| Polycyclic aromatic hydrocarbons（PAHs）,as one type of persistent organic pollutants,are widely exist in the environment and pose a serious threat to human health and ecosystem.The problems including complexity and diversity of sample matrix,and trace level of PAHs in samples seriously affect the accurate detection.Sample preparation plays a vital role during the analysis process and restricts the accuracy of the results.In-tube solid-phase microextraction（IT-SPME）,which possesses the advantages of simple operation,no（less）organic solvent,and facile on-line combination with high performance liquid chromatography（HPLC）,can make rapid and efficient analysis.Extraction materials determine the extraction selectivity and extraction efficiency,and further affect the sensitivity and accuracy of the analysis method,so they are the core parts of IT-SPME.Therefore,the development of novel extraction materials with excellent performance and satisfactory stability is the priority.Biochar,derived from the pyrolysis of biomass raw materials at high temperature,is an environment-friendly carbon-rich material with porous,large specific surface,and high stability.A large number of functional groups like-OH、C-O、-C=O,and-COOH on the surface of biochar can provide multiple interactions（hydrogen bonding,electrostatic,andπ-πstacking）to effectively adsorb organic pollutants and heavy metal ions,indicating a potential extraction material for IT-SPME.In this paper,common biomass wastes including corncob and pomelo peel were used as carbon sources to prepare two biochar materials.These two materials were separately coated onto the surface of stainless steel wires,and the wires were placed into the polyetheretherketone（PEEK）tube to develop two fibers-filled extraction tubes.On this basis,carbon fibers which were known as one of four types of high performance fibers were applied as the support,and then biochar nanospheres were in-situ grown onto the surface of carbon fibers using glucose as raw material,producing new biochar-functionalized carbon fibers.Inspired by this,another kind of biochar fibers was also prepared through carbonizing silk fibers directly.Two kinds of fibers were separately employed as extraction materials to develop fibers-IT-SPME tube.Combined with HPLC,the extraction performance of four tubes was evaluated,and the analytical methods were established and applied to on-line detection of PAHs.The specific research contents and results are as follows:1.A biochar material was prepared via carbonizing corncob at high temperature under oxygen-limited conditions,and then it was used as a coating to develop an extraction tube.Combined with HPLC,the tube was evaluated using eight PAHs as model analytes,and the effects of sampling volume,sampling rate,organic solvent content in sample,and desorption time on the extraction efficiency were carefully investigated.Under the optimum conditions,an on-line analytical method was established,it presented high sensitivity(LODs of 0.003-0.030ng mL-1and LOQs of 0.010-0.099 ng mL-1),high enrichment factors of 1864-2615,wide linear ranges(0.010-15.0,0.017-15.0,0.033-15.0,and 0.099-15.0 ng mL-1),and acceptable repeatability（intra-day RSDs of 0.1%-2.9%and inter-day RSDs of 1.6%-6.7%）.Finally,the method was successfully applied to the determination of trace PAHs in actual water samples,and the relative recoveries of PAHs in samples were in the range of 81.7%-116.8%.Compared with some reported methods based on other carbon materials,this method exhibited some advantages including on-line analysis and better accuracy.The developed extraction tube not only had good preparation reproducibility,but also showed satisfactory durability and chemical stability.2.A biocharcoal aerogel derived from pomelo peel was prepared via the facile freeze-drying for maintaining porous structure and then carbonization processes,it was further developed as the coating for IT-SPME.Combining IT-SPME with HPLC,the extraction performance of the tube was evaluated with eight PAHs.After optimizing the main extraction and desorption conditions,an analytical method was established with satisfactory performance including LODs of 0.005-0.050 ng mL-1,LOQs of 0.017-0.165 ng mL-1,linear range of0.017-15.0 ng mL-1（r≥0.999）,high enrichment factors of 1128-3425,and RSDs of repeatability less than 4.3%.The method was finally applied to detect trace PAHs in different samples including purified water,natural water,rain water,river water,aqueous honey solution,and aqueous pear syrup solution,and the relative recoveries were ranged from 83.3%to 120.9%.Compared with other methods,this method had comparable or better sensitivity and linear ranges except for on-line analysis.Compared with other extractive materials,biocharcoal aerogel possesses the advantages of simple preparation,abundant raw materials,low cost,environmental friendliness,and high stability,and it has a promising application prospect as adsorption material.3.The biochar nanospheres as the coating were in-situ prepared on the surface of carbon fibers with micron diameter by hydrothermal reaction using glucose as carbon source and carbon fibers as support.The morphological structure of material was characterized by scanning electron microscope（SEM）,and the biochar nanospheres were uniformly grown on the surface of carbon fibers.The fibers were filled into a PEEK tube to develop a fibers-IT-SPME device.Connected to HPLC,the extraction performance of the tube was evaluated by several PAHs.The extraction efficiency of carbon fibers coated with biochar nanospheres was significantly improved,and the enrichment efficiency of some analytes was increased to 293%than bare carbon fibers.The enrichment factors of all analytes were as high as 2973-3600,indicating the great improvement of the detection sensitivity of HPLC by three orders of magnitude attributed from the introduction of the tube.Under the optimized extraction and desorption conditions,an on-line analytical method was developed with low LODs of0.003-0.010 ng mL-1,wide linear range of 0.010-15.0 ng mL-1,and good repeatability（intra-day RSDs of 0.4%-1.6%and inter-day RSDs of 2.4%-4.4%）.Finally,the method was applied to test trace PAHs in environmental water samples,and the recoveries were in the range of 81.0%-118.7%,demonstrating good practicability of the method.Compared with other analytical methods,the method had lower LODs and more reliable accuracy.The results of stability test showed a long service life and excellent chemical stability of the developed extraction tube.4.Biochar fibers were prepared through high temperature carbonization of natural silk fibers.Characterized by SEM,it was found that some small holes were emerged on the surface of biochar fibers,which increased the adsorption sites.The biochar fibers were applied as extraction materials to develop a fibers-filled extraction tube.Coupled with HPLC,an on-line analytical method for PAHs was developed,and the analytical performance of the method was studied(LODs of 0.005-0.050 ng mL-1,LOQs of 0.017-0.165 ng mL-1,and linear range of0.017-20.0 ng mL-1).Finally,the method was applied to determine trace PAHs in tap water,water solution of soil extractant,river water,and bottled water,and the recoveries were between84.1%-115.8%.Compared with the reported methods,the method based on silk biochar fibers had the advantages like lower LODs,higher enrichment factors,and better stability.Based on the excellent properties of biochar materials,the common biomass wastes including corncob and pomelo peel were used as raw materials to prepare biochar materials,and then they were separately coated onto the surface of stainless steel wires to develop extraction coatings.Subsequently,in order to improve the firmness of the coating,biochar nanospheres were in-situ prepared on the surface of carbon fibers by hydrothermal reaction.Furthermore,biochar fibers were prepared by carbonizing silk fibers directly to avoid coating peeling off,which saved the preparation process of coating and improved the stability of the material.Compared with each other among four kinds of biochar materials,the properties including LODs,linear range,and enrichment factors based on biochar nanospheres-functionalized carbon fibers were better than other three materials.The reasons may be that carbon fibers with micron diameter can provide more amount of the extraction material in the tube,and the specific surface area of the carbon nanospheres on the surface of the carbon fibers is large,which can provide more adsorption sites,thus the extraction efficiency of the extraction tube is greatly improved. |
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