Transforming e-waste into value: ceramic capacitors as recyclable catalysts for the reduction of nitroarenes under mild condition

This study explores the potential of electronic waste components as catalysts, with a particular focus on ceramic capacitors, key elements in motherboard circuits. Particularly, commercial ceramic capacitors (CC) and those recovered from waste motherboards, provided by a WEEE collection facility (WC), were studied. After grinding, the samples were characterized to identify the present metals using Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy (SEM–EDX), Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP–OES), and X-ray Diffraction (XRD). Based on thermogravimetric analysis (TGA), the optimal temperature was selected for calcination, allowing for maximum removal of plastic polymers from the sample. The magnetic fractions of calcined CC and WC, designated MCC and MWC respectively, proved active in the aqueous-phase reduction of nitroarenes to anilines at room temperature using sodium borohydride (NaBH₄) as a reducing agent. MCC retained catalytic activity over five cycles, and MWC over three. Control experiments confirmed the heterogeneous nature of the catalytic system, identifying copper (Cu) as the principal active species, with potential contributions from iron (Fe) and nickel (Ni).