Preparation Of Active Carbon Nanofibers And Composite Nanofibers Membrance And Its Application In Capacitive Deionization

Capacitive deionization technology is a kind of the desalination method basing on the theory of electric double-layer capacitance.The key factor influencing the electrosorption performance of CDI is the electrode materials with a high specific surface area and a proper pore size distribution.Activate carbon nanofibers(ACF)material has a high specific area,good electrical and well chemical stability,which is similar to other porous Carbon material.Besides,ACF possesses the physical properties like flexibility and mechanical strength are.Comparing to other carbon materials such as graphene and carbon aerogels,ACF membranes have advantages of higher porosity,a faster ions migration rate and a more feasible modification of porous structure.Meanwhile,they can beconvenientlyused as the self-supported electrode.Nevertheless,it should be noted that the high specific surface area of ACF is partly donated by its micropores.Due to the double-layer overlapping effect,the micropores of the porous carbon electrode materials cannot be used as the double-layer capacitance,as a result,the micropore structure can't effectively contributedin the CDI desalination.In this paper,basing on the preparation of PAN-derived ACF material by electrospinning,the further activation of ACF is investigated,and the ACF composite material is prepared aiming at enlarging the pore size and enhancing the properties such as specific surface area and mesopore ratio.Futhermore,the specific capacitance and desalination performance of the electrode material is also tested.In the experiments,the parameters of electrospinning were explored,the stabilization,carbonization and activation process were optimized,meanwhile the characterization of prepared materials were analyzed in detail.On the basis of the preparation of CDI electrode materials,two kinds of CDI apparatus were designed and fabricated considering the advantage of Flow-through CDI model and the requirement of continuous desalination,respectively.The details are as follows:1)PAN fibers membrance material was prepared using electrospinning technology.Then the ACF nanomaterial was obtainedafter the subsequent processes of pre-oxidation,carbonization and activation treatment.Furthermore,KOH wasselected as the reagent to a secondary activation treatment of ACF,and the influence of the activator on the material properties was investigated.Experimental datum showed that with the increase of activation agent ratio,the specific capacitance and conductivity of the product were enhanced accordingly.However,the specific surface area and the mechanical properties of material were dropped.The weight ratioof KOH:ACF of the optimal groupwhich is noted as ACF-KOH-6,was 6.4:1.It has a specific surface area of 796 m2/g,a mesopore volume of 0.098 cm3/g and a specific capacitance of 180 F/g,which are increased by 66%,180%,63%respectively,compared to the ACF material without secondary activation.Using the optimal experimental material as the electrodes,the CDI performance was tested.2)Based on the electrospinning technology,the PAN-derived carbon nanofibers/MWCNTs composite was prepared,Through the methods of electrospinning parameters adjustment and fibers morphology controlling,the PAN/MWCNTs material with porous beads structure was resulted.Following with pre-stabilization,carbonization and activation,during which the cyclization reaction temperature and CO2 etching degree was controlled,the ACF/CNTs composite with porous beads structure and mesopore distributionwas prepared.Its specific surface area is 526 m2/g,the pore volume is 0.266 cm3/g andthe specific capacitance is 196 F/g.compared to the undoped ACF material,the above mentioned properties of ACF/CNTs increased by 15%,6.6 times and 74%accordingly.In this paper,the formation mechanism of the special porous morphology of the ACF composite material was also analyzed.Capacitive deionization performance was investigated using 200mg/L saline water at the voltage of 1.2 V.The adsorption was 7.76 mg/g,which was 189%as much as that of ACF material.3)A CDI apparatus based on the Flow-through CDI model was designed,which had a relative advantage of faster desorption rate in comparison with the Flow-by CDI apparatus.Simultaneously,the saline water treatment capacity can be improved on the fundament of current experimental scale.A continuous desalting CDI method and its experimental apparatuswas designed.This work made it possible to output the purified water and concentrated water at the same time in a single desalination module,meanwhile to carry out the desalination continuously.