Study on the Micro-mechanism of Controlling CH₄ and CO₂ Adsorption by Constructing Structural Defects in Coal Based...

Area of Science:

• Materials Science
• Geochemistry
• Computational Chemistry

Background:

• Structural defects in tectonic coal are critical for coalbed methane (CBM) adsorption and CO2 sequestration.
• Existing research lacks a detailed understanding of how intrinsic coal macromolecular defects influence gas adsorption mechanisms.
• Systematic analysis of typical defect types and their impact on CBM and CO2 adsorption is needed.

Purpose of the Study:

• To elucidate the regulatory patterns and microscopic mechanisms of various structural defects in tectonic coal on methane (CH4) and carbon dioxide (CO2) adsorption.
• To systematically analyze the effects of single vacancy (SV), double vacancy (DV), multiple vacancies (MV), Stone-Wales (SW), nitrogen (G-N), and sulfur (G-S) defects on gas adsorption.

Main Methods:

• Construction of periodic graphene models (7x7 aromatic layers) representing different defect types.
• Utilizing density functional theory (DFT) with the Dmol3 module to analyze defect bonding characteristics and formation energies.
• Investigating CH4 and CO2 adsorption on perfect and defective surfaces through analysis of electrostatic potential, density of states, dipole moment, work function, charge transfer, orbital hybridization, and interaction energy.

Main Results:

• Defect introduction alters aromatic layer structure, increases electron density and electrostatic potential, modifies energy levels, narrows the band gap, and enhances reactivity.
• Charge redistribution induced by defects is the primary mechanism for enhanced gas adsorption, with a stronger effect on the more polar CO2.
• Different defects exhibit varying adsorption capacities, with DV showing the highest CH4 adsorption enhancement and G-S showing the strongest CO2 adsorption.

Conclusions:

• Structural defects significantly enhance gas adsorption in tectonic coal by regulating electron transfer and electrostatic interactions.
• The findings provide critical theoretical support for CBM development, coal and gas outburst prevention, and CO2 geological sequestration.
• CO2 adsorption energies on defect surfaces are generally higher than those for CH4, highlighting the potential for CO2 capture in defective coal structures.