Capacitive deionization of high concentrations of hexavalent chromium using nickel–ferric-layered double hydroxide/molybdenum disulfide asymmetric electrode

To decontaminate wastewater affected by high concentrations of aqueous hexavalent chromium (Cr(VI)) and improve the capability of layered double hydroxide (LDH) as an electrode in the capacitive deionization (CDI) process, nickel-ferric-LDH (NiFe-LDH) and NiFe-LDH/molybdenum disulfide (NiFe/MoS2) were synthesized using a hydrothermal method. Characterization results indicated that the flower-like cluster framework of MoS2 was decorated with the NiFe-LDH. Addition of MoS2 improved the conductivity, capacitance reversibility, charge efficiency, coulombic efficiency, and stability of NiFe/MoS2. The CDI performance of aqueous Cr(VI) was evaluated using NiFe/MoS2 and activated carbon as the anode and cathode, respectively. The process reached equilibrium within 240 min. The deionization capacity and removal ratio for Cr(VI) (100 mg/L, 100 mL) were 49.71 mg/g and 99.42 %, respectively, at 1.2 V and 20 mL/min. The isothermal data were accurately described using the Langmuir model, and the theoretical maximum deionization capacity of NiFe/MoS2 for Cr(VI) was 106.2 mg/g. The interaction mechanisms included electrostatic attraction, surface complexation, and reduction. These findings indicate that NiFe/MoS2 has feasible applications in practical wastewater treatment for Cr(VI) removal.