Enhanced photoactivity of silica-embedded titania particles prepared by sol–gel process for the decomposition of trichloroethylene

Silica-embedded titania photocatalyst (X-silica/titania, X denotes at.% of silicon) of improved photoactivity was prepared by the sol–gel technique. The photoactivity of the X-silica/titania particles was increased by increasing the silica content and reached a maximum. The highest photoactivity was obtained when silica content was 30% and five times higher than that of Degussa P25. The embedding of amorphous silica into nanophase titania matrix helped to increase the thermal stability of titania which suppressed the formation of anatase into rutile and made it possible to calcine the silica/titania particles at higher calcination temperature. This high temperature heat treatment resulted in the high crystallinity of the silica/titania particles. Surface area of X-silica/titania particles was monotonically increased by increasing the silica content. The average pore size and pore volume, however, has a maximum at 30%, at which mesopores larger than 30 nm were observed. Therefore, we concluded that the large pore size and pore volume were responsible for the optimum composition of silica to titania. The enhanced photoactivity of silica-embedded titania particles was achieved by simultaneously increasing both the surface area and the crystallinity through embedding amorphous silica into titania.     

Adsorption of Ce(IV) Ions from Aqueous Solution by Silica Aerogels

The adsorption process of Ce(IV) ions from aqueous solution by the silica aerogels was studied. The silica aerogels with hydrophobicity were prepared by the sol-gel process, supercritical drying, and heat treatment. The SEM image and nitrogen adsorption-desorption isotherm show that the heat-treated silica aerogel was a co-continuous porous structure with high BET surface area and narrow pore size distribution. The adsorption of Ce(IV) ions onto the silica aerogels was found to be fitted well by pseudo-second-order kinetics and Langmuir isotherm model. The activation energy for Ce(IV) adsorption onto silica aerogels could be calculated to be about 17.88 kJ/mol, which implied that the attractive forces of adsorption were weak electrostatic forces accompanying most ion-exchange reactions. The thermodynamic parameters showed that the adsorption process was spontaneous and endothermic.     

钛改性硅胶块体吸附剂除湿性能研究

采用浸渍沉积法制得钛改性硅胶块体吸附剂.对块体吸附剂的孔结构进行表征;考察了改性硅胶吸附剂动、静态除湿性能以及在吸附/脱附过程中湿度场、温度场的变化.结果表明,改性后的硅胶,其微孔、中孔孔径有所减少,而孔容和比表面显著增大;钛改性硅胶的吸附性能好于硅胶,而脱附能力劣于硅胶;由于钛改性硅胶产生更多的吸附热,吸附时出口气流温度略高于硅胶,而脱附时正好相反.     

A boric acid-assisted hydrothermal process for preparation of mesoporous silica nanoparticles with ultra-large mesopores and tunable particle sizes

This work reports that monodispersed ultra-large mesopore mesoporous silica nanoparticles (LP-MSNs) can be facilely prepared by a simple and highly effective boric-assisted hydrothermal (BAH) process. This BAH process provides an easy and mild way to prepare LP-MSNs with tunable porous structure and mesopore size. Such BAH process enables the transformation from conventionally prepared MSNs with small mesopores (∼2.3 nm) into LP-MSNs with ultra-large mesopore size over 15 nm. This BAH process also enables reliable control over particle sizes (98 nm–278 nm) by varying synthesis conditions. The effect of different synthesis conditions on mesopore enlargement was investigated, including the amounts of initial ethanol, boric acid, and ethanol in mixtures during hydrothermal treatment (HT) and HT temperatures. It is newly found that the ethanol added in synthesis step (1st ethanol), boric acid and ethanol added in mixture during HT process (2nd ethanol) and HT conditions play synergistic roles in the preparation of LP-MSNs with variable mesopore sizes and particle sizes. The underlying principle of such mesopore enlargement by such experimental setup was also analyzed. The BET surface area, pore size, and total pore volume of typical LP-MSNs reach 238 m²/g, 15.3 nm, and 0.67 cm³/g, respectively. Such LP-MSNs can find different applications in various fields.     

