哈尔滨工业大学工学硕士学位论文
Abstract
Bisphenol A (BPA) is widely used in food-grade packaging materials and has been favored by people. However, at high temperature and pressure treatment, researchers found that BPA can be penetrated from packaging containers or plastics into food. As a result, BPA has entered the public horizon as a ubiquitous migratory contaminant of food packaging and aroused serious concerns about food safety issues. Up to now, a variety of methods have been developed for the detection of BPA, such as chromatography, fluorescence, etc. However, most of them require high sample extraction and purification, which requires tedious sample preparation and pretreatment procedures. Electrochemical sensor is an effective method for the detection and analysis of BPA because of its high sensitivity and simplicity. However, the response of conventional electrochemical sensors towards BPA is very weak, which makes it difficult to determine the BPA directly. Therefore, in order to increase the specific surface area of working electrode and enhance the response of BPA sensor, electrochemical sensors modified with advanced materials have been continuously developed for the detection of BPA.
In this paper, graphene-silver nanostructures (rGO-Ag) were prepared by a three-step reduction method using electrostatic force-directed assembly technique (ESFDA) with GO and AgNO3 as the reaction precursors respectively. The effects of chemical reduction system, mass ratio of precursors and annealing temperature on the structure and properties of rGO-Ag were also investigated. Meanwhile, the prepared rGO-Ag nanocomposites were characterized by SEM, TEM, XRD, FTIR, XPS and Raman. Besides, their oxidation resistance, stability and electrochemical properties were also studied. The results show that the prepared rGO-Ag nanostructures using hydrazine hydrate as chemical reduction system with the precursor mass ratio of 1: 1 and 700 °C annealing temperature have the best morphology and properties. SEM and TEM indicate that the Ag particles are separated from each other and dispersed uniformly between the graphene sheets. Besides, the average size of the Ag particles obtained by the statistical calculation is 27.01 nm. Meanwhile, the nanostructures of rGO-Ag also exhibit excellent oxidation resistance, high stability and good electrochemical activity.
The BPA electrochemical sensor modified with graphene-silver/poly-lysine composites (rGO-Ag/PLL) was prepared by electrochemical electropolymerization. The effects of different preparation parameters on the performance of BPA sensor were investigated, such as the the pH of buffer solution, the loading of rGO-Ag, the number of CV scanning cycles and the concentration of L-lysine monomer. And the obtained
哈尔滨工业大学工学硕士学位论文
optimal preparation parameters are as follows: the pH of PBS solution for electropolymerization of L-lysine is 9.0, the loading of rGO-Ag is 8 mg/mL (2.5 μL), the number of CV scanning cycles is 10 and the concentration of L-lysine monomer is 10 mM. The results show that the surface morphology of rGO-Ag nanostructures has changed significantly after PLL modification, showing a rugged state. In addition, the prepared rGO-Ag/PLL/GCE has the highest oxidation peak current response to BPA compared with GCE and rGO-Ag/GCE electrodes.
In order to achieve the accurate determination of BPA, we optimized its testing conditions, such as the pH of buffer solution, the accumulation time and potential. And the obtained optimal parameters are as follows: the pH of the test buffer is equal to 8.0, the deposition potential and deposition time are -0.4 V and 200 s, respectively. Based on the optimal experimental conditions, the fabricated electrochemical sensor exhibits a linear response to BPA in the range of 1-80 μM with the limit of detection (LOD) of 0.54 μM at a signal-to-noise ratio of 3. Considering demand of practical application, the reproducibility, stability and selectivity of the BPA sensor were evaluated and investigated. The results show that the fabricated sensor has good reproducibility, stability and anti-interference. Finally, the proposed method was applied to the quantitative analysis of drinking water containing BPA and obtained satisfactory results, indicating the BPA sensor could meet the requirements in practical applications.
Keywords: bisphenol A, electrochemical sensor, graphene, nanocomposites, differential pulse voltammetry