A second life for e-waste: a catalyst from discarded capacitors active in the reduction of nitroarenes to anilines

The aim of this study is to employ waste derived from electrical and electronic equipment (WEEE), such as capacitors from discarded printed circuit board (PCB), as catalysts in fine chemical reactions. The amount of electronic waste (e-waste) generated worldwide is constantly rising1. This type of waste contains potentially toxic and polluting substances, which pose a threat to human health and environment2. On the other hand, if properly managed, they become valuable resources thanks to their high content of critical raw materials (CRM)1. In this work the WEEE were initially ground to obtain a fine powder and some needles with a size less than 1 mm. Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-Ray Analysis (EDX) and Thermogravimetric analysis (TGA) of the milled samples revealed the presence of potentially catalytic metals (Cu and Fe)3 and plastic polymers. TGA results also allowed us to choose the suitable temperature for calcining the materials, carried out to eliminate the organic phase (plastic). The reductions of nitroarenes to their corresponding amines were selected as a class of reactions to test the catalytic activity of the materials (cat-wire and cat-powder) obtained from multilayer ceramic capacitors. As bench reaction we used hydrogenation of nitrobenzene to aniline in water, at room temperature, with NaBH4 as reducing agents. The magnetic catalyst, cat-wire, could be easily separated from the reaction mixture and recycled up to six times. Cat-wire was also active in the reduction of other substituted nitro compounds.