ZIF-8 Derived Porous Carbon Materials For Efficient Capacitive Deionization

For the low-carbon and sustainable development in current society,capacitive deionization?CDI?,a novel desalination technology,has attracted extensive attention among research fields due to its low energy consumption,non-secondary pollution and environmental friendliness.As the key factor in CDI system,new efficient materials for electrodes contribute to the development of CDI technology.In particular,the nanoporous carbon materials?NPCs?derived from zeolitic imidazolate frameworks?ZIFs?have large surface area,high nitrogen content and simple fabrication method,and have been used as CDI electrodes with good desalination performance.However,their micropore-dominant structures usually cause in increased electrical resistance and impairment for electric charges and ions in CDI process.Besides,their carbon structures are dominated by amorphous carbons,which harm electron transfer and conductivity.In this work,several ZIF-8 derived porous carbon materials with controllable porous structures and chemistry compositions are obtained to achieve good electrosorption capacity and rate.The specific research contents and conclusions as follows:?1?Herein,hollow ZIFs-derived nanoporous carbons?HZCs?were prepared via chemistry etching method and subsequent pyrolysis.The HZCs possess large specific surface area(642.7m² g^-1),high nitrogen content?8.7%?,rich mesopores and a unique hollow structure,resulting in fast diffusion for ions and low transfer resistance for charges.The specific capacitance of HZCs is 217.4 F g^-1 at a scan rate of 5 mV s^-1.The CDI test results suggest that HZCs electrode has an enhanced CDI performance with high electrosorption capacity of 15.31 mg g^-1 in 500mg L^-1 NaCl solution.Subsequent 20 adsorption-desorption experiment reveals a great regeneration stability of HZCs electrode for practical application.?2?In this section,we obtained ZIF-8 derived graphitized carbon materials?Z-Fe-C-X?with more sp² conductive graphitic carbon during the pyrolysis of Fe-doped ZIF-8?FZIF-8?.The Z-Fe-C-X have good graphitization,mesoporous structures and large surface area(609.2⁷22.6 m² g^-1).Among them,the sample carbonized at 900 ^oC?Z-Fe-C-9?with better porous structure and chemistry composition has the best electrochemical properties:a specific capacitance of 161.3 F g^-1 at a scan rate of 50mV s^-1.The CDI test results suggest the Z-Fe-C-9 electrode has an improved CDI performance with high electrosorption capacity of 10.88 mg g^-1 in 500 mg L^-1 NaCl solution.Moreover,the Z-Fe-C-9 electrode shows a good electrosorption stability over 10 adsorption-desorption cycles.?3?Exploring and designing new materials is one approach to develop CDI technology yet another would be to investigate other forms of CDI architectures.Particularly,hybrid CDI?hCDI?is a novel CDI system consisting of two different types of electrodes:one is a capactive electrode and another is a battery electrode.Herein,on the basis of the first two chapters,we synthesized Ag/hollow ZIF-8 cubic nanocrystals composite?HZIF-Ag?via chemical reduction,and finally obtained Ag coated ZIF-8 derived porous carbon composites?Ag/ZCs?.The Ag/ZCs remain porous structures and have rich mesopores.Besides,the CDI test results indicate the Ag/ZCs electrode has an excellent CDI performance compared with other two comparisons.A high electrosorption capacity of 19.81 mg g^-1 in 100 mg L^-1 NaCl solution at 1.2 V is achieved.The CDI regeneration experiment of Ag/ZCs electrode shows a good cycle stability over 5adsorption-desorption cycles in a single-pass CDI apparatus.