介孔氧化硅材料的合成、表征及在分离上的应用
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摘要
近年来，有序孔材料以其孔尺寸均一，在空间有序排列而成为材料科学研究的一个崭新方向，具有重要的理论研究和实际应用意义。特别是以命名为MCM-41的有序介孔材料的出现，因其具有孔道呈六方有序排列、孔径在1.5～20nm范围内可连续调节、高的比表面积和热稳定性等特点而在吸附、催化、分离、纳米技术以及光、电、磁等领域具有广泛的潜在应用价值，正成为众多领域的研究热点之一。
本文以阳离子表面活性剂——正十六烷三甲基溴化铵(CTAB)为结构模板剂，在强酸性条件下，通过水热反应合成了纯的介孔氧化硅材料。经XRD、TG／DTA分析，证实所合成的样品具有MCM-41材料的结构特征。分析了介孔氧化硅材料的合成过程，认为HCl、反应温度等因素对合成出具有六方结构特征的介孔材料具有重要作用。使用憎水有机物1,3,5-三甲苯(TMB)作为表面活性剂的辅助剂，以在相同的基本反应混合物中添加不同量的TMB的方式，进行了介孔材料孔径的调节。XRD结果表明，加入TMB可以有效增大介孔材料的孔径，达到调节介孔材料孔径的目的。
采用XRD、IR、SEM、N_2吸附曲线等测试手段对经540℃热处理后的介孔氧化硅材料的结构进行了表征。XRD、IR结果表明，经热处理后的介孔材料保持了MCM-41材料的结构特征，但孔径和墙厚发生了少量的收缩，且材料的结晶有序度随着TMB的加入量逐步增加；SEM结果表明，介孔氧化硅材料的颗粒形貌具有多样性，且随其有序度的逐渐增加其形状和大小逐渐变得规整。所进行的低温N_2吸附测试结果表明，各样品的N_2吸附等温线均为与中孔(介孔)特征对应的第Ⅳ类曲线；由Kelvin公式计算得到的孔径分布曲线说明，介孔材料具有较为集中的孔径分布；各样品的BET比表面积均比较高，且随孔径和有序度的增加而逐步增加。同时发现，TMB对介孔材料介孔结构的影响是有限度的，即在其加入量摩尔比小于0.4范
围内时，随着TMB加入量的增加，材料的孔径、结晶有序度等逐步增加；
但当加入量超过此值时则反而会下降。随后探讨了有机辅助剂影响材料介
孔结构的机理。
本文还尝试了介孔氧化硅材料在分离方面应用的研究。首先以刚合成
出的氧化硅－表面活性剂介孔粉末为原料并以低温锻烧工艺制备了孔径分
布狭窄、气孔率高的多孔支撑体；然后在支撑体表面上采用溶胶－凝胶浸渍
工艺制备出了不同孔径分布的介孔分子筛复合膜，所得分子筛复合膜保持
了MCM4 介孔氧化硅材料的结构特征。最后将介孔分子筛膜应用于空气
中NZ、OZ的分离。分离结果表明，所合成的介孔分子筛膜对空气具有一定
的分离性能，其分离空气的机理为努森扩散和压力扩散共同作用的结果。
Up to now, the study of ordered porous materials with monodispere sized pore regularly stacking in three (or two )-dimensional fashion is a frontier of materials science and technology since they are both fundamental and technological significance. Especially, the mesoporous silica materials (designated MCM-41), which is regarded as a novel nano-structured materials, are expected to show potential values in many fields such as adsorption, catalysis, optics, nano-technolohy, electronics, magnetics and chemical sensors because they exhibit hexagonal structure, the pore size which can be regulated from 1.5 to 20nm, high surface and thermal stability.
In this thesis, the pure mesoporous silica were synthesized through water-thermal reaction by using cationic surfactant cetyltrimethyl-ammonium chloride (CTAB) as template under strong acid condition. The results of XRD and TG/DTA show the as-sythesized materials have the structure charaterisics of MCM-41. As far as mesoporous materials are concerned, the pore size and its distribution are critical parameters. Here, the pore sizes of mesoporous materials were regulated by adding different amount of 1,3,5-trimethylbenzene (TMB) into the same basic reactant mixture as an organic assistant agent of surfactant. It was confirmed by XRD that the addition of TMB can add up the pore sizes of mesoporous materials effectively.
Then the characteristics of silica samples after calcination at 540℃ were investigated using XRD, IR, SEM, N2 adsorption technique. First of all, it is found from the analysis of XRD and IR that all mesoporous samples remain the hexagonal structure of MCM-41 phase, and their ordered degree can be enhanced with the addition of TMB, but pore sizes and wall thickness have a little contraction. It can be observed by SEM that different sample particle
exhibits different appearance and was reflect the ordered structure of different pore sizes mesoporous materials. It was analysized that all Na adsorption isotherms of the samples belong to Langmuir IV category which is related to mesoporous materials, and their regulation and BET surface rise with the pore size of them. It is also concluded from above investigations that the effect of TMB on mesoporous structure of MCM-41 is limited. That is, it can enhance the ordered degree and their pore sizes of mesoporous materials among the molar ratio of TMB is bellow x=0.4; but will decrease when it surpass the value.
