Boosted brackish water desalination and water softening by facilely designed MnO/hierarchical porous carbon as capacitive deionization electrode.

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, Ca) 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/HPC and polyaniline/HPC (PANI/HPC) composites were then synthesized using a facile, one-step hydrothermal method. Compared with the MnO electrode, the MnO/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/HPC-PANI/HPC CDI cell was up to 0.65 mmol g NaCl, 0.71 mmol g MgCl, and 0.76 mmol g CaCl, respectively, which were comparable and even higher than those of the previously reported CDI cells. Additionally, the MnO/HPC electrode presented a selectivity order of Ca ≥ Mg > Na, and the divalent cation selectivity was found to be attributed to their stronger binding strength in the cavity of MnO Multiscale simulations further reveal that the MnO/HPC electrodes with the unique luminal configuration of MnO and HPC as supportive framework could offer a great intercalation selectivity of the divalent cations and exhibit a great promise in hardness ion removal.