylene glycol (PEG), ions and acids, the control disciplinarians of surfactants to the shape and size of TiO₂, photocatalysis of the samples etc..The major work includes the following aspects:1. TiO₂/SiO₂ films are prepared by using TiCl4 and SiO₂ beads as the raw material and carriers respectively. The effect of PEG with different polymerization degree, Fe³⁺, polyethylene glycol 2000 (PEG2000) and Fe³⁺ doped together to the samples are studied.The results show that TiO₂ with uniform size and a large number can be obtained by using Sodium dodecyl sulphate (SDS) as the self-assembly medium, preparing sol and synthesizing in water bath at 80℃. The density and diameter of the holes become bigger and more uniform gradually with the increasing concentration of PEG. TiO₂ films are easier to split open when the concentration of PEG is too high, or the synthesis circle and polymerization degree of PEG are too much. The mixed phases of anatase and rutile can be obtained when PEG2000 is doped and the relative content of anatase increases with the increasing concentration of PEG2000. Photocatalytic experiments show that photocatalytic activity increases by doping PEG and the optimal concentration of PEG600, PEG2000 and PEG20000 are 12.0%, 2.0% and 0.10% respectively. And the optimal synthesis circle is two when PEG2000 is doped. Photocatalysis can be increased by doping Fe³⁺ and the optimal concentration is 0.00125%. And photocatalytic activity is higher by doping PEG2000 and Fe³⁺ together compared to doping separately.2. Preparation conditions of TiO₂/SiO₂ films in the system of TiOSO₄-H₂O-CH₆O₂ by using TiOSO₄ and SiO₂ beads as the raw material and carriers, modifying with Cu²⁺ or sulfuric acid (H₂SO₄) and photocatalysis are studied.The optimal preparation conditions of TiO₂/SiO₂ in this system are that the cubage ratio of TiOSO₄ (1.07 mol/L), C₂H₆O₂ and H2O is 2:3:3, preparing sol and synthesizing are in water bath at 80℃for 30min and 2h respectively, aging time in water bath is 12h and annealing time at 550℃is 2.5h. Compared to TiCl₄, TiO₂ with smaller size and higher relative content of anatase can be obtained by this method. Photocatalytic activity is the best when the samples undoped are annealed at 550℃. By doping Cu²⁺, photocatalytic activity increases and the optimal concentration is 0.10%. And the optimal synthesis circle is three. After treating with H₂SO₄, photocatalytic activity of TiO₂ also increases.3. TiO₂/glass films are prepared by using TiCl4 and glass slides as the raw material and carriers. The effect of nonionic surfactant PEG2000 and anionic surfactant Sodium dodecyl benzene sulfonate (SDBS) to the shape, size and structure of TiO₂ and photocatalysis are studied.PEG2000 and SDBS can both control the shape and size of TiO₂ particles. Annealing ambient and the concentration of PEG2000 can affect the shape of TiO₂ when PEG2000 is doped. After annealing in airtight ambient the shape of TiO₂ particle varieties from rod-like to sphere-like, whereas it varieties from irregular to egg-like in air ambient with the increasing concentration of PEG2000. And the size of TiO₂ obtained from air ambient is bigger. By doping SDBS and preparing in water bath, the shape of TiO₂ particle transforms from rod-like to sphere-like and again to rod-like with the increasing concentration of SDBS. And TiO₂ film arranges like a web consisting of some circles whose diameters are about 3um averagely when the concentration is 2.0 %. But the shape of TiO₂ is worm-like by preparing in ultrasonic ambient. After doping PEG2000 or SDBS, the size of TiO₂ becomes smaller at first and bigger afterward with the increasing concentrations of them. XRD patterns show that the relative content of rutile increases with the increasing concentration of PEG2000 and the relative content of anatase increases with the increasing concentration of SDBS. And pure anatase can be obtained when SDBS added is 40.0%. In photocatalytic experiments it can be concluded that PEG2000 and SDBS can both improve photocatalysis of the samples and the optimal concentration are 9.8% and 8.0% respectively.