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Abstract: Hydrogen adsorption and storage on calcium-decorated BC2N sheets doped by Boron or Carbon were investigated using the first-principles calculations. Unlike the weak bond between Ca atoms and pristine BC2N, doping boron or carbon atoms on BC2N sheet can significantly strengthen the Ca atoms on the BC2N, especially for BC2NBC and BC2NCN. It is observed that Ca decorated BC2NBC and BC2NCN possess strong donation and back-donation of Ca with the sheets, which is responsible for enhanced binding energy to eliminate the clustering problem. Up to four hydrogen molecules can stably attach to a Ca atom with an average adsorption energy of ∼0.3 eV, which is in the range that permits hydrogen recycling at ambient conditions. The Ca decorated BC2NBC and BC2NCN complexes can work as high-capacity hydrogen storage materials with the practical usable capacities of 8.36 wt% and 8.38 wt%, respectively. [Copyright &y& Elsevier]

Highlights: [•] The adsorption of CH4 on heterogeneity coal surface was studied by the DFT method. [•] We find the up mode of methane of the investigated complexes is preferred one. [•] All graphene models are very weak electron acceptor for methane. [•] The CH4–graphene complex can describe the interaction model in coal–methane system. [•] The interactions slightly depend on the adsorption sites and the orientations. [ABSTRACT FROM AUTHOR]

The adsorption of carbon dioxide on N-containing molecular segment models of coal (2-methylpyridine, C13H9N, C23H12N, and N-doped graphenes) has been investigated by the density functional theory including dispersion correction (DFT-D3) method. Four kinds of DFT-D3 methods (BLYP-D3, PBE-D3, BP86-D3 and TPSS-D3 functionals) were used to calculate the binding energy of CO2 with 2-methylpyridine, and the results were examined by benchmark value which was calculated by the coupled-cluster calculation with singles, doubles, and perturbative triple excitations [CCSD(T)] method in the complete basis set (CBS) limit. Due to its best performance, the BLYP-D3 functional was selected to investigate the binding of CO2 to N-doped hydrocarbon clusters (C13H9N and C23H12N). The adsorption of CO2 onto several different adsorption sites and orientations on coal surface models were systematically explored. Our research indicates that increasing the size of the π-system leads to an increase in binding energy. In the C13H9N···CO2 complex, the binding energy is in the range of −2.36–−2.66kcal/mol, while C23H12N···CO2 complex has the results of −3.24–−3.56kcal/mol. We also considered the adsorption of CO2 on the periodic monolayer and bilayer N-doped graphenes. However, as no significant intermolecular charge transfer exists in the physisorption models, the effect of finite ring size on the binding energies in complexes was not obvious. [ABSTRACT FROM AUTHOR]