扩孔剂对SiO2气凝胶微观结构与性能的影响

以正硅酸乙酯为硅源,乙醇为溶剂,在溶胶-凝胶法和CO2超临界干燥的基础上,采用分别加入聚乙二醇(400)、六次甲基四胺和尿素作为扩孔剂的方法制备低密度SiO2气凝胶.利用扫描电镜(SEM)、傅里叶变换红外光谱仪(FT-IR)、孔径分布及比表面积测试仪(BET)、纳米压痕仪对未加扩孔剂和加入不同扩孔剂所制备的SiO2气凝胶的表面形貌、结构、比表面积、孔径分布、力学性能以及密度进行研究.结果发现:随着增加扩孔剂的加入量, SiO2气凝胶的密度明显降低;与未加扩孔剂的样品相比,加入扩孔剂所制备的SiO2气凝胶的比表面积和孔径增大;其中,六次甲基四胺具有较佳的扩孔效果,制备得到的SiO2气凝胶的性能较佳,孔径分布主要集中在15~55 nm,平均孔径为35.4 nm,比表面积高达1006 m2· g-1,孔体积为5.3 cm3· g-1,孔隙率高达96.2;.     

TiO2∶Fe的EPR谱及其光催化特性研究

采用溶胶-凝胶法制备了TiO2∶ Fe材料,测试并分析了材料的电子顺磁共振谱,其结果显示溶胶凝胶法制备的Fe掺杂TiO2粉末在g=1.99和4.3处具有明显信号峰,归属于信号对应离子,并利用其积分值半定量分析了掺杂到晶体表面和内部Fe离子数目的多少及二者比值,发现对离子掺杂到内部而言直至掺杂浓度为0.6;仍未达到饱和,而对离子掺杂到表面而言,当掺杂浓度为0.4;时,该信号强度不再增强,掺杂到晶体表面的Fe离子数量达到饱和.使用紫外可见光谱仪测定了所制材料的光催化性能,所制的Fe掺杂TiO2纳米材料最佳掺杂浓度为0.1;,对甲基橙降解率是17.83;,比未掺杂材料降解率(16.31;)提高了9.32;,增强了光催化活性,其余掺杂浓度(0.0372;,0.2;,0.4;和0.6;)样品的光催化活性均比未掺杂样品的低,降低了光催化活性.     

铋铁共掺纳米TiO2复合薄膜的制备及光催化性能

本文以钛酸丁酯、硝酸铋、硝酸铁为主要原料,采用溶胶-凝胶法制备了铋铁共掺的纳米TiO2复合薄膜.用XRD、UV-VIS、SEM及降解率等方法对样品进行了表征.以甲基橙为降解物,考察Bi3+和Fe3+掺杂对TiO2复合薄膜催化剂的光催化活性影响及其机理研究.结果表明Bia+和F3+掺杂后,纳米TiO2复合薄膜光催化活性有了明显的提高.     

Nd~(3+)、Eu~(3+)、Tb~(3+)掺杂纳米TiO_2的制备及光催化性能的研究

采用溶胶-凝胶法制备了掺杂1 mol%Nd3+、Eu3+、Tb3+的TiO2纳米光催化剂,通过X射线衍射、比表面积、紫外-可见吸收光谱等对制备的光催化剂进行了表征,并通过甲基橙的光催化降解研究了样品的光催化性能。结果表明,稀土离子的掺杂能有效抑制TiO2纳米粒子的生长,进而增大比表面积,并且掺杂纳米TiO2光催化剂紫外-可见吸收带边都有一定的红移;掺杂纳米TiO2光催化剂的活性优于未掺杂纳米TiO2光催化剂,其中Eu3+/TiO2的光催化活性为最强。     

Ce掺杂TiO2纳米粉体的制备及其光催化性能研究

以钛酸丁酯为前驱体,冰醋酸为螫合剂,以硝酸铈为掺杂剂,采用溶胶.凝胶法制备了铈掺杂TiO2纳米粉体.研究了铈掺杂对TiO2相组成和晶粒尺寸的影响及不同掺杂量对TiO2光催化活性的影响,确定了Ce的最佳掺杂量.结果表明:Ce掺杂缩小了TiO2的锐钛矿相→金红石相(A→R)的相变温区范围,抑制了TiO2的晶粒增长.热处理温度升高,二氧化钛的比表面积下降.掺杂适量的铈提高了TiO2的光催化活性,Ce掺杂为0.05;摩尔分数时Ce-TiO2的光催化活性达到最佳,甲基橙降解率可达90;左右.     