The last aim of this thesis is to study the application of mesoporous materials in separation. At first, porous supporting which has a narrow pore distribution and high apparent porosity was prepared with the as-synthesized silica-surfactant mesoporous powder. Then the mesoporous molecular sieves composite membrane with different pore size were prepared on the supporting and applied for the air separation. The result shows that the molecular sieves membrane has rather separation performance for N2 and Oa and its separation mechanism is the interaction of Knudsen diffusion and pressure diffusion.
本文以阳离子表面活性剂——正十六烷三甲基溴化铵(CTAB)为结构模板剂，在强酸性条件下，通过水热反应合成了纯的介孔氧化硅材料。经XRD、TG／DTA分析，证实所合成的样品具有MCM-41材料的结构特征。分析了介孔氧化硅材料的合成过程，认为HCl、反应温度等因素对合成出具有六方结构特征的介孔材料具有重要作用。使用憎水有机物1,3,5-三甲苯(TMB)作为表面活性剂的辅助剂，以在相同的基本反应混合物中添加不同量的TMB的方式，进行了介孔材料孔径的调节。XRD结果表明，加入TMB可以有效增大介孔材料的孔径，达到调节介孔材料孔径的目的。
采用XRD、IR、SEM、N_2吸附曲线等测试手段对经540℃热处理后的介孔氧化硅材料的结构进行了表征。XRD、IR结果表明，经热处理后的介孔材料保持了MCM-41材料的结构特征，但孔径和墙厚发生了少量的收缩，且材料的结晶有序度随着TMB的加入量逐步增加；SEM结果表明，介孔氧化硅材料的颗粒形貌具有多样性，且随其有序度的逐渐增加其形状和大小逐渐变得规整。所进行的低温N_2吸附测试结果表明，各样品的N_2吸附等温线均为与中孔(介孔)特征对应的第Ⅳ类曲线；由Kelvin公式计算得到的孔径分布曲线说明，介孔材料具有较为集中的孔径分布；各样品的BET比表面积均比较高，且随孔径和有序度的增加而逐步增加。同时发现，TMB对介孔材料介孔结构的影响是有限度的，即在其加入量摩尔比小于0.4范
围内时，随着TMB加入量的增加，材料的孔径、结晶有序度等逐步增加；
但当加入量超过此值时则反而会下降。随后探讨了有机辅助剂影响材料介
孔结构的机理。
本文还尝试了介孔氧化硅材料在分离方面应用的研究。首先以刚合成
出的氧化硅－表面活性剂介孔粉末为原料并以低温锻烧工艺制备了孔径分
布狭窄、气孔率高的多孔支撑体；然后在支撑体表面上采用溶胶－凝胶浸渍
工艺制备出了不同孔径分布的介孔分子筛复合膜，所得分子筛复合膜保持
了MCM4 介孔氧化硅材料的结构特征。最后将介孔分子筛膜应用于空气
中NZ、OZ的分离。分离结果表明，所合成的介孔分子筛膜对空气具有一定
的分离性能，其分离空气的机理为努森扩散和压力扩散共同作用的结果。
Up to now, the study of ordered porous materials with monodispere sized pore regularly stacking in three (or two )-dimensional fashion is a frontier of materials science and technology since they are both fundamental and technological significance. Especially, the mesoporous silica materials (designated MCM-41), which is regarded as a novel nano-structured materials, are expected to show potential values in many fields such as adsorption, catalysis, optics, nano-technolohy, electronics, magnetics and chemical sensors because they exhibit hexagonal structure, the pore size which can be regulated from 1.5 to 20nm, high surface and thermal stability.
In this thesis, the pure mesoporous silica were synthesized through water-thermal reaction by using cationic surfactant cetyltrimethyl-ammonium chloride (CTAB) as template under strong acid condition. The results of XRD and TG/DTA show the as-sythesized materials have the structure charaterisics of MCM-41. As far as mesoporous materials are concerned, the pore size and its distribution are critical parameters. Here, the pore sizes of mesoporous materials were regulated by adding different amount of 1,3,5-trimethylbenzene (TMB) into the same basic reactant mixture as an organic assistant agent of surfactant. It was confirmed by XRD that the addition of TMB can add up the pore sizes of mesoporous materials effectively.
