Thermally-induced desulfurization and conversion of guanidine thiocyanate into graphitic carbon nitride catalysts for hydrogen photosynthesis
A cheap and easily-available organosulfur compound, guanidine thiocyanate, has been used to synthesize graphitic carbon nitride (g-C3N4) by a thermally-induced desulfurization and polymerization of the precursor. Photocatalytic activity experiments demonstrated that the g-C3N4 synthesized from guanidine thiocyanate exhibited a much higher H2 evolution rate than the reference sample prepared from dicyanamide. Further improvement in the activity was achieved by optimization of the condensation temperature. Based on X-ray photoelectron spectroscopy analysis, the samples synthesized at a high temperature of 700 °C feature a high crystallinity and a low density of surface defects, with an enhanced optical absorbance extending to the visible light region. As a result, the sample prepared at 700 °C has been found to be 7 times more reactive towards photocatalytic hydrogen evolution than the sample polymerized at the normal temperature of 550 °C. Other guanidine halides have also been applied to synthesize g-C3N4 materials, and the structure and activity of the resultant g-C3N4 were compared to the carbon nitride polymer from guanidine thiocyanate.