聚氨酯增强二氧化硅气凝胶常压干燥制备及其性能

以正硅酸乙酯(TEOS)为硅源,3-氨丙基三乙氧基硅烷(APTES)为偶联剂,聚氨酯为增强相,经水解缩聚形成凝胶后通过常压干燥工艺制备聚氨酯增强二氧化硅复合气凝胶.采用傅立叶红外光谱对样品的化学结构进行表征,并通过扫描电镜、比表面积与孔径分析仪,万能试验机和接触角仪等对所制得气凝胶的微观形貌、孔结构,力学和疏水性性能进行了分析.结果表明,所制备的气凝胶的孔径分布范围为2.0～25.0 nm,是一种具有三维网状结构的介孔材料,并且具有良好的力学性能,15wt;聚氨酯增强的气凝胶的压缩模量达到4MPa,同时疏水性也得到了提高,其接触角为77.73°.     

花状TiO2的制备及光催化性能研究

采用溶剂热法合成了花状TiO2,运用SEM、XRD和N2物理吸附-脱附等对其形貌、结构、比表面积和孔径进行了表征,并以甲基橙为模拟污染物研究了它们的光催化性能.结果表明,花状TiO2结构为锐钛矿相,是由纳米晶定向聚集形成纳米棒组成的3D花状结构,花状结构的直径在0.7～1.5 μm,平均直径在1.1μm,细小纳米晶聚集形成的纳米棒的直径在20～25 nm,长度100～ 150 nm.该样品具有较高的比表面积,表现出良好的光催化活性.     

可见光响应型Fe掺杂SiO2/TiO2光催化材料的制备及降解水中腐殖酸的研究

采用溶胶凝胶法制备了可见光响应型Fe掺杂SiO2/TiO2光催化材料,并采用TG-DTA、XRD、UV-vis、TEM及XPS等手段对其进行了表征.以水中腐殖酸的降解为探针反应,考察了可见光照射下Fe-SiO2/TiO2的光催化活性.XRD结果表明,Fe离子掺杂可抑制催化剂晶粒尺寸,600℃焙烧后的Fe-SiO2/TiO2为锐钛矿相结构.Ur-vis吸收光谱分析可看出Fe离子掺杂提高了催化剂对可见光的吸收能力,并使催化剂的吸收带边产生了红移.XPS光谱表明,催化剂表面存在着Fe2+和Fe3+.实验结果表明,Fe-SiO2/TiO2在可见光下对腐殖酸的光催化降解率优于SiO2/TiO2和TiO2.Fe-SiO2/TiO2具有较高光催化活性的主要原因为:Fe离子掺杂不仅使SiO2/TiO2催化剂的粒径减小和对可见光的吸收增强,而且在催化剂表面产生了有利于光生e--h+对分离的Fe3+/Fe2+氧化还原循环电对.     

钒掺杂纳米二氧化钛的制备及光催化活性研究

以钛酸四丁酯为钛前驱体,偏钒酸铵为掺杂离子给体.采用溶胶-凝胶法制备了V掺杂纳米二氧化钛粉体;并使用TGA-DSC、XRD、BET、SEM对其晶化温度与结构进行了表征.结果表明:V掺入促进锐钛矿相向金红石相转变、抑制晶粒长大、增大比表面积,纳米粉体颗粒呈分布较均匀的类球形晶粒.以亚甲基蓝为模型反应,考察了V掺杂量、煅烧温度对催化剂光催化性能的影响,结果表明:V掺杂的TiO2 粉体降解亚甲基蓝符合一级反应动力学规律;晶格中V4+能够作为电荷转移物种,有效的抑制光生电子与空穴的复合,增加了表面空穴浓度,提高TiO2 纳米粉体的光催化活性,当掺杂量为1.5 mol;,煅烧温度为450 ℃时,TiO2 具有最佳的光催化性能.     

氟改性TiO2的制备及光催化性能研究

以钛酸丁酯为钛源,氟化铵为氟源,采用溶胶凝胶法制备氟改性二氧化钛光催化剂,并用扫描电镜(SEM)、X射线衍射(XRD)、紫外可见光分度计(UV-Vis)、X射线光电子能谱(XPS)、光致发光荧光光谱仪(PL)、氮气吸附-脱附等方法对样品进行表征.以甲基橙(MO)为模拟污水,研究其光催化活性.结果 表明:F改性TiO2为纳米锐钛矿相,比表面积为141 m2/g.F以化学吸附态存在于TiO2的表面,形成(=)Ti-F基团,F的加入使得TiO2的吸收带边发生了红移,在甲基橙浓度为20 mg/L,紫外光照射时间为80 min时,F改性TiO2的脱色率最大达到了97;,具有较高的光催化活性.     

