Soft-templating approach for the synthesis of high surface area and superparamagnetic mesoporous iron oxide materials Atanu Mitra a,b,1 , Carlos Vázquez-Vázquez b , M. Arturo López-Quintela b , Bidyut K. Paul c , Asim Bhaumik a, * a Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India b Departamento de Química Física, Facultade de Química, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain c Surface and Colloid Science Group, Geological Studies Unit, Indian Statistical Institute, 203, B.T. Road, Kolkata 700108, India article info Article history: Received 17 September 2009 Received in revised form 28 December 2009 Accepted 25 January 2010 Available online 1 February 2010 Keywords: Iron oxide Mesoporous material Nanostructure Superparamagnetic Surfactant-templating abstract Designing pores of nanoscale dimension into a magnetic material can engineer the surface nanostructure, resulting in a mesoporous material with unique physicochemical properties. Here we report a simple soft-templating approach for the synthesis of new mesoporous iron oxide materials having semi-crystal- line pore wall by using an anionic surfactant sodiumdodecylsulfate as the structure-directing agent (SDA) or template at low temperature. On removal of the SDA molecules through solvent extraction the mes- ostructure is preserved and the material shows considerably high BET surface area and type IV isotherms corresponding to the mesopores. This mesoporous Fe 2 O 3 material showed superparamagnetic behavior and hence this template-assisted synthesis of mesoporous Fe 2 O 3 can find its potential utility in designing magnetic nanostructured materials. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction The supramolecular templating approach for the synthesis of mesoporous materials has been extensively practiced since the first report of the synthesis of ordered mesoporous silica, M41S by the Mobil researchers in 1992 [1]. Since then mesoporous mate- rials have attracted widespread attention for adsorption, catalysis and applications as hard templates for the synthesis of a wide range of mesoporous materials. A large number of porous metal oxides [2–12] has been synthesized, which possesses high surface area and tunable pore diameters vis-a-vis their nonporous coun- terparts. Nonporous iron oxides are one of the most intensively studied magnetic materials and have been widely used in many technological applications such as data recording and storage [13], various biomedical applications [14], catalysis [15], recharge- able lithium batteries [16], etc. The success of the nanostructured materials in many of the interesting applications like adsorption, catalysis [15], solid ion batteries [16], sensors [17], etc. depends on large surface area and uniform pore size distribution. Thus the synthesis of mesoporous iron oxide material with large surface area is of great importance. In this context it is pertinent to mention that the synthesis of mes- oporous composites having magnetic elements embedded in the nanochannels of the pores or in the porous framework is very chal- lenging. Tolbert et al. [18] have reported the synthesis and magnetic properties of the ordered, lamellar, iron oxide/surfactant compos- ites. However, to the best of our knowledge so far there are only very few reports in literature on successful synthesis of template-free mesoporous iron oxide having large surface areas [19–25]. Nano- crystalline iron oxide aerogels [19] have been prepared under post-synthesis method employing solid mesoporous silica as tem- plate and they exhibit BET surface area ca. 140 m 2 g 1 . Ordered Mes- oporous Fe 3 O 4 and c-Fe 2 O 3 synthesized by using post-synthesis hard templating route followed by oxidation–reduction processes possess further reduced surface area [20]. However, major draw- backs associated with this hard templating method are the addi- tional steps needed to prepare the silica backbones and the sacrificial use of the silica host, making this post-synthesis method quite elaborate and high-cost. Hence, a soft-templating approach via supramolecular assembly of surfactant towards the synthesis of ordered mesoporous iron oxide is highly desirable. In this context, Srivastava et al. [22] reported an amorphous mesoporous iron oxide with surface areas of up to 270 m 2 g 1 using a cationic alkylammo- nium surfactant. Jiao and Bruce [23] prepared two-dimensional and three-dimensional mesoporous iron oxide using decylamine as the template, which possess considerably high surface area. How- ever, the nature of the N 2 sorption isotherms, which is considered as most conclusive evidence for the presence of mesoporosity (type IV isotherm), could not be observed there. Herein, we report the synthesis of mesoporous iron oxide hav- ing high surface area using a simple one-step self-assembly of an 1387-1811/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2010.01.017 * Corresponding author. Fax: +91 33 2473 2805. E-mail address: msab@iacs.res.in (A. Bhaumik). 1 Present address: Department of Chemistry, Sree Chaityanya Collage, Habra, North 24 Parganas, West Bengal, India. Microporous and Mesoporous Materials 131 (2010) 373–377 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso