常压干燥溶胶－凝胶法制备Al_2O_3气凝胶
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摘要
氧化铝气凝胶是一种轻质、多孔、非晶态、块体纳米材料,其连续的三维网络结构可在纳米尺度控制和剪裁。由于其独特的网络结构,在基础研究方面,气凝胶的低温热学性质等已成为当今凝聚态物理研究的前沿。在应用方面,气凝胶已经被用于催化剂及催化剂载体、气体过滤材料等。因此,气凝胶具有重要的理论研究价值及广阔的应用前景。
本实验以无机铝盐九水和硝酸铝(Al(NO3)3·9H2O)为前驱体,乙醇为溶剂,以甲酰胺为干燥化学控制剂、环氧丙烷为网络诱导剂、盐酸和氨水作为催化剂,通过盐酸和氨水来控制控制PH值,经过溶胶-凝胶过程,采用常压干燥工艺,制备得到了轻质纳米多孔材料Al2O3气凝胶。
论文研究了溶胶-凝胶过程中乙醇用量、网络诱导剂环氧丙烷用量、干燥化学控制剂甲酰胺用量、表面改性时间和溶液pH值等对气凝胶的影响;讨论了溶胶-凝胶反应机理,研究了Al2O3气凝胶的表面化学,探讨了表面改性剂三甲基氯硅烷(TMCS)表面化学改性机理,TMCS是把湿凝胶表面上的极性基(-OH)转变成-Si(CH3)3,有效地防止了干燥过程中气凝胶骨架的收缩或坍塌;初步研究了超声波对凝胶的溶剂交换与表面改性的加速作用。通过实验确定了室温下制备Al2O3湿凝胶的优化工艺条件,体积比V(无水乙醇):V(环氧丙烷):V(甲酰胺)为23:0.8:6、超声波表面改性阶段V(三甲基氯硅烷):V(无水乙醇)为1:9。
用扫描电镜(SEM)、BET比表面测试仪和红外光谱分析等手段对块状气凝胶和纳米粉体产品的结构分别进行了表征。结果表明,用常压干燥得到的Al2O3气凝胶是一种多小孔、孔径分布较窄、大比表面积、具有纳米网络结构的非晶固体材料。
Al2O3 aerogels are a novel, low density, porous, non-crystalline, monolithic, nanometer materials, whose continuous network structures can be controlled and tailored at the nanometer scale. Due to their special network structures, aerogels are advanced nanometer materials that have high porosity and specific surface area, varied chemical structures, fascinating and useful properties.
In this thesis, Al2O3 aerogels were prepared with sol-gel method by ambient drying technique. The aerogels were made from AlNO3·9H2O ethanol in a definite ratio. If base catalysts are not added to the formulation, there action is impractically slow at room temperature, often requiring several days to each completion. The effects of the pH value on the gelations time were studied by using HCl and NH4OH catalysts.
The sol-gel process has been studied under different conditions and the mechanism of sol-gel process has been discussed. The mechanism about surface modification has been discussed,By detecting -Si(CH3)3 substituted for-OH species, surface modification was identified; acceleration effect of surface modification by the supersonic has been discussed. The optimal technological parameters for Al2O3 aerogels were obtained by experiment.
The structural and other physical properties of the products have been characterized by means of BET, SEM and IR analysis. The results show that the monolithic aerogels were coherent, non-crystalline, low density, high specific surface areas, nano-sized porous solid materials.
本实验以无机铝盐九水和硝酸铝(Al(NO3)3·9H2O)为前驱体,乙醇为溶剂,以甲酰胺为干燥化学控制剂、环氧丙烷为网络诱导剂、盐酸和氨水作为催化剂,通过盐酸和氨水来控制控制PH值,经过溶胶-凝胶过程,采用常压干燥工艺,制备得到了轻质纳米多孔材料Al2O3气凝胶。
论文研究了溶胶-凝胶过程中乙醇用量、网络诱导剂环氧丙烷用量、干燥化学控制剂甲酰胺用量、表面改性时间和溶液pH值等对气凝胶的影响;讨论了溶胶-凝胶反应机理,研究了Al2O3气凝胶的表面化学,探讨了表面改性剂三甲基氯硅烷(TMCS)表面化学改性机理,TMCS是把湿凝胶表面上的极性基(-OH)转变成-Si(CH3)3,有效地防止了干燥过程中气凝胶骨架的收缩或坍塌;初步研究了超声波对凝胶的溶剂交换与表面改性的加速作用。通过实验确定了室温下制备Al2O3湿凝胶的优化工艺条件,体积比V(无水乙醇):V(环氧丙烷):V(甲酰胺)为23:0.8:6、超声波表面改性阶段V(三甲基氯硅烷):V(无水乙醇)为1:9。
用扫描电镜(SEM)、BET比表面测试仪和红外光谱分析等手段对块状气凝胶和纳米粉体产品的结构分别进行了表征。结果表明,用常压干燥得到的Al2O3气凝胶是一种多小孔、孔径分布较窄、大比表面积、具有纳米网络结构的非晶固体材料。
Al2O3 aerogels are a novel, low density, porous, non-crystalline, monolithic, nanometer materials, whose continuous network structures can be controlled and tailored at the nanometer scale. Due to their special network structures, aerogels are advanced nanometer materials that have high porosity and specific surface area, varied chemical structures, fascinating and useful properties.
In this thesis, Al2O3 aerogels were prepared with sol-gel method by ambient drying technique. The aerogels were made from AlNO3·9H2O ethanol in a definite ratio. If base catalysts are not added to the formulation, there action is impractically slow at room temperature, often requiring several days to each completion. The effects of the pH value on the gelations time were studied by using HCl and NH4OH catalysts.
