Preparation Of Porous Carbon Materials And Its Application In Heavy Metal Ion Removal

The pollution of heavy metal ions in water pollution has become a global environmental problem due to the increasing population,environmental pollution,and industrialization.Recently,capacitive deionization（CDI）,as an emerging,environmentally friendly,energy efficiency,and economical technology,has received more attention in brackish water desalination than other traditional technologies,and is often used in the field of heavy metal ion removal.However,conventional carbon-based electrodes are limited by low electric double layer（EDL）capacitance and desalination capacity,which seriously affects their practical applications.According to EDL theory,atom/element doping,porosity,and high electrical conductivity in carbon materials are beneficial to improving the performance of CDI.The controllable pore structure can play a crucial role in CDI,and is an effective means to improve the deionization performance of electrode materials.It is shown that carbon nanofibers（CNFs）are an ideal electrode material because of their high electrical conductivity and specific surface area.Electrospinning is a facile method for preparing CNFs.Polyacrylonitrile（PAN）has become the most commonly used polymer in the production of CNFs by electrospinning due to it can obtain a stable structure through its characters of high carbon yield and elastic shear.However,the mechanical properties and adsorption capacity of heavy metal ions performance for CNFs prepared from pure PAN are inferior.In this paper,electrospun PAN nanofibers were modified to improve the CDI properties,and further greatly enhanced the adsorption capacity of heavy metal ions.The main contents of this thesis listed as follows:（1）Research on the application of controlled synthesis of Zn O modified nitrogen doped self-supporting carbon nanofiber membrane（Zn O@N-PCNM）in CDI.Firstly,ZIF-8 nanoparticles were synthesized.Flexible and layered porous carbon nanofiber membranes（PCNM）were prepared by electrospinning.ZIF-8 was applied the pore-forming agent due to it can produce layered and multi-stage pore structure on the surface and inside of the fiber during high temperature condition.The unique porous structure of ZIF-8 has a large specific surface area and can provide a large number of adsorption sites for the supercapacitor.On the other hand,ZIF-8 could convert to zinc oxide,which further form elemental zinc when reacted with carbon at high temperature condition.The high nitrogen content in the fiber could provide pseudocapacitance for the supercapacitor.In this case,the Zn O@N-PCNM can be used as the electrode owing to its large specific surface area,high nitrogen doping,and high elemental zinc loading.And results showed that the Zn O@N-PCNM carbon nanofibers exhibited a maximum specific capacity of 507.2 F g^-1and cycle stability,which was greatly improved than pure PAN carbon nanofibers.Furthermore,its heavy metal ion adsorption properties had also been significantly improved.（2）Controllable synthensized of carbon nanofiber（Zn/Co-NCNTs@PCNFs）composites loaded with Zn/Co modified carbon nanotubes,and explored its application in CDI.Employing Co-spun ZIF-8 and Co ions with PAN by electrospinning technology to prepare porous CNFs supported on carbon nanotubes（CNTs）.Among them,Co acts as a catalyst to induce the formation of CNTs,and thus improves the conductivity of the materials.The CNTs could increase the specific surface area of CNFs,and thus enhance the EDL of the material.The doping of Zn/Co ions introduce the redox reaction,and thus produce pseudocapacitance on the basis of EDL,which greatly increases the specific capacitance for the material.ZIF-8 could create a pore structure in CNFs,increase the contact area between the electrode and the electrolyte,and subsequently enhance the transport and storage of ions in the electrolyte.Results showed that Zn/Co-NCNTs@PCNFs electrode exhibited excellent electrical conductivity and 1281.8 F g^-1,which was improved a lot than the traditional CNFs.Furthermoer,the assembling capacitive deionization device showed excellent ability to remove heavy metal ions.In conclusion,CNFs combined with ZIF-8,and ZIF-8 with cobalt nitrate were synthesized through electrospinning technology,which exhibited excellent performance as supercapcitor and CDI electrode.Above combination offer new avenue for synthesis of supercapcitor and CDI electrode in the future.