Study On Novel Analytical Methods And Their Applications For The Rapid Detection Of Nitroaromatic Compounds

The nitroaromatic compounds (NACs) including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB),2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene (DNB), are used as high explosives in military armaments and a chemical intermediate in the manufacture of dyes and photographic chemicals. These highly toxic compounds in groundwater, soils, and sediments are toxic and cause health problems in both animals and human beings, including anemia, cataract development, abnormal liver function and skin irritation. Other effects include leukocytosis, peripheral neuritis, cardiac irregularities, renal irritation and bladder tumors. Even after degradations, the by-products are still toxic and carcinogenic to environment and our health. They have aroused great attentions and are placed on the list of stress control pollutants by United States Environmental Protection Agency. It is a necessity to develop accurate, sensitive, rapid, easy-to-use and portable methods to facilitate the detection, quantification and remediation of NACs.Recently, the chemically modified electrodes (CMEs) has been widely concerned. CMEs for quantitative analysis are kind of ideal unity of the separation, enrichment and determination. The distinguishing feature of CMEs is to endow the electrode with new and specific features, which has unique advantage to improve electrochemical sensitivity and selectivity. Due to its distinctly superiority, such as good selectivity and high sensitivity, high speed, low cost and on-line monitoring, CMEs shows their broad application prospect in food, environmental monitoring and military fields. Particularly, the CMEs based on molecules imprinted polymer have received extensively attention due to its significant advantages of mechanical/chemical stability, low cost, high selectivity and ease of preparation. Moreover, the CMEs can be employed in capillary electrophoresis (CE) system as amperometric detection (AD) for the simultaneous and sensitive measurements of target analytes. In recent years, CE-AD has been developed as an effective analytical method in environmental areas due to its high-separation speed and efficiency, low-sample consumption and short analysis time. Additionally, UV-Vis spectrophotometric analysis is also widely used in many fields because of simple, reliable, rapid sensitive measurement without any expensive and complex instruments.The main work of this paper is focus on the study of the novel principle and strategy for the rapid determination of NACs. In this dissertation, based on the functional nanoparticles, multiwalled carbon nanotube and molecularly imprinted polymers as supporting matrix, we have developed accurate, sensitive, rapid, easy-to-use and portable methods for the detection of NACs by combination of nanotechnology, molecularly imprinted technology, electrochemical sensor, capillary electrophoresis and colorimetric methods. Transmission electron microscopy (TEM), Scanning electronic microscopy (SEM), FT-IR spectrum and UV-Vis spectrum were used for characterization of the prepared nano-materials and modified film. The electrochemical behavior of NACs at the proposed CMEs was characterized by electrochemical impedance spectroscopy, differential pulse voltammetry (DPV) and cyclic voltammetry (CV). Additionally, the reaction mechanism of colorimetric determination of NACs was studied by UV-Vis spectrophotometry. The primary research work is as follows:Chapter 1 OverviewIn chaperl, we mainly introduced the hazardous and noxious effect of nitroaromatic compounds in our environment, the development of determination methods for trace nitroaromatic compounds, and then reviewed the basic principle the chemically modified electrodes, together with their application and development. Meanwhile, the development and application of nanotechnology and molecularly imprinted technology into electrochemical sensors was highlighted. Finally, we emphatically pointed out the purpose and significance of the dissertation, its innovation spot and content as well.Chapter 2 FDU-15-Pt composites with different Pt loading and their electrocatalytic reduction to ultratrace nitroaromatic compoundsFDU-15 is a hexagonal mesoporous material with nanometer-sized, highly ordered arrays and large special surface area. In this work, FDU-15-Pt with 2.0%, 5.0% and 8.0% Pt loading were synthesised and used for electrochemical detection of trace nitroaromatic compounds (NACs). The FDU-15-Pt samples were characterized by CO Chemisorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). It has been demonstrated that FDU-15-Pt with 2.0% Pt loading has the smallest Pt particle size of 2.9 nm, highest Pt metal dispersion of 37.7% and largest Pt metal surface area of 21.36 m2g-1. The FDU-15-Pt/PDDA modified electrode were assembled by electrostatic adsorption of Poly (diallyldimethylammonium chloride) (PDDA) and FDU-15-Pt. The 2.0% FDU-15-Pt modified sensor showed higher sensitivity for NACs than those of 5.0% and 8.0% FDU-15-Pt, which were verified by electrochemical experiments. A linear response over TNT concentration ranging from 8.8×10-9 M to 1.2×10-5 M was exhibited with a low detection limit of 2.9×10-9 M (S/N=3). Moreover, the proposed 2.0% FDU-15-Pt/PDDA modified sensor has been applied to the detection of NACs in spiked environmental water samples and shows promise for fast and accurate