Construction Of A Novel Phosphate Potential Sensor And Its Application In Water Quality Analysis In Sinopec Jiangsu Oilfield

Phosphorus content is an important indicator in the evaluation of oilfield water quality.The level of phosphorus in oilfield water systems not only affects the overall water cycle production system,but excessive phosphorus wastewater entering the environment can cause eutrophication of the water body,as can high levels of ammonia and nitrogen,leading to rapid growth of algae and thus affecting the balance of the aquatic ecosystem.Therefore,the regulation of phosphorus is of great importance.Phosphorus exists in nature mainly in the form of phosphate,which is currently detected by the traditional spectrophotometric method.As this method requires the addition of a large number of chemical reagents,it is not only complex and time consuming,but also produces a waste solution at the end of the test that can easily cause secondary pollution to the environment.Compared to traditional methods,Ion Selective Electrodes(ISEs)are easier to use,more sensitive,less expensive and do not cause secondary contamination.In conventional ion selective electrode detection systems,liquid contact ion selective electrodes consisting of a polymeric ion selective membrane,an internal filling fluid and an internal reference electrode are susceptible to common variables such as pressure and temperature.There are problems with complex maintenance,leakage and signal calibration.In contrast,all-solid ion-selective electrodes that eliminate the internal filling fluid and internal reference have become a hot research topic for such potential-based sensors.In this thesis,the following research was carried out with the aim of developing a phosphate potentiometric sensor with practical detection capabilities:(1)PANI/ITO electrodes were produced by electrodeposition of polyaniline on ITO conductive glass by constant potential deposition and by ultrasonic peeling.Three oxidation states of PANI/ITO electrodes were prepared at different voltages using phosphoric acid as the doping solution.LBPANI/ITO electrode in the fully reduced state,ESPANI/ITO electrode in the semi-oxidized state and PBPANI/ITO electrode in the fully oxidized state.The response sensitivity and stability of the three electrodes were investigated to determine the optimum doping potential;the response performance of the electrodes was tested for different doping times to determine the optimum preparation time.It is shown that the PBPANI/ITO electrode in the fully oxidised state has the optimum stability and response sensitivity at a doping time of 80 s.The electrode showed good linear response in the range of 1.00× 10-5～1.00 × 10-1 M,with a response sensitivity of 37.30 dec/mV(R2=0.9966)and a detection limit of 10-5.6 M.The response time of the electrode to the solution was around 4 s,and it had good acidbase adaptability(pH 4.0～8.0).The performance of the prepared PBPANI/ITO electrode as a potentiometric phosphate sensor was also investigated in terms of stability(n=10,RSD 1.76%)and lifetime(6 weeks at room temperature),and was successfully used for phosphate detection and analysis in oilfield re-injection water,lake water and tap water samples in real environments with satisfactory results.(2)To further prepare a phosphate potential sensor with a high sensitivity response.We pretreated the home-made cobalt electrode with high pressure anodic oxidation in sodium hydroxide solution to produce a uniform cobalt oxide passivation film on the electrode surface.The sensitivity and stability of the response of the electrode at different pretreatment times were investigated to determine the optimum preparation conditions.The results showed that the pretreated cobalt electrode had a good response in the range of 1.00 × 10-5～100×10-1 M.The response sensitivity was 67.22 mV dec,R2=0.9939 and the detection limit was 10-5.5 M.It was much higher than that of the untreated cobalt electrode..This far exceeded that of the untreated polished cobalt electrode(36～40 mV/dec).The performance of the pretreated cobalt electrode as a potentiometric phosphate sensor was also investigated in terms of lifetime(7 weeks at room temperature),response rate(≤40 s),stability(n=10,RSD 1.07%)and acid-base adaptability(pH 4.0～8.0),and the sensor was successfully used for phosphate in oilfield re-injection water,lake water and tap water samples The results were satisfactory.(3)On the basis of the above sensor research,we choose polyaniline as the intermediate solid contact layer and electrodeposited cobalt film as the sensitive layer to carry out the research on the construction of phosphate potential sensor with cobalt-doped polyaniline system.The parameters affecting the performance of Co/PANI/ITO electrode were optimized in terms of structure and preparation method.The results show that the Co/PANI/ITO electrode is constructed under the optimal conditions.In 1.00 × 10-5～1.00 × 10-1 M range with a linear response,in response to the slope of 35.10 mV/dec,R2=0.9911,the detection limit of 10-5.6 M,response speed ≤50 s.At the same time,the stability(n=10,RSDS=1.41%),service life(6 weeks at room temperature),acid and alkali resistance(pH 4.0～8.0)of Co/PANI/ITO electrode as a potential phosphate sensor were investigated.The ability of the electrode to detect phosphate content in oilfield reinjection water,lake water,tap water and samples is also verified,and the results are satisfactory.