Enhanced dye removal and supercapacitor performance of polyethyleneimine-impregnated activated carbon derived from local eucalyptus biochar

This study evaluated the effectiveness of low-cost eucalyptus biochar (EUBC) as a precursor for activated carbon (EUAC), for methyl orange (MO) removal and supercapacitor applications. The surface charge was made positive by impregnating EUAC with a 10% weight polyethyleneimine (PEI) solution, improving anionic MO adsorption. The impregnation was verified by SEM and XPS, showing a nitrogen content of 9.39%. The adsorption capacity of the 10% wt PEI/EUAC is 142 mg g-1, significantly surpassing previous reports. The adsorption mechanisms were described using the Sips isotherm and Elovich kinetics, indicating heterogeneous adsorption, physisorption and electrostatic interactions. In electrochemical tests, EUAC (263 F g-1) and 10% wt PEI/EUAC (244 F g-1) exhibited similar specific capacitances, six times higher than that of EUBC (40 F g-1) at a current density of 1 A g-1. However, EUBC electrodes exhibited nearly double the internal resistivity of those from EUAC and 10% wt PEI/EUAC, attributed to particle size, pore size, and surface area differences.