Page 84 - Visions of the Future Chemistry and Life Science

Chemistry on the inside 73

work will reveal advanced catalytic systems, possibly containing more
than one type of active site, and the control over pore dimensions will
allow an ever-increasing level of control over selectivity towards the
desired product. The ability to incorporate polarity-modifying groups will
also play a major role in transport processes, of great importance in both
catalysis and membrane processes.
Many other opportunities exist due to the enormous flexibility of the
preparative method, and the ability to incorporate many different species.
Very recently, a great deal of work has been published concerning methods
of producing these materials with specific physical forms, such as spheres,
discs and fibres. Such possibilities will pave the way to new application
areas such as molecular wires, where the silica fibre acts as an insulator,
and the inside of the pore is filled with a metal or indeed a conducting
polymer, such that nanoscale wires and electronic devices can be fabri-
cated. Initial work on the production of highly porous electrodes has
already been successfully carried out, and the extension to uni-directional
bundles of wires will no doubt soon follow.
The ability to produce threads, discs and spheres of defined size and
structure will be of great importance when the very promising initial
results from catalytic studies are applied on a larger scale. Processes using
heterogeneous catalysts require the ability to control particle size and
shape in order to ensure good mixing of all the reaction components, and
separations after reaction.
A further application of this technology will certainly be the fabrica-
tion of membranes of these materials. Membrane reactors have shown
great utility in many systems, where one component of a reaction mixture
can be separated by permeation through a membrane, thus driving a reac-
tion forwards, by continuous separation. Such continuous processes can
themselves save a great deal of waste.
Looking further ahead, the pores in these materials could be consid-
ered as analogous to ion channels in cell walls. If a hollow sphere of MTS
could be fabricated with e.g. an enzyme (or other cell component) inside,
one could imagine this as being an ‘inorganic cell’. The encapsulation of
the enzyme inside the cell could then possibly be used to protect the
enzyme from harsh conditions outside the cell, while allowing reaction
components to diffuse in, react, and diffuse out again. Already, some effort
is being expended on silica/biological composites, with significant
advances being made. Given the enormous strides made since the