TiO2/SiO2气凝胶微球的制备及其表征

以TiOSO4和硅溶胶为原料, 加入甲酰胺作为干燥控制化学添加剂, 采用W/O乳状液中的溶胶-凝胶法制备TiO2/SiO2凝胶微球, 通过正硅酸乙酯母液浸泡、溶剂交换、陈化和常压干燥技术制备TiO2/SiO2气凝胶微球, 采用光学显微镜、SEM、TEM和BET比表面及孔分布测定等手段对所得样品进行表征. 典型的气凝胶微球样品是由粒径15 nm左右, 粒度分布相当均匀的球状纳米粒子构成的轻质纳米多孔材料, 表观密度为177 kg•m-3, 比表面积372 m2•g-1, 平均孔径22.78 nm, 孔隙率高达92.0％, 微球的宏观粒径为50 m. 依据制备条件的变化, TiO2/SiO2气凝胶微球的宏观粒径可控在10～200 m之间, 表观密度为150～300 kg•m-3, 比表面积为300～400 m2•g-1, 平均孔径在18.71～22.78 nm之间变化.     

SiO2气凝胶的非超临界干燥法制备及其形成过程

通过对正硅酸乙酯的两步水解-缩聚反应速率的调控，使生成的醇凝胶具有比较完整的网络结构，配合乙醇溶剂替换和正硅酸乙酯乙醇溶液浸泡和陈化，改善和增强凝胶的结构和强度，在分级干燥下实现了SiO2气凝胶的非超临界干燥制备，并采用SEM、TEM、TG-DTA、XRD和吸附-脱附技术等手段对所得气凝胶样品进行表征.结果表明, 该气凝胶是由粒径约10 nm均匀球状纳米粒子构成的具有连续网络结构的低密度多孔材料，密度为200～400 kg•m－3，孔径分布在10～30 nm范围内，孔隙率约为91％，比表面高达625.65 m2•g－1.外观及微观构造与应用超临界干燥制得的气凝胶完全一致.调节反应体系中各组分的配比以及控制两步水解-缩聚过程中酸与碱的加入量可以获得不同密度的块状SiO2气凝胶.     

块状TiO2/SiO2气凝胶的非超临界干燥法制备及其表征

分别通过TiO2和SiO2的单独溶胶和TiO2/SiO2复合凝胶,并添加干燥控制化学添加剂甲酰胺,形成比较完善的凝胶网络结构,同时通过正硅酸乙酯的乙醇溶液浸泡,低表面张力溶剂替换和分级陈化以及干燥等步骤,实现了块状TiO2/SiO2复合气凝胶的非超临界干燥制备.所得TiO2/SiO2气凝胶为无色或乳白色轻质块状多孔固体,表观密度约0.4～0.9g/cm3,孔隙率约80%～95%.它由直径约10nm的TiO2和SiO2微粒相互分散复合而成,孔洞直径约几十纳米.其相态SiO2为无定形,TiO2为锐钛矿晶型.随着焙烧温度的升高,直到800℃不发生相变化.     

块状TiO2气凝胶的制备及其表征

随着以溶胶-凝胶法和超临界干燥技术为基础的气凝胶制备方法的逐步完善,已不断制备出多种气凝胶[1～3].由于TiO2具有半导体特性,它常被作为光催化剂而受到重视,但是TiO2气凝胶的结构强度远比SiO2气凝胶小,在制备过程中极易碎裂粉化,所以至今未见制备块状TiO2气凝胶的报道.Dagan等[4]曾用异钛酸丁酯为母体制得TiO2气凝胶,并发现水杨酸在TiO2气凝胶存在下的光解速率是一般TiO2粉末的10倍,但获得的仅为TiO2气凝胶粉末.张敬畅等[5]以无机盐为原料,采用溶胶-凝胶法结合超临界干燥技术制备了纳米级TiO2气凝胶,也未能得到块状TiO2气凝胶材料. 本文报道以正钛酸丁酯为原料制备块状TiO2气凝胶的方法,并用TEM,SEM,XRD和IR等手段对所获得的气凝胶进行了结构表征.     

