Templated growth of mesoporous aluminum phosphate tubules using protein molecules of tobacco

Abstract

Template-based approaches involving the co-operative organization of organic-inorganic assemblies as intermediates are emerging as a promising conceptual basis for future developments of porous inorganic materials. This field has been fuelled by new synthetic strategies such as “supramolecular templating” that have enabled precise engineering of pore size, shape and connectivity on the mesoscopic scale [1]. Randomly oriented layers of AlPO4 were synthesized and used as chemical sensors and low dielectric constant materials [2] earlier, but now, attention is being directed towards the formation of highly oriented films of metallic phosphates [3]. Development of AlPO4 based materials, in particular, has extended the compositional and structural diversity of the molecular sieves. Anisotropy induced by biomolecules leads to orientation and many exotic properties associated with the hierarchical structures and make them suitable for a range of applications including catalysis, ion-exchange separation, nuclear medicine and optics [4]. Though the synthetic templates namely latex fibers, polyurethane foams, starch gels, carbon nanotubes and organic molecules with long chains are being routinely employed for the synthesis of hierarchical inorganic frameworks [5], mineralization of biomolecular templates like tobacco mosaic virus (TMV) is a relatively new concept [6]. It leads to the formation of porous structures at nanolength scales that are strictly controlled by the presence of protein superstructures. Moreover, these biomolecular templates offer unusual symmetry and mesoscale ordering in the porous structures. Abundance and stability of the protein molecules present in tobacco leaves and their tendency to undergo self assembly has motivated us to use it directly as templates to synthesize self supporting hybrid films at liquid-air interface.