Synthesis of mesoporous silica by sol-gel mineralisation of cellulose nanorod nematic suspensions

Mesoporous silica was synthesised by sol-gel mineralisation using nematic liquid crystalline templates consisting of partially ordered suspensions of cellulose rod-like nanocrystals, ca. 145 x 13 nm in size. The nanorods were prepared by acid hydrolysis of cellulose powder and concentrated droplets evaporated onto glass slides to form nematic liquid crystals. Addition of an aqueous alkaline solution of pre-hydrolysed tetramethoxysilane to the droplets resulted in a birefringent cellulose-silica composite that was subsequently calcined at 400 degreesC for 2 h. Removal of the cellulose nanorod template produced a birefringent silica replica that exhibited patterned mesoporosity due to the presence of co-aligned cylindrical pores, approximately 15 nm in diameter and 10 nm in wall thickness. TEM studies suggest that a chiral imprint of the helically ordered cellulose nanorods was imposed on the silica structure, although further studies are required to confirm these preliminary observations. As cellulose nanorods can be prepared from renewable, inexpensive sources, they offer a cost-effective, environmentally benign route to the template-directed synthesis of mesoporous materials.