Improved Heat Insulation and Mechanical Properties of Highly Porous YSZ Ceramics After Silica Aerogels Impregnation

To further improve heat insulation and mechanical properties, silica aerogels were impregnated into highly porous yttria‐stabilized zirconia (YSZ) ceramics with well‐distributed pores fabricated by tert‐butyl alcohol ‐based gel‐casting process and pressureless sintering. Pore size distribution, room‐temperature thermal conductivities, and compressive strength of the YSZ ceramics before and after impregnation with silica aerogels were examined and compared, respectively. After impregnating porous YSZ ceramics with silica aerogels, the porosity displayed a little decrease, whereas the pore size significantly decreased by one order of magnitude. Based on this microstructure development, the room‐temperature thermal conductivities were significantly lowered and the compressive strength was also promoted. Therefore, the heat insulation and mechanical properties could be simultaneously improved by impregnating porous ceramics with silica aerogels.     

纳米孔超级绝热材料气凝胶的制备与热学特性

以正硅酸四乙酯(TEOS)为硅源，通过溶胶–凝胶及超临界干燥过程制备了SiO2气凝胶. 同时，采用相对廉价的多聚硅(E–40)为硅源，以三甲基氯硅烷(TMCS)为表面修饰剂，硅油为干燥介质, 在常压条件下制备了同样具有纳米多孔结构的SiO2气凝胶. 用透射电镜、扫描电镜及孔径分布仪对其结构进行了表征，并用动态热线法对其热学特性进行了测试. 结果表明: 两种方法制备的气凝胶均是典型的纳米孔超级绝热材料，后者热导率略高但成本低许多，所以更具应用推广潜力.     

Pore structure modification of silica matrix infiltrated with paraffin as phase change material

Temperature-controlling solid–liquid phase change material (PCM) infiltrated in a porous matrix is becoming attractive for aerospace applications. The properties of the pore structure are crucial factors in the selection of porous materials for PCM infiltration. The main purpose of this study is to adjust the pore structure of porous silica matrices with different molar ratios of ethanol (EtOH) and tetraethoxysilane (TEOS) for PCM infiltration. Five compositional ratios of EtOH/TEOS were introduced to prepare the silica with different pore size through sol–gel processing, and the pore structures were analyzed by N₂ adsorption–desorption measurements and scanning electron microscopy. Results indicate that the pore size increases with a larger value of the EtOH/TEOS molar ratio. Open cell pore structure and pore size of silica were observed and calculated. For EtOH/TEOS ratios of 10 and 20, the synthesized silica matrices had average pore sizes of 53.1 nm and 56.0 nm, respectively, exhibiting better infiltration. Moreover, the maximum mass fraction of paraffin as PCM in the silica matrices reached up to 75 wt%.     

Control of pore size in mesoporous silica templated by a multiarm hyperbranched copolyether in water and cosolvent

Worm-like mesoporous silica with various pore sizes has been prepared successfully templated by a multiarm hyperbranched copolyether (PEHO-star-PPO). The pore size of the resultant mesoporous materials can be controlled easily through adjusting the ratio of water to cosolvent. As the molar ratio of water to ethanol changes from 0.02 to 0.73, the pore size of the calcined materials can be enlarged from 32 to 94 Å, attributing to the aggregation behavior of the multiarm hyperbranched polymer in different systems. Moreover, the pore size of the obtained mesoporous silica can be also adjusted by selecting different kinds of cosolvent. The polarity and solubility of cosolvents are believed to be two important factors in affecting the pore size. Thus, a facile and efficient method for controlling the pore size of mesoporous silica has been developed by using hyperbranched polymers as templates.     

老化工艺对纳米多孔二氧化硅薄膜微观结构影响

本文主要探讨了老化时间与处理温度对纳米多孔二氧化硅薄膜结构的影响。结果表明随着老化时间的增加,薄膜的三维网状结构越明显、孔径分布更均匀、孔隙率越高、孔径越大。经450℃高温热处理后,颗粒长大,孔径增大,孔径分布不均匀,且薄膜厚度几乎不受老化时间的影响,说明湿凝胶薄膜在异丙醇气氛下老化后的强度是足够抵抗凝胶薄膜在异丙醇溶剂中老化放生的变化过程而引起的薄膜收缩。     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

