Crystalline Carbon Nitrides Characterisation, Intercalation and Exfoliation

Abstract

In recent years there has been significant interest in, and research into, carbon nitride materials for use in applications such as photocatalysis. The most commonly described C/N materials are referred to as graphitic carbon nitride (gCN), though due to the layered amorphous nature structural characterisation is difficult. Polytriazine imide (PTI) is a crystalline layered carbon nitride that is less explored within the literature compared to gCN due to its more difficult synthetic procedure. In this thesis the synthesis, characterisation, intercalation chemistry and exfoliation of PTI is explored. The synthesis of a related material, triazine based graphitic carbon nitride (TGCN) is explored and the product characterised in detail. PTI refers to the carbon, nitrogen and hydrogen framework (C6N9H3) within which different ionic intercalants can be accommodated; then give rise to several different crystalline materials with the same underlying carbon nitride backbone. The structure of these crystalline, layered PTI was synthesised by reversibly removing and replacing the intercalated ions without affecting the carbon nitride structure. The structures of these new materials was investigated and how changing the intercalant can be used to tune the structures and properties. This methodology may facilitate the fine-tuning and optimisation of carbon nitrides for a number of applications. I have also explored the exfoliation of the layered PTI materials. A number of methods have been used including intercalation and ultrasonication. Remarkably, however I found that the PTI gently, and even spontaneously dissolves to form solutions in highly polar organic solvents and even in water. This process takes place without the need for mechanical mixing, sonication or centrifugation. The resultant separated nanosheets solutions are characterised indepth. Few layer stacks of undamaged crystallites are observed. The photoluminescence of the nanosheets have been found to depend on the number of stacked layers, presenting exciting opportunities for optoelectronic devices.