自生纳米纤维增强SiO_2气凝胶的制备及性能研究

采用溶胶-凝胶法和乙醇超临界干燥工艺制备ZrOX/SiO2复合气凝胶,再经1 200℃高温热处理得到自生纳米纤维增强SiO2复合气凝胶。利用扫描电子显微镜、透射电子显微镜、X射线衍射、热重和氮气吸附等手段对气凝胶的结构和性能进行了分析,并且测试了样品的压缩强度及真密度。实验结果表明:自生纳米纤维增强SiO2复合气凝胶具有均匀的多孔网络结构,锆氧纳米纤维是以化学键连接复合的方式无序穿插在气凝胶中,对复合气凝胶的机械强度和隔热性能有明显的改善。经1 200℃热处理后的ZrOX/SiO2复合气凝胶比表面积为827.22 m2·g-1,压缩强度为9.68 MPa,真密度为0.23 g·cm-3。     

低密度薄水铝石晶体的水热生长过程

对Al2(SO4)3-CO(NH2)2-H2O体系在[Al3＋]=0.2 mol•L－1、[CO(NH2)2]:[Al3＋]=2∶1和反应2 h的水热条件下,不同反应温度的晶体生长过程进行了研究,得到呈多孔、针状团簇体状的微米级低密度薄水铝石晶体.采用ICP-AES、XRD、FT-IR、SEM、BET和粒径分布等手段对反应液和产物进行了分析和表征.结果表明,140 ℃时氢氧化铝凝胶或无定形粉体的析出已大部分完成,温度升高到180 ℃后,产物的结晶度变好,堆密度从117.2 kg•m－3相应增加到158.2 kg•m－3,比表面也从75.3 m2•g－1增加到88.3 m2•g－1,但平均粒径有所下降.晶体前驱体在550 ℃焙烧2 h后完全转化为形貌相似并且比表面增加的γ-Al2O3.     

高压Na2O-SiO2系输运性质反常的分子模拟

在6000 K, 0～100 GPa范围内，对一系列Na2O-SiO2二元系进行了分子动力学模拟.这些体系包括SiO2、Na2O•10SiO2、Na2O•5SiO2、Na2O•2SiO2、Na2O•SiO2、2Na2O•SiO2.模拟结果显示，在前4个体系中，氧扩散系数随压力变化反常.在 Na2O•10SiO2, Na2O•5SiO2, Na2O•2SiO2 中，硅的扩散系数随压力变化也出现反常.在这些体系中， 20 GPa处氧的扩散系数比常压下高出一个数量级.在上述各体系中，氧扩散系数随压力变化的峰值都在20 GPa处，以前报导的SiO2体系中氧扩散系数随压力变化的峰值在30 GPa处.还观察到，在SiO2体系中，氧扩散系数最大值大致相当于硅-氧配位数以五配位为主;而在Na2O•10SiO2体系中，氧扩散系数最大值大致相当于硅-氧配位数以六配位为主.     

β-FeOOH气凝胶的制备及表征

用氯化铁和氢氧化钠溶液为原料制得了块状β－ＦｅＯＯＨ气凝胶,构成气凝胶的基本粒子为长约１８ｎｍ、直径约５ｎｍ的棒状粒子,制备过程包括聚合铁水凝胶的制备和超临界干燥两部分。初步研究了溶液羟铁摩尔比（ＯＨ＾－／Ｆｅ＾３＋对气凝胶密度和比表面的影响,应用ＢＥＴ、ＴＥＭ、ＸＲＤ和Ｍｏｓｓｂａｕｅｒ谱等手段对气凝胶样品进行了表征。结果表明,气凝胶样品是由β－ＦｅＯＯＨ超细微粒构成的具有连续网络结构的多孔性块     

