CIESC Journal ›› 2019, Vol. 70 ›› Issue (5): 1663-1673.DOI: 10.11949/j.issn.0438-1157.20180940

• Thermodynamics • Previous Articles     Next Articles

DFT study on effects of hydrolysis degrees of 3-mercaptopropyltriethoxysilane on grafting mechanisms of nano-silica

Zhixin SHANG(),Xianglan ZHANG()   

  1. College of Chemistry and Environmental Engineering, China University of Mining and Technology, Beijing, Beijing 100083, China
  • Received:2018-08-20 Revised:2019-02-14 Online:2019-05-05 Published:2019-05-05
  • Contact: Xianglan ZHANG

γ-巯丙基三乙氧基硅烷水解程度对纳米二氧化硅接枝机理影响的DFT研究

尚志新(),张香兰()   

  1. 中国矿业大学(北京)化学与环境工程学院,北京 100083
  • 通讯作者: 张香兰
  • 作者简介:<named-content content-type="corresp-name">尚志新</named-content>(1987—),男,博士,<email>messi2008@126.com</email>|张香兰(1968—),女,博士,教授,<email>zhxl@cumtb.edu.cn</email>
  • 基金资助:
    山西省科技重大专项(20111101060)

Abstract:

In order to investigate the effects of hydrolysis degrees of 3-mercaptopropyltriethoxysilane (MPTS) on the grafting mechanisms of nano-silica, the grafting activities and grafting mechanisms of the hydrolyzed products in different degrees are systematically investigated based on density functional theory (DFT). The results show that the cluster model of nano-silica optimized by the GGA-PBE function is the most reasonable. The O atoms in surface silanols of nano-silica are the nucleophilic sites and the H atoms are the electrophilic sites. For MPTS and its hydrolyzed products, the O atoms are the nucleophilic sites and the Si atoms are the electrophilic sites. The LUMO orbitals shift to Si atoms and the HOMO orbitals to O atoms after hydrolysis. The electrophilic indexes of Si atoms and nucleophilic indexes of O atoms are all increased according to the Fukui function, indicating that the hydrolyzed products are more susceptible to be attacked by the surface silanols of nano-silica and the activities of grafting reaction are improved after hydrolysis. The active energies (E a) of grafting reactions for M0—M3 follow the order of M0>M3>M1>M2 (M0 is short for MPTS, M1, M2, M3 are short for the hydrolyzed products of first, second, and third order, respectively), the active energies are obviously reduced after hydrolysis. The grafting reactions of M0-M3 are SN2 nucleophilic substitution and exothermal reactions, but the mechanisms of the grafting reactions are quite different. For M0 — M2 the grafting reactions occur via the reaction channels of eliminating ethanol, but for M3 the grafting reaction occurs via the reaction channels of eliminating H2O. The steric hindrance and the electrophilicity of Si atoms have a significant effect on the grafting reactions of M0—M2.

Key words: computational chemistry, silica, grafting reaction, reaction kinetics, 3-mercaptopropyltriethoxysilane, hydrolysis degrees

摘要:

为探索γ-巯丙基三乙氧基硅烷(MPTS)水解程度对纳米二氧化硅接枝机理的影响,采用基于密度泛函理论(DFT)的量子化学方法,选择合适的泛函和合理的模型,系统研究了MPTS及其不同水解程度产物的反应活性及与纳米二氧化硅的接枝机理,为纳米二氧化硅改性工艺优化及改性效果的提升提供重要理论基础。结果表明:经数据对比确定GGA-PBE泛函优化后的纳米二氧化硅团簇模型为最合理模型。二氧化硅表面硅羟基中的氧原子为亲核活性中心,氢原子为亲电活性中心,MPTS及其水解产物中氧原子为亲核活性中心,硅原子为亲电活性中心。水解引起LUMO轨道向硅原子偏移,硅原子亲电指数提高,而HOMO轨道向氧原子偏移,氧原子的亲核指数提高,引起MPTS水解产物更容易受到二氧化硅表面硅羟基攻击,进而提高了接枝反应活性。MPTS的水解降低了接枝反应的活化能,不同水解程度产物接枝反应活化能(E a)顺序为M0>M3>M1>M2(M0、M1、M2和M3分别表示MPTS及其一级、二级和三级水解产物),接枝反应属于SN2亲核取代,且为放热反应。M0、M1和M2都是通过脱醇机理发生接枝反应,空间位阻效应和偶联剂中心硅原子的亲电性能为反应主要控制因素,而M3是通过脱水机理发生接枝反应。

关键词: 计算化学, 二氧化硅, 接枝反应, 反应动力学, γ-巯丙基三乙氧基硅烷, 水解程度

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