Preparation Of Novel Film Modified Electrodes And Their Applications For The Analysis Of Environmental Pollutants

Hydroquinone (HQ) and catechol (CC) are two important isomers of phenoliccompounds widely applied as essential raw materials in chemical industry fields. Thesefields include cosmetics, antioxidant, tanning, pesticides, medicines, photography andother synthetic applications. However, the phenolic compounds are highly toxic tohuman health even at extremely low concentration. Even worse, they are difficult todegrade in the ecological environment and accumulate in the environment, becomingthe main pollution sources for soil and water. Additionally, the phenolic compounds canenter the human body through the food chain, causing the disorder of the endocrine andthe nerve systems and/or the failure of the reproductive and immune function. Even so,the use level of phenolic compounds increased year after year due to the rapid economicdevelopment. As phenolic compounds are released into soil and water in the process ofsynthesis and application, it is important to detect their residues in soil and water forprotecting human health and for maintaining the sustainable development of ecologicalsystem.Due to the advantages of fast response, low cost, simple operation, high sensitivityand selectivity, electrochemically analytical methods have been widely applied indisease diagnosis, drug analysis and environmental monitoring. However, there are stilla few limitations for the conventional unmodified electrodes to detect HQ and CC, e.g.,high overpotential for oxidation of these phenolic compounds, poor detection selectivity,overlapped oxidation/reduction peaks. The aim of chemically modified electrodes is tocarry out the molecular design on the bare electrode surface. In other words, theelectrodes are applied special chemical and electrochemical properties by immobilizingion, molecular and polymer on their surface, thus, improving their detection sensitivityand selective. How to construct high sensitive and selective sensing interface is a keyfactor for the preparation of novel chemically modified electrode. In recent years,electrodes modified by organic molecules have attracted wide spread attentions owingto their good stability, reproducibility, abundant active sites, homogeneity inelectrochemical deposition and strong attachment on electrode surface. In this paper, wehave built a series of polymer film modified electrodes for detecting the organicenvironmental pollutants of hydroquinone and catechol. The contents were as follows:1. preparation and electrochemical properties of glassy carbon electrode modified by L-cysteine/Prussian blue.A glassy carbon electrode (GCE) modified by Prussian blue (PB) and L-Cysteine(L-Cys) composite film was prepared successfully by the method ofelectro-polymerization and pulse electrodeposition. The electrochemical behavior ofL-Cys/PB/GCE for detection of hydroquinone was investigated by cyclic voltmmetryand chronoamperometry. The results showed that in0.1mol/L PBS (pH7.0) buffersolution, L-Cys/PB/GCE exhibited excellent catalytic and enhancement effect on theelectrochemical oxidation of hydroquinone, and the oxidation peak current increased ca.5times compared to that at bare GCE. Under the optimal conditions, hydroquinoneconcentration was linear with peak current in the range of0.18-120μmol/L with acorrelation coefficient of0.9962, and the detection limit was0.065μmol/L (S/N=3).The proposed hydroquinone biosensor has good repeatability, reproducibility, selectivityand stability, and can be applied to determine the hydroquinone content in water sample.2. Preparation and electrocatalytic activity of glassy carbon electrode modified byL-cysteine/Glycine composite film.A novel voltammetric sensor based on a glassy carbon electrode modified withL-cysteine/glycine composite film (L-cysteine/glycine/GCE) was developed for thequantitative detection of catechol. The as-fabricated electrode exhibited goodelectrochemical performance with low electron transfer resistance. The results ofelectrochemical impedance spectroscopy (EIS) revealed that electron transfer throughL-cysteine/glycine film was more facile than that of the bare glassy carbon electrode.The electrochemical behavior of catechol was also investigated by cyclic voltammetry(CV) and differential pulse voltammetry (DPV) at the prepared electrode. The modifiedelectrode showed excellent electrocatalytic activity towards the oxidation of catechol inNaOH-KH2PO4buffer solution (pH=6.0). Under the optimum conditions, the linearrelationship between the oxidation peak current and the concentration of catechol can beobtained in the range from3μmol/L to280μmol/L with the detection limit as0.32μmol/L (S/N=3). In addition, the interference and stability study showed asatisfactory detection result by this electrode. Besides, the proposed method wassuccessfully applied to the determination of catechol in water samples with satisfactoryresults.3. A novel sensor for detection of hydroquinone based on methionine-Aunanoparticle modified glassy carbon electrode.A high sensitive electrochemical sensor based on methionine/gold nanoparticles (MET/AuNPs) modified glassy carbon electrode (GCE) was fabricated for thequantitative detection of hydroquinone (HQ). The as-modified electrode wascharacterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD)techniques. The electrochemical performance of the sensor to HQ was investigated