Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures

The exceptional electronic, magnetic, optical and catalytic properties demonstrated by many ceramic materials when confined to the nanoscale are well established. However, the synthesis of multicomponent metal oxide nanowires and nanoparticles is notoriously problematic due to the difficulty of controlling homogeneity and achieving the correct stoichiometry. In this paper, we demonstrate a selective route to nanowires or nanoparticles of a quaternary metal oxide product using sodium or ammonium alginate respectively. By pre-organizing metal cations within an alginate gel the nucleation and growth of precursor crystalline phases can be constrained to the nanoscale. On further calcination the alginate decomposition products prevent sintering of these precursor nanoparticles prior to conversion to the final product. The cooperative effect of polymer microstructure and decomposition products allows an exceptional level of control over nucleation, growth and transport of the intermediate phases and subsequently on the particle size and morphology of the final product.