Removal of toxic metal ions using chitosan coated carbon nanotube composites for supercapacitors

Environmental pollution and energy crisis are two major global challenges to human beings. Recovering energy from wastewater is considered to be one of the effective approaches to address these two issues synchronously. As the main pollutants in wastewater, toxic heavy metal ions are the potential candidates for energy storage devices with pseudocapacitive behaviors. In this study, toxic metal ions of Cr(VI) and Cu(II) are removed efficiently by chitosan coated oxygen-containing functional carbon nanotubes, and the corresponding equilibrium adsorption capacity is 142.1 and 123.7 mg g−1. Followed by carbonization of metal ions-adsorbed adsorbents, Cu- and CrN-loaded carbon composites can be obtained. Electrochemical measurements show that the supercapacitor electrodes based on Cu- and CrN-loaded carbon composites have specific capacitance of 144.9 and 114.9 F g−1 at 2 mV s−1, with superior electrochemical properties to pure chitosan coated carbon nanotubes after carbonization. This work demonstrates a new strategy for the resource-utilization of other heavy metal ions for energy devices, and also provides a new way to turn environmental pollutants into clean energy.