A simple synthesis of catalytically active,high surface area ceria aerogels

A simple synthetic route for preparing high surface area, structurally stable ceria aerogels is presented. Ceria aerogels were doped with 1% palladium: a water-gas shift (WGS) active metal. A reduced Pd/ceria aerogel and an as-prepared Pd/ceria aerogel are compared to determine the effect of pretreatment conditions on WGS activity. The BET surface area of the as-prepared ceria aerogel was 345 m²/g. CO chemisorption data and high-resolution TEM images indicate that the particle size of palladium on the reduced Pd/ceria sample was approximately 15 nm. X-ray photoelectron spectroscopy (XPS) data establish that the fraction of Ce³⁺ from Ce₂O₃ was approximately the same for both reduced and as-prepared samples. XPS data also indicate that approximately 44% of the palladium on the reduced Pd/ceria sample was converted to the metallic form. Each catalyst was tested for WGS activity. The reduced Pd/ceria sample exhibited the greatest WGS activity as compared with the other samples used in this study.     

Mixed-metal oxide aerogels for oxidation of volatile organic compounds

Aerogels of 100% silica, 8 wt% Zr in silica, 5 wt% V in silica and 100% zirconia were synthesized and tested as oxidation catalysts in the temperature range of 300–700°C for destruction of volatile organic compounds. The silica-based aerogels were all amorphous and had surface areas above 600 m²/g after oxidation. The zirconia aerogel was crystalline with a relatively low surface area of 250 m²/g. As catalysts for oxidation (using O₂ in He) of CH₃OH to CO₂, the zirconia aerogel exhibited the highest activity and best selectivity while the silica aerogel exhibited the poorest. Inclusion of Zr at levels as low as 8 wt% into the silica aerogel framework produced activities and selectivities which were very much like the zirconia aerogel. These properties have the impact of producing a Zr based catalyst with high activity, but with thermal stability afforded by Zr–silica mixtures.     

Zn2+掺杂高岭石基纳米TiO2光催化材料的表面特性研究

基于高岭石表面是以Si-O键为主的亲水表面且具有巨大比表面积,易于复合光催化优异的TiO2膜.以高岭石为基材,溶胶-凝胶法制备了具有光催化活性的Zn2掺杂TiO2/高岭石复合光材料.采用XRD、FrIR、Raman、XPS等技术对材料的晶体结构、分子结构、表面元素组成及化学态、纳米TiO2晶体膜的覆盖面积进行表征分析.结果表明:Ti-O与高岭石结构的Si-O发生化学键合,在高岭石表面形成Si-O-Ti键合的纳米TiO2晶体膜,占高岭石表面积的91.35;.掺杂的Zn2只是在TiO2晶体表面复合氧化成红锌矿,而不能进入TiO2晶格.物理化学复合增加了基材高岭石表面晶体缺陷,有利于TiO2晶体表面光生载流子的增生和传输.     

Preparation of zirconia aerogel by heating of alcohol–aqueous salt solution

Using zirconyl nitrate dihydrate as starting material, zirconia aerogel with high specific surface area was prepared by heating zirconyl nitrate dihydrate solution with an alcohol–aqueous mixture and supercritical drying method (SCFD). It was characterized by XRD, TEM and BET methods. The specific area of primary ZrO₂ aerogel could reach 675.6 m²/g which was much higher than that of documents so far. While both the specific surface area and pore volume decreased markedly on increasing the calciniation temperature. Contrast with the powder synthesized by ordinary trend, the content of t-ZrO₂ in the aerogel increased when the calcination temperature improved from 500 to 700 °C, the percentage of tetragonal phase was 86% at 700 °C. And it was very interesting that the particle size of the aerogel was bigger than 30 nm after being roasted in 1000 °C, the tetragonal phase still existed.     

