TiO2 SiO2 Aerogel Research Articles

Green water-based fabrication of SiO2–TiO2 aerogels with superhydrophobic and photocatalytic properties and their application on cotton fabric

Green water-based fabrication of SiO2–TiO2 aerogels with superhydrophobic and photocatalytic properties and their application on cotton fabric

Engineering SiO2–TiO2 binary aerogels for sun protection and cosmetic applications

SiO2‒TiO2 binary aerogels obtained by the methods of low-temperature (carbon dioxide) and high-temperature (isopropanol, hexafluoroisopropanol and methyl tert-butyl ether) supercritical drying are considered as multifunctional cosmetic pigments with high anti-shine power and photoprotective properties. The composition and structure of SiO2–TiO2 aerogels obtained by supercritical drying in various fluids were studied by IR spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption. The values of the sun protection factors SPF and UVAPF for the obtained materials are comparable to those of the commercial sunscreens Kronos 1171 and Kronos 2971, and the anti-shine power is approximately 1.5 times higher than that of kaolin-based materials.

Tungstate doped TiO2-SiO2 aerogels for preferential photocatalytic degradation of methamphetamine in seizure samples containing caffeine under simulated sunlight

Tungstate doped TiO2-SiO2 aerogels (W/TiO2-SiO2) was synthesized and photocatalytic degraded methamphetamine (MAT) preferentially in seizure samples which containing caffeine. As a control, TiO2 (P25) photocatalytic degraded both MAT and caffeine simultaneously. The degradation rate of MAT under simulated sunlight for TiO2 (P25), TiO2-SiO2 aerogels, W/TiO2 and W/TiO2-SiO2 are 28.1%, 64.2%, 74.1% and 98.8% within 60 min. The photocatalytic efficiency of W/TiO2-SiO2 for degradation of MAT is 7.0, 4.4 and 1.9 times higher than TiO2 (P25), TiO2-SiO2 aerogels and W/TiO2. The enhanced photocatalytic performance of W/TiO2-SiO2 could be attributed to increase the adsorption of MAT induced by tungstate-doping.

Synthesis of Ag doped SiO2-TiO2 aerogels with nano-sized microcrystalline anatase structure through IL control

In this paper, Ag doped SiO2-TiO2 aerogels with nano-sized microcrystalline anatase structure through a sol-gel way, ionic liquid(IL), 1 – butyl-3-methylimidazole bromide ([bmim]Br), is used as a structure control agent. The catalysts were characterized by SEM, XRD and nitrogen adsorption-desorption isotherms (BET analyses). The photocatalytic activities were investigated by degration of active brilliant blue under UV-light. It was demonstrated that IL facilitate the formation of mesoporous and anatase microcrystalline structure at around ambient condition, without calcination. Both at sol-step and gel-step, the concentration of IL aqueous solution prominently effected on the structure properties of catalysts. Surface area, crystalline grain dimension and mecroporous structure all played important roles in the degradation reactions. The catalyst with 1/10 Si/Ti ratio, 385.2 m2g-1surface area and 6.2nm crystalline grian size, showed excellent photocatalytic degradation rate up to 99.7%.

A novel TiO2-SiO2 aerogel nanocomposite absorbent: preparation, characterization and photocatalytic degradation effects on automobile exhaust

In this paper, a novel TiO2-SiO2 aerogel nanocomposite absorbent was successfully synthesized using the sol-gel and ambient pressure drying method, and its photocatalytic degradation effects on automobile exhaust were investigated for the first time. The microstructures and properties of the Nano TiO2-SiO2 aerogels were characterized using various methods, including x-ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FT-IR). The exhaust purification tests were conducted in a self-developed instrument to investigate the degradation effects of Nano TiO2-SiO2 aerogels on automobile exhaust through degradation rate. Experimental results showed that the Nano TiO2-SiO2 aerogels had a good photocatalytic degradation effect on automobile exhaust, and the degradation rates of CO, CO2, HC and NOx were 1.3%, 1.5%, 3.2% and 34.4%, respectively. The well-designed microstructure makes the Nano TiO2-SiO2 aerogels a stable photocatalytic material with high specific surface area and big average pore size, which has promising applications in environmental treatment.