共聚法制备疏水性SiO2气凝胶

以正硅酸乙酯为原料,应用溶胶-凝胶两步催化,甲基丙烯酸基丙基三甲氧基硅烷作为改性剂,无水乙醇为溶剂,共聚法常压下制备疏水性SiO₂气凝胶。运用原位红外在线监测反应历程,确定制备工艺步骤。运用N₂吸附仪、扫描电镜、红外光谱、TG-DSC对SiO₂气凝胶孔径分布、形貌、表面官能团及热稳定性进行分析。结果表明,经甲基丙烯酸基丙基三甲氧基硅烷改性的SiO₂气凝胶疏水性能良好,疏水的耐温性可达到407℃,比表面积为877.17 m²·g^-1, 由球形纳米颗粒堆积而成,颗粒尺寸范围在10～50 nm,孔径集中分布在1.9相似文献   

Facile synthesis of hydrophobic microporous silica membranes and their resistance to humid atmosphere

The ethylene-modified silica membranes were prepared by the acid-catalyzed co-hydrolysis and condensation reaction of tetraethylorthosilicate (TEOS) and ethylenetriethoxysilane (TEVS) in ethanol and the final materials were characterized by scanning electron microscope (SEM), water contact angle measurement, solid-state ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR), and N₂ adsorption. The modification leads to a transform from superhydrophilicity for the unmodified silica membranes to hydrophobicity for the modified materials. The ethylene-modified silica membranes are much less water sensitive than the unmodified materials because the hydrophobic ethylene groups replace a portion of the hydrophilic hydroxyl groups on the pore surface. The modified materials process a microporous structure with a narrow pore size distribution centered at 1.1 nm. Such a microporous structure can be stabilized after exposured to humid atmosphere for 450 h, in intense contrast to the collapse of the micropores in the unmodified silica membranes.     

仿生制备SiO2分离膜的实验

以表面活性剂十六烷基三甲基溴化铵(CTAB)在溶液中的自组装胶束为有机模板,对无机前躯体正硅酸乙酯(TEOS)的水解缩聚过程进行调控,于SiO2 无机膜中复制出了具有自组装体形状的三维孔结构。孔径分布测定结果表明优化物料条件下制备出的非担载SiO2 膜具有 1. 8nm的最可几孔径,平均孔径为 5. 3nm。对比传统的sol gel制膜方法,其孔径分布不受灼烧条件的影响。该膜的广角XRD分析结果表明组成介孔壁面的SiO2 为非晶型结构,该膜的小角度XRD分析结果进一步表明,膜内介孔道的排列形式为三维空间上的无序网络结构。将优化物料条件下的混合物旋涂于多孔Al2O3 陶瓷载体上,进一步制备出了SiO2 分离膜,该膜的SEM表征和气体渗透性能测定结果表明其完整性能较好。     

介孔二氧化硅合成及其吸附分离性能研究

以正硅酸乙酯为硅源,采用溶胶-凝胶法,通过调整合成体系pH与温度控制正硅酸乙酯的水解与缩聚过程,制备出4种不同孔径分布的介孔二氧化硅。以X射线衍射（XRD）、透射电镜（TEM）、N₂吸附-脱附、程序升温脱附（NH₃-TPD）、傅里叶红外光谱（FTIR）、热重（TG）等表征手段对二氧化硅物化性质进行表征,并考察4种介孔二氧化硅的烷/烯吸附分离性能。结果表明,介孔二氧化硅的硅羟基种类以自由羟基为主,随着合成终点pH增加,孔径增加,比表面积减少,硅羟基浓度降低,酸量减少,酸强度增加;孔径分布及酸性质对吸附分离性能影响明显,平均孔径为4.9 nm样品的酸强度适宜,分离度R_烷/烯>1,烯烃脱附速度快,吸/脱附速率比接近1,是较为理想的烷/烯分离吸附剂。     

Synthesis of Nanoparticulate Silica Composite Membranes by the Pressurized Sol–Gel Technique

A crack-free silica composite membrane has been synthesized from a nanoparticulate silica sol (particle diameter <10 nm) by a pressurized sol–gel coating technique developed in this study. The microporous silica layers with an estimated pore radius of 0.78 nm were deposited inside the pores (average pore size of 0.1 μm) of slip cast a-alumina support tubes. The microstructure of the coated layer was controlled by adjusting sol properties and pressurizing conditions. The room-temperature intrinsic permeability of N₂ through the silica membrane layer after heat treatment at 200°C is about 4.9 × 10⁻¹² mol·m/m²·s· Pa, and the mechanism of gas transport is Knudsen flow. The thermal stability of the silica composite membrane is excellent up to 500°C.     

