Cite this: RSC Advances, 2013, 3, 4207 Received 7th November 2012, Accepted 30th January 2013 Synthesis of mesoporous c-alumina nanorods using a double surfactant system by reverse microemulsion process3 DOI: 10.1039/c3ra22793f www.rsc.org/advances Sourav Ghosh and Milan Kanti Naskar* Mesoporous c-Al 2 O 3 nanorods were synthesized by a reverse microemulsion (water in oil, w/o) technique using an aqueous- based alumina sol, the anionic surfactant AOT (sodium bis(2- ethylhexyl sulfosuccinate)), the non-ionic co-surfactant Span 80 (sorbitan monooleate) and cyclohexane as an organic solvent. The c-Al 2 O 3 phase was obtained at 500 uC with a slight transformation to h-Al 2 O 3 at 700 uC–900 uC, while a mixed phase of c-, h- and a-Al 2 O 3 resulted at 1000 uC. The BET surface area, pore volume and average pore size of the 500 uC-treated sample was found to be 59.3 m 2 g 21 , 0.040 cm 3 g 21 and 2.65 nm respectively, which changed slightly in the temperature range of 500 uC–900 uC. The mesoporous c-alumina nanorods were formed through rod-like micelle formation in the presence of surfactant/co-surfactant in organic solvent, which was illustrated by a proposed mechanism. 1 Introduction The importance of alumina is well-known for its applications as catalysts, catalyst supports, adsorbents, membranes, ceramics and heat insulating materials due to its unique physico-chemical properties. The performance of alumina as adsorbents, catalysts and catalyst supports is affected by its textural and morphological characteristics. Therefore, the synthesis of nanostructured alu- mina with a tailored texture and morphology has attracted a great deal of attention in recent years. The synthesis of mesoporous alumina (MA) has been reported by different methods, like sol– gel, 1 evaporation-induced self-assembly (EISA), 2,3 using mesopor- ous carbon as templates, 4 etc. There are many methods for preparing MA with different morphologies, such as nanorods, 5 nanofibres, 3 petal-like flakes 6 etc. Recently Liu et al. 7 prepared nano-alumina with controllable morphologies. The formation of tubular hollow alumina nanofibres was reported by Lin et al. 8 Cai et al. 9 have shown the effect of anions and structure-directing agents on the synthesis of nanorod-like mesoporous c-Al 2 O 3 . Ma et al. 10 prepared boehmite and c-Al 2 O 3 nanorods by a solvothermal process. Very recently, Yu et al. 11 have synthesized c-Al 2 O 3 nanorods by sol–gel and supercritical technology. In this paper, we present a facile synthesis of mesoporous c-Al 2 O 3 nanorods following a reverse microemulsion (water in oil, w/o) technique. In this process, we used AOT (sodium bis(2- ethylhexyl sulfosuccinate)) as an anionic surfactant, Span 80 (sorbitan monooleate) as a non-ionic co-surfactant, cyclohexane as the organic (oil, o) phase and an alumina sol as the aqueous (water, w) phase in the reverse (w/o) microemulsion. Reverse microemulsions are thermodynamically stable isotropic media with a continuous oil phase and discrete water droplets which are compartmentalized by a surfactant monolayer into nanometer- sized liquid entities. The present method of preparing alumina nanorods by a reverse microemulsion is advantageous in terms of a room temperature process, low processing time and tailoring particle morphology. 2 Experimental Reagent grade aluminum nitrate (Al(NO 3 ) 3 ?9H 2 O), an ammonia solution, cyclohexane, triethylamine (TEA) and acetone were purchased from Merck, India and the surfactants AOT and Span 80, purchased from Sigma Aldrich, Germany, were used as starting chemicals without further purification. In a typical experiment, 6.8 g of AOT and 1 g of Span 80 were mixed into 50 mL of cyclohexane with stirring for 10 min followed by the addition of 12.5 mL of an alumina sol (prepared by dissolving 95 g of aluminum nitrate in 250 mL of water followed by controlled addition of ammonia with vigorous stirring at y70 uC to obtain a viscous sol (viscosity 20 mPa s) of pH 4). The mixture was stirred continuously for another 20 min to obtain an emulsion. Under stirring conditions, 5 mL of TEA was added dropwise into the emulsion to obtain gel particles. This was then filtered and washed with acetone three times followed by drying at 100 uC for 4–6 h. The dried powders were calcined at 500 uC for 1–4 h with a heating rate of 1 uC min 21 and at 700 uC, 900 uC, 1000 uC with a heating rate of 1 uC min 21 up to 500 uC/4 h followed by a heating rate of 5 uC min 21 up to those temperatures with a 1 h dwell time each. Sol–Gel Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata 700 032, India. E-mail: milan@cgcri.res.in; Fax: +91 33 2473 0957; Tel: +91 33 2473 3496 (Ext. 3516) 3 Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra22793f RSC Advances COMMUNICATION This journal is ß The Royal Society of Chemistry 2013 RSC Adv., 2013, 3, 4207–4211 | 4207 Published on 31 January 2013. Downloaded by Indian Institute of Science Education & Research Kolkata on 13/12/2013 09:16:15. View Article Online View Journal | View Issue