文献类型：期刊文献

英文题名：Evolution mechanism of surface hydroxyl groups of silica during heat treatment

作者：Cheng, Zhimin[1];Shan, Hongwei[1];Sun, Ying[1];Zhang, Ling[1];Jiang, Haibo[1];Li, Chunzhong[1]

机构：[1]East China Univ Sci & Technol, Sch Mat Sci & Engn, Shanghai Engn Res Ctr Hierarch Nanomat, Key Lab Ultrafine Mat,Minist Educ, Shanghai 200237, Peoples R China

年份：2020

卷号：513

外文期刊名：APPLIED SURFACE SCIENCE

收录：;EI(收录号：20200808208122);WOS:【SCI-EXPANDED(收录号:WOS:000523184600043)】；

基金：This work was supported by the National Natural Science Foundation of China (21838003, 91834301, 21878092), the Shanghai Scientific and Technological Innovation Project (18JC1410600), the Social Development Program of Shanghai (17DZ1200900, 18DZ2252400), the Innovation Program of Shanghai Municipal Education Commission, and the Fundamental Research Funds for the Central Universities (222201718002).

语种：英文

外文关键词：Silica; Surface hydroxyl group; Dehydroxylation; Activation energy

摘要：The surface hydroxyl groups of nano-silica have a great influence on its application properties. In this paper, the changes of the number of various hydroxyl groups after dehydroxylation and rehydration progress of silica were quantitatively analyzed by thermogravimetric (TG) analysis and Si-29 Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) measurements. According to the different stability of Si-O-Si bond formed after dehydroxylation, we propose two types of hydroxyl groups depending on the relative positions of them: chain adjacent hydroxyl groups (C-OHs) and spatially adjacent hydroxyl groups (S-OHs). DFT calculations indicate that two C-OHs dehydroxylation form a four-atoms ring structure, and the resulting O-Si-O bond angle deviation from optimal value is up to 19.56 degrees, and the average bond length of the Si-O bond increase more than 4.66%. Further more, its rehydration reaction activation energy (E-ar) is very low, even only 0.21 kJ/mol, so it is easy to re-open and return to hydroxyl groups under environmental conditions. Conversely, the S-OHs dehydroxylation form a stable multi-atoms ring. The DFT calculations are a good illustration of the phenomenon in which some unstable siloxane bonds in a dehydroxylated sample are restored to hydroxyl groups in TG analysis and Si-29 MAS NMR measurements.