Surface Functional Modification Of Carbon-based Materials And Mechanism For Removing VOCs

Formaldehyde（HCHO）and toluene（C₇H₈）are the most important gaseous pollutants in the indoor environment,which seriously affect human health.Therefore,an efficient and applicable indoor formaldehyde and toluene purification technology is urgently needed.In view of the characteristics of long volatilization period and low concentration level of formaldehyde and toluene in indoor environment,adsorption method is considered to be one of the most efficient indoor formaldehyde and toluene control technologies,which can quickly absorb formaldehyde and toluene at room temperature.Among many adsorption materials,activated carbon is considered as a commonly used adsorption material due to its excellent physical structure and tunable surface chemical properties.As a broad-spectrum adsorption material,the influencing factors in the adsorption process of different gaseous pollutants are different,so it is necessary to combine the properties of specific gaseous pollutants to perform functional modification to improve the adsorption performance.In this project,a simple and scalable method was used to controllably synthesize a class of nitrogen-containing group-modified activated carbon materials for efficient and durable adsorption of formaldehyde and toluene at room temperature.prospect.In addition to studying the influencing factors of adsorption performance,this topic also discusses the mechanism of adsorption reaction.The main research results are as follows:（1）In this project,tromethamine,tetraethylenepentamine and L-cysteine were used as modifiers to modify the activated carbon materials by amino functional modification,and a series of modified activated carbon materials were prepared.The formaldehyde adsorption performance test was carried out at room temperature,and it was found that the tromethamine modified activated carbon（T-10）had the best formaldehyde adsorption performance,with 90%removal rate for 100 ppm formaldehyde,and 1 ppm low concentration formaldehyde.More than 99%removal rate.The tetraethylenepentamine and L-cysteine modified activated carbons（P-10 and L-1）as their controls had poor formaldehyde adsorption performance,especially the adsorption performance of L-1 was lower than that of the original activated carbon.Through characterization,it was found that after modification,a large number of amino groups were found on the surface of activated carbon,which achieved the purpose of amino functional modification,and the microscopic morphology of modified activated carbon did not change significantly.Further research found that the specific surface area of T-10 was lower than that of the original activated carbon,but its adsorption performance was better than that of the original activated carbon.The specific surface area of P-10 and L-1 is larger than that of original activated carbon,the adsorption performance of P-10 is better than that of original activated carbon,and the adsorption performance of L-1 is lower than that of original activated carbon.The specific surface area is not an important factor affecting the adsorption of formaldehyde by amino-modified activated carbon.Through the study of the reaction mechanism,it was found that the removal mechanism of organic amine-modified activated carbon on formaldehyde:the first step,using the porous structure of activated carbon to enrich the physical adsorption of formaldehyde;the second step,Through the chemical adsorption reaction between the amino group and formaldehyde,the nucleophilic addition reaction between the amino group on the surface of the activated carbon and the carbonyl group of formaldehyde occurs to generate the intermediate product hydroxylamine,which is further dehydrated to generate imine organic compounds.The length of the modifier carbon chain and other functional groups may affect the nucleophilicity of the amino groups,thereby changing the adsorption performance.（2）In order to realize the efficient adsorption of toluene gas,the activated carbon was impregnated with urea and ammonium carbonate,and then the activated carbon was modified by heat treatment in a nitrogen atmosphere.The toluene adsorption capacity of the urea-modified activated carbon is nearly 1.5 times that of the original activated carbon.After impregnation with urea,calcination in nitrogen atmosphere at400°C can increase the micropore volume and specific surface area of activated carbon,thereby improving the adsorption performance of toluene.specific surface area,which in turn inhibits the ability to adsorb toluene.However,calcination of ammonium carbonate-impregnated activated carbon in nitrogen atmosphere reduces the specific surface area and micropore volume of activated carbon.However,C-600 with the lowest specific surface area and micropore volume was not the worst in toluene adsorption,indicating that the increase in specific surface area and micropore volume of activated carbon was not the only factor determining the toluene adsorption performance.Therefore,by calcining urea and ammonium carbonate modified activated carbon to introduce nitrogen-containing functional groups on the surface of activated carbon,the polarization of N can generate moreπelectron defect sites on the surface of activated carbon,and promote the electrostatic adsorption between the toluene and benzene ring structure and the surface of activated carbon.effect.Among the nitrogen-containing functional groups,the adsorption affinity of pyrrole nitrogen to toluene is the best,but too high calcination temperature will reduce the content of pyrrole nitrogen.Through the modification of urea and ammonium carbonate,nitrogen-containing functional groups are introduced on the surface of activated carbon,which realizes the adjustment of the microporous structure of activated carbon and the modification of nitrogen-containing functional groups on the surface.It effectively combines physical adsorption and electrostatic interaction,and improves the adsorption performance of activated carbon for toluene.