Preparation of modified mesoporous MCM-41 silica spheres and its application in pervaporation

doi:10.1016/j.powtec.2012.07.044

Powder Technology

Volume 231, November 2012, Pages 63-69

https://doi.org/10.1016/j.powtec.2012.07.044 Get rights and content

Abstract

Mesoporous MCM-41 silica spheres were synthesized via modified Stöber method and modified by silylation. The MCM-41 pore structures, surface properties and morphological features before and after modification were examined by XRD, SEM, TEM, FT-IR, TGA, ²⁹Si CP/MAS NMR and nitrogen adsorption–desorption. The results showed that the obtained MCM-41 silica had ordered mesoporous structure and spherical morphology. After silylation, the surface property of MCM-41 silica changed from hydrophilic to hydrophobic, whereas the MCM-41 framework and morphology were retained. The calcined and modified MCM-41 spheres were incorporated into a polydimethylsiloxane (PDMS) matrix, separately. It is clearly shown from the SEM image that modification of MCM-41 spheres greatly enhanced its interfacial adhesion with the polymer. The filled membrane was firstly used for pervaporation separation of dimethylcarbonate/methanol azeotropic mixture and displayed superior pervaporation performance than pure PDMS membranes.

Graphical abstract

Mesoporous MCM-41 silica spheres were synthesized and modified by silylation. The modified MCM-41 spheres were incorporated into a polydimethylsiloxane (PDMS) matrix. SEM image showed that modification of MCM-41 spheres could greatly enhance its interfacial adhesion with the polymer. The filled membrane displayed superior pervaporation performance.

Highlights

► Mesoporous MCM-41 spheres were successfully synthesized and modified by silylation. ► Modified MCM-41/PDMS hybrid membranes were prepared as a new membrane material. ► The interfacial adhesion between MCM-41 and PDMS could be enhanced by silylation. ► Selectivity and flux of modified MCM-41/PDMS membrane can be raised simultaneously.

Introduction

Since being originally developed in 1992 by Kresge's group [1], ordered mesoporous MCM‐41 has become the most popular member of M41S mesoporous material because of its hexagonal arrangement of uniform mesopores, highly specific surface (up to 1500 m² g^− 1), adjustable pore diameter (2–10 nm) and varied surface hydroxyl group for modification. Mostly, MCM-41 was irregularly shaped and sized. However, it is obvious that regular particle morphology would make it more useful as an advanced material in many different fields such as adsorbents, catalysts and stationary phases in chromatography [2], [3], [4].

Recently, mesoporous materials with controlled particle morphology have begun to catch the attention of many researchers in membrane separation science, especially in pervaporation (PV) separation. PV [5] is an energy-saving separation technology because it has lower energy demands, causes less environmental pollution and, most importantly, has no vapor–liquid equilibrium limitation. During the designation of PV membrane, many microporous molecular sieves [6], [7] (ZSM-5, silitelite-1, TS-1, and so on) have been commonly used as inorganic porous fillers in order to restrict membrane plasticization and improve membrane stability [8]. However, in some cases, such as removing dimethylcarbonate (DMC) from a dimethylcarbonate/methanol (DMC/MeOH) azeotropic mixture, microporous molecular sieves couldn't be used because their pore sizes are too small for DMC permeation. So mesoporous molecular sieves with controlled particle morphology are in great demand.

Unfortunately, ordered mesoporous MCM-41 always exhibits strong hydrophilic properties. In order to obtain good adhesion to hydrophobic PDMS polymer matrix [9], these materials need a tuning of surface properties from hydrophilicity to hydrophobicity [10]. So far, there are only a few reports on such MCM-41 sphere modification [11], [12] for the purpose of chromatographic [13] and catalytic applications [14]. However, there is still no research on modification of MCM-41 spheres aiming for composite membrane preparation in pervaporation.

In the present work, MCM-41 mesoporous silica spheres were synthesized using modified Stöber method [15] and were modified by three kinds of silane coupling agents with different alkyl chain lengths. The structure, morphology and surface property of calcined and modified MCM-41 silica spheres were carefully examined. Furthermore, modified MCM-41/PDMS filled membranes were prepared as a new pervaporation membrane material for removing DMC from DMC/methanol mixtures. The effect of the different kinds of modified MCM-41 silica and loadings on membrane PV performance was systematically investigated.

Section snippets

Materials

Polydimethylsiloxane (PDMS, RTV 615) was supplied by General Electric Silicones, USA. Chlorotrimethylsilane (CTMS, 98%), octyltrichlorosilane (OTCS, 97%), octadecyltrichlorosilane (ODTCS, 96%) and cetyltrimethylammonium bromide (C₁₆TAB, 99.9%) were received from Alfa Aesar, USA. Methanol, ethanol, pyridine, ammonia water (NH₃·H₂O, 25%) and heptane were purchased from Beijing Chemical Reagents Corporation, China. DMC was obtained from Tangshan Chaoyang Chemical Reagents Corporation, China.

X-ray diffraction (XRD)

Fig. 2 depicts the XRD pattern of calcined and modified MCM-41 spheres. For calcined MCM-41 silica, three Bragg peaks can be typically observed, a strong (100) as well as the (110) and (200) reflections of much lower intensity, suggesting the highly ordered hexagonal pore structure in the sample [16]. Modified MCM-41 exhibits a similar XRD pattern which clearly indicates that the basic framework ordering of the mesopores remains unchanged after surface silylation [17]. Compared with calcined

Conclusions

Mesoporous MCM-41 silica spheres were prepared via modified Stöber method, modified with three kinds of chlorosilanes (CTMS, OTCS and ODTCS) and examined by XRD, SEM, TEM, FT-IR, TGA, ²⁹Si CP/MAS NMR and nitrogen adsorption–desorption. The results clearly indicated that mesoporous MCM-41 silica spheres with ordered mesoporous structure, spherical morphology and hydrophobic surface layer were successfully obtained. The calcined and modified mesoporous MCM-41 spheres were for the first time

Acknowledgments

The authors greatly appreciate the financial support of the Major State Basic Research Program of China (2009CB623404), and the National Natural Science Foundation of China (2012AA03A607, 21176135).

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Preparation of modified mesoporous MCM-41 silica spheres and its application in pervaporation

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials

X-ray diffraction (XRD)

Conclusions

Acknowledgments

Journal of Membrane Science

Chemical Engineering Journal

Journal of Membrane Science

Microporous and Mesoporous Materials

Journal of Colloid and Interface Science

Microporous Materials

Desalination

Desalination

Journal of Membrane Science

Nature

Chemistry of Materials

Journal of Materials Chemistry

Chemistry of Materials

Membrane Handbook

Journal of Applied Polymer Science

Advanced Materials

The Journal of Physical Chemistry. B