byusing cyclic and differential pulse voltammetry, which revealed its excellentelectrocatalytic activity and reversibility towards HQ. The separation of anodic andcathodic peak (Ep) was decreased from471mV to75mV. The anodic peak currentachieved under the optimum conditions was linear with the HQ concentration rangingfrom8μmol/L to400μmol/L with the detection limit0.12μmol/L (S/N=3). Theas-fabricated sensor also showed a good selectivity towards HQ without demonstratinginterference from other coexisting species. Furthermore, the sensor showed a goodperformance for HQ detection in environmental water, which suggests its potentialpractical application.4. A voltammetric sensor based on eosin Y film modified glassy carbon electrodefor simultaneous determination of hydroquinone and catechol.By using cyclic voltammetry method, eosin Y film was electrodeposited on thesurface of glassy carbon electrode (GCE) to obtain the modified electrode (denoted aseosin Y/GCE). Scanning electron microscopy, electrochemical impedance spectroscopyand cyclic voltammetry techniques were used for morphology and electrochemicalproperty characterization of eosin Y/GCE. The electrocatalysis capability of eosinY/GCE to hydroquinone (HQ) and catechol (CC) was investigated by cyclicvoltammetry (CV) and differential pulse voltammetry (DPV) techniques. Comparedwith the bare GCE, eosin Y/GCE behaved an outstanding electrocatalytic activity andreversibility towards the oxidation of HQ and CC. The oxidation and reduction peakseparation was decreased from386to60mV for HQ and from340to56mV for CC ateosin Y/GCE, respectively. The differential pulse voltammetry results showed that theoxidation peaks of the two isomers in acetate buffer solution could be clearlydiscriminated with a peak potential separation of ca.111mV, which was wide enough todiscriminate the two dihydroxybenzene isomers. Under the optimal conditions, theoxidation peak currents were linear to HQ/CC concentration in the range from1μmol/Lto130μmol/L with the detection limit as0.14μmol/L (S/N=3) for HQ and0.12μmol/L(S/N=3) for CC, respectively. Moreover, eosin Y/GCE exhibited an excellentanti-interference ability. It was successfully applied to the simultaneous determinationof HQ and CC in spiked water samples with reliable recovery. 5. Simultaneous determination of hydroquinone and catechol based onL-histidine-erythrosine composite film modified glassy carbon electrode.By using cyclic voltammetry method, L-histidine and Erythrosine waselectrodeposited on the surface of glassy carbon electrode (GCE) to obtain the modifiedelectrode (denoted as L-his-Erythrosine/GCE). Scanning electron microscopy,electrochemical impedance spectroscopy and cyclic voltammetry techniques were usedfor morphology and electrochemical property characterization of L-His-Erythrosine/GCE. The electrocatalysis capability of L-His-Erythrosine/GCE to hydroquinone (HQ)and catechol(CC) was investigated by cyclic voltammetry(CV) and differential pulsevoltammetry (DPV) techniques. Compared with the bare GCE, L-His-Erythrosine/GCEbehaved an outstanding electrocatalytic activity and reversibility towards the oxidationof HQ and CC. The oxidation overpotentials of HQ and CC decreased significantly andthe corresponding oxidation currents increased remarkably. Due to the large separationof oxidation peak potentials (108mV), the concentrations of HQ and CC can be easilydetermined simultaneously. Under the optimum conditions, the oxidation peak currentsfor both HQ and CC increase linearly with the respective concentrations in the0.2μmol/L to110μmol/L concentration range, with the detection limits of0.19(HQ) and0.16μmol/L (CC)(S/N=3), respectively. Furthermore, the modified electrodeexhibited good reproducibility and selectivity. The modified electrode was successfullyapplied to the simultaneous determination of HQ and CC in actual water samples, therecoveries got by standard addition method were in the range of99.85%～100.6%(HQ)and99.17%～100.2%(CC).6. A novel electrochemical sensor for simultaneous determination of hydroquinoneand catechol based on the hybrid modified electrode composed of MnO2nanoparticles and Hemoglobin.Electrochemically active composite film that contains MnO2nanoparticles andHemoglobin (Hb) has been synthesized on glassy carbon electrode (GCE) by Cyclicvoltammetry (CV)(MnO2-Hb/GCE). Scanning electron microscopy (SEM) andelectrochemical impedance spectroscopy (EIS) were used for characterizing themorphology and electrochemical properties of MnO2-Hb/GCE. The electrocatalyticcapability of MnO2-Hb/GCE to hydroquinone (HQ) and catechol (CC) was investigatedby cyclic voltammetry(CV) and differential pulse voltammetry (DPV) techniques. Fromelectrocatalysis studies, both HQ and CC cause a pair of well-defined redox peaks at themodified electrode in pH5.8Na2HPO4-C4H2O7buffer solution. The difference on oxidation peak potential between the two isomers was110mV, which revealed that HQand CC could be identified entirely at the MnO2-Hb/GCE. Under the optimizedconditions, the anodic peak currents were linear to HQ and CC concentrations in therange from1μmol/L to300μmol/L, with the detection limit as0.18μmol/L (HQ) and0.19μmol/L (CC)(S/N=3), respectively. Moreover, MnO2-Hb/GCE exhibited anexcellent anti-interference ability. Further, the proposed method has been successfullyapplied to simultaneous determine the two isomers in real water samples withoutprevious chemical or physical separations.