Physico-Chemical nanomaterials science

Enhancing visible light photocatalytic activity of g-C3N4 based nanostructures by the molten salt approach
Vitaliy Shvalagin, Nataliia Andriushyna, Yulia Siroshenko, Anna Korzhak, Stepan Kuchmiy
Photochemistry department, L.V. Pisarzhevskii Institute of Physical Chemistry of the NAS of Ukraine. Prospect Nauki, 31, Kyiv, Ukraine
E-mail: vitaliy.shvalagin@gmail.com

It is shown that additional heat treatment in the melt of LiCl + KCl salts of graphite carbon nitride (g-C3N4) [1], obtained by calcining melamine in the presence of air, leads to a significant increase in photocatalytic activity of metal-containing nanocomposites on its basis in the reaction of molecular hydrogen evolution from aqueous solutions of electron-donor substrates under the action of visible light, the influence of a number of factors on such process is established. Under optimal conditions, the photocatalytic production rate of H2 with the participation of the nanocomposite based on the thermally treated g-C3N4 and the palladium nanoparticles is almost 50 times higher than the nanocomposite based on original g-C3N4, and the quantum yield of hydrogen evolution reaches 25% when irradiated with light at   400 nm.
It is established that in contrast to the initial carbon nitride, g-C3N4 obtained by treatment in salt melt exhibits high photocatalytic activity in the processes of gas-phase partial oxidation of alcohols with air to the corresponding aldehydes or ketones under the action of visible light. Processes run with high selectivity for the target product. In some cases, the photocatalytic reaction can be controlled to lead to complete oxidation of both the initial substrate and the corresponding aldehyde.
The significant influence of the additional post-synthetic heat treatment of g-C3N4 in the melt salts on its photocatalytic properties may be due to an increase in light absorption in the visible spectral range and an improvement in the crystallinity of the samples, which leads to a reduction in the number of structural defects that may act as recombination centers for photogenerated charges. The additional heat treatment can also lead to a partial exfoliation of output carbon nitride, which contributes to the separation of photogenerated charges in such nanostructures and, accordingly, the growth of their photocatalytic activity.

1.	Lin L., Ou H., Zhang Y., Wang X. Tri-s-triazine-Based Crystalline Graphitic Carbon Nitrides for Highly Efficient Hydrogen Evolution Photocatalysis // ACS Catal.–2016.-6.-P. 3921.