In Situ Fabrication Of TiO₂ Nanostructures On The Nickel-Titanium Fiber Substrates And Their Applications In Solid-phase Microextraction

Solid phase microextraction(SPME)is a simple,environmentally friendly,solvent-free,easy-to-use and automated microextraction technology that effectively increases the efficiency of pre-treatment of complex environmental water samples.Compared to commercial fused silica fibers,the preparation of metal fiber coatings has attracted attention due to their good thermal stability,mechanical strength,and ease of control.In this thesis,three different SPME coatings were grown in situ on nickel-titanium alloy(NiTi)fiber substrates.The enrichment,separation and analytical performance of the prepared fibers were evaluated.The thesis consists of the following chapters:Chapter 1:A brief introduction to SPME technique is described,including its theory,extraction devices and modes,development,advantages and limitations of SPME technology and application fields.Thereafter,the idea and main content of this research were presented.Chapter 2:A nickel-titanium oxide(NiO/TiO2)coating was in situ grown on a NiTi fiber substrate by anodic oxidation.After annealing,a uniform and dense Ni-free coating of rutile phase TiO2 submicrorods(TiO2SRS)was formed.In particular,TiO2SRs were embedded into the NiTi fiber substrate and oriented outwards,leading to high mechanical stability,large contact surface area and open access structure.In SPME,the TiO2SRs coating showed high extraction capacity and excellent extraction selectivity for polycyclic aromatic hydrocarbons(PAHs)among the studied aromatic compounds.The key factors affecting SPME of PAHs were further investigated and optimized coupled to high-performance liquid chromatography with ultraviolet detection(HPLC-UV).Under theoptimized conditions,the proposed method presented linear ranges from 0.05 to 250 ?g·L-1 with correlation coefficients more than 0.998 and limits of detection(LODs)from 0.002 to0.120 ?g·L-1.Relative standard deviations(RSDs)for the intra-day and inter-day repeatability for the single fiber varied from 2.1%to 5.0%and from 3.6%to 5.5%for five replicates of PAHs,respectively.The fiber-to-fiber reproducibility for five fibers fabricatedin different batches ranged from 4.2%to 6.2%at the spiking level of 20 ?g·L-1,respectively.This SPME-HPLC-UV method was successfully applied to the selective concentration and sensitive determination of PAHs in different environmental water samples.Furthermore,the NiTi@TiO2SRs fiber can be fabricated in a precisely controllable manner,and has high stability and long service time.Chapter 3:Ni-doped TiO2(NiO/TiO2)microparticles was in-situ grown on a NiTi fiber substrate by a simple anodic oxidation process.After annealing,temperature-assisted morphological transformation from particle-like to needle-like Ni-free TiO2 coating was observed.The novel TiO2 nanothorns(TiO2NTS)fiber,render a three-dimensional feature,which showed homogeneous rutile films consisting of highly oriented crystals.In particular,the vertically grown structure could enlarge the effective surface area,open access sites and showed high extraction capacity and excellent extraction selectivity for PAHs among the studied aromatic compounds in SPME.The key factors for the extraction of PAHs were further investigated and optimized coupled to HPLC-UV.Under the optimized conditions,the developed method showed good linearity in the ranges of 0.05-250 ?g·L-1 with correlation coefficients of>0.999.LODs were 0.006-0.080 ?g·L-1.RSDs were below 5.0%for intra-day analyses and 5.9%for inter-day analyses.This SPME-HPLC-UV method was successfully applied to concentration and determination of PAHs in real water samples.Furthermore,the fabricated NiTi@TiO2NTs fiber showed high sensitivity,outstanding extraction efficiency and good reproducibility.Chapter 4:A composite of oxide particles is obtained by anodization using a NiTi fiber as a substrate.After the programmed annealing,the uniform TiO2 coating was prepared.The extraction performance of the prepared NiTi fibers on typical aromatic compounds was investigated by HPLC-UV.The results show that the Ni-free TiO2 coatings exhibit good extraction selectivity for UVFs.Under the optimized conditions,the method has a good linear relationship(the correlation coefficient>0.998)in the range of 0.05-250?g·L-1,and LODs of the proposed method were 0.008-0.082 ?g·L-1.The intra-day and inter-day repeatability of single fiber was 3.4%-5.0%and 3.9%-5.2%,respectively,and the fiber-to-fiber reproducibility was 4.9%-6.2%for the extraction of spiking water with 50?g·L-1 each analytes(n=5).The proposed method was successfully applied to highly efficient concentration and sensitive determination of target UVFs from real water samples with recoveries of 88.4%-10%.The fiber preparation method is simple and easy to control.