Three-dimensional TiO2/SiO2 composite aerogel films via atomic layer deposition with enhanced H2S gas sensing performance

The SiO2 aerogel films with three dimensional (3D) networks were chosen as the templates to deposit TiO2 nanoparticles by atomic layer deposition (ALD). The microstructure, morphology and gas sensing properties of the composite aerogel films were investigated. The composite aerogel films kept the mesoporous structures with TiO2 nanoparticles uniformly coated on. After the 500℃ calcination, the TiO2 nanoparticles changed from amorphous to anatase phase. The calcined composite aerogel films were used to fabricate the gas sensor to detect H2S gas. The sensor had an excellent gas sensitivity of 1.34 with the response and recovery time of 53 and 74s, respectively, at 250℃ when the H2S gas concentration was as extremely low as 0.5ppm. The sensor still had a high gas sensitivity with the H2S concentration of 10ppm even when the operating temperature was 100℃. Compared to other H2S gas sensors based on TiO2 materials, the enhanced sensing performance could be due to the larger specific surface area of the aerogel template，the smaller grain size and the lattice mismatch between TiO2 nanoparticles and SiO2 aerogels, which made the composite aerogel films had more active sites and lattice defects, resulting in the increase of oxygen vacancy and enhancement of the gas sensitivity.

Influence of Silicon Content on the Photocatalytic Activity of Methyl Orange by TiO2-SiO2 Composite Aerogels

TiO2-SiO2 aerogel has been synthesized at an ambient pressure with a silica-precursor of waterglass and a titania-precursor titanium tetrachloride with a variable silicon content (10%, 20%, 30%) by sol-gel method/surface modification. The photocatalytic performance of these materials was tested by degrading the methyl orange following UV light irradiation at l =465nm. The experimental results have shown that the as-prepared aerogels have entirely consisted with anatase crystalline phase. With the increase of silicon content, the photocatalytic degradation capacity of the as-synthesized aerogels was decreased. When the silicon content is 10%, the best catalytic degradation effect was obtained, the decolorizing efficiency of MO is detected as 97.13% after 160 mins exposure to UV light irradiation.

Effect of Heat-Treatment on the Microstructure and Properties of SiO<sub>2</sub>-TiO<sub>2 </sub> Aerogels Synthesized via Supercritical Drying

Monolithic SiO2-TiO2 aerogels were prepared via supercritical drying using tetraethoxysilane and tetrabutyltitanate as precursors and ethanol as solvent. Influence of the heat-treatment on the microstructure and properties of SiO2-TiO2 aerogels were investigated in detail. The results showed that the as-prepared SiO2-TiO2 aerogels had low densities, high specific surface areas, small average pore diameters, and three-dimensional nanoporous structures. The anatase TiO2 phase of SiO2-TiO2 aerogels could form during supercritical drying process, and the transition to rutile TiO2 phase occurred after experiencing 1200°C for 2 h. SiO2-TiO2 aerogels containing 30 wt% TiO2 (ST3) still presented relatively high specific surface area of 451 m2/g even they undergo the treatment of 1000°C for 2 h. And the SEM images indicated that the agglomerated particles derived from ST3 appeared gradually to some extent. The glassy luster of ST3 heat-treated at 1200°C for 2 h illuminates SiO2 started to vitrify. Besides, the thermal conductivity of ST3 at room temperature is up to 0.03257 W·m-1·K-1.

Methyl tert-butyl ether as a new solvent for the preparation of SiO2–TiO2 binary aerogels

SiO2–TiO2 binary aerogels have been synthesized for the first time using methyl tert-butyl ether as supercritical fluid. It has been shown that the aerogels prepared in methyl tert-butyl ether and isopropanol contain nanocrystalline anatase and that amorphous SiO2–TiO2 aerogels with a homogeneous distribution of their components can be obtained in CO2. A considerable contribution to the large specific surface area of the aerogels is made by micropores, especially when supercritical drying is carried out in CO2 and isopropanol.

