Efficient Nickel and Cobalt Recovery by Metal–Organic Framework-Based Mixed Matrix Membranes (MMM-MOFs)

Green energy transition has supposed to give a huge boost to the electric vehicle rechargeable battery market. This has generated a compelling demand for raw materials, such as cobalt and nickel, which are key common constituents in lithium-ion batteries (LIBs). However, their existing mining protocols and the concentrated localization of such ores have made cobalt and nickel mineral conundrums, and their supplies experience shortages, which threaten to slow the progress of the renewable energy transition. Aiming to contribute to the sustainable recycling of these valuable metals from LIBs and wastewater, in this work, we explore the use of four mixed matrix membranes (MMMs) embedding different metal–organic frameworks (MOFs), i.e., MIL-53(Al), MIL-53(Fe), MIL-101(Fe), and {SrIICuII6[(S,S)-serimox]3(OH)2(H2O)}·39H2O (SrCu6Ser) in polyether sulfone (PES), for the recovery of cobalt(II) and nickel(II) metal cations from mixed cobalt–nickel aqueous solutions containing common interfering ions. Whereas the neat PES membrane slightly contributes to the adsorption of metal ions, showing reduced removal efficiency values of 10.2 and 9.5% for Ni(II) and Co(II), respectively, the inclusion of MOFs in the polymeric matrix substantially improves the adsorption performances. The four MOF@PES MMMs efficiently remove these metals from water, with MIL-53(Al)@PES being the one that presents better performance, with a removal efficiency up to 95% of Ni(II) and Co(II). Remarkably, SrCu6Ser@PES exhibits outstanding selectivity toward cobalt(II) cations compared to of nickel(II) ones, with removal efficiencies of 63.7 and 15.1% for Co(II) and Ni(II), respectively. Overall, the remarkable efficiencies, versatility, high environmental robustness, and cost-effective synthesis shown by this family of MOF@PES MMMs situate them among the best adsorbents for the extraction of this kind of contaminants.

Physical Techniques.Elemental analyses (C, H, and N) were performed at the microanalysis service of the Dipartimento di Chimica e Tecnologie Chimiche of the Università della Calabria (Italy).FTIR spectra were recorded on a Nicolet-6700 spectrophotometer as KBr pellets.The thermogravimetric analysis was performed on crystalline samples under a dry N2 atmosphere with a Mettler Toledo TGA/STDA 851 e thermobalance operating at a heating rate of 10 ºC min -1 .S3.

S21
Powder Diffraction Measurements: Fresh polycrystalline samples of MIL-53(Al), MIL-53(Fe), and MIL-101(Fe), pristine PES membrane and MOF@PES MMMs were deposited on a flat plate with a 5 cm diameter prior to being mounted on a Bruker D2 PHASER Diffraction System with Cu-Kα radiation (λ = 1.54056Å).Five repeated measurements were collected at room temperature (2θ = 2-50) and merged in a single diffractogram.Gas Sorption: The N2 adsorption isotherms at 77 of samples of MIL-53(Al), MIL-53(Fe), MIL-101(Fe) and SrCu6Ser were carried out on crystalline samples with a BELSORP MINI X instrument.Samples were activated at 70 °C under reduced pressure (10 -6 Torr) for 16 h prior to carry out the sorption measurements.The Brunauer-Emmett-Teller (BET) surface areas were calculated from the N2 adsorption isotherm according to the criteria reported by Rouquerol et al. and de Lange et al. 1

Figure S2 .Figure S3 .
Figure S2.Water contact angle of the top surface of pristine PES and MOF@PES MMMs membrane.

Figure S6 .
Figure S6.N2 (77 K) adsorption isotherms for the activated compounds a) MIL-53(Al); b) MIL-53(Fe); c) MIL-101(Fe) and d) SrCu6Ser.Filled and empty symbols indicate the adsorption and desorption isotherms, respectively.The samples were activated at 70 °C under reduced pressure for 16 h prior to carry out the sorption measurements.

Figure S9 .
Figure S9.Comparison of significant macro-mechanical parameters between the investigated materials: Young's modulus (E) yield strength (  ) elongation to failure (  ) and ultimate tensile strength (  ).

Figure S11 .
Figure S11.Variation of the concentration of Ni(II) ion vs time.Solid lines are a guide for eyes.

Figure S12 .
Figure S12.Variation of the concentration of common metal ions found in oligo-mineral water and Ni(II) cations added, with MIL-53(Al)@PES MMM vs time.Graphics are organized from data reported in TableS3.

Figure S13 .
Figure S13.Variation of the concentration of Ni(II) and Co(II) ion vs time.Solid lines are a guide for eyes.

Table S1 .
Equilibrium maximum loading and removal efficiency determined by soaking 20 mg of polycrystalline samples of the selected MOFs in a 10 mL aqueous solution containing the suitable metal salt (1000 mg/g of Ni(NO3)2 or 2000 mg/g of Co(NO3)2].Graphics are reported in Figure5.

Table S3 .
Residual of Ni 2+ concentration a,b in an oligo-mineral aqueous solution (volume 100 mL) containing Ni(NO3)2 at an initial concentration of ca. 1 ppm in presence of multi-ions as interfering media.Graphics are reported in FigureS6.
a LOD: 0.015 ppb.b Each experiment was performed in triplicate and results are reported as average values ± 3 SD.

Table S4 .
Mean composition of Li-ion battery (smartphone battery).

Table S5 .
Residual of Ni2+and Co 2+ concentration a,b in an oligo-mineral aqueous solution (volume 100 mL) containing Ni(NO3)2 at an initial concentration of ca. 1 ppb (top) and Co(NO3)2 at an initial concentration of ca. 5 ppb (bottom) in presence of multi-ions as interfering media.Graphics are reported in FigureS6.
a LOD: 0.015 ppb.b Each experiment was performed in triplicate and results are reported as average values ± 3 SD.

Table S6 .
Residual of Ni2+and Co 2+ concentration a,b in an oligomineral aqueous solution (volume 100 mL) containing Ni(NO3)2 at an initial concentration of ca. 1 ppb (top) and Co(NO3)2 at an initial concentration of ca. 5 ppb (bottom) in presence of multiions as interfering media after regeneration and reuse of the MOF@PES MMMs.
a LOD: 0.015 ppb.b Each experiment was performed in triplicate and results are reported as average values ± 3 SD.S9