Macrocyclic ligand-embedded graphene-in-polymer nanofiber membranes for lithium ion recovery

Ensuring a stable and diverse lithium supply is becoming increasingly important for battery-related industries. Herein, we propose the concept of integrating a molecular receptor and graphene-in-polymer nanofibers to create highly durable and reusable membranes for selective lithium ion recovery. Specifically, macrocyclic chelating ligand (12C4) molecules as ion receptors were incorporated into a graphene-in-polyethersulfone (PES) nanofiber (CGPNF) membrane. The CGPNF membranes with diameters of approximately 100 nm showed an increase in diameter and surface roughness after lithium ion adsorption. Theoretical calculations indicated that the graphene nanosheets provide intermolecular interactions for the uniform dispersion and stable entrapment of the molecular receptors in the nanofibers. In addition, nitrogen sorption tests revealed that the graphene nanosheets improve the stability of the nanofibers, allowing for more effective porosity and surface area. The graphene nanosheets also increased the surface roughness and chemical inhomogeneity of the CGPNF membrane, thereby increasing its hydrophilicity. The adsorption isotherms of the CGPNF membranes were more accurately described by a pseudo second-order model, indicating that the adsorption kinetics are governed by a chemisorption process, namely, host–guest interactions. Finally, in a flow system, the CGPNF membrane showed a maximum adsorption capacity of 86.3 mg g−1 for lithium ions and retained more than 93 % of its initial adsorption capacity after 10 regeneration cycles.