Creating a new electrode material of supercapacitors from the waste multi-walled carbon nanotubes

Abstract Many adsorbents are discarded after removing pollutants, which always re-contaminates environment due to a release of pollutants again. The purpose of this study is to reuse the waste multi-walled carbon nanotubes (MWCNTs) who remove methylene blue (MB) from waste water as electrode material of supercapacitor. Herein, with a combination of polypyrrole (PPy), MWCNTs/MB/PPy composites are synthesized via chemical in-situ polymerization. The structure tests of the composites indicate that adsorption of MB changes MWCNTs from hydrophobic to hydrophilic. Additionally, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectrum (EIS) tests in three-electrode system demonstrate that at a current density of 5  mA cm−2, the specific capacitance of MWCNTs/MB/PPy composites is 446 F g−1. This result is higher than that of PPy and MWCNTs/PPy composites due to an extra pseudo-capacitance provided by MB. Moreover, a symmetric supercapacitor of MWCNTs/MB/PPy composites is assembled to successfully light a light emitting diodes (LED), which powerfully reveals the potential application of MWCNTs/MB/PPy composites. Obviously, the waste MWCNTs can be reused, meaning the dyes adsorbed on MWCNTs have no chance to pollute the environment again.