Construction Of Functional Interfaces Based On The Nanostructured Gold And Palladium-iron Films And Their Applications Of Catalytic And Sensing Properties

Since prepared successfully, nano-metallic materials have been widely used in various fields of research and application. Because of their unique properties compared with traditional materials, nano-materials play a more and more important role in the fields of research with bright prospects of application. Therefore, continuously improving and developing the new preparation method of nano-materials are of considerable current research interest. Compared with the traditional chemical synthesis of metal nanostructures, the electrochemical technique has many intrinsic advantages, such as mild reaction conditions, environment friendly, wide application, good controllability, high purity of products, and so on. Due to the superior catalytic property, nano-metallic materials (like nano-structured Au, Pd, etc) hold an important place in catalysis fields and have become a research focus.The aim of this paper is to fabricate the nanostructured Au and bimetallic Pd-Fe thin film materials by some simple and novel electrochemical methods, and to construct the new functional interface based on the as-prepared materials. Moreover, the catalytic performance of the as-prepared thin films was investigated. And the potential application of the bimetallic Pd-Fe thin film in electrochemical treatment of wastewater containing chlorinated organic compounds was discussed. Furthermore, as sensing elements, horseradish peroxidase and glucose oxidase were immobilized on the nanostructured Au thin film to construct bioelectrochemical sensors. In order to explore their potential application in the environmental monitoring and the life sciences, the sensing properties of the bioelectrochemical sensors were investigated when4-chlorophenol and glucose were used as the substrate, respectively.The main contents of this paper include:(1) Electrochemical behavior and amperometric detection of4-chlorophenol on nano-Au thin films modified glassy carbon electrodeIn recent years, with the water pollution becoming more and more serious, the types and amounts of organic pollutants in wastewater are increasing. Especially, due to the effect of "teratogenesis","carcinogenesis","mutagenesis" and the features of high toxicity, persistence and biological concentration, and many of chlorinated organic compounds have been list as the priority pollutants by EPA (United States Environmental Protection Agency). Therefore, the detection and degradation of chlorinated organic compounds have been always the important subjects in the environmental engineering field.The nanostructured Au thin film was prepared on glassy carbon electrodes by a template-free, double-potential step technique. And its structural feature can be controlled well by adjusting the deposition time. The nano-Au thin film shows a higher catalytic activity toward the electrooxidation of4-chlorophenol (4-CP) than the bulk Au and glassy carbon electrode. For the electrooxidation of4-CP, fouling of the Au thin film was observed as a dramatic current decrease of oxidation peak in the first anodic sweep and the diminishing reduction peak of Au oxides during the consecutive cyclic voltammetric scan. In order to discuss the feasibility to the amperometric detection, the effect of4-CP concentrations on the electrochemical behavior of nano-Au thin films in H2SO4solutions was investigated by linear sweep voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. The results demonstrated that the electrode was hardly suffered from fouling at the low4-CP concentration. With the increase of4-CP concentrations, more serious fouling was observed on the electrode. The nano-Au thin film has a good sensing capability and an electrochemical sensor for4-CP at the mM concentration range with a fast amperometric response was achieved. The amperometric detection of4-CP was performed at+0.85V with a linear detection range from0.2to4.8mM and a detection limit of0.11mM (S/N=3).Through this simple electrodeposition method, the structural feature of nano-Au films can be controlled conveniently, which ensures the repeatability of the electrochemical detection.(2) Amperometric detection of4-chlorophenol based on horseradish peroxidase modified nanostructured Au thin filmsWith the rapid development of nanotechnology, a great number of nanomaterials, especially the noble metal, have been introduced into the bioelectrochemical sensor. However, severe fouling will be caused by oligomers and polymers as a result of chemical coupling of the corresponding phenoxy radicals during the electrooxidation of phenolic compounds on nano-Au thin film electrodes. So in order to enhance the resistance to fouling and improve the detection sensitivity, HRP was immobilized on the nanostructured Au thin film to construct the HRP/nano-Au biological function interface, considering its excellent catalytic activity toward chlorophenols.A nano-structured Au film was directly formed on the GCE substrate by double-potential step electrodeposition. The as-prepared nanostructured-Au thin films provide an excellent microenvironment for the immobilized of HRP and retention of its activity. And the