Preparation And Properties Of A Novel All-solid-state Ammonium Ion Selective Electrode

Ammonia nitrogen was not only the total control index of water quality pollutants in China,but also an important monitoring index of water environment quality.The content of ammonia nitrogen was often used to judge the quality of water quality and the degree of water pollution.At present,spectrophotometry and ammonia gas sensing electrode were mainly used to monitor ammonia nitrogen in water,while the former had some disadvantages such as pretreatment of water sample and toxicity of chromogenic agent,while the latter had strict detection conditions and needed to adjust the pH value of water sample by strong alkali.The hydrophobic permeable membrane of the ammonia gas sensing electrode was easy to be contaminated.The detection of ammonia nitrogen by electrode method had developed rapidly in recent years because of its simple structure,fast response and wide range of detection.However,the traditional liquid-connected ion selective electrode had some disadvantages,such as internal reference solution leakage,difficulty in miniaturization of electrodes and so on.The all-solid-state ion selective electrode used the solid-state contact layer instead of the internal reference solution in the traditional electrode.The electrode had the advantages of simple structure,easy miniaturization,convenient for in-situ real-time monitoring of ammonia nitrogen,and had potential application prospect,but the research and development was still in its infancy.In this thesis,polyaniline and poly?3,4-ethylenedioxythiophene?solid-state contact layers were prepared by electrochemical method to replace the internal reference solution to realize ion/electron transduction.Combined with the optimized formula of PVC sensitive membrane,two kinds of PVC sensing membrane all-solid-state ammonium ion selective electrodes were successfully developed.A new type of ammonium ion sensitive membrane based on butyl acrylate was synthesized by ultraviolet photopolymerization,and the preparation process of solid-state contact layer and ammonium ion sensitive membrane was optimized.An all-solid-state ammonium ion selective electrode without external plasticizer was successfully developed.The performance of the all-solid-state ammonium ion selective electrode was evaluated and analyzed.The main conclusions of this thesis are as follows:1.An all-solid-state ammonium ion selective electrode with polyaniline?PANI?as solid-state contact layer was prepared,and the effect of preparation conditions of all-solid-state contact layer on the response performance of the electrode was discussed.The number of scanning circles and scanning potential would affect the thickness,surface state and oxidation degree of the polyaniline contact layer,thus affecting the response performance of the electrode.The best preparation process of polyaniline was as follows:1 mol/L aniline hydrochloride as electrolyte,scanning rate 50mV/s,scanning potential 0.45 to 0.90 V,scanning 15 times.2.The formula of plasticized PVC ammonium ion sensing membrane solution was optimized,and the effects of the selection and dosage of plasticizer and ionic additive on the response performance of the electrode were discussed.Plasticizer could reduce the glass transition temperature of PVC and increase the fluidity of ion carriers in the polymer sensitive membrane,while the addition of ion additives could increase the anion sites on the sensitive membrane,which made the electrode more sensitive to detect ammonium ions.The plasticizer of PVC sensitive film was DOS,and the dosage of132mg/m L,ion additive KTClPB was 0.33mg.3.An all-solid-state ammonium ion selective electrode with poly?3,4-ethylenedioxythiophene?as solid-state contact layer was prepared,and the effect of preparation conditions of solid-state contact layer on the response performance of the electrode was discussed.The template-free method could spontaneously form a dense ordered structure.The dopant made the long chain of the polymer fully expand.The polymerization potential affected the reaction rate,surface distribution and oxidation degree of the polymer chain.The amount of polymerization was closely related to the film thickness of the solid-state contact layer.The optimum preparation process of poly?3,4-ethylenedioxythiophene?was as follows:the mixed solution of 0.01 mol/L EDOT and 0.1 mol/L Na₂SO₄ was used as electrolyte,the polymerization potential was1.0V and the polymerization charge was 0.02C.4.The all-solid-state ammonium ion selective electrode of PVC sensitive film in the solid-state contact layer of PANI and PEDOT showed Nernst response with slopes of59.30 mV/dec and 56.08 mV/dec over the concentration range of 10-1?10-5 mol/L.The detection limit were 10^-5.35.3 mol/L and 10^-5.65.6 mol/L,respectively.Compared with PANI,PEDOT had lower resistance and larger low frequency capacitance,and had better stability and faster response speed.Compared with the commercial electrode,the two kinds of electrode could eliminate the interference of Na⁺and improve the selectivity of K⁺.The detection results of the electrodes were accurate and the performance were stable.5.An all-solid-state ammonium ion selective electrode with butyl acrylate sensitive film was prepared.The optimal response performance of the electrode was obtained by using butyl acrylate as polymerization monomer and polyaniline as solid-state contact layer.The response slope of the electrode was 55.53 mV/dec over the concentration range of 10^-1?10^-55 mol/L.And the detection limit was 10^-5.35.3 mol/L.The electrode had excellent anti-interference to common ions.The electrode had good stability and reproducibility without adding plasticizer at the same time.The all-solid-state ammonium ion selective electrode had the advantages of simple and compact structure,stable performance,long service life and good selectivity,and had a wide application prospect in the field of environmental monitoring such as municipal sewage and industrial wastewater.