Study of TiO2 nanocrystallites in TiO2SiO2 composites

In situ synthesis and hydrothermal crystallization of nanoanatase TiO2 -SiO2 coating on aramid fabric (HTiSiAF) for UV protection

TiO2 -SiO2 thin film was prepared by sol-gel method and coated on the aramid fabric to prepare functional textiles. The aramid fabric was dipped and withdrawn in TiO2 -SiO2 gel and hydrothermal crystallization at 80(°) C, then its UV protection functionality was evaluated. The crystalline phase and the surface morphology of TiO2 -SiO2 thin film were characterized using SEM, XRD, and AFM respectively. SEM showed hydrothermal crystallization led to a homogeneous dispersion of anatase nonocrystal in TiO2 -SiO2 film, and XRD suggested the mean particle size of the formed anatase TiO2 was less than 30 nm. AFM indicated that hydrothermal treatment enhanced the crystallization of TiO2 . UV protection analysis suggested that the hydrothermally treated coated textile had a better screening property in comparison with TiO2 -SiO2 gel and native aramid fabric.

Electrical conductivity of activated carbon-metal oxide nanocomposites under compression: a comparison study

From a granular commercial activated carbon (AC) and six metal oxide (Al2O3, Fe2O3, SnO2, TiO2, WO3 and ZnO) precursors, two series of AC-metal oxide nanocomposites were prepared by wet impregnation, oven-drying at 120 °C, and subsequent heat treatment at 200 or 850 °C in an inert atmosphere. Here, the electrical conductivity of the resulting products was studied under moderate compression. The influence of the applied pressure, sample volume, mechanical work, and density of the hybrid materials was thoroughly investigated. The DC electrical conductivity of the compressed samples was measured at room temperature by the four-probe method. Compaction assays suggest that the mechanical properties of the nanocomposites are largely determined by the carbon matrix. Both the decrease in volume and the increase in density were relatively small and only significant at pressures lower than 100 kPa for AC and most nanocomposites. In contrast, the bulk electrical conductivity of the hybrid materials was strongly influenced by the intrinsic conductivity, mean crystallite size, content and chemical nature of the supported phases, which ultimately depend on the metal oxide precursor and heat treatment temperature. The supported nanoparticles may be considered to act as electrical switches either hindering or favouring the effective electron transport between the AC cores of neighbouring composite particles in contact under compression. Conductivity values as a rule were lower for the nanocomposites than for the raw AC, all of them falling in the range of semiconductor materials. With the increase in heat treatment temperature, the trend is toward the improvement of conductivity due to the increase in the crystallite size and, in some cases, to the formation of metals in the elemental state and even metal carbides. The patterns of variation of the electrical conductivity with pressure and mechanical work were slightly similar, thus suggesting the predominance of the pressure effects rather than the volume ones.

Characteristics of supported nano-TiO2/ZSM-5/silica gel (SNTZS): photocatalytic degradation of phenol

Photocatalytic degradation of phenol was investigated using the supported nano-TiO(2)/ZSM-5/silica gel (SNTZS) as a photocatalyst in a batch reactor. The prepared photocatalyst was characterized using XRD, TEM, FT-IR and BET surface area analysis. The synthesized photocatalyst composition was developed using nano-TiO(2) as the photoactive component and zeolite (ZSM-5) as the adsorbents, all supported on silica gel using colloidal silica gel binder. The optimum formulation of SNTZS catalyst was observed to be (nano-TiO(2):ZSM-5:silica gel:colloidal silica gel=1:0.6:0.6:1) which giving about 90% degradation of 50mg/L phenol solution in 180 min. The SNTZS exhibited higher photocatalytic activity than that of the commercial Degussa P25 which only gave 67% degradation. Its high photocatalytic activity was due to its large specific surface area (275.7 m(2)/g), small particle size (8.1 nm), high crystalline quality of the synthesized catalyst and low electron-hole pairs recombination rate as ZSM-5 adsorbent was used. The SNTZS photocatalyst synthesized in this study also has been proven to have an excellent adhesion and reusability.

Porous TiO2/SiO2 composite prepared using PEG as template direction reagent with assistance of supercritical CO2

Titania-silica mesoporous composites have been prepared using polyethylene glycol (PEG) 20,000 as a template direction reagent with the assistance of supercritical carbon dioxide (SC CO(2)). For this preparation method, the composite precursors of tetrabutyl titanate (TBTT) and tetraethyl orthosilicate (TEOS) were dissolved in supercritical CO(2) and impregnated into PEG 20,000 using SC CO(2) as swelling agent and carrier. After removal of the PEG template by calcination in air at suitable temperatures, porous titania-silica composites were obtained. Effects of CO(2) pressure and temperature have been studied on the impregnation ratio during the supercritical fluid condition. The composite products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy, nitrogen sorption-desorption experiments, scanning electronic microscope (SEM), and transmission electron microscope (TEM). XRD and nitrogen sorption-desorption experimental results indicate that the titania-silica composite crystallized in anatase phase and has a preferable BET surface area up to 301.98 m(2)/g. It was also demonstrated that the microstructure and macroproperty of TiO(2)/SiO(2) composites depend strongly on the experimental pressure during the impregnation process in SC CO(2). At suitable CO(2) pressure, silica even can be found in a single crystalline structure in nature by observation of TEM. At the same time, SEM indicates that the composite product existed in a spheric form or a cubic form inserted with many holes. So this work provides a new route to control and obtain the special micrography of TiO(2)/SiO(2) composites with the aid of suitable polymer templates in supercritical CO(2).