Evolution mechanism of SO₂ adsorption on palygorskite (100) surface modified by APTES: Effect of different grafting modification

The effects of 3-aminopropyltriethoxysilane (APTES) with different grafting modifications on the (100) surface of palygorskite (PAL) have been examined in the current work using the first principles method. Our finding results show that the chemisorption is probably occurring because the adsorption energies of the single, double, and three-tooth APTES-PAL (100) surface systems are -66.45, -199.55, and -153.63 kJ/mol, respectively, all below -18.86 kJ/mol (or -0.2 eV). Moreover, the different grafting structures of the APTES-PAL (100) surface have different adsorption characteristics, showing that H2O was produced in the double and three-tooth APTESPAL (100) surface systems and H2 was produced in the single-tooth APTES-PAL (100) surface system. Additionally, the rate-determining step to adjust the effectiveness of the adsorbent is the H atom broken from the NH2 group of APTES combining with the O atom of SO2. These insights will be used to develop clay composite materials in the future for gas adsorption.