| Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardant, and studies have proved its biological toxicities such as endocrine disrupting, immunotoxicity, endocrine effects, nephrotoxicity, and developmental toxicity. TBBPA exists not only in the enrivonmental medium, but also in the animals even in humans, and has been regarded as a potential permanent organic pollutant. Although there are several reports about electrochemical detection of TBBPA, they almost belong to indirect methods. Therefore, it is imperative to develop new and direct electrochemical sensing methods and strategies for sensitive, simple, fast and accurate determination of TBBPA.Objective:The objective of this research work was to build several direct, high sensitive electrochemical sensing systems for tetrabromobisphenol A based on nanomaterial and surfactant enhancement effects, and investigate their enhancement mechanism and practical application.Methods:Several chemical modified electrodes were constructed by drop-coating method or electrodeposition method. Scanning electron microscope and atomic force microscope were used to characterize their surface morphology. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behaviors on different modified electrodes. Electrochemical impedance method and chronocoulometry were used to study the enhancement mechanism of different sensing membranes. Besides, detection parameters were optimized to improve the sensitivity.Results:The results mainly contain the following six parts:(1) The electrochemical behaviors of TBBPA were studied with cyclic voltammetry, and the influences of pH were investigated. It was found that TBBPA had the strongest and irreversible signal response in acetate buffer with pH of 4.6. Then, the oxidation mechanism of TBBPA was studied, and one electron and one proton were involved. Differential pulse voltammetry was used to study the response of trace amount of TBBPA, and it showed that glassy carbon electrode (GCE) had poor activity toward TBBPA oxidation and could not be qualitified for trace TBBPA detection.(2) Acetylene black (AB) particles were dispersed into different systems by ultrasonication, including dimethyl formamide (DMF), chitosan (CS) aqueous solution, and the mixture of dihexadecyl hydrogen phosphate (DHP)/water. After that, three kinds of acetylene black (AB) films with different morphology and electrochemical reactivity were prepared by evaporating the solvents. The prepared AB films exhibited different enhancement ability toward TBBPA oxidation on the surface of AB films, and the enhancement mechanism of AB films prepared by different dispersion system were investigated. As a result, a sensitive electrochemical sensor based on the remarkable enhancement effects of AB film was developed for the rapid detection of TBBPA. The linear range was from 10 to 350 ?g L"1, and the detection limit was 6.08 ?g L-1 (cal.11 nM). This new sensing system was used for the analysis of TBBPA in water samples, and good recoveries in the range of 99.3-104.5% were obtained.(3) Electrochemcial behaviours of TBBPA in the presence of cation, anion and nonionic surfactants were studied. It was found that the oxidation response of TBBPA obviously decreased in the presence of anion surfactants and slightly increased in the presence of nonionic surfactants, while greatly increased in the presence of cation surfactants. The response signals of TBBPA on CPE were improved obviously by cetyltrimethylammonium bromide (CTAB), and the enhancement mechanism was further studied. It was found that the existence of CTAB facilitates the electron transfer of TBBPA, and increased the accumulation efficiency on CPE surface. Based on the strong interface enhancement effects of CTAB, a sensitive and convenient sensing platform was developed for TBBPA. The linear range is from 2.5 to 800 nM, and the detection limit is 0.99 nM. This new sensing system was used in water sample analysis, and the values of recovery were over the range from 94.59% to 102.75%.(4) Three types of hydrophobic surfactants with one, two and three C18-alkyl chains, including octadecyltrimethylammonium bromide (OTMA), dioctadecyldimethy-lammonium bromide (DODMA) and trioctadecylmethylammonium bromide (TOMA), were used to construct sensing films for TBBPA. The electrochemical behaviours of TBBPA on the surface of these three kinds of films were studied. Different surfactant-modified GCEs had different signal enhancement ability toward TBBPA oxidation. Surface morphology analysis revealed that the modification of surfactants on GCE increased the surface roughness and introduced three-dimensional structures. Experimental results indicated that signal enhancement abilities of surfactant films were heavily dependent on the molecular structures, and DODMA film was more active for the oxidation of TBBPA. As a result, a sensitive and simple electrochemical sensing platform was developed for TBBPA. The linear range is from 1.0 to 500?g L-1,and the detection limit is 0.57?g L-1 (1.05 nM). This new sensing system was used to detect TBBPA in e-waste samples, and the results were consistent with the values that obtained by high-performance liquid chromatography.(5) Graphene nanosheets (GS) were prepared via solvent exfoliation and used to modify GCE, and then further modified with dioctadecyldimethylammonium bromide (DODMA). On the surface of single DODMA or GS film, the direct oxidation peak currents of TBBPA increased effectively. Interestingly, the oxidation signals of TBBPA further enhanced greatly on the GS-DODMA composite film. The synergetic signal enhancement mechanism was studied, and the greatly-increased accumulation efficiency was the main reason. As a result, a novel electrochemical sensing platform was successfully developed for TBBPA based on the synergetic signal enhancement of GS-DODMA composite film. The linear range is from 0.1 to 400 ?g L-1, and the detection limit is as low as 41.8 ng L-1 (76.8 pM). The practical applications in water samples manifested that this new determination system was accurate and feasible.(6) Various gold nanoparticles (AuNPs) were in situ prepared on the electrode surface through electrochemical reduction under different potentials such as -0.60,-0.50,-0.40,-0.30 and -0.20 V. The reduction potential heavily affected the surface morphology and electrochemical activity of AuNPs such as effective area and catalytic ability, as confirmed using atomic force microscopy and electrochemical impedance spectroscopy. The electrochemical behaviors of TBBPA were studied, and it was found that surface morphology significantly influenced the oxidation signal which showed difference on the different AuNPs. Interestingly, the existence of 2-mercaptobenzothiazole (MBT) further improved the oxidation signals of TBBPA on AuNPs, displaying obvious synergetic enhancement toward TBBPA oxidation. The influences of deposition potential, pH value, MBT concentration and accumulation time were examined on the oxidation signals of TBBPA. As a result, a novel electrochemical platform was developed for direct determination of TBBPA. The linear range is from 0.5 to 30 ?g L-1, and the detection limit is as low as 0.12 ?g L-1 (0.22 nM). This new sensing system was used in water sample analysis, and the values of recovery were over the range from 97.2% to 103.6%. The proposed method is not only accurate and feasible, but also very promising in the field of automation monitoring due to that the preparation and renewing of sensing film are easily fulfilled by electrochemical processes.Conclusions:Based on the signal enhancement of nanomaterials including acetylene black, graphene, AuNPs, and surfactants with different structures, several highly sensitive detection methods were developed for TBBPA detection, and the enhancement mechanisms were detailedly investigated. Furthermore, the proposed methods were eventually applied in the practical samples analysis with high accuracy and good practicability. |
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