Study On Nano-Material Electrochemical Sensors And Their Applications In Environmental Monitoring

The use of nanostructured materials for catalysis and analysis is an extremely promising prospect. Due to the quantum size effect, the surface and interface effect, the small size effect and the macroscopic quantum tunnel effect, nanoparticles have drawn much attention for their physical and chemical advantages over bulk materials. Nano-materials have been widely applicated in the reaserch field of electrochemical sensors.There are two main trends in the field of chemically modified electrodes for catalysis and analysis: one is chemically modified electrodes based on polymer films, the other is bimetallic or multimetallic composite modified electrodes. Bimetallic (or multimetallic) nanoparticles are of greater interest than corresponding monometallic ones for the improvement of the catalytic properties of metal particles. This is because bimetallization can improve catalytic properties of the original single-metal catalysts and create a new property, which can often be explained in terms of synergistic effect associated with changes on electrode surface. Bimetallic (or multimetallic) modified electrodes can also reduce costs by the addition of non-noble metal. Although bimetallic nanoparticles exhibit a high activity and selectivity, particle coalescence greatly limited their application. Hence, bimetallic nanoparticles coated on supporting materials, such as polymer films or metallic oxide, can improve the situation and enhance electron conductivity and catalytic activity of the catalysts.As the demand of the public for ambient quality advanced, environmental pollution problem caused by formaldehyde is increasingly concerned. The determination techniques of formaldehyde are developing towards fast, sensitive, simple and convenient ones. Nowadays, chemical sensor, espically nano-noble-metal chemical sensor is hotspot in fast determination study field.To develop a practicable system of electrochemical sensor for the determination of environmental contaminants such as formaldehyde, the voltammetric behavior of monometallic and bimetallic noble nanoparticles modified on polymer films or metallic oxide are investigated. Novel electrochemical sensors are proposed based on the interactions between noble nanoparticles and polymer films or metallic oxide, with aims to develop the sensitivity, selectivity and stability. Health risk assessment (HRA) for groundwater is simply introduced in the end of the paper. In detail, the main results are as follows:1. Palladium nanoparticles and Nafion film modified glassy carbon electrodes (Pd/Nf/GCE) were electrochemically deposited through cyclic voltammetry (CV). Scanning electron microscope (SEM) was employed to characterize the surface structure. Electrocatalytical behaviors of the modified electrode were investigated by cyclic voltammetry and differential pulse voltammetry (DPV). Experimental conditions were optimized and a voltammetric method for determining formaldehyde was developed.2. The modified electrode of DNA film and nano-gold was fabricated through electrochemical deposition method and the morphology of electrode surface was characterized by scanning electron microscopy and atomic force microscopy (AFM). Experimental results showed that the modified electrode exhibited a remarked electrocatalytic activity toward formaldehyde.3. An electrochemical sensor was introduced based on electrodepositing zirconia and Pt nanoparticles on glassy carbon electrode by cyclic voltammetry. Scanning electron microscopy was used to characterize the morphology of electrode surface. The electrocatalytical behaviors of the modified electrode towards formaldehyde were investigated by cyclic voltammetry and linear sweep voltammetry (LSV). Quantitative analysis of formaldehyde was also studied.4. Platinum-palladium (Pt-Pd) nanoparticles were electrochemically deposited on Nafion (Nf) film coated glassy carbon electrode. Bimetallic (Pt-Pd) nanoparticles were found to be uniformly dispersed on Nafion film, as confirmed by scanning electron microscopic analysis. Energy dispersed X-ray analysis (EDS) was used to characterize the composition of metal present on the nanoparticle-modified electrodes. The electrocatalytical behaviors of the electrode were investigated by cyclic voltammetry and linear sweep voltammetry. Experimental results showed that the electrode exhibited a remarked electrocatalytic activity for the oxidation of formaldehyde, attributed to synergistic effect of the alloy deposit associated with changes in the adsorption features of the Nafion surface.5. Pd-Au core-shell nanoparticles were deposited onto the Nafion film coated glassy carbon (denited as PdAu/Nf/GC) electrode via galvanic replacement reaction. Scanning electron microscopic analysis and energy dispersed X-ray analysis was used to characterize the composition of metal present on the nanoparticle-modified electrodes. Studies of cyclic voltammetry demonstrated that the modified electrode exhibited a high electrocatalytic activity toward formaldehyde.6. To assess the health risk of the groundwater pollution caused by a substandard landfill site nearly a city in northern China, the water samples were collected from five representative civil wells situated near the city. Formaldehyde, ammonia nitrogen, nitrite nitrogen, volatile phenol, zinc, sexavalent chrome, mercury, manganese, pH values, fluoride, total hardness of the samples were determined according to the standard determination methods of domestic drinking water GB/T 5750-2006. The assessment of health risk was carried out.