Molecular Designing APTES For Precise Modification Of Palygorskite To Achieve Efficient Gas Adsorption From Study

Palygorskite（PAL）is a resource-rich,low-cost,renewable,non-toxic,and non-hazardous adsorbent substrate with a very large specific surface area and excellent ion exchange and adsorption capabilities that is widely utilised in the environmental,water treatment,and chemical sectors.However,in high humidity settings,the hydroxyl groups and hydrogen bonding on its surface might lead to rapid hydrolysis and loss of adsorption capabilities.According to research,silane modification can effectively improve the stability and adsorption capability of palygorskite.In addition,quantum chemistry and molecular simulation techniques can reveal the interaction between the modifier and the modified material at the molecular and atomic levels,which not only fills the gap that experimental means cannot reach the molecular scale,but also further investigates the physicochemical properties and microscopic mechanisms of the material.This study provides theoretical guidance on the design and performance optimization of PAL materials at the molecular level by using the density functional theory（DFT）method of first principles,which helps to deeply understand the adsorption performance and mechanism of 3-aminopropyltrimethoxysilane（APTES）modified PAL and provides new methods and ideas to improve the adsorption performance enhancement of PAL.The study includes two systems:a first-principles study on the surface of palygorskite（100）modified by APTES and molecular simulation calculations on the adsorption of SO₂ by APTES-modified palygorskite.The following conclusions were drawn:（1）The interaction mechanism of the developed molecular model of the contact between the PAL（100）surface and APTES was investigated using molecular dynamics simulations,and the results revealed that the interaction between APTES and PAL is attracting rather than repulsive.Because of the establishment of a bonding connection between them,the silane bonding functional group prefers to bind with the silicone hydroxyl group on the PAL surface.APTES exhibits less diffusion ability on the PAL surface and its structure is more stable.The different grafting states of APTES were found to affect the inter-and intramolecular interactions between APTES and PAL（100）surfaces by first principle calculations.For the single-,double-,and three-grafted states of APTES-PAL（100）,the charge transfer rates from the PAL（100）surface to APTES are 0.68,1.02,and 0.77 e.The binding energy results show that the double-grafted state of PAL（100）has better modification performance than the other states,with the lowest value of-181.91 k J/mol.In addition,by analyzing its potential energy surface,it was found that the double-grafted state has lower energy barriers（94.69,63.11 and 153.67k J/mol）in the modification process.（2）The adsorption performance and mechanism of the pore size and（100）surface of PAL and the molecular configuration of the single-,double-and three-grafted states of APTES-PAL（100）surface for SO₂ adsorption were investigated using the density functional theory of the first principle calculations,and the results showed that the top site and the bridge site on the PAL（100）surface are the more stable adsorption sites.By calculating the adsorption energy and charge transfer of SO₂ on the PAL surface,the adsorption energy and charge transfer of the top site and bridge site（-12.25 and-9.43k J/mol,0.017 and 0.029 e）were larger than those of the hollow site（51.85 k J/mol and0.015 e）.In addition,the interaction between the PAL（100）surface and SO₂ makes the3p orbitals of the S atoms and the 2p orbitals of the O¹ and O² atoms in the SO₂ molecule overlap each other leading to the variation of the total electronic density of state profile near the fermi energy level.The effect of different graft modifications on the surface of APTES-PAL（100）on SO₂ adsorption was investigated based on the density functional theory.The binding of the broken H atom in the-NH₂ group of APTES to the O atom of the SO₂ molecule is the decisive speed step for the effectiveness of the adsorbent.The chemisorption of SO₂ by APTES-PAL（100）was found to occur by calculating the adsorption energies of the single-,double-and three-grafted APTES-PAL（100）surface systems,which were-66.45,-199.55,and-153.63 k J/mol,respectively.In addition,different graft structures on the APTES-PAL（100）surface had different adsorption properties,mainly in the double-and three-grafted APTES-PAL（100）surface systems where H₂O was produced,and in the single-grafted APTES-PAL（100）surface system where H₂ was produced.