Department of Chemistry, Missouri State University, 901 S. National Avenue, Springfield, MO 65897, United States.
J Colloid Interface Sci. 2010 Feb 15;342(2):614-9. doi: 10.1016/j.jcis.2009.10.083. Epub 2009 Nov 10.
Transport across alumina nanoporous membranes can be altered via surface attachment of alkylated trimethoxysilane compounds. The mechanism of attachment has been previously assumed to be monolayer silane coverage through full chemisorption regardless of reaction conditions. This chemisorption arises via covalent Si-O-Al bond formation resulting from condensation between the three putative silanols (due to hydrolysis of the three Si-OCH(3) bonds) and hydroxides present on the alumina surface. If this model was correct, methanol would be produced in large quantities in the reaction solution, and the methoxy moieties would no longer be present on the silane molecule. The results presented in this paper utilized FT-IR and both solution and solid-state NMR to examine the chemical nature of octadecyltrimethoxysilane (ODTMS) present on the alumina surface. The FT-IR results confirm the presence of the silane on the membrane. The (1)H solution NMR results indicate small but detectable methanol production during attachment. The solid-state NMR results demonstrate that the methoxy proton NMR integrated peak intensities remain in nearly the same ratios present in the free silane, concluding that the majority of methoxy groups are intact while the silane is attached to the membrane surface. These three results suggest that monolayer surface coverage and chemisorption through full covalent bonding is not the primary means of attachment for ODTMS on the surface of alumina nanomembranes under these reaction conditions.
通过在氧化铝纳米多孔膜表面附着烷基三甲氧基硅烷化合物，可以改变其传输性能。之前人们认为，无论反应条件如何，其附着机制都是通过单层硅烷覆盖的完全化学吸附。这种化学吸附是通过氧化铝表面存在的三个假定硅醇（由于三个 Si-OCH(3) 键的水解）和氢氧化物之间的缩合，形成共价 Si-O-Al 键而产生的。如果这个模型是正确的，那么在反应溶液中会大量生成甲醇，并且硅烷分子上的甲氧基部分将不再存在。本文利用傅里叶变换红外光谱（FT-IR）以及溶液和固态核磁共振（NMR）技术，研究了氧化铝表面十八烷基三甲氧基硅烷（ODTMS）的化学性质。FT-IR 结果证实了膜上存在硅烷。（1）H 溶液 NMR 结果表明，在附着过程中会产生少量但可检测到的甲醇。固态 NMR 结果表明，甲氧基质子 NMR 积分峰强度在游离硅烷中保持几乎相同的比例，这表明大多数甲氧基基团在硅烷附着到膜表面时仍然完整。这三个结果表明，在这些反应条件下，ODTMS 在氧化铝纳米膜表面的主要附着方式不是单层表面覆盖和通过完全共价键的化学吸附。
