Purpose <p>This study aims to advance sustainable materials science and environmental conservation by integrating e-waste recycling and energy storage. A simple and efficient route was developed to convert hazardous waste toner powder into valuable products and their electrochemical performance for energy storage applications was evaluated.</p> Methods <p>Carbonaceous gas emitted during the pyrolysis of waste toner powder was used to synthesize multiwalled carbon nanotubes (MWCNTs) in a three-stage reactor system. The obtained MWCNTs were functionalized and loaded with solid and reduced solid residues to obtain a magnetic MWCNTs composites. XRD, FE-SEM, XRF, XPS, Raman spectroscopy and VSM studies investigates the compositional and magneto-structural properties of the prepared nanocomposites.</p> Results <p>The electrochemical properties of the solid residue, functionalized and magnetized MWCNTs were evaluated. The functionalized MWCNTs (f-MWCNTs) and magnetite loaded functionalized MWCNTs (f-MWCNTS/SR (M_s = 13.27&#xa0;emu/g)) exhibited maximum specific capacitance of 72 and 79 F/g, while retaining ∼ 85 and 82% of its initial capacitance even after 5000 cycles.</p> Conclusion <p>This study provides a facile route to upcycle hazardous waste toner powder into valuable products, and the MWCNTs obtained were found to be suitable for supercapacitor applications.</p> Graphic Abstract <p></p>