| In recent years, heavy metal pollution has become a major concern with the people’sawareness of environmental protection. Atomic absorption spectrometry (AAS) is one ofthe commonly used methods for the analysis of metal elements. However, when theelement concentration is very low, especially in a complex sample, a sample pre-treatmentmethod is often necessary to improve the sensitivity and selectivity of the analyticalmethod.Traditional sample pre-treatment methods are often tedious, time-consuming and needlarge volumes of samples and toxic organic solvents. In order to overcome thesedisadvantages, some new sample pretreatment techniques have been developed, such asmicrowave-assisted extraction (MAE), supercritical fluid extraction (SFE), solid-phaseextraction (SPE), solid phase micro extraction (SPME), cloud point extraction (CPE),single-drop microextraction extraction (SDME), hollow fiber-based liquid phasemicroextraction (HF-LPME), liquid-phase microextraction based on solidification offloating organic drop (SFO-LPME) and magnetic solid-phase extraction (MSPE). MSPEhas high extraction capacity and extraction efficiency, and magnetic adsorbent can berecycled and reused. In MSPE, phase separation can be achieved only by applying anexternal magnetic field. The method is relatively simple. MSPE has been applied for theextractions of some trace contaminants.The thesis is mainly concerned with the following aspects:1. A graphene magnetic nanoparticles (G-Fe3O4) was prepared and used as the adsorbentfor the preconcentration of trace amount of copper using1-(2-pyrrole azo)-2-naphthol(PAN) as chelating reagent prior to its determination by flame atomic absorptionspectrometry. This MSPE method, which takes the advantages of both the high graphenenanoparticle adsorption and the easy phase separation of the magnetic materials from thesample solution, could avoid the time-consuming experimental procedures often invovlvedin the traditional solid phase extraction, such as centrifugation and filtrations. Variousexperimental parameters affecting the extraction efficiencies were investigated. Under theoptimum conditions, the concentration factor for the analyte was86.4. The linearity of themethod was in the range from0.5to100ng/mL with the correlation coefficient (r) of 0.9981. The limit of detection (S/N=3) of the method was0.067ng/mL. The relativestandard deviations (RSDs) varied from2.4%to5.2%(n=5), and the recoveries of themethod were in the range from94.5%to103.0%. The method proved to be simple,convenient and sensitive for the determination of copper in environmental water samples.2. A new method for the determination of trace nickel in water samples was developedby MSPE coupled with flame atomic absorption spectrometry. Parameters that affect theextraction efficiency, such as the pH of sample solution, extraction time, the amount of theadsorbent and the desorption conditions were investigated and optimized. Under theoptimum conditions, the linearity of the method was obtained in the range of0.50~150ng/mL with the correlation coefficient (r) of0.9983. The enrichment factor for nickel was100, The limit of detection was0.1ng/mL (S/N=3). The method has been successfullyapplied to the analysis of target nickel in Tap water, Park lake water and Factorywastewater samples with satisfactory results. The spiking recoveries ranged from95.6%to102.9%with the relative standard deviations falling between2.0%~4.1%.3. A dispersive liquid–liquid microextraction based on solidification of floating organicdroplet (DLLME-SFO) was developed as a new approach for the extraction of tracecadmium in water samples followed by the determination with flame atomic absorptionspectrometry.8-hydroxy quinoline and1-dodecanol were used as chelating agent andextraction solvent respectively in the DLLME-SFO. The experimental parameters relatedto the DLLME-SFO such as the type and volume of the extraction and dispersive solvent,extraction time, and the concentration of chelating agent were investigated and optimized.In the experiment, the enrichment factor for cadmium was133. The method was linear inthe range from0.5to500ng mL-1of cadmium in the samples with the correlationcoefficient (r) of0.9987and limit of detection of0.3ng/mL. The method can be used forthe determination of cadmium in water samples. The recoveries for the samples spikedwith cadmium at5.0and10.0ng/mL were in the range between92.2%and104.7%. Therelative standard deviations (RSD) varied from2.5%to5.1%. The method was used for thedetection of trace cadmium in water samples.4. A graphene-based magnetic nanocomposite was synthesized and used as an adsorbentfor the removal of a dye from aqueous solutions. The morphology and inner structure ofthe magnetic adsorbent were characterized by both transmission electron microscopy andX-ray diffraction. The adsorption characteristics of the graphene magnetic nanocompositeadsorbent were examined using an organic dye fuchsine as the adsorbate. The adsorptionkinetics, adsorption capacity of the adsorbent, and the effect of the adsorbent dosage andsolution pH on the removal efficiency of fuchsine were investigated. Freundlich model andLangmuir model were used to study the adsorption isotherms. The resultant kinetic datawere well fitted by a pseudo second-order model. The graphene magnetic nanocompositeproved to be an efficient adsorbent and could be easily used for separation purposes. |
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