Design And Sampling Performance Of VOCs Adsorbent Tube

Volatile organic compounds(VOCs)is considered to be an important parameter for assessing indoor and outdoor ambient air quality.Sample collection is an important process for monitoring the level of VOCs in the ambient air.Compared with other sampling techniques,adsorption tubes can effectively enrich the low concentration VOCs in a relative large volume of air.With the advantages of low detection limit,convenient handing and low loss rate,adsorption tube sampling has become one of the most commonly used sampling methods for VOCs.Adsorbent material in the adsorption tube is the key factor to determine the sampling efficiency.To date,the commonly used commercial adsorbent materials are Tenax(poly-(2,6-diphenyl-p-phenylene oxide)and activated carbon,which have their own advantages,as well as some limitations and selectivity.Because of various structures and properties of VOCs,single adsorbent material can hardly achieve satisfied goal of comprehensive enrichment of atmospheric VOCs.Therefore,it is necessary to further investigate the sampling efficiency of new adsorbent materials for VOCs,and provide more choices for sampling of VOCs.In this study,carbonaceous materials such as activated carbon fiber(ACF)and multi-walled carbon nanotubes(MWCNTs),etc.were used as adsorbent materials for the design of VOCs adsorption tubes.Their adsorption and desorption performance on different types of VOCs were evaluated.The preliminary application test of these adsorption tubes in the collection of ambient air VOCs in an industrial area was carried out.In this study,several adsorption materials including ACF,MWCNTs,hydroxylatedMWCNTs(HMWCNTs),inorganic silica gel(SG)were selected and filled in tubes respectively.The main parameters of design and filling were based on China's Ministry of Ecology and Environmental Protection Environmental Protection Standard(HJ 734-2014)and US Environmental Protection Agency(EPA)Method TO-17.Using the Tenax TA adsorption tube as a comparion,these designed adsorption tubes were subjected to a room temperature adsorption-thermal desorption experiment.The thermal desorption(TD)combined with gas chromatography-mass spectrometry(GC-MS)was used to determine the recovery rates of 36 different types of VOCs and evaluate the adsorption and desorption performance of single material adsorption tubes on each VOC.The overall adsorption performance of single material adsorption tube of MWCNTs was better than other materials.The average recoveries of aromatic hydrocarbons,halogenated aromatic hydrocarbons,oxygenated VOCs and terpenes in MWCNTs adsorption tube were 88%±1%,60%±1%,87%±0%,and 117%±0%,respectively.The adsorption and desorption of aromatic hydrocarbons was higher than that of Tenax TA adsorption tube.The overall adsorption performance of HMWCNTs and ACF were only better than Tenax for several VOCs.Based on the results of single material adsorption tube,the adsorption materials such as Tenax TA,ACF,MWCNTs and HMWCNTs were combined to design the composite adsorption tubes Tenax TA-ACF(T-A),MWCNTs-ACF(M-A)and HMWCNTs-ACF(H-A).The overall adsorption performance of the composite material adsorption tubes T-A and M-A for aromatic hydrocarbons,halogenated hydrocarbons and some oxygenated VOCs were better than that of Tenax TA adsorption tube.The average adsorption desorption recovery rate of aromatic hydrocarbons,halogenated hydrocarbons and oxygenated VOCs by composite adsorption tube T-A and M-A were 83%±10%,96%±12%,84%±6% and 82% ± 4%,90% ± 12%,90% ± 11%,respectively.The improvement of the adsorption and desorption performance of the three kinds of combined tubes on the halogenated aromatic hydrocarbons was not significant.The results of T-A,M-A tubes in the sampling VOCs in one industry park ambient air collection were better than those of commercial tube of Tenax TA,which indicated that these tubes could be applied in the sampling of VOCs in environment.