| Having risen as a new membrane separation technology in the field ofdesalination and sewage treatment, Forward Osmosis (FO) attracts a widespreadattention nowdays. Its special structure plays an important role in limiting waterflux and salt rejection rate. In contrast to traditional organic polymer, thequasi-symmetric inorganic thin film (QSTFI-FO membrane), which is preparedusing micro interface sol-gel method, with TEOS as a precursor and the thin layerof stainless steel mesh as the support base, has a higher water flux and lowerreverse salt flux. However, the research of QSTFI-FO membrane is just undergoing.This paper investigated the impact properties and operating conditions on solpreparation QSTFI-FO membrane, the former included drying control agents andreaction time, while the latter included support pretreatment method and sinteringtemperature. Several kinds of electron microscopy, fourier transform infraredspectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, thermalgravimetric analysis and other methods have been uesd to characterize themembrane structure. FO tests have been conducted to evaluate the membraneperformance. First, the sol properties were investigated. Drying control agents onmembrane preparation showed little effect of the type and quantity of functionalgroups PEG400amount of inorganic membrane surface, but with the increasingamount of PEG400(PEG400: TEOS=0.125:1~0.5:1), particle size of the gapconstituting the gel network becomes more uniform and network structure of theinorganic film grows to be complete and thermal stable. In the range of300~450°C, the heating rate should be strictly controlled to prevent cracking ofinorganic membranes. When extracting in a certain concentration, the FOmembrane has a better performance as increasing the ratio of the inorganicPEG400and TEOS (PEG400: TEOS=0.125:1~0.5:1). The duration of reactiontime of hydrolysis plays an important role in condensation reaction of theprecursor extent. With the increase of the hydrolysis time, the three-dimensionalnetwork constituted the O-Si-O, along with the combined amount of water and anorganic functional group gradually increasing. The morphology of the membraneis more uniform in the reaction time of ranging from1.5h to2.5h, however, withthe increase of the reaction time, the surface of the film cracks badly. For thereaction time of2.5h, the inorganic film has a very good forward permeability, butif the reaction time is too long or too short, it will have a poor forward osmosisperformance.Secondly, the effect of operating conditions on membranes preparation is also studied. Preparation of sintering temperature of the membrane showed that whenthe sintering temperature raised to350℃to550℃, leading to a uniformly filmnetwork surface, reducing the roughness of the film surface, and then the FOmembrane performance gradually improved. However, as the sinteringtemperature reached650℃, film surface became rough and inhomogeneous,sometimes even with cracks or pinholes, and lowered the forward permeability.With the increase of the sintering temperature, the average pore size graduallyincreased. Surface hydroxyl content was the principal effect of pretreatment of thesubstrate. The more the substrate surface hydroxyl content, the better hydrophilicmembrane QSTFI, and also the better uniform particle size in the film network,and more uniformly distributed pore size in the membrane. In the process ofpretreating the base material, as the surface hydroxyl content of the substrateincreased in some range, the roughness of the film reduced. But when the hydroxylcontent was too large, the thick of the active layer QSTFI film surface increased,resulting in a slight increase in roughness. Moreover, the increase of the surfacehydroxyl content of the base material improved the performance of the FOmembrane QSTFI. |
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