Confined growth of iron cobalt nanocrystals in mesoporous silica thin films: FeCo–SiO2 nanocomposites

Mesoporous silica films with controlled porosity were utilized as the host matrices to prepare FeCo–SiO₂ nanocomposites through an impregnation process. The mesoporous silica films were first impregnated with a solution containing Co(II) and Fe(III) ions and then submitted to a reduction treatment under H₂ flow. FeCo nanocrystals growth took place inside the mesopores, and their monodisperse size was dictated only by the size of the mesopores. We illustrate this process by the use of two different silica film matrices having different pore size and mesophase symmetry as the templates for the growth of FeCo alloy nanocrystals. The films and the nanocomposite samples were investigated by grazing-incidence small-angle X-ray scattering, X-ray diffraction and transmission electron microscopy. Unimpregnated mesoporous silica samples before and after the same thermal reduction treatment were also studied in order to investigate the mesopore structure variation upon the reduction treatment.     

Influence of the composition and temperature of heat treatment of porous glasses on their structure and light transmission in the visible spectral range

The pore structure and light transmission of high-silica porous glasses in the visible spectral range have been investigated as a function of the heat treatment temperature and the composition of the initial two-phase alkali borosilicate glass. The character of light transmission in porous glasses has been analyzed in the framework of the concepts of structural features of their pore space and the processes occurring in the porous glass during heating. It has been demonstrated that an increase in the temperature of heat treatment of porous glasses with different compositions leads to an increase in the pore size and a decrease in their specific surface area (with a nearly constant total porosity), which is associated with the processes of overcondensation of pores due to the rearrangement and the change in the packing density of secondary silica particles. It has been revealed that the introduction of phosphate and fluoride ions into the initial sodium borosilicate glass results in an increase in the light extinction coefficient of porous glasses due to the increase in the sizes of phase-separated inhomogeneity regions in the initial two-phase glasses, the formation of larger pores, and the presence of nanosized microcrystalline phases in porous glasses.     

Preparation of Silica Nanostructured Spheres by Sol Spray Drying

Silica nanostructured spheres were obtained by spray drying of silica sol prepared in situ. Their morphologies were significantly affected by the aggregation of the primary particles in the sol. They had the mode of the pore sizes which was about the same order as Laser Particle Size Analyzer (LPA) diameter. Increasing the mixing ratio of the larger particles (20 nm) to smaller ones (7 nm) decreased the Brunauer, Emmett and Teller (BET) specific surface area, as expected. Pore volume decreased with the pore size distribution broadened and the mean pore diameter was not affected by the increase, due to the decrease in aggregation of the primary particles. Either the increase in the drying temperature and use of ethanol as a cosolvent made the agglomerates hollower, the larger of which with thinner shell transformed to doughnut type agglomerates, due to the structural and hydrodynamic instabilities.     

Preparation of Silica Nanostructured Spheres by Sol Spray Drying

Silica nanostructured spheres were obtained by spray drying of silica sol prepared in situ. Their morphologies were significantly affected by the aggregation of the primary particles in the sol. They had the mode of the pore sizes which was about the same order as Laser Particle Size Analyzer (LPA) diameter. Increasing the mixing ratio of the larger particles (20 nm) to smaller ones (7 nm) decreased the Brunauer, Emmett and Teller (BET) specific surface area, as expected. Pore volume decreased with the pore size distribution broadened and the mean pore diameter was not affected by the increase, due to the decrease in aggregation of the primary particles. Either the increase in the drying temperature and use of ethanol as a cosolvent made the agglomerates hollower, the larger of which with thinner shell transformed to doughnut type agglomerates, due to the structural and hydrodynamic instabilities.     

碳化过程中大水灰比水泥浆体孔结构的变化(英文)

使用特殊的增黏剂与聚羧酸减水剂,制备了掺加石灰石粉、高炉矿渣、硅灰等混合材的普通波特兰水泥浆体和和低热硅酸盐水泥浆体(水粉比为1.0)。这些水泥浆体在20℃的水中养护4年后基本完全水化。这些硬化水泥浆体在5%(质量分数)CO2、相对湿度66%和温度20℃条件下进行碳化,对比研究碳化前后水泥浆体孔结构的变化。结果显示:碳化浆体内孔直径大于10nm的孔体积明显减少;碳化浆体的孔径分布向大孔径范围偏移;掺加混合材的硬化水泥浆体结构明显趋于松散;与不掺加任何混合材的水泥浆体相比,掺加混合材的水泥浆体的孔径更大。