Papers by Keyword: TiO₂-SiO₂

Abstract: The aim of the research was to develop the area of mesoporous thin films of a binary TiO₂–SiO₂ system. Sol was synthesized from tetraethylorthosilicate as the silica source and titanium isopropoxide solution as the TiO₂ source, while triblock copolymer surfactant (Pluronic F 127 (10% solution in water, (P))) was used as the mesostructure-directing agent. In this paper we present sol-gel obtained TiO₂–SiO₂ with a mesoporous structure. The effects of added titanium on the mesostructure and on the porosity are presented and discussed. Four different molar percentage ratios of Ti: Si were used for the synthesis of mixed TiO₂–SiO₂ mesoporous thin films on glass substrate. The mesoporous structure of thin films was characterized by X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), scanning electron microscopy (SEM) and the water contact angle. These mesoporous TiO₂–SiO₂ thin films could have many potential applications in many areas such as separation membranes, catalysis, optics, and self-cleaning surfaces.

Abstract: A new environmental friendly catalyst, H₄SiW₆Mo₆O₄₀/TiO₂-SiO₂ was prepared by impregnation method, the synthesis of cyclohexanone 1,2-propanediol ketal was the probe reaction to optimize the synthetic condition of catalyst. The reactive condition of catalyst was optimized by orthogonal test method. The optimum conditions are n (TiO₂): n (SiO₂)= 3: 1, 20 % mass ratio of m (H₄SiW₆Mo₆O₄₀): m (TiO₂-SiO₂), the calcined time is 3 h and 300 °C of activated temperature. Using H₄SiW₆Mo₆O₄₀/TiO₂-SiO₂ as catalyst, adipic acid was synthesized from the oxidation of cyclohexanone by 30 % H₂O₂. Influences of dosage of H₄SiW₆Mo₆O₄₀/TiO₂-SiO₂, reaction temperature, volume of hydrogen peroxide and reaction time were discussed. Experimental results showed that H₄SiW₆Mo₆O₄₀/TiO₂-SiO₂ is a good catalyst for synthesis of adipic acid. When n (cyclohexene): n (H₂O₂): n (H₄SiW₆Mo₆O₄₀/TiO₂-SiO₂)= 100: 979: 0.04, reaction temperature is 130 °C and reaction time is 5 h, under the optimum conditions, the yield of adipic acid is 45.9 %.

Abstract: The environmental friendly catalyst, H₄SiW₁₂O₄₀/TiO₂-SiO₂ was prepared by the impregnation method. The synthesis of cyclohexanone glycol ketal was as the probe reaction and investigated the different influences on the catalytic activity of H₄SiW₁₂O₄₀/TiO₂-SiO₂ by the quality of the carrier TiO₂-SiO₂ ratio, load of heteropoly acid, catalyst preparation conditions of the activation time and the calcination temperature, etc. The results showed the best condition for the preparation of the catalyst is the mass ratio of TiO₂ and SiO₂ is 1: 5, the load ratio of H₄SiW₁₂O₄₀ is 10 %, calcination temperature is 300 oC and the roasting time is 3.0 h. Under the condition of the molar ratio of aldehydes (ketones) and glycol (1,2-propanediol) is 1: 1.6, the mass percent of the catalyst is 1.4 %, and the reaction time of 70 min, the yields of eight kinds acetal (ketal) are 71.6 %~ 90.5 %.

Abstract: In this paper, TiO₂-SiO₂ composite aerogels were prepared via ambient pressure drying by sol-gel and sol pre-modification method. The pre-modification solution consists of hexamethyldisiloxane (HMDSO) as buffering agent, trimethylchlorosilane (TMCS) as modifier and hexane as organic solvent. The pore structure of TiO₂-SiO₂ composite aerogels was characterized by N₂ adsorption-desorption method. The effects of HMDSO/TMCS volume ratio on the pore structure and properties of TiO₂-SiO₂ composite aerogel were studied. The results indicate that the pre-modification of TiO₂-SiO₂ composite sol by adding HMDSO/TMCS/Hexane solution could shorten the preparation period. Increasing the amount of HMDSO is favorable for obtaining TiO₂-SiO₂ composite aerogel with higher specific surface area and pore volume. The best volume ratio of HMDSO/TMCS/composite sol for preparing mesoporous TiO₂-SiO₂ composite aerogels were 12:6:120 and 12:12:120, with which the specific surface area and pore volume of the obtained TiO₂-SiO₂ composite aerogel are 425.2～645.4 m²/g and 0.80～2.85 m³/g, respectively.

Abstract: TiO2-SiO2 nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) within the micro-emulsion. The average size of synthesized TiO2-SiO2 nanoparticles was about in the size range of 20-100 nm. The effects of synthesis parameters, such as the molar ratio of water to precursor and the molar ratio of water to surfactant, are discussed.

Abstract: Through X-ray photoelectron spectroscopy, by the aid of Ar+ sputtering, chemical composition and the valence state of elements on surface and at depth of TiO2-SiO2 thin films and metal substrates have been studied. Results show that: on surface, elements of Cr, Mn, Ti, Fe exist in the form of their respective stable state, but Si is unstable and exhibits stoichiometrical disturbance when heat treated at 800°C; at depth, after sputtering for 5 minutes and 17 minutes, elements of Cr, Mn, Ti and Ni exist in the form of their respective stable state, but Si and Fe are unstable and exhibit stoichiometrical disturbances; at depth, after sputtering for 57 minutes, all of the Cr, Mn, Ti, Si, Ni and Fe exist in the form of their respective stable state. Results of chemical composition and their content by weight percent of TiO2-SiO2 thin films and metal substrates reveal that: Fe, Cr, and Mn diffuse from metal substrates to the thin films in scale; Ni diffuses few and Si collects to the metal substrate surface