Studies On Capacitive Deionization Performance And Electrode Fouling Characteristics Of Activated Carbon Fiber Electrode

Capacitive deionization(CDI)is a new type of water treatment technologywhich has received widespread attention in recent years.It uses charged electrodes to adsorb waterborne particles and charged particles to enrich dissolved salts and charged particles in water,the soluble organic and inorganic salts are concentrated on the surface of the electrode and the water is purified,which is often used for brackish water desalination and drinking water softening.CDI has the advantages of low energy consumption,low cost,simple operation,easy operation,and no secondary pollution as compared with traditional desalination technology,it has obvious features and advantages,and has good development potential and application prospects.The deep research and discussion on the theoretical basis and practical application of CDI not only has important theoretical significance,but also has a certain guiding role in practical application.In this paper,activated carbon fiber(ACF)is used as the adsorption electrode and stainless steel wire mesh is used as the collector,CDI module and cyclic desalination device are self-manufactured and designed.Testing and characterizing the electrodes with scanning electron microscope(SEM),nitrogen adsorption and desorption technology,cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS),and the effects of operating voltage,circulating flow rate,initial concentration,and electrodes spacing on desalination of activated carbon fiber electrodes were systematically analyzed,determin the optimal working conditions,and conducting continuous electro-adsorption/desorption experimentsunder optimal working conditions,then testing and characterizing the repetitive electrodes.The results indicate that:Under the experimental conditions,with the increase of the initial concentration of sodium chloride solution,the desalting capacity of the electrode becomes larger,the time for the electrode to reach the adsorption equilibrium becomes shorter,but the salt removal rate decreases;desalting capacity and salt removal rate increase with increasing operating voltage and circulation flow rate;in the range of 1 to 4mm,2mm is the best electrode spacing.The optimal operating conditions obtained were:voltage 1.5 V,circulating flow rate 20 ml/min,and electrodes spacing 2 mm.Under optimal working conditions,15 consecutive cycles of electrosorption/desorption experiments were performed in an initial concentration of 100 ?S/cm sodium chloride solution,demonstrated that the desalination of activated carbon fiber electrode has good continuity and repeatability,the salt removal rate decreased from 85%to 81%for 15 cycles.Comparising unused electrodes and electrodes after 15 cycles in sodium chloride solution,it can be seen that the microscopic appearance of the electrode used for recycling is almost unchanged,however,the specific surface area and specific capacitance both slightly decreased,and the electrode impedance slightly increased.According to the dynamic simulation,the desalting process of ACF electrode conforms the pseudo-second-order kinetics model.In order to further study the pollution caused by soluble organic matter and heavy metal ions on the electrodes,micro amounts of benzoic acid,humic acid and copper ions were added to the sodium chloride solution respectively,to study the effect of these impurities on the desalting performance of CDI and the contamination of electrodes.And the fouling characte'ristics of electrodes were characterized by scanning electron microscope(SEM),nitrogen adsorption and desorption technology,cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The results indicate that:After being polluted by different contaminants,the electroadsorption performance of electrodes showed a different trend of decline,and its surface appeared granular and flaky organic and inorganic fouling;the benzoic acid caused the pore blockage to reduce the specific surface area by 10.8%,while the humic acid and copper ions had little effect on the specific surface area;due to the decrease of the specific surface area,the specific capacitance decreasedby 43.3%and 18.8%respectively after the electrodes fouled by the benzoic acid and the humic acid;the reduction of effective adsorption sites caused the specific capacitance to drop by37.2%after the electrodes fouled by the copper ions;after the electrodes being fouled,the fouling on the surface or in the pores hindered the transfer of electrons between the fibers,so the electrochemical performance decreased.