Synthesis of TiO2–SiO2 aerogel via ambient pressure drying: effects of sol pre-modification on the microstructure and pore characteristics

TiO2–SiO2 composite aerogels were prepared via ambient pressure drying by sol–gel and surface modification for both the sol and gel samples. The organosilane reagents of decamethyltetrasiloxane (DMTSO)/trimethylchlorosilane (TMCS) and hexamethyldisiloxane (HMDSO)/TMCS were introduced into the TiO2–SiO2 composite sol for pre-modification respectively, and subsequently the TMCS/hexane solution was used for surface modification of the obtained TiO2–SiO2 composite gel. The effects of sol pre-modification on the microstructure and pore characteristics of TiO2–SiO2 composite aerogels were investigated. The results indicate that HMDSO/TMCS coupling reagents is more appropriate for the pre-modification of TiO2–SiO2 composite sol than the DMTSO/TMCS reagents. The best volume ratio of HMDSO/TMCS/composite sol for preparing mesoporous TiO2–SiO2 composite aerogels is in the range of 1:0.33:10–1:1.0:10, with which the specific surface area and pore volume of the obtained TiO2–SiO2 composite aerogels are 492–645 m2/g and 2.63–2.85 m3/g, respectively. The results of adsorption and photocatalytic degradation of rhodamine B show that the as-prepared TiO2–SiO2 composite aerogels have higher adsorption/photocatalysis. Particularly, the as-prepared TiO2–SiO2 composite aerogels with HMDSO/TMCS showed prominent adsorption capability with the adsorption rate attaining to 89.4 % within 60 min.

Sol–gel synthesis of sodium silicate and titanium oxychloride based TiO2–SiO2 aerogels and their photocatalytic property under UV irradiation

Binary titania–silica metal oxides (TiO2–SiO2) have preferentially been used as photocatalysts for the degradation of organic contaminants under UV irradiation. Herein we synthesized TiO2–SiO2 aerogel powders with different Si-to-Ti ratios suitable for decolorization of organic pollutants using less expensive silica source (sodium silicate) and titanium oxychloride as a titania precursor. Consequently, the surfaces of the alcogels were hydrophobized using trimethylchlorosilane (TMCS) as a silylating agent to yield hydrophobic aerogel powders at ambient pressure drying. The as-prepared samples were calcined at different temperatures ranging from 200 to 1000°C to evaluate the effect of the heat treatment in the microstructure of the aerogels. The physico-chemical properties of the aerogels were examined by XRD, FTIR, XRF, TEM, SEM, N2 gas physisorption studies, TGA/DTA and diffusive reflectance spectrometry analyses. It was found that calcination temperature is an important factor in improving the porosity and crystallinity of the aerogels however; it has a detrimental effect on the hydrophobicity and photochemical performance of the aerogels. The as-synthesized aerogels were hydrophobic and exhibited the highest activity toward decolorization of methylene blue. The hydrophilic aerogels were obtained after calcination at temperature ⩾500°C however; the formed samples possessed lower activities. Hydroxyl radicals (OH) detection experiment performed in the presence of the photocatalysts indicated that the generation of radicals during irradiation increases with increasing illumination time.

Photo catalytic oxidation of TNT using TiO2-SiO2 nano-composite aerogel catalyst prepared using sol–gel process

The degradation of nitro aromatics like trinitrotoluene (TNT) released in the waste water from explosive process plants is the serious problem due to toxic and explosive nature of TNT. The poor response of TNT to biodegradation enhanced the gravity of the problem. We have demonstrated that high specific surface area TiO2–SiO2 nano-composite aerogel is promising photo catalyst in successful treating of TNT contaminated aqueous solution. The TiO2–SiO2 composite aerogel with nominal content of 20 and 50% TiO2, used as catalyst, were prepared by co-precursor sol–gel method using titanium isopropaxide and tetramethylorthosilicate as source of titania and silica, respectively. The XRD studies confirmed formation of anatase phase of crystalline TiO2 with nano sized crystallites. The TiO2–SiO2 aerogel showed specific surface area of 1,107 and 485 m2/g for the aerogels containing 20 and 50% TiO2, respectively. The 100 ppm TNT solution was treated, in 700 ml capacity reaction vessel, using H2O2 oxidizer and TiO2–SiO2 aerogel catalyst in presence of UV light (8 W UV lamp). Using TiO2–SiO2 (50/50) aerogel with surface area of 485 m2/g, we succeeded to reduce the TOC to 1 ppm within 3.5 h where as using TiO2/SiO2 (20/80) aerogel with surface area of 1,107 m2/g, the TOC was reduced to about only 7 ppm in the same time. It revealed that the combination of high TiO2 content and high specific surface area is an important factor to achieve effective and faster degradation of TNT for complete mineralization.

