Study On Novel Molecularly Imprinting Strategy And Its Applications For The Electrochemical 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. So the determination of NACs is of great importance and there is a necessity for accurate, sensitive, rapid, easy-to-use and portable method to facilitate the detection, quantification and remediation of NACs, which has been widely applied in forensics, antiterrorist activities and global environmental projects.Recently, the chemically modified electrodes (CMEs) have 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 have attracted world's attention and shows their broad application prospect in the fields of life science, food safety and environmental monitoring etc.The main work of this paper is focus on the study of novel molecularly imprinted polymers (MIPs) for the rapid determination of NACs. In this dissertation, we combined the molecularly imprinted technology and electrochemical sensor together to prepare some novel MIPs modified electrodes by using different kinds of materials as supporting matrix, such as conductive polyaniline nanofibers (PANIs), multiwalled carbon nanotube (MWCNTs), gold nanoparticles (Au). We have developed chemically modified electrodes with improved selectivity and sensitivity, which exhibited long-term stability of electrode and could be applied in environmental detection. Scanning electronic microscopy (SEM), FT-IR spectrum and UV-visble spectrum were used for characterization of the MIPs and modified film. The electrochemical behavior of the MIPs and CMEs was characterized by electrochemical impedance spectroscopy, differential pulse voltammetry (DPV) and cyclic voltammetry (CV). We are adhering to an organic combination of nanotechnology, molecularly imprinted technology, chemically modified electrodes and environmental chemistry. The primary research work is as follows:Chapter 1 OverviewIn chapter 1, we mainly introduced the hazardous and noxious effect of nitroaromatic compounds in our environment, the determination methods for trace nitroaromatic compounds, and then reviewed the basic principle of 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 Composites of Polyaniline Nanofibers and Molecularly Imprinted Polymers for Recognition of 1,3-Dinitrobenzene (DNB)This paper reports a monomer strategy for imprinting of 1,3-dinitrobenzene (DNB) molecules at the surface of conductive functional polyaniline nanofibers (PANIs) for the first time. It has been demonstrated that the vinyl functional monomer layer on the PANI surface can not only direct the selective occurrence of imprinting polymerization, but can also drive DNB templates into the polymer through charge-transfer complexing interactions between DNB and functionalized PANIs. These two basic processes lead to the formation of DNB-imprinted polymers at the surface of polyaniline nanofibers. The capacity to uptake DNB shows that selectivity coefficient in the nano fibers polymers is nearly three times as high as that of traditional imprinted materials and the nanofibers polymers also possess high selectivity toward DNB in comparison to similar nitroaromatic compounds. A linear response of DNB concentration between 2.20×10-8 and 3.08×10-6 mol/L was exhibited with a detection limit of 7.33×10-9 mol/L (S/N=3). These results reported here could form the basis of a new strategy for preparing various polymer-coating layers on polyaniline supports and the molecular imprinting techniques discussed could also find applications in the fields of separation, trace detection, and environmental monitoring.Chapter 3 Construction of Multiwalled Carbon Nanotubes/Polyethyleneimine and Molecularly Imprinted Polymers for Recognition of 2,4-Dinitrotoluene (DNT)A 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 CV and DPV. 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 1.0×10-6 mol/L with the detection limit of 1.0×10-9 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 Trinitrotoluene (TNT) In 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 mol/L with a detection limit of 1.3×10-8 mol/L (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.