Ladva, Satyam; (2019) The Synthesis and Characterisation of Carbon-Nitrogen Related Organic Materials for Photocatalyst and Other Applications. Doctoral thesis (Eng.D), UCL (University College London).

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Abstract

The aim of this project is to design, synthesise and characterise s-triazine based carbon nitride materials that show potential for use as fully renewable, organic photocatalyst materials for the purpose of generating hydrogen fuel through water splitting. Whilst existing materials do exist that can perform this technique, the inorganic constituents of these existing materials prevent them from being fully renewable and, in most situations, makes them difficult to synthesise - especially at room temperatures and ambient pressures. The method used in this project to improve upon existing organic photocatalyst materials was to develop more efficient techniques to create covalent organic structures that retain the structural benefits of graphene whilst including electrical storage properties recorded for nitrogen-doped graphene, in the form of an s-triazine structure. This was achieved by first focussing on improving the existing most efficient s-triazine based carbon nitride synthesis approach, polycondensation Ionothermal synthesis, by improving its output efficiency and then later adapting the technique so it could be implemented into existing industrial applications more effectively. Improvement of the existing technique was achieved through the use of a dynamic vacuum, with the graphitic carbon nitride material confirmed through XPS, XRD, FTIR and other characterisation techniques, the adaptation of the technique to make it more industrially useful was achieved through incremental development of the Ionothermal synthesis approach. This transition resulted in the creation of an ALD-type approach, which resulted in carbon nitride films (characterised by XPS, XRD, ATR-IR, Raman spectroscopy and various microscopy techniques) conformally coating onto a variety of substrates at room temperature. Whilst the synthesis reaction mechanism was determined to be different to those found in existing literature, through gas-phase mass spectrometry, various experimental parameters ranging from: synthesis temperature, ramp rate of temperature, ion gun depth profiling and others were determined to allow for precise control of the carbon nitride film formed with regards to its physical and chemical properties. As a consequence of this control, not only did the carbon nitride films show promise as potential photocatalyst materials, but they also showed promise as anti-microbial surfaces and could be used in the development of an XAES based D-parameter technique to determine the content of sp2 and sp3 nitrogen in a pure carbon nitride based material, composed of only sp2 and sp3 carbon and nitrogen. Finally, the usefulness of the s-triazine component for photocatalyst applications was also presented through the synthesis and characterisation of a phenolic triazine framework which is structurally like graphitic carbon nitride but contains a phenolic group that allows for a much more tuneable band gap. From the results of this project, evidence of the use, or potential use, of pure organic materials has been shown for several applications in addition to photocatalytic water splitting. However, unlike existing synthesis techniques, the vapour deposition technique developed in this project has demonstrated the potential of the organic materials to coat conformally onto a variety of substrates thus allowing for easy synthesis of carbon nitride based hybrid materials - thus compensating for the slightly lower efficiencies measured by the pure organic materials in comparison to purely inorganic structures.

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