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Wang, Hongji (2013): Investigations into carbon nitrides and carbon nitride derivatives. Dissertation, LMU München: Fakultät für Chemie und Pharmazie



Carbon nitrides and carbon nitride derivatives are promising photocatalysts. The main focus of this thesis is the synthesis and characterization of various carbon nitrides (incompletely condensed melon, carbon nitride doped cesium titanate, ultra-long calcined melon, and OH-melem). Those carbon nitrides were then tested with regard to their photocatalytic properties. In the first part of chapter 3 of this thesis, we focus on a material called ‘‘melem oligomer’’. Two different synthesis routes were applied (open system and half open system) and the composition and structure of this material was studied. Melem with two different crystalline structures and some amorphous residues were found in the product. We also tested the photocatalytic activity of melem oligomer and confirmed hydrogen production from water with a relatively low rate of 2 μmol g-1 h-1. In the second part of chapter 3, we synthesized ultra-long calcined melamine which may have a morphology similar to the ‘‘g-C3N4 nanosheets’’. We analyzed both the composition and structure and investigated the efficiency of the presumed g-C3N4 nanosheets for hydrogen production from water. Ultra-long calcined melamine showed the best photoactivity which is twice that of melon at 490 °C. This is most likely due to the interesting morphology and high surface area. In chapter 4, melem oligomer was doped with cesium titanate in situ. Different calcination times were applied and various characterization techniques were used to investigate the composition, structure and morphology of the obtained materials. The efficiency of this hybrid photocatalyst for hydrogen production did not show higher photoactivity than the pure carbon nitrides except in the case of 16 h calcination which was the optimum calcination time overall. In chapter 5, OH-melem with a composition close to 2-oxo-6,10-diamino-s-heptazine, which could be a precursor of oxygen-doped g-C3N4, was synthesized and characterized by various techniques. Crystallinity is rather low in this oxygen containing species. NMR spectra differ from melem or cyameluric acid and XPS results confirm the presence of C=O groups. Overall, different carbon nitrides and carbon nitride derivatives were synthesized and chemically investigated to gain further knowledge on their synthesis, chemical properties and their resulting application as photocatalysts.