Tunable electronic landscape in covalently linked dimer graphene architectures: Heteroatom engineering for selective monitoring and capture of toxic gases.

Density functional theory (DFT) calculations are employed to investigate the structural, electronic, and gas-monitoring properties of pristine covalently linked dimer armchair hexagonal graphene (2AHG) and its heteroatom-doped derivatives (Al, B, N, O, P, S, and Si). The adsorption behaviour of environmentally hazardous CO2, SO2, and NO2 gases on pristine and doped 2AHG surfaces is systematically analyzed. Structural and binding energy results confirm that covalent dimer coupling, and heteroatom substitution preserve the thermodynamic stability of the graphene framework while inducing controlled lattice distortion. Electronic structure analysis reveals significant tunability of the HOMO-LUMO gap upon doping, leading to enhanced electronic sensitivity toward gas adsorption. CO2 exhibits weak physisorption with rapid recovery times, indicating suitability for reversible gas monitoring. In contrast, SO2 and NO2 show strong chemisorption, pronounced charge transfer, and substantial band-gap modulation, particularly on doped 2AHG surfaces, resulting in extremely long recovery times and suggesting potential for irreversible gas capture. Spin-polarized calculations further demonstrate that NO2 adsorption induces marked spin asymmetry. Overall, heteroatom-engineered 2AHG emerges as a versatile and robust platform for selective gas monitoring and capture applications.