Triazoles: A New Class of Precursors for the Synthesis
of Negatively Charged Carbon Nitride Derivatives
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Abstract
Carbon nitride polymers were prepared
for the first time by the
pyrolysis of 3,5-disubstituted-1,2,4-triazole derivatives, namely,
3,5-diamino-1,2,4-triazole [<b>1</b>] and 3-amino-1,2,4-triazole-5-thiol
[<b>2</b>], in bulk as well as in LiCl/KCl salt melts. The reaction
of [<b>1</b>] and [<b>2</b>] in bulk yields condensed
heptazine-based polymers, while in LiCl/KCl eutectics it leads to
the formation of well-defined potassium poly(heptazine imides), according
to the results of <sup>13</sup>C NMR and XPS investigations, whose
formation resembles that of emeraldine salts of polyaniline. The density
functional calculations supported the structural model suggested for
potassium poly(heptazine imide) polymer. Owing to the specific reaction
path, the products obtained from triazoles therefore show electronic
properties rather different to known carbon nitrides, such as band
gap and conduction and valence bands positions. With the degree of
crystallinity of the reference materials, triazole-derived carbon
nitrides are characterized by almost complete absence of steady photoluminescence,
since charge separation and delocalization upon excitation seem to
be improved. As a consequence, photocatalysts prepared from [<b>2</b>] outperform classical carbon nitrides in a model dye degradation
reaction and mesoporous graphitic carbon nitride in hydrogen evolution
reaction under visible light irradiation. On its turn, [<b>1</b>] can be conveniently used as a comonomer in order to prepare carbon
nitrides with improved visible light absorption