One of the interests in our group is the application of biopolymers to ‘sol-gel’ methods. Sol-gel chemistry is a useful alternative to more traditional solid-state methods since the solution-state precursor ensures a completely homogeneous mixture of metal components. This can be very important, particularly in the synthesis of ternary or quaternary phases. Sol-gel routes also generally require much lower synthesis temperatures.
One of the first applications of biopolymers to sol-gel chemistry came from Dr Simon Hall at the University of Bristol, who prepared nanowires of YBCO superconductors using chitosan from crustacean shells. Since then, biopolymers have been shown to offer remarkable control over growth and morphology of crystals in diverse ceramic materials. This is due to the strong metal-binding exhibited by biopolymers and consequently their ability to influence nucleation of crystalline phases.
A particular interest of ours is the synthesis of composite materials from biopolymers. We focus mainly on catalyst/support combinations for various applications such as fuel-cell electrocatalysts or methanol reforming. We are also investigating scaling up of the biopolymer sol-gel synthesis as a potentially sustainable route to functional materials.
Remarkably, we’ve shown that it’s possible to form 3-phase composites (e.g. metal carbide + metal oxide + carbon) from a single, homogeneous mixture of metal salts with biopolymers. Metal carbides and nitrides make extremely useful catalysts for a wide range of processes but are relatively difficult to synthesize with a high surface area. It is also particularly difficult to synthesize composites containing nitrides and carbides. Composite structures are valuable in many catalytic systems as a means of dispersing and maximizing the active sites or preventing sintering of the active phase. People have previously supported carbides and nitrides on oxides but normally by multistep methods and so the single-step sol-gel route is really exciting.