Chemical reactions of graphitic carbon nitride films with glass surfaces and their impact on photocatalytic activity

Abstract

Thin films of graphitic carbon nitride (g-CN), a visible-light-driven photocatalyst, have recently attracted interest in applying the material to photoelectrochemical cells for water splitting and high-throughput photocatalysis. In typical syntheses,...

Insights into chemical reactions of graphitic carbon nitride with alkali halides

“…In addition, the reaction scheme for the deprotonation of NH groups that bridges heptazine monomers is also elusive. As previously shown [25], a strong base removed protons from those molecular parts. Since the reaction between g-CN and alkali halides does not appear to involve a strong base at first glance, its mechanism should be unveiled.…”

“…However, incorporating NaCl causes new absorption bands at 994, 1147, and 2179 cm −1 , labelled with asterisks. This spectral feature is very similar to the IR spectrum of the g-CN film formed on soda glasses [25]. The vibrational absorptions at 994 and 1147 cm −1 are assigned to the symmetric and asymmetric modes of NC 2 groups that bridge melem monomers and are bonded to the alkali cations [27], respectively (see the inset in the left panel of figure 2(a)).…”

“…Again, as in NaCl, the vibrational absorptions originating from NC 2 groups bonded to the alkali cations and cyanamide groups emerge (bands indicated by asterisks in figure 5). The introduction of the cyanamide groups into melon causes a type-II heterojunction, which facilitates free-charge separation, as verified by time-resolved photoluminescence spectroscopy [25]. There should be common underlying mechanisms of the reaction with alkali halides, which we will address in what follows.…”

“…Gaussian fitting resolved the components at 2150 and 2182 cm −1 (the inset in the right panel of figure 2(a)). The two peaks originate from the stretching mode of cyanamide groups bonded to Na + and H + , respectively [25]. These bands grow with the increasing NaCl fraction, but their absorbances become almost constant at x > 10 (figure 2(c)).…”

“…The water filtrate of the calcined melon:alkali halide mixture is indeed alkaline with a pH of 9.65-11.10, which could support the presence of Na 2 CO 3 and/or NaOH. Inferred from the fact that the reactions of melem or melon with NaOH cause cyanamide moiety [25], the resultant base will produce cyanamides from heptazine, and the molecules will modify melon.…”