Reaction Mechanism Of The Sol-Gel Process

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Results and discussion Reaction mechanism of the sol-gel process Monodisperse silica NPs can be prepared by hydrolysis and condensation of alkoxysilanes in a mixture containing alcohol, water, and catalyst. The chemical reactions describing the hydrolysis and condensation of TEOS and MTES are shown in Fig. 3. As shown in this figure, TEOS can be hydrolyzed and condensed to form SiO2 colloid particles in mixture of Methanol, NH4OH and H2O after being stirred for 1 h at room temperature. Similar to the results reported by Wang et al., the obtained inorganic silica (SiO2) colloid particles have active hydroxyl groups on their surfaces. When MTES is added into the SiO2 colloid sol, the ethoxy groups of MTES can be immediately hydrolyzed, generating 1–3 hydroxyl groups on each molecule (Wang et al., 2012). Then the polycondensation reaction between the hydrolyzed MTES molecules and hydroxyl groups on the surface of the existing SiO2 colloid particles can occur. As a result, the hydrophobic methyl groups can be successfully grafted on the surface of SiO2 colloid particles. This process has been already confirmed by Yang et al.(Yang et al., 2010). The fabrication process of the coating on the PP membrane is schematically shown in Fig. 4. After preparing the sol solution, Piranha treated membranes were dipped in transparent alcosol. The silica NPs then can form hydrogen bonds with OH groups of the Piranha-treated samples. Optimization of sol-gel reaction parameters by using

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