Synthesis And Application Of TiO₂Based Composite Oxides

TiO₂has been widely used in pigments, fine ceramics, plastics, rubber, chemicalfiber, cosmetic, enamel, ceramics, electronic materials, photocatalytic purification andcatalyst carrier, due to its stable physical and chemical properties, excellent pigmentperformance, and better electrical and optical properties. TiO₂has three different crystalstructures: rutile, anatase, and brookite. Anatase TiO₂with good photocatalyticperformance has been widely used and studied; Rutile TiO₂has good ultravioletabsorption ability, which is the preferred inorganic UV shielding materials; Brookite TiO₂has no more practical application.Rutile TiO₂is the most stable structure, while the anatase and brookite TiO₂areunstable. Anatase can transform to rutile type at a higher temperature within the range of400℃¹200℃. Therefore, energy consumption is high in manufacturing rutile TiO₂. A lotof research results show that rutile TiO₂can be prepared in the low temperature or thetemperature transforming anatase to rutile type can be lowered by introducing some otherelement as matrix of composite oxide in the synthesis of TiO₂. In the field of thephotocatalytic degradation reaction, the catalytic performance can be enhanced obviously,and the photocatalytic efficiency can be greatly increased by using some elements dopedTiO₂complexes as catalyst.In this paper, based on the relatively low price of titanium sulfate as Ti precursor,TiO₂-SnO₂, ZnO coated rutile TiO₂-SnO₂and Fe-dopted TiO₂composite oxides wereprepared by the simple method with urea as precipitant. Crystal formation and ultravioletabsorption performance of the composites oxides were investigated. Then thephotocatalytic degradation of papermaking waste liquid was studied using TiO₂-SnO₂andFe-dopted TiO₂as catalyst.TiO₂-SnO₂composite oxide was prepared in the condition of low temperaturehydrothermal. The effect of the ratio of n(Ti⁴⁺)/n(Sn⁴⁺) on the crystal structure of theproduct was studied by XRD. The results showed that rutile TiO₂was obtained when ratioof n(Ti⁴⁺)/n(Sn⁴⁺) was6⁸. The effects of the content of urea and the reaction time on the crystal form and the relationship between the content of urea and the product yieldwere investigated. The morphology and dispersion of products in static state with differentn(Ti⁴⁺)/n(Sn⁴⁺) were studied by SEM, and then the morphology in the mixing reactionmanner was compared. The ratio of TiO₂and SnO₂in TiO₂-SnO₂compounds wasdetermined by spectral analysis of Ti element and Sn element on the surface of product.The rutile TiO₂-SnO₂composite has the best ultraviolet absorption ability in syntheticcompounds, and can be used as ultraviolet shielding materials. Finally, the formationmechanism of TiO₂-SnO₂compound crystal was analyzed.ZnO-coated rutile TiO₂-SnO₂composite oxide was prepared in the condition ofn(Ti⁴⁺)/n(Sn⁴⁺)=6by using high temperature roasting dehydration after homogeneousprecipitation method. The coating state of ZnO for rutile TiO₂-SnO₂was studied by XRDwith different ratio of n(Zn²⁺)/[n(Ti⁴⁺)+n(Sn⁴⁺)]. The results showed whenn(Zn²⁺)/[n(Ti⁴⁺)+n(Sn⁴⁺)]≥3, TiO₂-SnO₂was completely coated by ZnO. Compared withpure ZnO, and TiO₂, ZnO-coated rutile TiO₂-SnO₂composite oxide has the strongestultraviolet absorption capacity in Uv-vis absorption test. Then the morphology of productwas observed by SEM, and the fully coated state of ZnO for TiO₂-SnO₂was testified bythe spectrum analysis. ZnO-coated rutile TiO₂-SnO₂composites can be prepared byhomogeneous precipitation method. The craft and operation are simple and easy to realizeindustrialization, and the product can be used as high-performance ultraviolet shieldingmaterials.Fe-dopted TiO₂composite oxide was prepared with ammonia, urea and NaOH asalkali source reacting with Ti（SO4）2and Fe（NO3）3·9H2O. After calcination, the XRD testwas used to analyze the conversion of TiO₂crystal type. In the use of ammonia water andthe NaOH, two kinds of adding methods were used. With urea as alkali source, thereaction was operated under90℃after adding urea to fully dissolve in the reaction liquid.The effects of alkali source, responses and n（Ti4+）/n（Fe3+） mole ratio and heat treatmenttemperature on the crystal structure of product were investigated systematically. UsingNaOH as precipitant, the specific products of crystal type can be not obtained in any case.Anatase TiO₂can be obtained by using urea as alkali source, while anatase and rutilemixed crystal structure can be obtained with ammonia as reactant. And the proportion of anatase and rutile of composite was determined by the mole ratio of n（Ti4+）/n（Fe3+） andreaction. It was found that the pure TiO₂structure was influenced by the alkali source andthe products do not have a specific structure by adding NaOH to Ti（SO4）2. Fe-dopted TiO₂has a degree of absorption of visible light.Compared with pure TiO₂and P25, photocatalytic oxidation degradation of themethyl orange, dodecyl benzene sulfonic acid sodium and papermaking waste liquid wereanalyzed in under the irradiation of natural light using the TiO₂-SnO₂composite oxide andFe-dopted TiO₂by urea alkali source as catalyst. Photocatalytic experiments of thedifferent composition of TiO₂-SnO₂and Fe-dopted TiO₂were carried to examine theeffects on the performance of photocatalytic oxidation of catalysts. It was found that eachcompound in the appropriate proportion has ideal photocatalytic activity. The morphologyof TiO₂-SnO₂and the surface composition of sample were observed by SEM and EDAX,respectively. Ultraviolet absorption tests of TiO₂-SnO₂, Fe-dopted TiO₂, P25and pureTiO₂were carried out. In this study, the prepared TiO₂-SnO₂and Fe-dopted TiO₂havegood application prospect due to good performance in the photocatalytic degradationreaction.