Structural characterisation of binary SiO2/TiO2 nanoparticle aerogels by X-ray scattering

The effect of SiO2 to TiO2 aerogels content on their local structure is evidenced from X-ray scattering measurements. TiO2-SiO2 aerogels were prepared by sol-gel method followed by supercritical drying with liquid CO2 and heat treatment. The local structure of TiO2-SiO2 system was investigated by analysing the atomic pair distribution function PDF, G(r), obtained from X ray scattering data The modified coordination radius values obtained for the first coordination spheres by addition of SiO2 denotes a diminution of the atom packing in this system. The PDF of the 300°C heat treated TiO2 aerogel sample shows well-defined features allowing an unambiguous structure search and refinement. In particular, the first peak in the PDF of the precursor phase is quite narrow and centered at about 1.9 Å, which is the Ti-O distance in Ti-O6 octahedra. This observation shows that well-defined Ti-O6 octahedra are already formed during the homogeneous precipitation stage of the chemical process. Inspecting the data from the analysis of the atomic pair distribution function G(r) one remarks the occurrence of Si-O pair as a first coordination formation at a distance of 1.49 Å and the interatomic distances at 2.18 Å for the first Si—Si and 3.58 Å for the second Si—Si bond.

Impact of supercritical drying and heat treatment on physical properties of titania/silica aerogel monolithic and its applications

Abstract TiO2–SiO2 monolithic aerogels were homogeneously prepared using sol–gel method. Critical point of drying of TiO2–SiO2 gels with ethanol was studied for 30, 60, 90 and 120 min. Subsequently, the gels were dried with supercritical ethanol, resulting in amorphous aerogels that crystallized following heat treatment at 550 °C from 1 to 5 h. The TiO2–SiO2 aerogels were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area measurements. The molar ratio of SiO2:TiO2 was 6 and the synthetic strategy revealed that TiO2–SiO2 aerogel, had a surface area ∼868 m2/g, particle size ∼40 nm, density ∼0.17 g/cm3 and 80% porosity. The finding indicated that from economic point of view, TiO2–SiO2 gel should be supercritical dried for 30 min and heat-treated for 5 h. The TiO2–SiO2 aerogel monoliths photocatalyst synthesized using sol–gel method provided insight into the characteristics that make a photocatalyst material well-suited for photodegradation of phenol and cyanide in an industrial waste stream containing Cl−, S2− and NH4+. Interestingly, after multiple reuse cycles (i.e. ≥7), photodegradation systems with regenerated photocatalyst showed a slightly decreasing of photoactivity ∼2–4%. The overall kinetics of photodegradation of either phenol or cyanide using TiO2–SiO2 aerogel photocatalyst was found to be of first order.

Microstructural characterization and properties of ambient-dried SiO2 matrix aerogel doped with opacified TiO2 powder

Hydrophobic silica-based aerogels with different nano-TiO2 additive were successfully synthesized by an ambient pressure drying method. After aging and washing of wet gel, surface modification with cyclohexane was followed to replace the solvent with the pores of wet gel to reduce the surface tension during ambient drying. The synthesized SiO2–TiO2 aerogels thermally treated at 350 °C were light and crack-free, and the density was 0.125–0.138 g/cm3. The microstructure and physical characteristic of the SiO2–TiO2 aerogels were characterized by FTIR, SEM, EDS and BET. Their specific surface was in the range of 785–1210 m2/g and their average pore size was between 30 and 45 nm. Nano-TiO2 powders are physically embedded by SiO2 aerogel, and there is an obvious Ti–O–Ti and Si–O–Si bonding group based on structural analysis.

Kinetics and Mechanism of 2,3,6-Trimethylphenol Oxidation by Hydrogen Peroxide in the Presence of TiO2–SiO2 Aerogel

The product and kinetics studies of 2,3,6-trimethylphenol (TMP) oxidation by 30% aqueous Н2О2 in the presence of a heterogeneous catalyst, TiO2–SiO2 aerogel, are performed in an MeCN medium. The main reaction products are 2,3,5-trimethyl-1,4-benzoquinone and 2,2",3,3",6,6"-hexamethyl-4,4"-biphenol. The reaction is first-order in Н2О2 and fractional order (1–0) in TMP. The reaction rate is proportional to the catalyst amount and depends on the water concentration in the reaction mixture in a complex manner. The results suggest the formation of an active intermediate on the titanium center. In this intermediate containing both a TMP molecule and the hydroperoxide group, inner-sphere one-electron oxidation of TMP occurs to give the phenoxyl radical.

