Treating waste with waste: Efficient separation of Ni(II) from wastewater by a waste-derived polyimide foam with rationally designed structure

The separation and upcycling of nickel from industrial wastewater is significant because it is harmful to the environment and human health. With the development of special engineering plastics industry, a substantial amount of polyimide (PI) scrap is generated. In this study, an amine and carboxyl functionalized PI (PI-AC) was prepared from waste-derived PI foam for the adsorption and separation of Ni(II). The adsorption performance of PI-AC can be modulated by adjusting the ratio of functional groups. PI-AC demonstrated rapid adsorption kinetics (<5 min) for Ni(II) and effectively adsorbed Ni(II) from real wastewater in column experiments. PI-AC shows a competitive dynamic adsorption capacity for Ni(II) (222.59 mg/g) as compared with most of the reported adsorbents. Furthermore, the successful removal of Ni from low-concentration simulated Ni-containing wastewater (7.18 mg/L) results in a residual Ni concentration (0.001 mg/L) that complies with the emission standard. The macroporous structure of the PI foam enables rapid adsorption of nickel and column adsorption was successfully achieved. The adsorption performance exhibited maintained stably even after five cycles, demonstrating excellent recoverability. The characterizations, comparison studies, and DFT calculations demonstrated that one nitrogen atom in the amine group and one oxygen atom in the carboxyl group act as a bidentate ligand to chelate with Ni(II). This study opens a new way for the treatment of wastewater using PI foam scrap, which coincides with the idea of "treating the waste with waste".