Fabrication And Application Of Novel Nanoporous Carbon Coating In Solid-phase Microextraction Of Typical Organic Pollutants From Water Samples

The analysis of trace organic pollutants from water samples has great significance in the field of environmental analytical chemistry.However,the complexity of real water matrix makes it challenge to obtain the analysis results accurately.Sample pretreatment is an important means to solve this problem.Among various sample pretreatment technologies,solid phase microextraction(SPME)has developed rapidly since its invention.This technology is mainly based on a miniature extraction phase,which can make sampling,isolation,enrichment,and injection in a single,solvent-free step.Thus,the coating material plays a critical role in this technology,which determines the sensitivity and application of SPME.However,the commercial SPME fiber usually has many drawbacks such as low sensitivity and selectivity,long analysis time,limited ability to virious analytes.Hence,the relationship between the extraction performance of organic pollutants(such as:polycyclic aromatic hydrocarbons)and coating materials of morphology,porosity,structure,composition is studied in this thesis.The main contents and conclusions are presented as follow:(1)Two nanomaterials with different morphologies are synthesized just through changing the concentration of 2-methylimidazole based the“shape-transforming method in an aqueous system”.This process is simple and harmless.The ZIF nanoleaves derived carbons(NLCs)and ZIF-dodecahedrons derived carbons(DHCs)are obtained by direct carbonation.Then the two materials are coated on the stainless steel wires to form SPME fibers with the same thickness.The NLCs coated fiber shows 1.2-46.5 higher enrichment ability than that of DHCs coated fiber because it can provide more active sites for the adsorption of organic analytes.The obtained fiber is used to concentrate the polycyclic aromatic hydrocarbons from real environmental water and soil samples successfully.Finally,the prepared fiber and commercial fiber are used to extract the degradation products of bisphenol A.From the chromatograms,it is found that the nanoleaves derived carbon coated fiber has higher enrichment capacity and could be used to detect more kinds of analytes.(2)Considering the relatively large molecular size of PAHs,the hollow mesoporous carbon spheres are coated on the stainless steel wires to form SPME fibers.The characterization results show that the fiber coating posses a large specific surface,high porosity,uniform pore size and strong hydrophobicity.Then,the fiber is used to extract polycyclic aromatic hydrocarbons from the complex water samples.The experimental parameters,including extraction and desorption conditions,are optimized.And the extraction performance comparison of self-made fiber with commercial fibers is conducted.It is found that the appropriate mesoporous size(2.57 nm)is favorable for the adsorption of relatively large molecular analytes.These results show that the fiber has a wide linear range with 5-2000 ng L^-1,low detection line from 0.20 to 1.15 ng L^-1,excellent repeatability with the RSD of 5.8-9.0%and reproducibility with the RSD of 4.1-8.6%for polycyclic aromatic hydrocarbons.Moreover,the extraction efficiency of the fibers has no significant decline after 120 adsorption-desorption cycles.So the hollow mesoporous carbon sphere is a promising adsorbent for analytical application of water samples.(3)As a special class of metal organic frameworks,zeolitic imidazole framework-8(ZIF-8)has been prepared by using zinc nitrate and 2-methylimidazole.After carbonization,the solid carbon nanocubes are obtained.Simultaneously,the hollow carbon nanocube materials are prepared by an etching approach and pyrolysis.Then the two carbon materials are coated on the stainless steel wires to form SPME fibers.Due to abundant active sites provied by the hollow structure,hydrophobic interactions and?-?interactions,the hollow carbon nanocubes coated fiber exhibits 1.1-2.2 times higher enrichment performance than solid carbon nanocubes coated fiber towards polycyclic aromatic hydrocarbons.It can be seen from the kinetic adsorption and calculation results that hollow carbon nanocube materials have a faster kinetic rate.And the extraction equilibrium time of hollow carbon nanocubes coated fiber is significantly shorter than that of solid carbon nanocubes coated fiber.These results indicate that the unique hollow structure and abundant mesoporous structure are important factors in determining the extraction performance of the fibers.Finally,the prepared fiber can be successfully used for the determination of polycyclic aromatic hydrocarbons from the real water samples.(4)The actual sample matrix is usually complex.It is necessary to construct new coating with high enrichment efficiency for broad-spectrum pollutants.The double-shelled hollow zinc oxide/carbon(Zn O/C)is synthesized by immerging ZIF-8 powder in the tannic acid solution combined with direct carbonization.After that the Zn O/C is coated on the stainless steel wire to form SPME fiber(Zn O/C-F).The fiber is used to simultaneously extract the polar(chlorophenols)and nonpolar(benzene compounds)pollutants in the water samples.The extraction efficiency of Zn O/C-F is about 1.6-2.4 times higher than ZIF-8-derived pure zinc oxide coated fiber towards chlorophenols,is about 1.3-2.2 times higher than ZIF-8-derived pure carbon coated fiber towards benzene compounds.The result shows that the uniformly dispersed Zn O and carbon framework can provide abundant adsorption sites.The Zn-OHs can bond with chlorophenols through hydrogen bonding and the carbon can adsorb benzene compounds through hydrophobic interaction and?-?stacking interaction.On the other hand,the efficiency of Zn O/C-F is about 2-3 times higher than that of the ZIF-8-derived solid Zn O/C coated fiber,it is found that the double-shelled hollow structure is favorable for the sensitive extraction of analytes.