Hydrogen adsorption by g-C3N4 and graphene oxide nanosheets

The adsorption behavior of hydrogen for synthesized graphitic carbon nitride (g-C3N4) and graphene oxide nanosheets was compared. The structure of the prepared g-C3N4 and graphene oxide samples were studied using TEM, FT-IR spectroscopy and surface area analysis. Textural results of the prepared nanosheets show that the surface area, total pore volume, and average internal diameter of g-C3N4 and graphene oxide samples are similar. The hydrogen adsorption isotherms at 298 K, up to 22 bar pressures were as Type III and the maximum hydrogen storage capacities at 22 bar and 296 K were 1.06 and 1.27 mmol/g for graphite oxide and g-C3N4 samples, respectively. The adsorption results were fitted by Freundlich model, which was related to reversible multilayer adsorption on non-uniform surface active sites with different affinities of both g-C3N4 and graphene oxide adsorbents. Isosteric heat of adsorption of hydrogen on the graphene oxide varies from 8.6 kJ.mol-1 (at low hydrogen uptake) to 4.3 kJ.mol-1. These results are the range of 10.1 to 4.8 kJ.mol-1 for the prepared g-C3N4 sample at same hydrogen uptake. The results show that the interaction between hydrogen molecules and tri-s-triazine units in g-C3N4 structure are stronger than carbon atoms in graphene oxide structure.