Exceptional capacitive deionization desalination performance of hollow bowl-like carbon derived from MOFs in brackish water

Electrode Materials for Desalination of Water via Capacitive Deionization

Recent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco-friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion-exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes.

Nanoarchitectonics of heteroatom-doped hierarchical porous carbon derived from carboxymethyl cellulose carbon aerogel and metal-organic framework for capacitive deionization

Capacitive deionization (CDI) using porous materials offers a sustainable solution for providing affordable freshwater, but the low salt adsorption rate of benchmark carbon materials significantly limit the practical implementation. Herein, we utilized carboxymethyl cellulose sodium (CMC) as the carbon skeleton to produce a composite carbon aerogel loaded with ZIF-8 (ZIF-8/CMC-CA). The presence of ZIF-8 nanoparticles improved the pore structure of the material and provides a certain pseudo capacitance by introducing N. Compared with ZIF-8 derived carbons (ZIF-8-C), the CMC provided a good three-dimensional structure for the dispersion of ZIF-8 nanoparticles, reduced the agglomeration of particles. Furthermore, numerous carboxyl and hydroxyl groups on CMC enhanced the hydrophilicity of materials. Due to the interconnected structure, ZIF-8/CMC-CA exhibited excellent conductivity, a high specific surface area, and offered suitable channels for the rapid entry and exit of ions. In a three-electrode system, the total specific capacitance of the ZIF-8/CMC-CA electrode was 357.14 F g^-1. The adsorption rate of ZIF-8/CMC-CA was 2.02 mg g^-1 min^-1 in a 500 mg L^-1 NaCl solution. This study may provide new insight for modifying and fabricating electrode materials for practical CDI applications.

Design of Uniform Hollow Carbon Nanoarchitectures: Different Capacitive Deionization between the Hollow Shell Thickness and Cavity Size

Carbon-based materials with high capacitance ability and fast electrosorption rate are ideal electrode materials in capacitive deionization (CDI). However, traditional carbon materials have structural limitations in electrochemical and desalination performance due to the low capacitance and poor transmission channel of the prepared electrodes. Therefore, reasonable design of electrode material structure is of great importance for achieving excellent CDI properties. Here, uniform hollow carbon materials with different morphologies (hollow carbon nanospheres, hollow carbon nanorods, hollow carbon nano-pseudoboxes, hollow carbon nano-ellipsoids, hollow carbon nano-capsules, and hollow carbon nano-peanuts) are reasonably designed through multi-step template method and calcination of polymer precursors. Hollow carbon nanospheres and hollow carbon nano-pseudoboxes exhibit better capacitance and higher salt adsorption capacity (SAC) due to their stable carbonaceous structure during calcination. Moreover, the effects of the thickness of the shell and the size of the cavity on the CDI performance are also studied. HCNSs-0.8 with thicker shell (≈20 nm) and larger cavity (≈320 nm) shows the best SAC value of 23.01 mg g-1 due to its large specific surface area (1083.20 m2  g-1 ) and rich pore size distribution. These uniform hollow carbon nanoarchitectures with functional properties have potential applications in electrochemistry related fields.