Nanocomposite Modified Electrodes Applied To Detection Of Heavy Metals And Hydroquinone

Toxic heavy metal ions and some toxic organic compounds in water are great threats for human beings and living organisms, so their trace analyses are very important. Anodic stripping voltammetry (ASV) for trace element speciation analysis merits that not only pocesses high sensitivity, good resolution, suitability for simultaneous determination of metal elements, but also needs inexpensive equipment and is easy to operate. Modification of specific chemical groups on the electrode surface can improve the detection sensitivity and selectivity. Carbon nanotubes (CNTs) as a relatively new nanomaterial that display attractive structural, mechanical and electronic properties, have been widely used in analytical chemistry. It is interesting and useful to synthesize new nanocomposites for environmental analysis. In this thesis, recent advances in heavy metal ions and phenolic sensing are briefly reviewed, and detailed studies on several nanocomposite-modified electrodes for environmental analysis are carried out. The main contents are as follows.1. A 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS)-multiwalled carbon nanotubes (MWCNTs) nanocomposite/Bi film modified glassy carbon electrode (GCE) was constructed for the differential pulse stripping voltammetric determination of trace Pb2+ and Cd2+. This electrode was more sensitive than ABTS-free Bi/GCE and Bi/MWCNTs/GCE. Linear responses were obtained in the range from 0.5 to 35μg L-1 for Cd2+ and 0.2 to 50μg L-1 Pb(Ⅱ), with detection limits of 0.2μgL-1 for Cd2+ and 0.1μg L-1 for Pb2+, respectively. This sensor was applied to the simultaneous detection of Cd2+ and Pb2+ in water samples with satisfactory recovery.2. The covalent tethering of cysteamine to chitosan (CS) chains yields thiol functionalized CS (CS-SH), and the CS-SH film cast on a glassy carbon electrode (GCE) is very stable in acidic solutions and possesses strong adsorbability to Hg(Ⅱ), as confirmed by quartz crystal microbalance (QCM) measurements. The CS-SH-multiwalled carbon nanotubes (MWCNTs) nanocomposite modified GCE is applied for square wave voltammetric determination of Hg(Ⅱ). The electroanalytical procedure comprises two steps:the chemical accumulation of Hg(Ⅱ) under open-circuit conditions followed by the electrochemical detection of Hg(Ⅱ) using square wave stripping voltammetry. Linear responses are obtained in the range from 0.01 to 0.14μmol L-1, with a limit of detection of 0.003μmol L-1(S/N=3) under optimized conditions. This sensor has been applied to the detection of Hg(Ⅱ) in water samples with satisfactory recovery.3. A new biomolecular immobilization platform based on enzyme-catalyzed polymerization for electrochemical biosensing and biofuel cell applications. Dopamine (DA) is selected here as a new and detailedly examined substrate for Laccase (Lac)-catalyzed polymerization, and the oxidation and polymerization of DA is studied by UV-Vis spectroscopy, cyclic voltammetry, quartz crystal microbalance (QCM), and scanning electron microscopy (SEM). Casting the aqueous mixture of DA, Lac and multiwalled carbon nanotubes (MWCNTs) on a glassy carbon electrode (GCE) has yielded a polydopamine (PDA)-Lac-MWCNTs/GCE electrode that can determine hydroquinone (HQ) down to a concentration as low as 20 nmol L-1 (S/N=3).