Potentiometric Sensor Based On Carbon Paste Electrode For Monitoring Total Residual Chlorine In Electrolytically Treated Ballast Water

With the development of world economy and maritime trade,our country has become the largest shipping country in the world.Ship transportation plays an indispensable role in the world trade.In the process of ocean transportation,Ballast Water(BW),which is used to ensure the safe and stable operation of ships,may also cause invasion of foreign organisms and threat the environment and human health.Therefore,ballast water treatment technology has become more and more important.Ballast water treatment methods include mechanical methods,physical methods,and chemical methods.Among them,the electrolysis method in the chemical methods has become the most important method for ballast water treatment due to its simple operation,low cost,safty,and good sterilization effect.Cl2,NaClO,and HClO present in the electrolytically treated BW are all effective for killing alien marine species.The total concentration of these active species is termed as the total residual chlorine(TRC).It is found that the sterilization is not sufficient when TRC concentration is less than 5 mg·dm-3.On the contrary,when the TRC concentration in the electrolytically treated BW is higher than 15 mg·dm-3,the strong oxidation of the solution may do harm to the environment of the discharged area and cause serious corrosion of the ship steel.Therefore,on-line monitoring of TRC in BW is required.At present,TRC detection methods mainly include chemical analysis,spectrophotometry,amperometric methods,chemiluminescence technology,etc.These methods are usually cumbersome to operate,costly,and cannot be operated continuously,so all of them are not suitable for TRC monitoring.For the detection of TRC concentration in BW,the potentiometric method is more suitable due to its easy operation,low cost,and high sensitivity.However,there are only a few studies on the potentiometric method for detecting the TRC concentration in BW.Therefore,developing a potentiometric sensor with low cost,simple operation and rapid online detection of TRC concentration in BW not only has broad application prospects,but also has important significance for the research of new detection technologies.Our research group has been engaged in basic theories and applied basic research of electrochemistry for a long time.Since 2009,we have carried out research work on the electrolysis treatment of ship ballast water.In the previous researches,we have studied glassy carbon electrode(GC),Pt electrodes as redox potential methods for TRC monitoring.Ferrocene-enhanced polyvinyl chloride-coated electrodes(Fc-ZephCl-PVC-GC),and Prussian blue(PB)-enhanced polyvinyl chloride coated electrodes are also proposed for this purpose.The studies show that the potential of the Fc-ZephCl-PVC-GC electrode exhibits a good linear relationship with the logarithm of the TRC concentration in the range of 1-20 mg·dm-3.The response time of the electrode is less than 50 s with good reversibility.The common ions in seawater have no obvious interference to the electrode potential.However,the polymer film delaminates after a week,leading to the failure of the electrode.In this thesis,the requirements and methods of ballast water treatment,TRC detection methods and the application progress of carbon paste modified electrodes are first reviewed systematically.A new type of potentiometric sensor based on modified carbon paste electrodes(CPE)for detection of TRC is prepared.The main research contents of the thesis include:(1)Preparation and performance test of Ferrocene modified carbon paste electrode(Fc-CPE).Firstly,the possible binders are screened,the liquid paraffin was determined as the best binder of the electrode.Then Fc was selected as the active modifier.Through series experiments,the optimal composition of the sensor was determined as follows:the mass of Fc of 0.15 g,the mass of graphite powder of 0.6 g,the mass of liquid paraffin of 0.25 g.The performance of the sensor was tested under the best composition.The results show that,under optimal conditions,the open circuit potential(OCP)of the electrode is in linear proportion to logarithm of TRC within the TRC concentration range of 1-15 mg·dm-3,which conforms to the Nernstian behavior with a slope of 54.23 mV/dec.The electrode can response in about 40 s,and shows good reproducibility and stability.Common ions in seawater have no obvious interference to the sensor.The life-span of the electrode is about 2 weeks.The electrode is easy to prepare,low in cost,and exhibiting good selectivity and reproducibility.The addition of Fc improves the response performance of the electrode.(2)Preparation and performance test of β-cyclodextrin(β-CD)inclusion Fc modified carbon paste electrode.A β-CD-Fc-CPE electrode was prepared by using β-CD-Fc inclusion compound as the electroactive material.Through series experimentation,the optimal composition of the sensor was determined as follows:the mass of the β-CD and Fc inclusion compound of 0.15 g,the mass of graphite powder of 0.65 g,the mass of liquid paraffin of 0.2 g.The performance of the sensor was tested under the best ratio and found that the β-CD-Fc inclusion can improve the stability and life-span of the electrode.The results show that the life-span of the electrode had not been significantly extended but the addition of β-CD made the electrode potential more stable,and the OCP of the electrode was in linear proportion to logarithm of TRC within the TRC concentration range of 1-15 mg·dm-3 the slope is 66.97 mV/dec,and the sensitivity is improved.The β-CD-Fc-CPE showed good stability,selectivity,and reproducibility.The preparation of the electrode was simple with low cost.The sensor is promising for the detection of TRC in electrolytic treatment of BW in the future.