Incorporation of Functional Metal Oxide Materials in Chemical Microsystems

ABSTRACTTiO2-SiO2 aerogel with various TiO2 contents was successfully deposited into a microchannel. SEM, XPS and liquid-phase photocatalytic oxidation reaction of phenol were used to examine the TiO2-SiO2 aerogel's microstructure and reactivity. The TiO2 content has a significant effect on the aerogel network and its adhesion on the microchannel. High open and cross-linking or ordered macroporous structure can be formed in TiO2-SiO2 aerogels with lower TiO2 content (5wt% or 10wt%). The conversion of phenol is around 36.6% during the reaction when this aerogel incorporated microchannel is used as microreactor.

In situ XANES study on TiO2–SiO2 aerogels and flame made materials

The structures of TiO2–SiO2 based aerogels and flame made particles, used as epoxidation catalysts, are compared by X-ray absorption near edge structure (XANES) spectroscopy and in situ XANES during dehydration of the calcined catalyst samples. The results are interpreted in terms of the titanium species present in the catalyst and the catalytic performance in the test reaction, the epoxidation of 2-cyclohexene-1-ol by tert-butylhydroperoxide (THBP) at 90 °C. XANES shows that tetrahedral titanium sites are the favoured sites at low TiO2 concentrations (1–3.2 wt.% in this study). The catalytic performance (turnover frequency, selectivity) of such aerogels or flame made materials with low TiO2 content is much better than that of corresponding samples with high TiO2 content. In aerogels, regardless of the TiO2 content, the amount of titanium with tetrahedral coordination increases significantly after dehydration at elevated temperature. In contrast, the pre-edge height and its position in the XANES spectra of the flame made catalyst samples is comparable, even without dehydration, to that of TS-1, which contains titanium in tetrahedral coordination. Thus the extent of tetrahedral Ti is intrinsically high in flame made catalysts and increases only slightly during the drying process. This behaviour can be attributed to the hydrophobic character of the flame made materials and ameliorates the catalytic performance, i.e. the selectivity.

A new environmentally friendly method for the production of 2,3,5-trimethyl-p-benzoquinone

A new environmentally friendly method for the production of 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, Vitamin E precursor) based on the oxidation of 2,3,6-trimethylphenol (TMP) with aqueous H2O2 over various Ti-containing mesoporous silicate materials is reported. Both well-organized Ti-containing mesoporous mesophase silicate (Ti-MMM), having hexagonal arrangement of uniform mesopores, and amorphous TiO2–SiO2 mixed oxides (aerogels and xerogels) produced TMBQ with good to high yield. All the materials studied have been proved to operate as truly heterogeneous catalysts. No titanium leaching occurred from the solid matrixes during the oxidation process. Titanium dispersion and its accessibility were found to be crucial factors determining the catalytic properties. For samples with similar titanium loading, both the catalytic activity and TMBQ yield appeared to fall in the order TiO2–SiO2 aerogel>Ti-MMM>TiO2–SiO2 xerogel and correlate with average mesopore diameter and mesopore volume. The best results (96–98% selectivity to TMBQ at 99–100% TMP conversion) were obtained with TiO2–SiO2 aerogels, containing 1.7–6.5wt.% Ti.

Preparation of SiO2-TiO2 aerogels using supercritical impregnation

The preparation of SiO2-TiO2 aerogels by supercritical impregnation of titanium alkoxides into silica alcogels was investigated. A mixture of CO2 and 2-propanol with dissolved titanium tetraisopropoxide modified with acetylacetone was used as the impregnation medium. Prior to the experiments, the supercritical behaviour of the impregnation solution was investigated. The microstructure and properties of aerogels prepared by the supercritical impregnation method were almost identical to those generated by the liquid impregnation. However, the time for impregnation was substantially decreased and the homogeneity of the impregnated titanium distribution on the aerogel increased.