Investigations into carbon nitrides and carbon nitride derivatives

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.