Preparation Of Microelectrodes Using Microfabrication Technique And Their Application In The Field Of Biological Wastewater Treatment

Microelectrodes(MEs) are regarded as a powerful tool for micro-scale measurements and are used for analysis of environmental samples in the past decades. Because of their properties of sturdy nature,metal and metal-metal oxide-based MEs have been widely used.Although many efforts have been made to improve the fabrication methods,some inherent disadvantages still exist,such as complicated fabrication procedures,low success rate,poor reproducibility,non-renewability and difficulty in making multi-sensor device.Microfabrication techniques,which are used for manufacturing small electrodes of any required planar patterns with excellent reproducibility,good stability and good accuracy,have attracted increasing interests. In this thesis,a needle-type gold-based integrated ME was fabricated by using microfabrication techniques including photolithography,ion-beam deposition and ion-beam etching techniques.A simple,efficient and reliable procedure for fabricating ME was established.The integrated ME tip contained a reference ME,a working ME and a counter ME with 70μm wideth,100μm thickness and 5 mm length.The electrochemical properties and anti-interference ability were investigated,and the results indicate that the integrated MEs had a good stability and an electrochemical activity.Furthermore,the integrated MEs could be used to electrochemical analysis and chemically modified to expanding their functions.An innovative procedure based on the utilization of a negative photoresist,SU-8,was proposed,following which mieroeleetrodes of any desired entire shape could be constructed by using photo-mask at micron-scale readily and reproductively.This new fabrication procedure had a large freedom and a wide range of applicability.Chemically modified electrode(CME) was one of the most effective way to expand the electrode function.In this thesis,a thin layer Pt-Fe nanoparticles was co-deposited on the tip of the working microelectrode,and this CEM could be used to quantitatively analyze the nitrite concentration.A three-dimensional nano-structured dendritic silver was deposited on the working microelectrode tip,and this CEM could be used to quantitatively analyze nitrate and dissolved oxygen(DO) concentrations simultaneously.The electrochemical properties of the CMEs were investigated by using cyclic voltammetry and the CMEs were found to have a good linear response to nitrite,nitrate and DO.Thus,the CMEs could be used to analyze the samples.The micro-structure of the CMEs surface was observed with scanning electron microscope, and the electrochemical properties of the CMEs were found to be related to their structures and composition.The CMEs had good stability,strong anti-interference ability and could be used as a nitrite,nitrate and DO sensor.Recently,aerobic microbial granules have received increasing interests because they have a dense structure,good settling ability,and microbial diversity,compared with activated sludge flocs.Evaluation of the distributions of concerned substances in aerobic granules will produce a better understanding of their characteristics in bioreactors.In this thesis,the distribution of nitrite,nitrate and DO was measured by using the CMEs.The DO level decreased at the granule surface and did not become depleted in the granule inner layer.Meanwhile,nitrite and nitrate concentrations were higher in the surface than those in the inner layer.This result suggests that the active ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were mainly located in the upper layer 300μm thickness of the granules,and that denitrification should not occur in the granules.Nitrogenous substances are widely present in the environments,resulting in a harmless to human health.Efficient and environmentally friendly removal of nitrate in groundwater is an important issue.In this thesis,400 nm-width gold wire microelectrode arrays were fabricated by using holographic lithography and microfabrications techniques,and then three-dimensional nano-structured dendritic silver was electrochemically deposited on the microelectrode array surface.The silver nanostructure was characterized using scanning electron microscope and synchrontron radiation hard X-ray three-dimensional imaging.The microelectrode could electrochemically reduce nitrate in water without dosing of any chemicals.In this way, a new method for nitrate removal in water was established.Microbial fuel cells(MFCs) could simultaneously generate electricity and treat wastewater.Because of small size and high output,mini-MFCs have a great potential to play an important role in military,homeland security and medical fields.In this thesis,a novel mini-MFC gold wire electrode array was fabricated by using microfabrication techniques,and a new mini-MFC reactor was fabricated with this electrode array.The power generation ability of Shewanella oneidensis MR-1 in this reactor was evaluated.The maximum power density of this reactor was 2499 mW/m~2. This new mini-MFC reactor had a better power generation ability compared to other mini-MFCs based on carbon electrode.Therefore,the fabricated mini-MFC has a great application prospect.