酚醛/SiO2双体系凝胶网络结构杂化气凝胶的制备与性能

通过Sol-Gel反应过程控制,调节酚醛树脂(PR)溶液和SiO2溶胶液的凝胶时间,共凝胶反应制备PR和SiO2凝胶网络互穿的PR/SiO2杂化气凝胶.考察了杂化气凝胶表观密度、收缩率、孔结构、微观形貌、热稳定性和力学性能随SiO2气凝胶含量的基本变化规律.研究结果表明：伴随SiO2气凝胶含量的增加,PR/SiO2杂化气凝胶表观密度正比增加;同纯PR有机气凝胶相比,杂化气凝胶孔结构得到明显改善,当[TEOS] = 1.50 mol/L时,平均孔径减小了一半,降至0.25 μm,比表面积由24.60 m2/g增至44 m2/g左右;微观形貌照片显示有机气凝胶网络骨架中的大孔逐渐被SiO2溶胶粒子填充,变成更细小疏松的孔结构形貌,孔径分布明显变宽,SiO2气凝胶在PR凝胶骨架中纳米尺度内均匀分散;无机SiO2气凝胶的引入能有效提高有机气凝胶骨架结构的强度和热稳定性,纳米分散SiO2溶胶粒子的热阻隔效应抑制了PR有机骨架的热分解速率,当[TEOS] = 1.00 mol/L时,杂化气凝胶的Tmax由539 °C提高到602 °C,热分解温度区间明显展宽.     

TiO2-SiO2复合气凝胶：常压干燥制备及性能表征

以廉价的四氯化钛和工业水玻璃为原料,通过溶胶-凝胶法制得TiO2-SiO2复合湿凝胶,用三甲基氯硅烷(TMCS)/乙醇(EtOH)/正己烷(Hexane)混合溶液对湿凝胶进行改性,常压干燥制备了TiO2-SiO2复合气凝胶.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、红外光谱(FTIR)、X射线衍射(XRD)及N2吸附/脱附法对复合气凝胶的形貌和性质进行了分析.结果表明,TiO2-SiO2复合气凝胶具有连续多孔结构,150℃干燥后复合气凝胶的比表面积为1 076 m2·g-1,孔体积为4.96 cm3·g-1;经550 ℃热处理后,复合气凝胶仍然具有高的孔隙率,比表面积为856 m2·g-1,孔体积为3.46 cm3·g-1.吸附和光催化降解罗丹明B的结果表明,复合气凝胶同时具有较好的吸附和光催化性能,其吸附/光催化协同作用活性优于纯SiO2气凝胶和锐钛矿TiO2粉末;且重复利用四次降解率仍然可达到89%.     

超临界干燥法制备SiO2气凝胶的研究

通过溶胶－凝胶法和超临界干燥技术制得了ＳｉＯ２气凝胶，研究了溶液的ｐＨ值对凝胶时间及气凝胶密度的影响，应用ＸＲＤ、ＳＡＸＳ、ＴＥＭ和等方面对气凝胶样品的结构进行了初步研究，结果表明，ＳｉＯ２气凝胶是连续网络的非晶态纳米多孔固体，其基本粒子的平均直径约１０ｎｍ．     

Cellulose–silica composite aerogels from “one-pot” synthesis

Cellulose–silica composite aerogels were prepared via “one-pot” process: aqueous solutions of cellulose–8 wt% NaOH and sodium silicate were mixed, coagulated and dried with supercritical CO₂. The system was studied both in the fluid and solid (dry) states. Cellulose and sodium silicate solutions were mixed at different temperatures and concentrations; mixture properties were monitored using dynamic rheology. The gelation time of the mixture was strongly reduced as compared to that of cellulose–NaOH solutions; we interpret this phenomenon as cellulose self-aggregation inducing partial coagulation due to competition for the solvent with sodium silicate. The gelled cellulose/sodium silicate samples were placed in aqueous acid solution which completed cellulose coagulation and led to in situ formation of sub-micronic silica particles trapped in a porous cellulose matrix. After drying with supercritical CO₂, an organic–inorganic aerogel composite was formed. The densities obtained were in the range of 0.10–0.25 g/cm³ and the specific surface area was between 100 and 200 m²/g. The silica phase was shown to have a reinforcing effect on the cellulose aerogel, increasing its Young’s modulus.     

