Study On Quantum Chemical Simulation Of Formaldehyde Treatment By Modified Carbon Materials

As the main pollutant of indoor air pollution,formaldehyde has attracted much attention due to its wide release sources and high toxicity.The existing formaldehyde treatment technologies can be classified into physical methods,chemical methods and biological methods,among which adsorption method and advanced oxidation method are widely used.Carbon material adsorption is the most commonly used method for the treatment of formaldehyde in the air.The Electro-Fenton oxidation method can completely degrade formaldehyde in solution,and carbon material is a common Electro-Fenton cathode.Improving the adsorption capacity of carbon materials to formaldehyde in the gas phase and liquid phase is an important means to promote the treatment effects of the above two technologies.Oxygen-containing functional groups and nitrogen doping have a great influence on the adsorption of formaldehyde by carbon materials,but the microscopic mechanism and specific effect are still unclear.Therefore,it is of great significance to explore the effects of oxygen-containing functional groups and nitrogen doping on the adsorption of formaldehyde by carbon materials.In this paper,quantum chemical simulations were used to explore the oxygen-containing functional groups（edge carbonyl,edge ether,edge hydroxyl,edge pyrone,edge quinone,edge lactone,basal epoxy,basal hydroxyl,edge epoxy and edge carboxyl groups）and nitrogen doping（pyridine nitrogen,pyrrolic nitrogen,and graphitized nitrogen）on the adsorption of gaseous and liquid formaldehyde by carbon materials.The effect of oxygen-containing functional groups and nitrogen doping on the electronic structure of carbon basal plane was analyzed,and the types of oxygen-containing functional groups and nitrogen doping that promoted formaldehyde adsorption were analyzed.On this basis,the mechanism of promoting the adsorption of formaldehyde was analyzed,which provided theoretical support for the oxidation of formaldehyde by the promoted adsorption method and the Electro-Fenton system.The effects of oxygen-containing functional groups and nitrogen doping on liquid-phase formaldehyde adsorption were first calculated.The oxygen-containing functional groups and nitrogens that promote the adsorption of liquid-phase formaldehyde are doped with edge carboxyl groups,edge hydroxyl groups,edge pyrone groups,edge ether groups,pyrrole nitrogens,and pyridine nitrogens.The edge carboxyl groups and edge hydroxyl groups significantly promoted the marginal adsorption of formaldehyde in liquid phase,and their adsorption energies were-6.39 kcal/mol and-4.32 kcal/mol,respectively.It was demonstrated that electrostatic interactions have an important effect on the adsorption of liquid-phase formaldehyde by the marginal carboxyl and edge hydroxyl groups.The pyrrolic nitrogen promotes the planar adsorption of liquid formaldehyde on the carbon basal plane to a certain extent,and the adsorption energy is-6.54 kcal/mol.The dominance of dispersion between pyrrole nitrogen and formaldehyde adsorption was determined.After the Bohem titration method was used to neutralize the carboxyl functional groups on the surface of KMn O₄modified activated carbon,the adsorption effect of activated carbon on liquid formaldehyde decreased significantly.After neutralizing the carboxyl and lactone functional groups,the adsorption rate of activated carbon to liquid phase formaldehyde was improved.The experimental trend was consistent with the simulation results,which confirmed the accuracy of the simulation results.Then the effects of oxygen-containing functional groups and nitrogen doping on the adsorption of gas-phase formaldehyde by carbon materials were calculated.The adsorption energy results show that other than pyrrole nitrogen the nitrogen doping and all oxygen-containing functional groups can promote the adsorption of gas-phase formaldehyde.For edge adsorption,edge carboxyl group,edge hydroxyl group,pyridine nitrogen,edge ether group and edge quinone group greatly promoted the adsorption of gas-phase formaldehyde,and their adsorption energies were-9.86 kcal/mol,-7.62 kcal/mol,-5.67 kcal/mol,-4.78 kcal/mol and-4.75 kcal/mol.The dominant role of dispersion in gas-phase formaldehyde adsorption by edge ether group and pyridine nitrogen was confirmed,and electrostatic interaction and dispersion effect were dominant in edge carboxyl group,edge hydroxyl group and edge quinone group in adsorption of formaldehyde.For edge adsorption,the adsorption energy of formaldehyde by basal plane hydroxyl groups is as high as-7.94 kcal/mol.It is clear that the dispersion effect has a prominent contribution to the adsorption of gas-phase formaldehyde on the basal plane hydroxyl group.Compared with the adsorption of liquid-phase formaldehyde,the modified carbon base has better adsorption effect on gas-phase formaldehyde,mainly because the water and formaldehyde in the liquid-phase will form a competitive adsorption.Experiments show that the adsorption effect of activated carbon on formaldehyde is significantly enhanced after KMn O₄ modification,which proves the rationality of the simulation results.In this paper,by simulating the adsorption properties of gas and liquid formaldehyde on modified carbon materials,the oxygen-containing functional groups and nitrogen doping species that promote the adsorption of formaldehyde are determined,and the mechanism of promoting adsorption is analyzed,which is of great significance for the adsorption of formaldehyde by carbon materials.It provides theoretical support for the Electro-Fenton system carbon material cathode to get rid of the limitation of the reaction area.