Preparation Of Modified Activated Carbon Electrode For Capacitive Desalination

Capacitive deionization (CDI) with the characteristics of low energy consumption, highefficiency and no secondary pollution has been becoming a promising technology for thedesalination of seawater and brackish water. Activated carbon (AC) with the properties of highspecific surface area, rich pore volume and easy to obtain is the most commonly used electrodematerial. But the traditional AC has some drawbacks, such as poor hydrophily and lowmesoporosity, which have limited the diffusion of ions on the electrode during the desalinationprocess. This paper focuses on the studies about the preparation of modified AC electrode withbetter pore size distribution and improved hydrophilicity by ZnCl2treatment and modification ofpolydopamine. Capacitors assembled with the modified AC electrode were used forelectrochemical and CDI test. Due to the improvement of pore size distribution and hydrophilicity,the ions will be much facilely adsorbed on the electrodes during the CDI process and the saltremoval and current efficiency have been improved greatly. The findings of this paper were asfollows:1. The activated AC was obtained through AC impregnation in ZnCl2solution followed byheat treatment under the nitrogen gas condition. The BET specific surface area and mesoporousvolume were improved accordingly. FTIR-Raman was taken to analyze the surface composition ofactivated sample. The capacitor was assembled with AC electrode after ZnCl2activated processing,and which had an improved desalination performance compared with the pure AC electrode. Theeffect of activation temperature on specific surface area and electrochemical property was studied.The results showed that the specific surface area reduced at a higher temperature, but the specificcapacitance and salt removal of the corresponding electrode enhanced. Especially at the activationtemperature of800℃, the salt removal reached10.5mg/g,2.3times higher than the pure ACelectrode. Morever, the activated electrode is easy to be produced and its recirculating stability isgood.2. The modified AC with hydrophilic polydopamine coating on its surface was obtainedthrough dispersing AC in alkaline dopamine solution and stirring for some time at room temperature. The results of XPS and FTIR demonstrated the successful loading of polydopaminecoating. The contact angle test showed the improvement of hydrophility on polydopamine coatedAC. The polydopamine coated electrodes were then assembled into symmetric capacitor fordesalination. The influence of dopamine polymerization time on desalination performance wasinvestigated. It indicated that through extending the polymerization time, more polydopamine wascoated on the electrode, but too much polydopamine coating resulted in the decay of the specificcapacitance and desalination capacity due to the reduced conductivity and the block of porechannels inside activated carbon. On the electrode with the4h dopamine polymerization, thedesalination performance had been dramatically improved, comparing with the pure AC electrode.Under the optimized conditions, the salt removal of the12mg/g and salt removal rate of0.35mg/(g.min) were obtained respectively. The recirculating stability is good with consistentdesalination amount per cycle during repeatedly charge-discharge running. The preparationprocess is very simple and the method is deployed for batch manufacturing. The polydopaminemodified AC electrode was easy to prepare fabricated and can be used for longtime desalination.