Then the characteristics of silica samples after calcination at 540℃ were investigated using XRD, IR, SEM, N2 adsorption technique. First of all, it is found from the analysis of XRD and IR that all mesoporous samples remain the hexagonal structure of MCM-41 phase, and their ordered degree can be enhanced with the addition of TMB, but pore sizes and wall thickness have a little contraction. It can be observed by SEM that different sample particle
exhibits different appearance and was reflect the ordered structure of different pore sizes mesoporous materials. It was analysized that all Na adsorption isotherms of the samples belong to Langmuir IV category which is related to mesoporous materials, and their regulation and BET surface rise with the pore size of them. It is also concluded from above investigations that the effect of TMB on mesoporous structure of MCM-41 is limited. That is, it can enhance the ordered degree and their pore sizes of mesoporous materials among the molar ratio of TMB is bellow x=0.4; but will decrease when it surpass the value.
The last aim of this thesis is to study the application of mesoporous materials in separation. At first, porous supporting which has a narrow pore distribution and high apparent porosity was prepared with the as-synthesized silica-surfactant mesoporous powder. Then the mesoporous molecular sieves composite membrane with different pore size were prepared on the supporting and applied for the air separation. The result shows that the molecular sieves membrane has rather separation performance for N2 and Oa and its separation mechanism is the interaction of Knudsen diffusion and pressure diffusion.
引文
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[3] 齐凯，牛忠伟，容建华，等．有序孔材料的发展现状．材料导报，2001，15(6)：47-51
[4] 谢永贤，陈文，徐庆．有序介孔材料的合成及机理．材料导报，2002，16(1)：51-53
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[23] J. Y. Ying, C. P. Mehnert, M. S. Wong. Synthesis and applications of supramolecular-templated mesoporous materials. Angew Chem Int Ed. 1999, 38: 56～77
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[2] C. T. Kresge, M. E. Leonowicz, W.J. Roth, et al. Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature, 1992, 359: 710～712
[3] 齐凯，牛忠伟，容建华，等．有序孔材料的发展现状．材料导报，2001，15(6)：47-51
[4] 谢永贤，陈文，徐庆．有序介孔材料的合成及机理．材料导报，2002，16(1)：51-53
[5] 吴越，刘持标．介孔无机固体材料的合成、特性和应用前景，石油化工，1998，27(3)：212～220
[6] 王连洲，施剑林，禹剑，等．介孔氧化硅材料的研究进展，无机材料学报，1999，14(3)：333～341
[7] 陈航榕，施剑林，禹剑，等．非硅组成有序介孔材料合成及应用．硅酸盐学报，2000，28(3)：259～263
[8] 张立德，牟季美．纳米材料和纳米结构．北京：科学出版社，2001．413～437
[9] 许磊，王公尉，魏迎旭，等．MCM-41介孔分子筛合成研究．催化学报，1995，20(3)：247～255
[10] Q. Huo, D. J. Margolese, U. Ciesla, et al. Organization of organic molecules with inorganic molecular species nanocomposite biphase arrays. Chem. Mater., 1994, 1176～1191
[11] M. E. Davis. Organizing for better synthesis. Nature, 1993, 364: 391
[12] A. Corma, From microporous to molecular sieve materials and their use in catalysis. Chem. Rev., 1997, 97: 2373～2382
[13] 伏再辉，尹笃林，赵伟，等．中孔载体上组装Ti催化活性的研究．无机化学学报，2000，7(4)：624～629
[14] H. Yang, N. Coombs, I. Sokolov, et al. Free-standing and oriented mesoporous silica films grown at the air-water interface. Nature, 1996, 381: 589～598
[15] 徐应明，王榕树．介孔钛硅分子筛表面功能膜的制备及对水体中铅的去除作用．高等学校化学学报，1999，20(7)：1002～1006
[16] 王宏志，高濂，郭景坤．纳米结构材料．硅酸盐通报，1999，(1)：31～34
[17] 解思深，李文治，王超英，等．利用介孔材料制备碳纳米管的形貌结构和Raman散射研究。中国科学，1997，27(7)：630～635
[18] 邹炳锁，解思深．无机介孔固体制备及其在纳米科技中的应用．中国科学，1995，24(10)：587～594
[19] S. Beck, J.C. Vartuli, W.J. roth, et al. A new family of mesoporous molecular sieves prepared with liquid crystal template. Am. Chem. Soc., 1992, 114: 10834～10843
[20] 许宜铭．高纯度中孔分子筛MCM-41的合成与表征，高等学校化学学报，1999，20(5)：670～674
[21] 王连洲，禹剑，施剑林，等．合成条件对介孔氧化硅材料孔径尺寸的影响．硅酸盐学报，1999，27(1)：22～27
[22] 王连洲，施剑林，张文华，等．合成温度对介孔氧化硅材料相结构的影响．硅酸盐学报，1999，27(6)：685～691
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