immobilized HRP plays an important role in the electrochemical detection of4-CP. From the SEM and CV results, it was demonstrated that the immobilized HRP had a significant positive effect on the anti-fouling performance of the electrode material. In the presence of H2O2as co-substrate, the HRP modified electrode displayed a high catalytic activity toward4-CP. Furthermore, the enzyme modified electrode was used as a4-CP bioelectrochemical sensor, exhibiting a linear relationship in the concentration ranges of2.5to40μM and62.5to117.5μM with a detection limit of0.39μM (S/N=3) at an applied potential of-0.55V. The HRP modified electrode displays an excellent sensing performance with high sensitivity and good stability. A bio-electrochemical sensor of4-CP with a fast amperometric response was achieved.(3) Direct electrochemistry of glucose oxidase immobilized on nanostructured gold thin films and its application to bioelectrochemical glucose sensorWith its intrinsic advantage in high sensitivity and selectivity, fast response, easy operation, and continuous on-line detection, bioelectrochemical sensors have received increasing attention in clinical medicine, biochemistry and environmental monitoring. And the rapid development of nano-materials greatly accelerates the miniaturization of bio-electrochemical sensor. Due to its unique adsorptive properties and good biocompatibility, the nano-material is widely used in constructing the biological function interface. Considering its good catalytic activity, excellent biocompatibility, high surface energy, optical properties and quickly direct electron transfer, nano-Au can not only be directly used as electro-catalyst of a small organic molecules, but also provide a large specific surface for the immobilization of enzymes to construct novel and superior bio-electrochemical sensors.Nano/submicron structured Au films with were directly fabricated onto the glassy carbon electrode (GCE) by the combination of electrodeposition and galvanic replacement technology, which can provide a facile method to prepare morphology-controllable Au films and a more convenient boundary for enzyme immobilization than Au nanoparticles. Glucose oxidase (GOx) was stably immobilized via a simple physical adsorption method onto the nanostructured Au thin films. An obvious advantage of the as-prepared enzyme electrode is that the nano-Au films provide a favorable microenvironment for GOx and facilitate the electron transfer between the active center of GOx and electrodes. Cyclic voltammetry results indicate that the immobilized GOx displayed a direct, reversible and surface-confined redox reaction in the phosphate buffer solution. Furthermore, the enzyme modified electrode was used as a glucose bio-electrochemical sensor, exhibiting a linear relationship in the concentration ranges of2.5to32.5μM and60to130μM with a detection limit of0.32μM (S/N=3) at an applied potential of-0.55V. Due to the excellent stability, sensitivity and anti-interference ability, the Au thin films are hopeful in the construction of glucose biosensors.(4) Facile fabrication of nanostructured Pd-Fe bimetallic thin films and their electrodechlorination activityNanostructured Pd-Fe bimetallic thin films were directly fabricated on glassy carbon substrates by means of galvanic replacement of partial Fe0nanoparticles by Pd(II) ions. The composition and morphology of such Pd-Fe thin films are strongly dependent on the sacrificial Fe film templates. The nano/submicron structured Fe thin films were fabricated by a template-free, double-potential step electrodeposition technique. The size and morphology of the Fe nanoparticles that constitute the Fe thin films can be controlled well by adjusting the concentration of Fe2+ions in electrolyte solutions. Taking electrochemical reductive dechlorination of carbon tetrachloride (CT) as the research object, we investigated the removal efficiency of the as-prepared bimetallic Pd-Fe nano-catalysts under different conditions. Due to the good synergistic effect between Pd and Fe, the as-prepared Pd-Fe thin films with the novel microstructure display a high activity toward the electrochemical reductive dechlorination of CT. The Pd/Fe weight ratio in the bimetallic films is an important parameter that affects the dechlorination activity of the bimetallic catalysts and can be adjusted by selecting nanostructured Fe film templates with different thickness and surface morphology. When the weight ratio of Pd/Fe is5.9, the bimetallic thin film catalyst exhibits the highest dechlorination activity. The activation energy (Ea) for dechlorination by different types of hydrogen is in accord with the removal efficiency of CT, and a minimum Ea and the highest removal efficiency were obtained at-0.2V. Besides, the removal efficiency of CT increased considerably with increasing temperature. The dechlorination reaction of CT complied with pseudo-first-order kinetics.The present study will provide a new path to fabricate low-temperature high-efficiency nano-catalysts for the electrochemical reductive dechlorination of chlorinated organic compounds. The obtained results are of fundamental importance to give an in-depth understanding of electrochemical reductive dechlorination mechanism of chlorinated organic compounds.