Fabrication Of Nanostructed Metal Oxides On The Nickel-titanium Alloy Substrate And Their Applications In Solid-phase Microextraction

Solid phase microextration?SPME?,as a versatile,nonexhaustive sample preparation technique,integrates extraction,isolation and preconcentration into one step.SPME technology is a miniaturized and solvent-free extraction technique,less amount of sample is required and are suitable for the evaluation of the increasingly prominent environmental pollution problem.Due to the drawbacks of commercial fused-silica fibers,such as a limited number of available fibers,expensiveness,easy breakage and poor solvent resistance,it is of great significance to develop a variety of novel SPME coatings.Currently,more researched are focused on the preparation of the coating on the metallic fiber substrates.In this thesis,three kinds of nickel-titanium alloy?NiTi?SPME fibers were studied and were applied to the extraction,concentration and determination of target analytes in environmental water samples.The thesis consists of the following chapters:Chapter 1: An introduction about SPME technique is described,including its theory,devices,advantages and limitations,materials of coatings and their applications in SPME.Furthermore,metal oxides are mainly introduced at last.Chapter 2: Hydrothermal oxidation was used to prepare a NiTi solid-phase microextraction fiber.The experimental results demonstrated that a nanoporous NiTi oxide composite coating was in situ grown on the surface of NiTi substrate by direct oxidation in aqueous H₂O₂ solution at 80 ?.The resulting composite oxide coating includes more nickel and less titanium.The prepared NiTi fiber was used to extract typical aromatic compounds coupled with HPLC-UV and exhibited good extraction selectivity for polycyclic aromatic hydrocarbons?PAHs?.The key factors affecting extraction efficiency of PAHs were examined.Under the optimized conditions,the calibration curves were linear in the range from 0.05 to 200 ?g L-1 with correlation coefficients of 0.999,and the limits of detection ranged from 0.026 to 0.056 ?g L-1.Furthermore,relative standard deviations?RSDs?for intra-day and inter-day repeatability of the single fiber varied from4.82% to 6.17% and from 5.40% to 6.53% for five replicates of PAHs at the spiking level of 50 ?g L-1,respectively.RSDs for the fiber-to-fiber reproducibility of five fibers prepared in different batches ranged from 6.37% to 8.42%.The developed method was suitable for selective enrichment and detection of target PAHs in environmental water samples with relative recoveries from 87.36% to 108.2% and RSDs below 8.05%.Moreover,this novel NiTi fiber is mechanically strong and chemically stable,and its preparation is precisely controllable.Chapter 3: An arrow-like zinc oxide nanosheets?ZnONSs?coating was electrodeposited on titanium and nickel oxide composite nanosheets?Ti O2/Ni OCNSs?coating which was in situ grown on the pretreated NiTi wire by hydrothermal treatment for SPME.The SPME performance of the fabricated fiber was investigated for concentration and determination of ultraviolet?UV?filters coupled to HPLC-UV.The main parameters affecting extraction performance were investigated and optimized.Under the optimized conditions,the calibration graphs were linear over the range 0.05²00 ?g L-1.The limits of detection of the proposed method were 0.09⁰.065 ?g L-1.The intra-day and inter-day repeatability of single fiber was 4.6%⁵.5% and 5.4%⁶.8%,respectively,and the fiber-to-fiber reproducibility 6.7%⁷.9% for the extraction of spiking water with 50 ?g L-1each analytes?n=5?.The proposed method was successfully applied to highly efficient concentration and sensitive determination of target UV filters from real environmental water samples with recoveries in the range of 86.8%¹05.9%.Moreover,this NiTi-based fiber could be fabricated in a highly reproducible manner.A single fiber is competent for all of the analyses in the entire sample sequence.Chapter 4: Zinc oxide nanoflakes?ZnONFs?were fabricated on a NiTi wire via electrochemical process for SPME.Prior to the growth of ZnONFs,the NiTi wire was hydrothermally treated for in situ growth of Ti O2/Ni O nanoflakes?Ti O2/Ni ONFs?as a seeding base.The applied potentials and reaction time were used to precisely control the dimensions of vertically oriented hexagonal ZnONFs on the NiTi fiber substrate.After annealing at 600 ?,the resulting fiber shows selective affinity towards non-polar aromatic compounds such as polychlorinated biphenyls?PCBs?and PAHs.The first application was proposed for the extraction and preconcentration of PCBs coupled to HPLC-UV.Due to high surface-to-volume ratio,double-sided open access sites and enhanced structural stability,the novel ZnONFs coating presents high extraction capability,rapid extraction kinetics and superior cycling stability compared to the commercial polydimethylsiloxane coating.The proposed method shows good linearity for PCBs in the range of 0.1 to 200 ?g L-1.Limits of detection were in the range of 0.020⁰.17 ?g L-1.RSDs for the single fiber repeatability and for the fiber-to-fiber reproducibility of the proposed method were below 9.76% and 7.55%,respectively.Satisfactory accuracy and precision were achieved for the selective preconcentration and the determination of PCBs in rain water,river water and wastewater samples.