Determination Of Phenolic Pollutants In Soil And Water Samples Based On Nanomaterials Modified Electrodes

Phenolic compounds are persistent organic pollutant with high toxicity, which can cause theendocrine disorder of the biology, the reproductive and immune dysfunction, nerve behaviorand developmental disorders. Phenolic compounds have also carcinogenicity, teratogenicityand mutagenicity. However, the use level of phenolic compounds increased year after yearwith the rapid development of economy. Up to now, phenolic compounds are mainly used inthe fields of plastic, dye, pesticide, papermaking and petrochemical industry. Becausephenolic compounds can release into soil and water in the process of synthesis and application,it is important to detect their residues in soil and water.Due to the advantages of operation simplication, fast response, high sensitivity, low costand low pollution, electrochemically analytical methods have been widely applied in diseasediagnosis, drug analysis and environmental monitoring. Therefore, we carefully investigatedthe electrochemical bahaviour of some phenolic compounds at nanomaterial modifiedelectrodes, and the content of these phenolic compounds in soil and water samples wasdetected. This dissertation is divided into six main parts:（1） An amperometric bisphenol A （BPA） biosensor was fabricated by immobilizingtyrosinase on multiwalled carbon nanotubes （MWNTs）-cobalt phthalocyanine （CoPc）-silkfibroin （SF） composite modified glassy carbon electrode （GCE）. In MWNTs-CoPc-SFcomposite film, SF provided a biocompatible microenvironment for the tyrosinase to retain itsbioactivity, MWNTs possessed excellent inherent conductivity to enhance the electrontransfer rate and CoPc showed good electrocatalytic activity to electrooxidation of BPA. Thecyclic voltammogram of BPA at this biosensor exhibited a well defined anodic peak at0.625V. Compared with bare GCE, the oxidation signal of BPA significantly increased; therefore,this oxidation signal was used to determine BPA. The effect factors were optimized and theelectrochemical parameters were calculated. The possible oxidation mechanism was alsodiscussed. Under optimum conditions, the oxidation current was proportional to BPAconcentration in the range from5.0×10^-8to3.0×10^-6M with correlation coefficient of0.9979and detection limit of3.0×10^-8M （S/N=3）. The proposed method was successfully applied to determine BPA in soil samples and the recovery was in the range from96.5%to105.5%.（2） The electrochemical behavior of bisphenol A （BPA） was investigated on Mg-Al layereddouble hydroxide （LDH） modified glassy carbon electrode （GCE） by cyclic voltammetry（CV）, differential pulse voltammetry （DPV）, linear sweep voltammetry （LSV） andchronocoulumetry （CC）. The cyclic voltammogram of BPA on the modified electrodeexhibited a well defined anodic peak at0.454V in0.1M pH8.0phosphate buffer solution（PBS）. The experimental parameters were optimized and the kinetic parameters wereinvestigated. The probable oxidation mechanism was proposed. Under the optimizedconditions, the oxidation peak current was proportional to BPA concentration in the rangefrom1×10^-8to1.05×10^-6M with the correlation coefficient of0.9959. The detection limitwas5.0×10^-9M （S/N=3）. The fabricated electrode showed good reproducibility, stabilityand anti-interference. The proposed method was successfully applied to determine BPA insoil samples and the results were satisfactory.（3） An amperometric sensor was fabricated based on immobilized CoTe quantum dots（CoTe QDs） and PAMAM dendrimer （PAMAM） onto glassy carbon electrode （GCE） surface.The cyclic voltammogram of BPA on the sensor exhibited a well-defined anodic peak at0.490V in0.1M pH8.0PBS. The determination conditions were optimized and the kineticparameters were calculated. The linear range was1.3×10^-8-9.89×10^-6M with the correlationcoefficient of0.9999. The limit of detection was estimated to be1×10^-9M. The currentreached the steady-state current within about5s. Furthermore, the fabricated sensor wassuccessfully applied to determine BPA in real water samples.（4） A glassy carbon electrode was modified with hydroxyapatite nanopowder （HA-NP） andcharacterized by TEM and SEM. The electrochemical behavior of4-nitrophenol （4-NP） and2,4-dinitrophenol （2,4-DNP） was investigated by the fabricated electrode,respectively. Theoxidation peak current of4-NP and2,4-DNP at the modified electrode was increased（compared to the base GCE）, thus indicating that the HA-NP exhibits a remarkableenhancement effect on the electrochemical oxidation of4-NP and2,4-DNP. The effects ofloading with HA-NP, pH value, scan rate and accumulation were examined. The oxidationpeak current of4-NP and2,4-DNP is proportional to their concentration in the range from1.0 to300μmol/L and2.0to600μmol/L, respectively. The detection limit are0.6μmol/L （4-NP）and0.75μmol/L （2,4-DNP）（at an S/N=3）. The method is simple, selective and sensitive. Itwas successfully applied to the determination of4-NP and2,4-DNP in water samples.（5） The graphene-chitosan composite film modified glassy carbon electrode （GCE） wasfabricated and used to determine4-aminophenol （4-AP）. In0.1M pH6.3phosphate buffersolution, the redox peak currents of4-AP increased significantly and the peak-to-peakseparation decreased greatly at graphene-chitosan composite film modified GCE comparedwith bare GCE and chitosan modified GCE, indicating that graphene possessedelectrocatalytic activity towards4-AP. The experimental conditions were optimized and thekinetic parameters were investigated. The oxidation mechanism was discussed. Under theoptimal experimental conditions, the oxidation peak current was proportional to4-APconcentration in the range from0.2to550μmol/L with the correlation coefficient of0.9930.The detection limit was0.057μmol/L （S/N=3）. Using the proposed method,4-AP wassuccessfully determined in water samples with standard addition method, suggesting that thismethod can be applied to determine4-AP in environments samples.（6） The mixture of carbon materials was prepared by simple and fast method based onelectrolyzing graphite rod in KNO₃solution under the constant current. The transmissionelectron microscope （TEM） indicated that the mixture was comprised of graphene nanosheetsand carbon nanoparticles, and some carbon nanoaprticles were adsorbed on the surface ofgraphene nanosheet. The mixture modified glassy carbon electrode showed excellent catalyticand adsorptive ability towards the redox of hydroquinone （HQ）. The effect factors, such as pH,scan rate, accumulation time and accumulation potential, were optimized. Thechronocoulometry investigation demonstrated that the mixture can effectively increase theelectrochemical active surface. Under the optimal determination conditions, the oxidationpeak current was proportional to HQ concentration in the range of0.1to100and100to600μmol/L. The detection limit was estimated to be0.01μmol/L （S/N=3）. The developedelectrode was further applied to determine HQ in soil samples with satisfactory results.