Novel Solid-state Electrodes:Preparation, Characterization, And Their In-situ Analyses For Aqueous Nutrients

Nitrogen,phosphorus,silicon are the necessary nutrients for biological growth,they exist as ammonium salts,nitrates,phosphates,silicates and other nutrients in water.Excessive nutrient content in water,especially in aquaculture water,may cause eutrophication,which will lead to the death of aquatic organisms.And the low level of nutrient content will reduce water production.The changes of nutrient content in sea water will also have effect on its biological productivity.Thus,analyzing the content of nitrogen,phosphorus,silicon and other nutrients in water has both essential ecological and economic significance.The traditional methods for the determination of nutrient in water are spectrophotometry,ion chromatography,titration,gas chromatography,fluorescence spectrophotometry,and atomic absorption spectroscopy,etc.These methods are tedious,time-consuming,and will produce toxic wastes.The most important deficiencies is that,they all need sampling,and require pretreatment of samples,so the accuracy of the results are poor.Electrode method is the new,rapid,and convenient method for measurement of water samples.In this paper,all solid-state electrodes,including Ag/AgCl reference electrode,ammonium,phosphate and silicate ion selective electrodes,were prepared and their detection performance was studied.1.Ag/AgCl reference electrodeWe find the constant current method is most efficient for electrodeposition of AgCl,after comparing the cyclic voltammetry,constant voltage and constant current methods.During the preparation process,a layer of silver particles with diameters of 30-60 nm were electroplated on the silver wire,which could effectively improve the sensitivity of the electrode.And a layer of polyacrylonitrile film was coated on the electrode after deposition of AgCl,which improved the anti-sulfur performance and the lifespan of the electrode.This silver/nano silver/silver chloride/polyacrylonitrile reference electrode could be used longer than 2 months with Nernst slope of 58 mV/decade,and response time of less than 1s.2.Ammonium ion selevtive electrodeWe prepared the ammonium electrode with nonactin as the ammonium io nop ho re,the formula of the sensitive membrane was provided by Sigma.This electrode has structure of silver/nano silver/polyaniline/copolymer of aniline and 2,5-dimethoxyaniline/sensitive membrane.A 0.6 mm silver wire was used as the electrode substrate,and polyaniline as the solid electrolyte.The layer of silver nanoparticles was beneficial to improve the electrode sensitivity,the 2,5-dimethoxy aniline was added to reduce the conductive barrier between the solid electrolyte and the ion sensitive film.The Nernst slope of the prepared ammonium ion electrode was 55 mV/decade,with linear range of 10-1-10-4 M and detection limit of 10-4 7 M.The response time of the electrode in the linear range was less than 1 s.It was suitable to be used in solutions with pH range of 2.6-10.1,and the lifetime of this ammonium electrode was up to 3 months.3.Phosphate electrodeWe firstly fabricated an Ag/AgCl+ LaPO4 inorganic phosphate electrode based on the principle of dissolution/precipitation equilibrium.This phosphate ion selective electrode with slopes of 22.17-24.04 mV/decade was prepared with LaPO4 as the ion sensitive membrane.Then a gold/polyaniline/phosphate doped polyaniline organic phosphate electrode was prepared using phosphoric acid doped polyaniline as ion sensitive membrane.This electrode could be used either in fresh water system or in seawater system.In both systems,the linear range of the electrodes was 10-1-10-6 M,the detection limit was 10-6 M,and the response time was less than 1 second.The potential drift of the electrode was 0.05 mV/h when observed in a 10-3 M KH2PO4 solution containing 3.5%NaCl for 12 hours,and the service life of the electrode in this solution was more than 40 days.4.Silicate electrodeIn this part,a gold/nano lead/lead silicate insoluble salt silicate electrode was fabricated.Firstly,the nanometer lead was electroplated on the surface of the gold wire.Secondly,the nano lead was converted to lead hydroxide.Then the lead hydroxide was reacted with silicic acid colloid in the autoclave to form lead silicate.VI Finally,the electrode was immersed in the lead nitrate solution to remove byproduct silicon barium.The electrode prepared by this method had a Nemst slope of 29.98-30.99 mV/decade in the sodium silicate solution.The response time of the electrode was less than 10 seconds,the Nernst response linear range was 10-1-10-5 M and the detection limit was 10-5 35 M.The solid-state Ag/AgCl reference electrode and ammonium,phosphate and silicate ion selective electrode prepared in this thesis were all made of precious metals.Thus the electrodes were all equipped with characteristics of small size,good conductivity,good pressure resistance and corrosion resistance.These electrodes could be used for both lab testing and in-situ monitoring.And could be used either alone or integrated in the self-made multi-parameter electrochemical sensor to test a variety of chemical composition in water at the same time.It could be used in river,lake,sea and other natural water bodies,as well as aquaculture water,industrial wastewater and urban sewage.It could achieve the early warning of water eutrophication,analyze the marine water group and seawater nutrition migration,monitor the quality of aquaculture water and discharge water.Thus people might take timely measures to control the deterioration of water quality.