An organic/inorganic hybrid mesoporous silica memb

Authors: Yong Chen Long Wu Jinyu Zhu Yi Shen Siwen Gan Anqi Chen

Publish Date: 2010/04/06

Volume: 18, Issue: 2, Pages: 251-258

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Abstract

An organic/inorganic hybrid mesoporous silica membrane composed of mesoporous silica materials inside the channels of polycarbonate filtration membrane PC was synthesized by using aspirationinduced infiltration method and the surfactant in asprepared membrane was removed by employing templateextraction method The obtained materials were characterized by scanning electron microscopy SEM energy dispersive spectroscopy EDS Xray diffraction XRDtransmission electron microscopy TEM and N2 adsorption–desorption measurement The SEM images and EDS elemental analyses show that assynthesized materials in PC are onedimensional silica rods estimated as 200 nm in diameter and 9 μm in length Moreover the results of XRD TEM and N2 adsorption–desorption analysis clearly demonstrate that such silica rods are mesoporous materials with twodimensional hexagonal mesostructure and the average mesopore diameter is about 30 nm In addition the porosity of organic/inorganic hybrid mesoporous silica membrane was further examined by molecule permeation It is found that small molecule such as rhodamine B can transport across the membrane but relatively large molecule such as horse radish peroxidase can not transport across the membrane indicating that it is sizeselectivity of such a membrane for molecule permeation which has the potential application in the molecule filters to separate biomacromolecule from small moleculeSince the first report of of MCM41 by Kresge et al in 1992 1 the synthesis characterization and application of ordered mesoporous materials OMMs has attracted extensive attention because these materials with uniform pores in the 2~50 nm size range have wide application in catalysis separations drug delivery etc 2 3 4 While most investigations on the OMMs have focused on powder materials the possibility to make OMMs as thin films is particularly attractive due to that these OMMs membranes have important applications in a wide variety of fields including optics 5 sensors 6 adsorption and separation processes etc 7 8 Recently the conventional mesoporous films formed on the surface of a solid substrate have been extent to the hybrid mesoporous membranes composed of arrays of OMMs with unique and tunable mesophase structures within the confined channels of porous membrane by numerous academic labs 9 10 11 12 13 14 15 16 However all of those investigations have almost focused on the inorganic hybrid mesoporous silica membranes formed by using inorganic porous membrane that is anodic alumina membranes AAMs as the hard template 9 10 11 12 13 14 15 16It is wellknown that in addition to AAMs organic porous membranes OPMs such as polycarbonate filtration membrane PC have often been used as the hard template in the templatesynthesis of onedimensional nanomaterials 17 18 Therefore if OPMs are employed as the hard templates in the synthesis of hybrid mesoporous silica membranes the organic/inorganic hybrid mesoporous silica membranes composed of inorganic mesoporous silica materials in organic porous membranes could be obtained In view of some advantages of OPMs over AAMs such as mechanical flexibility and chemical stability under the acid or basic condition it is expected that those organic/inorganic hybrid mesoporous silica membranes can expand the application area of such hybrid membranesTo our knowledge only one example of organic/inorganic hybrid mesoporous silica membranes has been reported by Liang etc until now 19 However it should be noticed that in their work the synthesis process took four days by employing conventional hydrothermal method Moreover the prepared membrane was destroyed during the procedure of calcination up to 550 °C for removing the surfactants from membrane which undoubtedly restrict the application of assynthesized materials in the membrane science and technology Therefore it is indeed necessary to further explore more efficient methods to shorten the preparation time and especially to ensure the structural integrity of asprepared membrane such as the simple and rapid aspirationinduced infiltration method proposed by Yamaguchi etc 10 as well as the templateextraction method under low temperature to remove surfactant from mesoporous silica materials 20Herein we present the synthesis of an organic/inorganic hybrid membrane composed of CTABtemplated rodlike mesoporous silica materials in PC by employing the aspirationinduced infiltration method In addition the templateextraction method was employed to remove the surfactant from the assynthesized membrane Moreover the molecule permeation across such an organic/inorganic hybrid mesoporous silica membrane was examined to investigate its porosity and explore its potential application in the sizeselective separation of biomacromolecule from small moleculeThe preparation of precursor solution and procedure for the synthesis of a hybrid mesoporous silica membrane in short HMSM in this work by using PC as the hard template is similar with the previous reports on the CTABtemplated mesoporous silica films or AAMstemplated hybrid mesoporous silica membrane 3 10 Firstly the precursor solution containing cetyltrime thylammonium bromide CTAB tetraethylorthosilicate TEOS was prepared as follows a mixed solution containing ethanol 77 g TEOS 116 g and 1 mL of HCl 28 mM was refluxed at 60 °C for 90 min After that ethanol 15 g 4 mL of HCl solution 55 mM and CTAB 15 g were added to the refluxed solution which was stirred for 30 min to give the precursor solution Then the precursor solution were dropped onto a porous polycarbonate filtration membrane with pore diameter of 02 μm Anodisk 47 Whataman which was set in an ordinary membrane filtration apparatus Under moderate aspiration two millilitres of the precursor solution filtrates across the membrane twice and the membrane was dried for 5 min under vacuum at room temperature every time Finally the surfactant CTAB was removed from the membrane not by calcination but by the templateextraction method with EtOH/HOAc as described in the ref 20 due to the low temperature of heatresistance of PC 140 °C After that an organic/inorganic HMSM was successfully synthesizedSEM images were measured on a HITACHI3400 equipped with Quantax400 EDS Bruker Ins Germany and TEM measurements were conducted using a JEM2100 JEOL Japan To obtain the SEM images and TEM sideview of silica rods the prepared membranes are completely or partly etched by the organic solvent dichloromethane After completely etching hard template PC the free silica rods were collected by the porous filtration membrane of polyvinylidene fluoride PVDF Φ50 mm 022 μm MosutechInc China The TEM sideviews of assynthesized membrane were obtained after the membrane was embedded in an epoxy resin and cut by mechanical polishing N2 adsorption–desorption measurements were conducted on a micrometrics ASAP2020 instrument Micromeritics USA and the asprepared membranes were cut into small pieces of about 5–6 mm square and placed into the measurement cell In addition the product was identified by XRD with Cu Kα radiation by using PW3040/60 X’Pert PRO Xray Panalytical Ins Netherlands

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