Multi-scale Simulation Study On Dynamic Adsorption Mechanism Of Activated Carbon For Formaldehyde

Exploring the dynamic mechanism of pore structure and surface functional groups on formaldehyde adsorption is the key to identifying the underlying reason for the low adsorption capacity of activated carbon for formaldehyde.The surface oxygen modification of activated carbon is considered to be an effective adsorbent for removing formaldehyde from indoor air,while the effect of coexisting water on the adsorption of formaldehyde by oxygen enriched carbon is unclear.This article explores the dynamic laws of formaldehyde adsorption by different pore structures and functional groups of activated carbon using a combination of multi-scale simulations,and summarizes the fundamental reasons for the low formaldehyde adsorption capacity of activated carbon.Analyzed the comprehensive impact mechanism of water on the promotion/hindrance of formaldehyde adsorption on activated carbon,analyzed the reasons for the formation of water clusters,and explored the formation laws and mechanisms of water films.The results show that the narrow range of effective adsorption pore size in activated carbon is one of the fundamental reasons for the low formaldehyde adsorption capacity.The micropores with a pore diameter of "4-7 ?" in activated carbon play a leading role in adsorption,and at this time,the micropores can only accommodate one formaldehyde.For larger micropores,although multiple formaldehyde molecules can be accommodated simultaneously,there is a strong interaction between these multiple formaldehyde molecules,which can deform or even desorb the adsorbed formaldehyde molecules.The rapid decline in the adsorption capacity of functional groups is another reason.Although carboxylic groups may form hydrogen bonds with formaldehyde at the early stage of adsorption,they can only be adsorbed through weak van der Waals forces at the later stage.Carboxyl groups can produce a double layer adsorption of formaldehyde,and the adsorbed formaldehyde tends to be arranged vertically with each other.The results of co adsorption research indicate that,with the increase of adsorption time,the stronger interaction force generated by the formation of more hydrogen bonds between water and oxygen functional groups,as well as the clogging of pores by water molecules accumulated around the adsorption sites,are the main obstacles to the adsorption of formaldehyde on carbon surfaces in humid environments.An oxygen functional group with pre adsorbed water/formaldehyde can hold at least one water,but due to the weak interaction force that water molecules can easily replace,it can hardly adsorb another formaldehyde.The adsorption of water on a single carbon sheet ranges from 7 to 8 ?,while the adsorption of formaldehyde on a single carbon sheet ranges from 6 to 7 ?.During the formation of water masses,a water film always forms first to hinder adsorption.The main difference between water masses and water films is whether the water molecules in the middle of the pores can be subjected to forces from the carbon sheets on both sides.If the "carbon layer water hydrogen bond water clusters hydrogen bond water carbon layer" condition is reached,water masses can be formed.Through experiments and multiscale simulations,this article has deeply explored the dynamic laws and internal mechanisms of adsorption of formaldehyde and water by activated carbon with different pore structures and functional groups.The research results have laid a solid foundation for the effective treatment of indoor formaldehyde.