Abstract
Capacitive deionization (CDI) is a promising technique for brackish water desalination. However, its salt electrosorption capacity is insufficient for practical application yet, and little information is available on hardness ion (Mg(2+), Ca(2+)) removal in CDI. Herein, hierarchical porous carbon (HPC) was prepared from low-cost and renewable microalgae via a simple one-pot approach, and both MnO(2)/HPC and polyaniline/HPC (PANI/HPC) composites were then synthesized using a facile, one-step hydrothermal method. Compared with the MnO(2) electrode, the MnO(2)/HPC electrode presented an improved hydrophilicity, higher specific capacitance, and lower electrode resistance. The electrodes exhibited pseudocapacitive behaviors, and the maximum salt electrosorption capacities of MnO(2)/HPC-PANI/HPC CDI cell was up to 0.65 mmol g(-1) NaCl, 0.71 mmol g(-1) MgCl(2), and 0.76 mmol g(-1) CaCl(2), respectively, which were comparable and even higher than those of the previously reported CDI cells. Additionally, the MnO(2)/HPC electrode presented a selectivity order of Ca(2+) ≥ Mg(2+) > Na(+), and the divalent cation selectivity was found to be attributed to their stronger binding strength in the cavity of MnO(2.) Multiscale simulations further reveal that the MnO(2)/HPC electrodes with the unique luminal configuration of MnO(2) and HPC as supportive framework could offer a great intercalation selectivity of the divalent cations and exhibit a great promise in hardness ion removal.