Study On Electrode Modification And The Effect On Capacitive Deionization Performance

The freshwater shortage can be solved by desalination of seawater/brackish water or remediation of polluted water from both the perspective of source and treatment.Capacitive deionization(CDI)can be applied to both seawater desalination and radioactive wastewater treatment,which is high efficiency and environmental protection.The electrode,as the main component of the CDI device,is an important factor affecting the electrosorption performance.Based on the principle of CDI technology and the characteristics of the electrode,starting from the influencing factors of the CDI electrode,the dissertation mainly focuses on the modification of the conductive agent,the simplification of the electrode preparation method,the preparation of active materials,which also systematically studies the electroadsorption performance of the modified electrode and the mechanism of action.The main contents of the dissertation are as follows:The main contents of the dissertation are as follows:(1)The effect of oxygen-plasma-modified carbon black(PCB)on the CDI performance was studied from the point of view of the conductive agent,which is an influencing factor of the electrode performance,and the related mechanism was explored.The electrode assembled by modified carbon black as a conductive agent and activated carbon as active material has a higher salt adsorption capacity(32.54 mg g-1),6.63 times that of the unmodified electrode(4.91 mg g-1),According to the experiments of salt removal rate and charge efficiency,the modified electrode has a faster ion removal rate(3.25 mg g-1 min-1)and a higher charge efficiency(45.13%),which are 15.48 times and 16.12 times of the unmodified electrode,respectively.The morphology,structure,specific surface area,hydrophilicity and electrochemical properties of carbon black and electrode before and after modification were characterized,and the interaction mechanism between H2O molecules and carbon black was studied by molecular dynamics simulation.The above results show that the plasma-modified conductive method can not only be applied to the desalination of seawater,heavy water softening,wastewater purification and other fields but also can be used in other kinds of active material electrode preparation,which has universal applicability.(2)Laser-induced graphene(LIG)with a three-dimensional porous structure has been prepared by CO2 laser ablation of polyimide films according to the factors that affect the electrode performance,namely fluid collection and electrode preparation method.LIG materials with different morphologies and functions were obtained by adjusting the laser power,which is used as CDI electrodes to adsorb uranyl(UO22+)ions in radioactive wastewater.The LIG electrode showed a high adsorption capacity of 805.36 mg g-1 in 60 mg L-1 UO22+solution when the laser power was 6 W,indicating the feasibility of the LIG film as a CDI electrode.The mechanism of electroadsorption shows that the excellent CDI performance of the LIG6 electrode is mainly due to the double-layer capacitance of graphene.The results show that the LIG film can be directly used as a CDI electrode,which not only plays the role of the active material and fluid collection but also reduces the need for conductive agents and adhesives.Besides,it avoids the complicated operation of distributing slurry and coating electrodes,and simplifies the electrode preparation process,and achieves excellent electroadsorption performance,which is expected to become a new CDI electrode substrate.(3)The UO22+ions on the LIG6 electrode surface are easy to desorption after a long time of electroadsorption due to the ion repulsion effect of double-layer capacitance.To improve the hydrophilicity and electroadsorption performance of the LIG6 electrode,CO4S3 material with pseudocapacitance property was loaded on the LIG6 electrode surface by electrochemical deposition technology to remove UO22+ions from wastewater.The combination of laser ablation technology and electrochemical deposition technology simplifies the process of electrode preparation,and avoids the tedious operation of equipping the electrode slurry and coating the electrode.The loading of the CO4S3 nanosheet improves the specific surface area and the hydrophilicity of the electrode,which provides more adsorption sites for UO22+.The LIG6/Co4S3-15 composite electrode exhibits a high adsorption capacity of 2702.79 mg g-1 and good cyclic stability in 60 mg L-1-UO22+solution,which is attributed to the synergistic effect of the double layer capacitance of LIG6 and Co4S3 pseudocapacitance.Finally,the electroadsorption mechanism of the electrode is explained,that is,the synergistic effect of electrostatic adsorption,chemical adsorption and electrochemical reduction.This work provides a reference for the preparation of CDI electrodes and the efficient removal of radioactive wastewater.The dissertation simplifies the preparation process of the electrode by the conductive agent,fluid collector,active material and preparation method of the CDI electrode,and improving the electroadsorption performance,and explores the relevant mechanism in depth.The research promotes the development of CDI technology in the field of seawater desalination and treatment of radioactive wastewater,which is expected to promote commercialization and industrialization.