determination of trace NACs in real samples.Chapter 3 Composites of Multiwalled Carbon Nanotubes/Polyethyleneimine and Molecularly Imprinted Polymers for 2,4-Dinitrotoluene (DNT) RecognitionA novel strategy for imprinting of 2,4-dinitrotoluene (DNT) molecules at the surface of functionalized multiwalled carbon nanotubes/polyethyleneimine (Fun-MWCNTs/PEI) was developed to prepare a highly selective DNT-imprinted electrochemical sensor. The electrochemical characteristics of the imprinted Fun-MWCNTs/PEI-MIPs sensor were investigated by cyclic voltammetry and differential pulse voltammetry. The Fun-MWCNTs/PEI-MIPs modified electrode showed excellent electrocatalytic activity to DNT and the current responses were in good linear from 2.2×10-9 mol/L to 1.0x 10-6 mol/L with the detection limit of 1.Ox 10-9 mol/L (S/N=3). Additionally, the imprinted films provided a greater number of effective imprinted sites at the surface or in the proximity of surface of Fun-MWCNTs/PEI-MIPs, and thus showed high selectivity toward DNT in comparison to similar nitroaromatic compounds. The surface molecular imprinted strategy developed a new way for rapid, sensitive and selective measurement of trace DNT, and showed potential utility in the on-line monitoring of in the fields of industry and environmental monitoring.Chapter 4 Two-dimensional molecular imprinting approach for the electrochemical detection of TrinitrotolueneIn this work, we demonstrated a sensitive and selective electrochemical sensing protocol for the detection of TNT prepared from alkanethiols self-assembled on AuNPs modified glassy carbon (GC) electrode with preadsorbed templates of TNT. It demonstrated that the 2D molecular imprinting monolayers (MIMs) can provide a better site accessibility and lower mass-transfer resistance, while the AuNPs can enhance electrode conductivity, facilitate the electron transfer and increase the amount of TNT-imprinted sites. The prepared sensor showed not only high selectivity toward TNT in comparison to other similar nitroaromatic compounds (NACs), but also a wide linear range over TNT concentration from 4.0×10-8 to 3.2×10-6 M with a detection limit of 1.3×10-8 M (S/N=3). Moreover, the imprinted sensor has been applied to the determination of TNT in spiked environmental water samples and shows promise for fast and sensitive measurement of trace levels of TNT in real samples.Chapter 5 Simultaneous determination of nitroaromatic compounds in water using capillary electrophoresis with amperometric detection on an electrode modified with a mesoporous nano-structured carbon materialIn this article, a carbon disk electrode modified with mesoporous carbon material(CMK-3) was used in CE with amperometric detection system for the simultaneous determination of four types of important nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT),1,3,5-trinitrobenzene (TNB),2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene (DNB). Compared with the bare carbon electrode, the CMK-3 modified electrode greatly improved the sensitivity at a relatively positive detection potential due to its excellent electrocatalytic activities, high conductivity and large effective surface area. The four analytes could be well separated and detected within 480 s. A good linear response was obtained for TNB, DNB, TNT and DNT from 8.4 to 5.0×103μg/L, with correlation coefficients higher than 0.9992. And the detection limits were established between 3.0 and 4.7μg/L for the four investigated nitroaromatic compounds (S/N=3). The CMK-3-modified electrode was successfully employed to analyze coking wastewater, tap water and river samples with recoveries in the range of 94.8-109.0%, and RSDs less than 5.0%. The presented results demonstrated that the CMK-3-modified carbon electrode used in CE with amperometric detection was of convenient preparation, high sensitivity and good repeatability, which could be employed in the rapid determination of practical samples.Chapter 6 Fe3O4 Magnetic Nanoparticles as Peroxidase Mimetics and Their Application in Colorimetric Determination of 2,4-dinitrotoluene (DNT)Fe3O4 nanoparticles have received considerable attention because of their unique properties, such as ease of production, strong magnetism, biological and chemical inert. In this article, we prepared Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) by co-precipitation method, which possess intrinsic peroxidase-like activity. We found that the Fe3O4 nanoparticles not only can catalyze the oxidation of a peroxidase substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate acid) (ABTS) by H2O2 to produce the colored product with maximum absorbance at 417 nm, but also can catalyze the oxidation of 2,4-dinitrotoluene (DNT) by H2O2 and consume the H2O2 in reaction system. On the basis of the reactions mechanism described above, we established a new reaction system of Fe3O4MNPs-ABTS-H2O2-DNT for determination of trace amount of DNT. In this method, the existence of DNT can cause a color change of the reaction system. The colorimetric method showed good response toward DNT detection with a linear range from 5×l0-7～2.0×10"5 M. In additional, the reactions mechanism and influence factors of proposed Fe3O4MNPs-ABTS-H2O2-DNT system were also discussed. These results reported here basically established a simple, rapid and sensitive strategy for colorimetric detection of NACs, which showed great potential application in the on-line monitoring of NACs in environmental water samples.