3D flaky MnO2 nanoflower decorated carbonized polyaniline as cathode material for hybrid capacitive deionization to remove Pb2+ and Zn2+from aqueous solution

The K-CP/MnO 2 composite was prepared by loading manganese dioxide (MnO 2 ) nanosheets onto potassium hydroxide (KOH) activated carbonized polyaniline (K-CP) via low-temperature hydrothermal reaction. The composite demonstrated high efficiency in removing Pb 2+ and Zn 2+ in the hybrid capacitive deionization (HCDI) technology. K-CP/MnO 2 presents a core-shell structure with conductive K-CP as the core and electrochemically active MnO 2 constructed by porous nanosheets as the shell. The disordered entanglement of K-CP and MnO 2 nanoflakes significantly increases the interlayer spacing, optimizes the pore distribution, creates favorable conditions for charge and ion transport, and realizes the synergistic effect of electric double layer (EDL) adsorption and Faradaic reactions. The specific capacitance (SC) of K-CP/MnO 2 at 5 mV s −1 is 112.03 F g −1 , which is nearly 3.76 times that of CP (29.82 F g −1 ). At a voltage of 1.2 V (100 mg L −1 ), the electrosorption capacity (SAC) of the K-CP/MnO 2 electrode for Pb 2+ and Zn 2+ is 124.66 and 96.86 mg g −1 , respectively. After 15 adsorption/desorption cycles in the HCDI device, the adsorption capacity for Pb 2+ and Zn 2+ is retained at 86.81% and 82.59%, respectively. The experiments indicate that the removal of Pb 2+ primarily occurs through electrosorption, redox reactions, and surface complexation, while Zn 2+ is inserted into the channel provided by MnO 2 and participates in the solid phase reaction. The K-CP/MnO 2 composite prepared in this study offers a novel approach for designing high-performance HCDI electrodes and achieving the selective removal of heavy metals.