Mixed matrix membranes comprising of Matrimid and –SO 3 H functionalized mesoporous MCM-41 for gas separation Asim Laeeq Khan b , Chalida Klaysom a , Amit Gahlaut a , Asad Ullah Khan b , Ivo F.J. Vankelecom a,n a Centre for Surface Chemistry and Catalysis, Faculty of Bioengineering Sciences, KU Leuven, Kasteelpark Arenberg 23, PO Box 2461, 3001 Leuven, Belgium b Department of Chemical Engineering, COMSATS Institute of Information Technology, Lahore, Pakistan article info Article history: Received 4 March 2013 Received in revised form 2 July 2013 Accepted 5 July 2013 Available online 12 July 2013 Keywords: Mixed matrix membranes MCM-41 Gas separation abstract Ordered mesoporous silica spheres (MCM-41) were used as fillers in polyimide (Matrimid) based mixed- matrix membranes (MMMs). The filler particles were functionalized with sulfonic acid (–SO 3 H) groups to increase the separation performance of the membranes by increasing the CO 2 solubility. The fast diffusion of gases through the mesoporous materials, accompanied by this increased interaction with CO 2 , resulted in the simultaneous increase of gas permeability and selectivity. The functionalized membranes showed up to 31% increase in CO 2 permeability and 14% increase in CO 2 /CH 4 selectivity. In order to study the stability of these newly developed MMMs, they were tested at different operating conditions (temperatures, mixed-gas feeds and CO 2 feed concentration). & 2013 Elsevier B.V. All rights reserved. 1. Introduction The upper bound curve reported by Robeson suggests that the current polymeric materials have reached a permeability–selectiv- ity tradeoff [1–3]. This demands the discovery of new materials and procedures for the synthesis of novel membranes with improved performance. Inorganic membranes have shown the potential to surpass the upper-bound through their high flux and molecular sieving properties. However, their commercial applica- tion is limited due to their brittleness, high cost and insufficient film-forming properties [4]. One of the emerging strategies to enhance the performance of membrane materials involves the fabrication of mixed matrix membranes (MMMs) by dispersing inorganic filler particles in polymer matrices. These membranes combine the processability and low cost of polymers with the superior permselective properties of the fillers [5–10]. Depending on the type and loading of the fillers, MMMs could also signifi- cantly reduce the cost of membranes in comparison to their expensive inorganic membranes. However, the synthesis of MMMs is accompanied by several challenges [11,12]. One of the most important criterions is to achieve good adhesion between the inorganic filler and the polymer matrix. Generally, glassy polymers such as polyimide possess a good separation performance [13,14]. However, the use of such poly- mers for the fabrication of MMMs has proven to be difficult due to their poor interfacial contact with the filler as a consequence of the rigidity of the polymer chains. Several attempts have been made to prepare defect-free MMMs comprising of glassy polymers and fillers [15–19]. Yong et al. added 2,4,6-triaminopyrimidine (TAP) to the polymer-filler dope solution in order to enhance the interaction between zeolite fillers and Matrimid polyimide via the formation of hydrogen bonds [15]. The resultant showed improved interfacial contact via formation of hydrogen bonding and the membranes exhibited enhanced permselective properties. Maha- jan et al. approached this by annealing the membrane close to the glass transition temperature of the polymer to increase tempora- rily the flexibility of the polymer chains [11]. In our previous study, covalent linkage was introduced between zeolite 3A particles and acrylate modified polysulfone, resulting in the formation of defect- free membranes [5]. Vankelecom et al. attempted to improve the compatibility by silylation of the external zeolite surface. The membrane showed better performance under the optimized con- ditions for the grafting of silylating agent [16]. The modification of the external filler surface by the formation of nano-whisker structures have also led to significant improvement in the success- ful formation of MMMs. Bae et al. and Lydon et al. used different techniques to synthesize surface nanostructures [17–19]. The membranes showed improved dispersion and better polymer- filler contact. Among the various types of inorganic fillers used for MMMs, mesoporous silica materials have proven to be promising fillers for gas separation membranes, mainly due to their very high porosity which favors fast gas diffusion [20–22]. In this work, ordered mesoporous silica spheres (MCM-41) were chosen as fillers due to Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2013.07.011 n Corresponding author. Tel.:+32 16 321594. E-mail address: ivo.vankelecom@biw.kuleuven.be (I.F.J. Vankelecom). Journal of Membrane Science 447 (2013) 73–79