Thermal Nanowiring of E-Waste: A Sustainable Route for Synthesizing Green Si₃N₄ Nanowires

This paper details a sustainable process for synthesizing green Si₃N₄ nanowires (NWs) from high volume fractions of electronic waste (e-waste). Obsolete computers were manually dismantled, and the glass fraction of the monitors (GCM) and their plastic shells (PS) were separated and used as silica and carbon sources, respectively. E-waste is the world's fastest growing waste stream, and although considerable research effort is currently focused on metals recovery, there are few options for the huge volumes of glass and plastic waste left behind. Using a blend of GCM and PS, we applied a novel route, thermal nanowiring at 1550 °C under nitrogen purge in atmospheric pressure. FE-SEM studies revealed the resulting Si₃N₄ NWs, with diameters of 75-250 nm, mostly appeared to turn in random directions and exhibited twisted pattern along their axes, indicating the Si₃N₄ crystalline grew through a screw-dislocation-driven mechanism. In a comparison experiment, waste toner powder with iron oxide (∼38 wt %) was added as a source of Fe to the GCM-PS blend to enable the investigation of its catalytic effect on the morphology of the Si₃N₄ synthesized. The addition of the toner powder resulted in long Si₃N₄ nanobelts (up to 40 μm) with traces of liquid droplets on their tips, indicating the Fe had promoted the formation of the long and straight nanobelts via the vapor-liquid-solid VLS mechanism. The novel route, thermal nanowiring described here, confirms a new opportunity to transform a globally significant waste burden into value-added 1D materials, thereby simultaneously delivering economic and environmental benefits.