Silica material has limited hydrostability when it is produced as a thin film. In order to mitigate this restriction a modification strategy is needed. This article provides details of mesoporous hybrid organo-silica thin films that were successfully fabricated from a combination of a dual silicate precursor of tetraethyl orthosilicate/triethoxy vinyl silane, using organic catalysts. The research investigated the effect of calcination temperatures (350°C and 600°C) on the materials, and compared the application of single (citric acid) and dual catalysts (citric acid and ammonia) during fabrication of the thin film.
The tetraethyl orthocycate (TEOS) is mainly used as a silica precursor. Silanol content of silica material is the main cause of low hydrostability which led to resulting in poor performance, especially in water treatment. The stronger bond strength formed by incorporating a carbon structure from triethoxy vinyl silane (TEVS). The xerogel fabrication resulted in the composition of TEOS: TEVS: EtOH: HNO3: H2O: NH3 to be 0.9: 0.1: 38: 0.00078: 5: 0.0003. . The purpose is to study the structure of organosilica xerogel calcined at 350oC, 450oC and 600oC in the Fourier-transform infrared (FTIR) using rapid thermal processing. The deconvolution of FTIR spectra calculated using the Fityk software. The result of the best xerogel peak shows at calcination of 450°C with peak area siloxane of 15.39, silanol of 3.32 and silica carbon of 3.85.
The sol gel process is one of the processes used in the manufacture of thin films on membranes because it can control the pore size in the resulting silica matrix. In addition, another way to build membrane size can be done by adding catalysts and precursors to be used. In this study, using a combination of tetraethyl ortho silicate (TEOS) and triethoxy vinyl silane (TEVS) precursors and citric acid as a catalyst to produce a silica matrix with mesoporous size so that it is suitable for application in the desalination process. The organo silica membrane was calcined at 350 ° C for 1 hour using the RTP calcination technique under vacuum, thus preventing the decomposition of carbon in the silica matrix. The membrane was dipcoated 4 times to obtain 4 layers. The FTIR (Fourier-transform Infrared Spectroscopy) test was carried out to see the functional groups on xerogel, namely silanol, siloxane and carbon. In addition, the performance of this membrane is carried out by desalination through pervaporation using 0.3% NaCl feed water with variations in feed air temperature, namely 25 ℃, 40 ℃ and 60 ℃. The resulting flux of air value increased with increasing feed water temperature, namely 6.1; 11.2; and 12.1 kg.m-2h-1 while the resulting salt rejection was 99.72; 99.64 and 99.23%. So that the organo silica membrane is suitable when applied to the desalination process through pervaporation.
Currently, xerogel has been applied as a filtration material, especially in membrane desalination. However, the xerogel matrix structure for desalination have to be designed properly in order to allow rejection of salt and obtain good hydro-stability, thus, silica precursor in the form of TEOS (tetraethyl orthosilicate)/TEVS (triethoxy vinyl silane) and organic acid catalyst are suitable material for fabrication. The aim of this study is therefore to fabricate and perform deconvolution of TEOS/TEVS xerogel by adding single or dual catalyst, using FTIR (Fourier-transform Infrared Spectroscopy) and Fityk software. The xerogel was fabricated by dried silica sol and calcined using RTP technique (rapid thermal processing) at 450 °C. Prior to this fabrication, the silica sol was synthesized by sol gel method, using a mixture of silica precursor TEOS/TEVS, ethanol solvent, and varied addition of single catalyst (citric acid) as well as dual catalyst (citric acid + ammonia) for 2 hours, at 50 °C. Subsequently, the xerogel was characterized by FTIR and the deconvolution was obtained through Gaussian approach, with Fityk software. All TEOS/TEVS xerogel samples indicated existence of silanol (Si-OH), siloxane (Si-O-Si) and silica-carbon (Si-C) functional groups. The xerogel deconvolution of TEOS/TEVS using single catalyst exhibit a peak area ratio of Si-OH/Si-O-Si, and this is similar to the dual catalyst counterpart of 0.24 (unit area) and 1.86 (unit area), for Si-C area ratio. This shows the addition of single catalyst was enough to produce deconvolution in TEOS/TEVS xerogel, dominated by siloxane functional group and carbon bonds with the ability to enhance membrane material hydro-stability’s fabrication.
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