Spermine, spermidine and their analogues generate tailored silicas

Biosilicifying organisms such as diatoms, sponges and higher plants deposit ornate "glassy" siliceous materials with well defined properties such as particle size and porosity at precisely controlled growth rates. Here we present the in vitro synthesis and characterisation of "glassy" silica with tailored properties by using naturally occurring amines - spermidine and spermine - and their analogues. These additives were found to regulate the growth rates, particle sizes, maturation, surface areas, porosities and morphologies of the siliceous materials prepared. In particular, the combination of unique catalytic effects and aggregation behaviours that are dependent on or related to chain length, intramolecular N-N spacing and C : N ratio of the additives was found to be responsible for controlling materials properties. Mechanisms regulating the generation of silicas showing a range of material characteristics are proposed.