原硅酸四乙酯在气-水界面的水解和缩合：对二氧化硅纳米颗粒形成的影响,ACS Applied Nano Materials

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原硅酸四乙酯在气-水界面的水解和缩合：对二氧化硅纳米颗粒形成的影响
ACS Applied Nano Materials ( IF 5.3 ) Pub Date : 2021-12-22 , DOI: 10.1021/acsanm.1c03250
Harpreet Kaur ₁ , Shilpi Chaudhary _{1,

2} , Harsharan Kaur ₃ , Monika Chaudhary ₃ , Kailash C. Jena _{1,

3}

Affiliation

二氧化硅（SiO ₂) 众所周知的二氧化硅前体原硅酸四乙酯 (TEOS) 的纳米颗粒通常是通过有前景的溶液凝胶无机聚合工艺合成的。单分散二氧化硅纳米粒子具有从牙科纳米复合材料的形成到抗反射涂层的潜在应用。在本研究中，我们使用和频发生（SFG）振动光谱系统地研究了TEOS的原位界面分子结构及其在空气-水界面水解和缩合过程中对界面水结构的影响。随着水的存在，每个 TEOS 浓度的 CH 拉伸区域的 SFG 强度随时间逐渐降低反映了乙氧基的消除，这是水解过程的标志。更远，从 OH 拉伸区域中 SFG 信号的显着增强揭示了水解过程的影响。TEOS 水解之后是缩合，其中 ≡Si─O^–带电物质被形成≡Si─O─Si≡桥接网络所取代。冷凝过程的特征反映在 OH 拉伸区域中观察到的增强 SFG 信号的逐渐降低。DLS 测量证实了随着 TEOS 浓度的增加，单分散二氧化硅纳米粒子的形成作为最终产物的尺寸变化从 1.75 到 4.67 nm。我们还探讨了三种不同 pH 值（2.0、5.8 和 9.0）下的 pH 依赖性 SFG 研究。从在空气 - 水界面观察到的 TEOS 分子结构揭示了主要的 pH 依赖性水解过程。

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Hydrolysis and Condensation of Tetraethyl Orthosilicate at the Air–Aqueous Interface: Implications for Silica Nanoparticle Formation

The silica (SiO₂) nanoparticles of a well-known silica precursor tetraethyl orthosilicate (TEOS) are generally synthesized via a promising solution-gelation inorganic polymerization process. The monodisperse silica nanoparticles have potential applications ranging from the formation of dental nanocomposites to antireflective coatings. In the present study, we have systematically investigated the in situ interfacial molecular structure of TEOS and its impact on the interfacial water structure during the processes of hydrolysis and condensation at the air–aqueous interface using sum-frequency generation (SFG) vibrational spectroscopy. With the presence of water, a gradual decrease in the SFG intensity in the CH-stretch region for each concentration of TEOS with time reflects the elimination of ethoxy groups, which is a signature of the hydrolysis process. Further, the impact of the hydrolysis process is revealed from the significant enhancement in the SFG signal in the OH-stretch region. The hydrolysis of TEOS is then followed by condensation in which the ≡Si─O^– charged species are replaced by forming the ≡Si─O─Si≡ bridging network. The signature of the condensation process is reflected with the gradual decrease in the observed enhanced SFG signal in the OH-stretch region. The formation of monodispersed silica nanoparticles as an end product of size variation from 1.75 to 4.67 nm with the increase in TEOS concentration is confirmed with the DLS measurements. We have also probed the pH-dependent SFG studies at three different pH values (2.0, 5.8, and 9.0). The dominant pH-dependent hydrolysis process is revealed from the observed molecular structure of TEOS at the air–aqueous interface.

更新日期：2022-01-28

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