Fabrication of titania and titania–silica aerogels using rapid supercritical extraction

Titania (TiO₂) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO₂ and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO₂ aerogels were powdery with BET surface areas of 130–180 m²/g, pore volumes ~0.5 cm³/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m²/g) and pore volume (2.0–2.6 cm³/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m²/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm³/g. Preliminary solar simulator studies show that TiO₂ and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution.     

Porous silicon oxycarbide glasses from organically modified silica gels of high surface area

High surface area alkyl-substituted silica aerogels and xerogels were successfully prepared by sol-gel processing and supercritical drying. The gels were further heat treated in inert atmosphere to temperatures as high as 1000°C. Surface areas and pore structure of the gels and gels pyrolyzed at high temperatures were determined by multipoint BET surface area measurement. The aerogels and xerogels exhibited surface areas of about 1100 m²/g. No significant effect of pH was found on the surface areas of gels in the two step sol-gel process, but gels of low pH showed smaller pore diameter and higher density. Xerogels showed smaller surface area, pore size, and pore volume compared to aerogels. Upon pyrolyzing in inert atmosphere, the surface areas of all the gels decreased with temperature as a result of collapse of micropores and shrinkage of mesopores. Unlike pure silica gel, which loses almost all surface area and densifies at 1000°C, the advantage of the alkyl-substituted gels is that they maintained a high surface area of 400 m²/g at 1000°C.Also with the Department of Agronomy.     

THE FABRICATION OF CARBON AEROGELS BY GELATION IN ISOPROPANOL WITH BASIC CATALYST

A new method for the fabrication of carbon aerogels is reported in this paper. Resorcinol and furfural were gelated in isopropanol with basic catalysts and then dried directly under isopropanol supercritical condition, followed by carbonization under nitrogen atmosphere. The bulk densities of carbon aerogels obtained are in the range of 0. 21g/cm3～0. 27g/cm3 and the sizes of the interconnected carbon nano-particles are in the range of 20nm～30nm. All of the aerogel samples exhibit high BET surface areas in the range of 730m2/g～900m2/g. The bulk density, micro-porevolume, meso-pore volume and meso-pore diameter can be controlled by gelation conditions such as R/I ratio and R/C ratio.     

水热均匀沉淀法合成中孔氧化锆

以尿素为均匀沉淀剂,用水热法合成了中孔ZrO2前体,经热处理（500～550 ℃,2 h）得到晶态（t或m相）短程有序中孔ZrO2.BJH脱附孔径约为4～6 nm, BET比表面积约为60～90 m2•g－1.     

LaMnO3稀土纳米材料及催化性能

As catalytic materials, nanometer rare earth perovskites LaMnO3 were p repared by NaOH Na2CO3 coprecipitation, followed by supercritical drying, vacuu m drying and air drying respectively. The effect of drying processes was studied on the catalyst performance through XRD, TEM, SEM and BET analysis. The results demonstrated that about 30 nm LaMnO3 particles could be prepared by three dryin g processes respectively. The catalyst materials LaMnO3 dried in vacuum presente d the largest specific surface area as 28.71 m2•g－1. Compared to the catalyst prepared by dipping cordierite directly in the salt solutions, nanometer LaMnO3 showed better catalytic activity. The light off temperatures for CO and HC oxid ation were both lowered by 100 ℃, and its NOx conversion could be up to 100 ％ at 570 ℃.     

Effects of Hydrogen and Hydrogen Sulfide on Cumene Cracking Catalyzed by Pt/WO3-ZrO2. Control of Acidic and Metallic Functions

Synthesis of alumina aerogels was carried out by hydrolysis of aluminium isopropanolate and butanolate in benzene, methanol and isopropanol solutions as components of support precursors followed by gelation, drying under supercritical conditions and calcination. The influence of the type of precursor and solvent, synthesis temperature as well as drying and calcination temperature on bulk density, specific surface area and total pore volume was investigated.