Low-temperature Preparation Of Photocatalytic TiO₂ Sol And Research On Its Factors

In recent years, decomposing contaminants by means of photocatalysis has become one of the most prosperous sections. As a photocatalytic material, TiO2 has been drawn more and more attention of scientists due to its unique physical and chemical properties. Lots of efforts have been made towards the preparation of nano TiO₂ powders and films with high photocatalytic property, multiphase photocatalytic mechanism, enhancing quantum-efficiency of TiO₂. However, seldom reports can be found about the study of TiO₂ sol. Furthermore, the need for high-temperature treatment in traditional sol-gel method limits the choice of substrates to heat-resistant materials and also limits the coating on large-area substrates, which is difficult to be calcined. Based on the actuality, an approach to the low-temperature preparation of photocatalytic T1O2 sol was proposed in this paper, and the influencing factors of resultant TiO₂ sol was also presented.The TiO₂ sol was prepared via sol-gel method, Ti(OC₄H₉)₄ was chosen as a precursor, and alcohols as impregnant, acid as catalyzer. A new reaction system and the relevant technical route were adopted, and TiO₂ sol containing TiO₂ crystals was prepared at low temperature, which directly had photocatalytic activity without the typical high-temperature treatment in traditional sol-gel method. In addition, the influence of catalyzer, impregnant and the amount of precursor on the structure and photocatalytic activity of TiO₂ sol was investigated detailedly. The results as follows:1. The variety and amount of catalyzer have significant influence on the structure and photocatalytic activity of TiO₂ sol. Different catalyzer induces different morphology of samples: when weak acid such as HAc and H3PO4 is used as a catalyzer, the acid radical will form complex with precursor, and thus the viscosity is large and crystallization is poor. However, when strong acid such as HC1 and HNO3 is used as a catalyzer, the viscosity of TiO₂ sol is small, and the morphology of crystal is regular and thus the photocatalytic activity of TiO₂ sol is well. Under the strongly acidic condition (PH=0.96), the phase of TiO₂ colloidal crystal is rutile and anatase, companied with little brookite phase. With the increase of PH value, rutile phase decreases, while brookite phase increases.2. The variety and amount of impregnant have great influence on the structure and photocatalytic activity of TiO₂ sol. The crystallization of TiO₂ colloidal crystal becomes poorwith increasing the length of carbon chain, and wasn't affected obviously with the increase of hydroxy group in the carbon chain, and the site of hydroxy group does not affect the crystallization;the length of carbon chain and site of hydroxy group have no influence on the crystal phase of TiCh colloidal crystal, but the amount of hydroxy group in the carbon chain can affect the crystal phase. When monohydric alcohol is used, the crystal phase consists of anatase and brookite. However, dihydric alcohol used as impregnant will induce single anatase crystal phase. Furthermore, the photocatalytic activity of T1O2 sol is increase with the length of carbon chain. The amount of impregnant has no effect on the crystal phase, but can affect the degree of crystallization. More amounts or less amounts of impregnant will induce poor crystallization.3. The content of precursor can not affect the crystal phase, but will influence the morphology of TiC>2 sol. When the content of precursor is 3.19%, the resultant TiC>2 sol is homogeneous and clear, and the crystallization of TiC>2 colloidal crystal is well, so the TiC>2 sol has higher photocatalytic activity.