Study On The Application Of New Carbon Materials In The Determination Of Volatile Organic Compounds

Volatile organic compounds（VOCs）have become one of the main pollutants for atmospheric pollution,they are harmful to human health and ecological environment due to their toxicity,carcinogenicity and mutagenicity.With the continued growth of VOCs and improvement of emission standards,the detection of VOCs is more and more important.Solid adsorption-thermal desorption gas chromatography mass spectrometry is the most widely used method for VOCs detection at present.The key is the selection of solid adsorbent.Currently commonly used solid adsorbent is mainly dependent on imports.The price is expensive,therefore,the development of cheap and good performance of alternative adsorbent will be able to greatly reduce the cost of VOCs detection,which has a certain use value and guiding significance.The new carbon molecular sieve material Scalpha 1500 was prepared by KOH activation method,using resin as raw material.Scalpha 1500 was applied to replace Carboxen 1000 to form new adsorption tubes.With imported carbon molecular sieve Carbonxen 1000 as reference,various characterization methods such as scanning electron microscopy（SEM）,X-ray spectroscopy（EDS）,N₂ isothermal adsorption-desorption and X-ray diffraction（XRD）were applied to investigate the apparent morphology,elemental composition,pore structure,thermal stability,crystalline phase composition and surface functional groups of these two materials.Scalpha 1500 was applied to replace Carboxen 1000 to form a new adsorption tube.The performance of these two adsorption tubes in VOCs determination was analyzed by thermal desorption-gas chromatography-mass spectrometry according to HJ 734-2014 and DB12/524-2020 standards.In additon,the aging-adsorption-desorption cycle of the two adsorption tubes was tested for 150 times with five benzenes as the target compounds to analyze the changes in the adsorption performance of the two adsorption tubes before and after cycling and to evaluate the service life of the adsorption tubes.After that,SEM,EDS,TG,XRD,FT-IR and N₂ isothermal adsorption-desorption were applied to analyze the physicochemical properties changes of two adsorption tubes before and after 150 cycles.The main results of the research are as follows:（1）The surface morphology of Carboxen 1000 was smooth and flat,and Scalpha 1500 was rough and wrinkled.The composition of the two types of carbon molecular sieves was different,but carbon was the main element,followed by sulfur and oxygen elements.Carboxen1000 had higher carbon content and was more pure,but Scalpha 1500 had a larger specific surface area.In TG analysis,Carboxen 1000 showed better thermal stability,but there was no significant difference in phase composition and surface functional groups between the two carbon molecular sieves.（2）The parameters of desorption temperature,desorption time and desorption flow rate were optimized as 300℃,6 min and 50 mL/min,respectively.The background,adsorption resolution and penetration performance of the new adsorption tube（CB1500）had no significant difference with those of the HJ 734-2014 recommended adsorption tube（Carbon300）.Among the 24 VOCs analysis results,the detection limits（S/N=3）of CB 1500 and Carbon 300 for 24 kinds of VOCs were 1.5～16.0μg/m³ and 1.4～14.0μg/m³ respectively.The quantification limits（S/N=10）of CB 1500 and Carbon 300 for 24 kinds of VOCs were 1.5～16.0μg/m³ and 1.4～14.0μg/m³ respectively.The spiked recoveries for 24 target compounds in CB 1500 and Carbon 300 were 93%～107%and 92%～113%respectively.Among the 116 VOCs analysis results,the detection limits（S/N=3）of CB 1500 and Carbon300 for 24 kinds of VOCs were 0.39～9.39μg/m³ and 0.38～9.21μg/m³ respectively.The quantification limits（S/N=10）of CB 1500 and Carbon 300 for 24 kinds of VOCs were 1.30～31.30μg/m³ and 1.28～30.69μg/m³ respectively.The spiked recoveries for 24 target compounds in CB 1500 and Carbon 300 were 93.5%～108.5%and 93.7%～110.7%respectively.The results showed that the linear relationships and recoveries of 24 and 116 compounds tested by the two adsorption tubes were within the standard requirements.（3）In the life test,the adsorption performance of the two adsorption tubes did not change significantly during 150 cycles,indicating that the two had the same service life.The surface morphology,surface functional groups and thermal stability of the two kinds of carbon zeolites did not change significantly before and after 150 cycles,but the specific surface area of the two kinds of carbon zeolites increased after the cycle,which may be due to the partial collapse of the carbon skeleton during the 150 cycles of heating.