Bimetallic metal-organic framework derived porous carbon nanostructures for high performance membrane capacitive desalination

Membrane-based capacitive deionization (MCDI) is a promising method for desalination that is expected to alleviate the problem of water shortage. Typical CDI processes show limited efficiency in salt removal and experimental results suggest that an improvement in electrode materials could be the cornerstone of MCDI. In this study, bimetallic metal-organic frameworks (BMOFs) have been used as precursors to develop porous carbons for MCDI electrodes. BMOFs are a unique class of MOFs that possess two types of metal ions with properties dependent on the ratio of the metal ions. In our work, we have synthesized a series of BMOFs with different molar ratios of Zn and Co based on ZIF-8 and ZIF-67. By controlling the molar ratio between Zn and Co, we are able to synthesize BMOF-derived porous carbons with different particle sizes and graphitization degrees. Furthermore, the porous carbon derived from a BMOF of Zn : Co = 3 : 1 exhibits a superior salt removal capacity of 45.62 mg g^-1 in a 750 mg L^-1 NaCl solution at 1.4 V. We attribute this performance to the large ion-accessible surface area and improved electrical conductivity of the carbon derived from the BMOF.