First-principles study of toxic industrial gases adsorption on magnesium (4,4)-Porphyrin nanoballs: Electronic structure, dipole moment modulation, and high-sensitivity gas sensing performance.

The adsorption behavior of five Toxic industrial gases (TIGas) - cyanogen chloride (CNCl), cyanogen (C2N2), dichloroacetylene (C2Cl2), hydrogen cyanide (HCN), and phosgene (COCl2) - on a Mg-porphyrin nanoball was investigated using density functional theory (DFT). The gases interacted with the nanoball via their primary functional groups, exhibiting negative, physical, and reversible adsorption. In all configurations, gas adsorption induced a significant increase (approximately 134 %) in the nanoball's band gap, leading to a substantial reduction in conductivity. Equilibrium distances between the gases and the central magnesium ions ranged from 2.25 to 3.9 Å, confirming physisorption. The recovery times were in the microsecond, nanosecond, and picosecond ranges, respectively, indicating rapid adsorption-desorption dynamics. Natural Bond orbital (NBO) analysis revealed electron transfer from the highest occupied molecular orbital (HOMO) of the gases to the lowest unoccupied molecular orbital (LUMO) of the nanoball, reducing the positive charge on magnesium ions while increasing the gas molecules' positive charge. Within the porphyrin rings, nitrogen atoms lost electron density, whereas carbon atoms gained electrons from the nanoball's wings. Frontier molecular orbital (FMO) and charge transfer analyses further supported electron donation from the gases to the nanoball. The Mg-porphyrin nanoball's six adsorption sites enable saturation-free detection of toxic industrial (TI) gases, even in the presence of oxygen, nitrogen, or humidity.