化学学报 ›› 2004, Vol. 62 ›› Issue (1): 22-27. 上一篇    下一篇

研究论文

29Si NMR研究Stöiber反应的化学动力学

刘瑞丽1, 徐耀1, 李志宏1, 吴东1, 孙予罕1, 高红昌2, 袁汉珍2, 邓风2   

  1. 1. 中国科学院山西煤炭化学研究所, 煤转化国家重点实验室, 太原, 030001;
    2. 中国科学院武汉物理与数学研究所, 波谱与原子分子物理国家重点实验室, 武汉, 430071
  • 投稿日期:2003-06-02 修回日期:2003-09-01 发布日期:2014-01-26
  • 通讯作者: 孙予罕 E-mail::E-mail:yhsun@sxicc.ac.cn;Tel.:0351-4084072;Fax:0351-4041153.
  • 基金资助:
    国家自然科学基金重点项目(No.20133040)、山西省自然科学基金(No.20031030)资助项目.

Liquid-state 29Si NMR Study on the Chemical Kinetics of Stöiber Synthesis

LIU Rui-Li1, XU Yao1, LI Zhi-Hong1, WU Dong1, SUN Yu-Han1, GAO Hong-Chang2, YUAN Han-Zhen2, Deng Feng2   

  1. 1. State Key Laboratory of Coal Conversion, Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001;
    2. State Key Laboratory of Magnetic Resonance & Atomic & Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071
  • Received:2003-06-02 Revised:2003-09-01 Published:2014-01-26

Stöiber反应以低分子量的醇为溶剂,由正硅酸乙酯(TEOS)在氨催化下水解缩聚形成高度分散的尺寸为5~2000 nm的球形SiO2颗粒,是溶胶-凝胶过程的典型反应.通过液体29Si NMR研究Stöiber反应水解和缩聚的动力学过程,确定了反应过程的中间体是Q01,而不是文献所说的Q16.得到了TEOS碱性条件下决速步的水解速率方程r=<kh[TEOS][NH3]0.457·[H2O]0.051,其速率常数为kh=7.32×10-3 mol-0.5·dm1.5·min-1 (T=25℃),利用过渡态理论得到决速步以外的反应方程的速率常数.同时得到了反应活化能Ea和指前因子A的值.结果表明,温度升高,所有反应的速率均增大,决速步的反应速率增大得较多,说明升高温度更有利于Q01的生成;水量的改变对所有反应速率几乎没有影响;催化剂的用量对其水解和缩聚速率影响较大.

关键词: 动力学, 29Si NMR, Stöiber反应, 溶胶-凝胶

Stöber syntheses, the ammonia-catalyzed reactions of tetraethoxysilane with water in low molecular weight (MW) alcohols, produce highly monodisperse, spherical silica nanoparticles with size ranging from 5 to 2000 nm. It is the initial hydrolysis and polycondensation process that have been investigated by liquid-state 29Si NMR. We found that the intermediate species was Q01; the reaction equation of the rate-determining step was r=kh[TEOS]·[NH3]0.457[H2O]0.051; the constant value was kh=7.32×10-3 mol-0.5·dm1.5·min-1 (T=25℃). In the meantime, the reaction rate constant values of those non-rate-determining steps by using the transition state theory were calculated, and the values of the activation energy and the Arrhenius constant were also derived. The results suggested that the reaction rates of the hydrolysis and condensation become faster with increasing the temperature, and the rate constant value of the rate-determining step increases larger than that of non-rate-determining step, indicating that high temperature is more favorable for the hydrolysis of TEOS. The molar ratios of H2O/TEOS and NH 3/TEOS were adjusted to examine the effect of H2O and NH 3 and we found that the reaction rates of hydrolysis and condensation of TEOS largely depended on the concentration of NH 3 but not that of H2O.

Key words: kinetics, 29Si NMR, Stöber synthesis, sol-gel