Abstract
Porous graphene (PG) has a promising future for gas storage owing to its unique pore characteristics and large specific surface area. The adsorption properties of PG and Mn atoms decorated PG (Mn-PG) for methane (CH4) molecules have been studied based on the first-principles density functional theory. It is discovered that the optimum adsorption position of CH4 on PG is the carbon ring pore, and the adsorption energy is − 0.174 eV. The optimal position of the PG system decorated by single Mn atom is the central hole of the carbon ring, and the optimal position of the two Mn atoms is that Mn atoms are, respectively, located at different carbon ring holes on the opposite side of PG, with an average binding energy of − 4.101 eV. The modification of the Mn atom enhances the electronegativity of the PG substrate and forms a negative electrical center at the carbon ring, which facilitates the enhancement of the adsorption performance of the CH4 molecules that are positively charged with the surface. The CH4 molecule, close to Mn atom shows negative charge, and its strong electrostatic interaction with positively charged Mn atom is dominant, resulting in higher adsorption energy. The surface of CH4 molecule far away from the Mn atom is positively charged, the weak electrostatic interaction with the negatively charged PG substrate and the Van der Waals interaction between CH4 molecules are dominant, and the adsorption energy is low. The CH4 molecules are adsorbed on the PG surface through the electrostatic interaction with Mn atoms and PG substrate as well as the intermolecular force of CH4 molecules. The Mn-PG system is single-sided adsorption 6 CH4 molecules, and the average adsorption energy is − 0.345 eV. When two Mn atom modification PG, 12 CH4 molecules can be adsorbed on both sides, and the average adsorption energy is − 0.338 eV, the adsorption capacity is up to 38.43 wt.%.
Highlights
With the development of science and technology, people have been exploring the earth deeply, but at the same time, it brings various problems such as energy depletion and environmental pollution
The modification of Mn atom enhances the electronegativity of Porous graphene (PG) substrate and forms a negative charge center at the carbon ring, which is beneficial to enhance the adsorption performance of CH4 molecules with positive charge on the surface
The CH4 molecules are adsorbed on the PG surface through the electrostatic interaction with Mn atoms and PG substrates as well as the intermolecular force of CH4 molecules
Summary
With the development of science and technology, people have been exploring the earth deeply, but at the same time, it brings various problems such as energy depletion and environmental pollution. The adsorption and storage of methane gas is a hot topic in scientific research, which is an effective means to solve the greenhouse effect and low-carbon energy substitution problem. Liang et al [14] pointed out that a porous metal-organic framework ST-2 can store the same amount of methane at 130 bar and 298 K as the CNG storage method at 250 bar, and the maximum storage capacity can reach 289 cm3/cm under high pressure. Liu et al [16] found that the adsorption capacity of CH4 in DUT-49 MOF materials can reach 24.0 wt.%, and pointed out that the surface area, pore size and pore volume of MOFs and COFs have an important influence on the gas storage capacity of CH4. Some materials have reached this standard, they are stored under high pressure or high temperature, so it is difficult to apply them in practice
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