The sol-gel process has been studied under different conditions and the mechanism of sol-gel process has been discussed. The mechanism about surface modification has been discussed,By detecting -Si(CH3)3 substituted for-OH species, surface modification was identified; acceleration effect of surface modification by the supersonic has been discussed. The optimal technological parameters for Al2O3 aerogels were obtained by experiment.
The structural and other physical properties of the products have been characterized by means of BET, SEM and IR analysis. The results show that the monolithic aerogels were coherent, non-crystalline, low density, high specific surface areas, nano-sized porous solid materials.
引文
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[5]P.G.Savva, K. Goundani ,J.Vakros , K.Bourikas, et al, A.Lycourghiotis,Ch. Kordulis Benzene hydrogenation over Ni/Al2O3 catalysts prepared by conventional and sol–gel techniques, Applied Catalysis,2008,79,199–207
[6]丛培源,赵惠忠,沉淀剂对Al2O3-SiO2气凝胶的影响,耐火材料,2007,41 (3),194–196
[7]刘朝辉,苏勋家,侯根良等,超级绝热材料Si02气凝胶的制备及应用,2005,33(12),21–23
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[9]FRICKE J,EMMERLING , Aerogels-recent progress in productions,techniques and novel application,SolGel Sci,Technol ,1998,13.299-303
[10]陈龙武,甘礼华,气凝胶,化学通报,1997,8,21-27
[11]侯万国,孙德军,张春光等,应用胶体化学,北京:科学出版社,1998.125-126
[12]李文翠,新型纳米材料炭气凝胶的制备、表征及应用研究:[博士学位论文],大连理工大学,2002
[13]SHEN Jun,WAN Guoqing ,WAN Yu,et al,Preparation of silica aerogels and study of surface modi-fication and thermal conductivity, Journal of Tongji University ,Natural Science,2004,32 (8),1106-1110
[14]沈军,王钰,吴翔等,气凝胶一种结构可控的新型功能材料,材料科学工程,1994,12(3),1-50
[15]王钰,周斌,吴卫东等,硅气凝胶材料的研究进展,功能材料,1995,26(1),15-19
[16]蒋伟阳,结构可控的纳米多孔气凝胶材料,材料导报,1997,11(4),49-52
[17] RICGARD D G, TEESSIE L,RICHARD G,Sol-gel preparation of supported metal catalysts,Catalysis Today,1997,35,293-317
[18] KIRKBIR K,MURATA H,MEYERS D,et al,Drying of aerogels in different solvent s between at mospheric and supercritical pressures, Jnon-Cryst Solids,1998,225,14-18
[19] ABECASIS WOL FOVICH M,ROTTER H,LANDAU M V,et al,Texture and nanost ructure of chromia aerogels prepared by urea assisted homogeneous precipitation and low-temperature supercritical drying,J Non-CrystSolids,2003, 318,95-111
[20]Kcoon L,Despetis F, Phalippou J,Ultralow density silica aerogels by alcohol supercritical drying,Journal of Non-crystalline Solids,1998,(225),96—100
[21]Wang J,Shen J,Zhhou B,Cluster structure of silica aerogel investigated by laser ablation Nano-structured Materials,1998,10(6),909—916
[22]孙奉玉,吴鸣,李文钊,二氧化钛的尺寸与光催化活性的关系,催化学报,1998,19(3),229-233
[23]Deng Z S,Wang J,Wu A M,High strength SiO2 aerogel insulation,Journal of Non-crystaline Solids,1998,(225),101-104
[24]Andrew Mills,RichardH Davies,David Worsley,Water Purification by Semiconductor Chemical Society Review,1993.417-425
[25]梁长海,炭气凝胶及其研究进展,材料科学与工程,1998,16(6),13-18
[26]Jun Li,Xianyou Wang ,Ying Wang , et al, Structure and electrochemical properties of carbon aerogels synthesized at ambient temperatures as supercapacitors, Journal of Non-Crystalline Solids,2008,354,19–24
[27]I.Adachi,K.Fujita,T.Fukushim,Study of a proximity focusing RICH with a silica aerogel radiator, Nuclear Instruments and Methods in Physics Research, 2007,581,415–418
[28]何飞,赫晓东,李垚,SiO2-Al2O3干凝胶的制备与性能研究,功能材料,2007,6(38),938-944
[29]余桂郁、杨南如,溶胶-凝胶原理及工艺过程,硅酸盐学报,1993,6,60-65
[30] Aurelien Florin Popa,Laurence Courthe oux, et al,Eric Gautron Aerogel and Xerogel Catalysts Based onθ-Alumina Doped with Silicon for High Temperature Reactions, Eur. J.Inorg.Chem,2005,543-554
[31]沈军,吴广明,周斌,碳气凝胶的微结构控制,2007,(6)35,779-782
[32]任洪波,张林,万小波等,以环氧化合物为凝胶促进剂制备块状氧化铁气凝胶,原子能科学技术,2007,3(41),288-291
[33]Theodore F,Baumann,Alexander E, Sarah C,Synthesis of High-Surface-Area Alumina Aerogels without the Useof Alkoxide Precursors, Chem. Mater,2005, 17,395-401
[34]姚连增,李小毛,蔡维理等,SiO2气凝胶的制备与表征,硅酸盐学报,1998,26(3),319-323
[35]MASON T J, The Uses of Ultrasound in Chemistry, Cambridge ,The Royal Society of Chemistry,1990,1-26
[36]HORST C,KUNZ U,ROSENPLAENTER A,et al,Activated solid - fluid reactions in ultrasound reactors,Chem EngSci,1999,54 (13),2849 -2858
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