Synergistic inhibition mechanism of inhibitor ions (Ca ²⁺ , Cl ⁻ ) on oxygen-containing functional groups in coal

To explore the synergistic action mechanism of inhibitor ions (Ca2+, Cl−) on oxygen-containing functional groups in coal, this paper analyzed the microscopic action mechanism of inhibitor ions on common oxygen-containing functional groups in coal by combining Fourier Transform Infrared Spectroscopy (FTIR) experiments with quantum chemical calculations. On the basis of Peakfit software to analyze the change of oxygen-containing functional groups, Gaussian 16 software package combined with Multiwfn and VMD software was used to optimize the coal models and their geometric configurations after interaction with inhibitor ions. The results show that the relative content of oxygen-containing functional groups in the coal is significantly reduced after adding CaCl2 solution. This reflects the synergistic inhibitory effect of the inhibitor ions. After conducting IGMH and AIM analysis on the equilibrium configuration of the interaction between the coal models and a single ion, the interaction essences of Ca2+ and Cl− with the coal models were obtained, respectively. According to the calculation results of the interaction energy, it is found that in the case of ion coexistence, the high charge density of Ca2+ and the polarization effect of Cl− act synergistically on the oxygen-containing functional groups in coal, increasing the absolute value of the interaction energy and structural stability. Furthermore, through electrostatic potential and frontier orbital analysis, it was further concluded that the synergistic mechanism of the inhibitor ions is also manifested in the transfer of active sites and the alteration of frontier orbital energy. The two act synergistically on the active groups in coal in many aspects, effectively inhibiting the coal spontaneous combustion (CSC) and significantly improving the inhibition effect.