Application Of Porous Materials For Selective Solid Phase Microextraction Of Odorous Compounds

Water is the source of life,however,in recent years,the unpleasant discharge of production and domestic sewage seriously damaged water resources.The odors are a type of water environment problem that causes people's attention.The olfactory organic pollutants in water have a wide range of sources and types,and the concentration of olfactory thresholds in various environmental medias are very low.Some olfactory organic contaminants can cause serious odors in the water even a concentration as low as ng L-1.Due to the low olfactory threshold,high-sensitivity analysis of olfactory organic pollutants has become one of the difficult problems to overcome in the field of water quality monitoring.Pretreatment is a key step in the analysis process of the environmental sample,which has an important influence on the accuracy and sensitivity of the analysis of the target pollutants.Solid-phase microextraction(SPME)is a commonly used sample preparation technique,with the advantages of short analysis time,small sample size,no need for organic solvent,and simple operation.It can be used together with gas chromatography,liquid chromatography,and other chromatographic instruments,and has high application potential in the analysis of odor-stained organic pollutants.However,the commercial SPME fibers are mostly prepared by physical impregnation,and the coating and the fused silica matrix fibers are not well bonded,resulting in poor mechanical and chemical stabilities and hence a short service life.Moreover,the extraction processes on commercial fobers are easily disturbed by environmental medias such as the dissolved organic matters.Therefore,it is necessary to develop new SPME fibers with high stability,sensitivity and anti-interference for olfactory organic pollutants in water bodies.In this study,two common types of ordered porous materials(zeolitess and porous carbons)were used as SPME coating materials.We studied the adsorption and extraction behaviors of these materials for many common olfactory organic pollutants(such as mercaptans and chloroaromatics),and examined the main environmental factors affecting the above processes.Finally,a SPME analysis method for olfactory organic pollutants based on the tested coating materials was established.The main results are as follows:(1)Zeolites with different pore sizes and different silica-alumina ratios were used as adsorbents to study their adsorption behaviors for tert-butyl mercaptan and benzenethiol.It was found that the pore filling effect and hydrophobic interaction are two important mechanisms of the adsorption process.Copper-modified zeolites have a strong adsorption capacity,due to the special ?-complexation of copper ions and-SH in thiol olfactory pollutants.We studied the effect of water chemistry conditiongs on the adsorption processes.It was found that when the solution pH was higher than the pKa of adsorbate,the adsorbates were deprotonated,leading to a lower hydrophobicity of the adsorbate and hence a weakened adsorption on zeolite.Dissolved humic acid had no obvious effect on the adsorption process,which was mainly attributed to the pore steric hindrance effect of the microporous pores of the zeolite.In addition,the zeolites had a high thermal stability,and the material can be recycled by heat treatment.(2)A porous carbon SPME(i.e.,MOF-C)coating was prepared by direct carbonization of MOF.Scanning electron microscopy results showed that a regular carbon coating could be synthesized on the stainless steel wire using the direct carbonization method,and the coating thickness was 10 ?m.X-ray diffraction and N2 adsorption-desorption showed that the coating material was a porous carbon in microporous structures(specific surface area 298.6 m2 g-1).We then examined the analytical performance of the homemade MOF-C fiber for five typical aromatic olfactory organic pollutants(2-chlorophenol,2,4,6-trichlorophenoxyphene,2-methoxy-3-isobutylpyrazine,benzenethiol,4-methylbenzenethiol).The effects of extraction time,extraction temperature,salt concentration,desorption time and desorption temperature on the extraction effect were analyzed by the orthogonal test.The results showed that the extraction temperature and extraction time were two significant factors.In comparison with five commercial fibrous coatings,MOF-C coating had higher extraction efficiency for the five odor contaminants.The study also found that MOF-C coating had good anti-interference,and the presence of dissolved organic matter has a far less influence on the extraction efficiency of MOF-C than commercial coatings.In addition,MOF-C coating also had good thermal stability and chemical stability.The weight loss of the fiber was less than 10%at 428?.Acid,alkali,and solvent treatments had no significant effect on the morphology and extraction efficiency of the coating.The established analysis method based on MOF-C had high sensitivity,low detection limit(0.01-0.5 ng L-1)and wide linear range,which can meet the requirements of trace analysis of actual environmental samples.