Synthesis of sodium silicate-based hydrophilic silica aerogel beads with superior properties: Effect of heat-treatment

This work demonstrates the synthesis of hydrophilic and hydrophobic high surface area silica aerogel beads with a large pore volume. Wet gel silica beads were modified and heat-treated under atmospheric pressure after modification of the surface by trimethychlorosilane (TMCS). The effects of heat treatment on the physical (hydrophobicity) and textural properties (specific surface area, pore volume, and pore size) of silica aerogel beads were investigated. The results indicated that hydrophobicity of the silica aerogel beads can be maintained up to 400 °C. The hydrophobicity of the silica aerogel beads decreased with increasing temperature in the range of 200-500 °C, and the beads became completely hydrophilic after heat treatment at 500 °C. The specific surface area, cumulative pore volume, and pore size of the silica aerogel beads increased with increasing temperature. Heating the TMCS modified bead gel at 400 °C for 1 h resulted in silica aerogel beads with high surface area (769 m²/g), and large cumulative pore volume (3.10 cm³/g). The effects of heat treatment on the physical and textural properties of silica aerogel beads were investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric and differential analysis (TG-DTA), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer, Emmett and Teller (BET) and BJH nitrogen gas adsorption and desorption methods.     

Preparation and properties of alumina-organic compound aerogels

A wet alumina gel was obtained by cross-linking alumina sol particles from a hydrolyzed aluminum alkoxide with hexamethylene diisocyanate. The alumina gel cross-linked with hexamethylene was supercritically dried in a CO₂ extractor. The bulk density of the dried alumina-hexamethylene was one-third that of an alumina aerogel. Boehmite phase was observed in the dried alumina-hexamethylene aerogel. Needle-like texture was observed in the alumina-hexamethylene fired at a temperature of 1200°C for 5 h. The specific surface area of the dried alumina-hexamethylene aerogel was found to be less than that of the alumina aerogel, while its pore sizes were larger. The aerogel had a larger specific surface area after firing at 1200°C for 5 h. This larger surface area was attributed to a θ-phase in the alumina-hexamethylene aerogel, while the alumina aerogel had an -phase at that temperature. It is concluded that the temperature of the a phase transformation in the alumina-hexamethylene aerogel was higher than in the alumina aerogel. This difference was attributed to the lower packing density resulting from the addition of an organic compound, the existence of boehmite crystallites and the needle-like texture.     

Hf/Ta/W单掺锐钛矿相TiO2的电子结构和光学性质的第一性原理研究

运用第一性原理赝势方法计算过渡金属X(Hf、Ta、W)单掺锐钛矿相TiO2后的电子能带结构、态密度和光学性质.计算结果表明,X掺锐钛矿相TiO2,使得掺杂后体系的体积增大,并随着X掺杂浓度的增加而增大;掺杂体系的禁带宽度都比纯TiO2的要小;由能带图可知,Ta、W单掺后,费米能级进入导带,说明这两种单掺体系属于N型半导体;随着不同浓度Hf、Ta、W的掺入,发现吸收光谱都发生了不同程度的红移,其中Ta、W掺杂体系的光响应范围覆盖了整个可见光区域,对比所有掺杂体系发现Ti0.9375 W0.0833 O2在可见光区域的光响应能力最强,这些现象说明X的掺入大大提升了TiO2光催化能力.     

Synthesis of silica aerogel blanket by ambient drying method using water glass based precursor and glass wool modified by alumina sol

Silica aerogel blankets have been synthesized by ambient drying technique using cheap water glass as the silica source and glass wool modified by alumina sol. One step solvent exchange and surface modification were simultaneously conducted by immersing the wet hydrogel blanket in EtOH/TMCS/hexane solution. The synthesized silica aerogel blanket was light with the density of 0.143-0.104 g/cm³ and 89.4-95% porosity. The microstructure of silica aerogel blanket exhibits a porous structure consisting of glass fibers of diameter ∼2.5 μm interconnected with solid silica clusters (5-20 μm).     

Preparation and characterization of monolithic alumina aerogels

Alumina aerogels were prepared by a sol-gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m²/g. It was transformed to γ-Al₂O₃ after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.     

Ultralow density silica aerogels prepared with PEDS

This paper deals with the synthesis of ultralow density silica aerogels using polyethoxydisiloxanes (PEDS) as the precursor via sol-gel process followed by supercritical drying using ethanol solvent extraction. Ultralow density silica aerogels with 5 mg/cc of density were made for the molar ratio by this method. A remarkable reduction in the gelation time was observed by the effect of the catalyst NH₄OH at room temperature. The microstructure and morphology of the ultralow density silica aerogels were characterized by the specific surface area, S_BET, SEM, TEM and the pore size distribution techniques. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is about several nm. The specific surface area of the silica aerogel is 339 m²/g and the specific surface area, pore volume and average pore diameter decrease with increasing density of the silica aerogel.