Covalently decorated crown ethers on magnetic graphene oxides as bi-functional adsorbents with tailorable ion recognition properties for selective metal ion capture in water

[Display omitted] •Bi-functional magnetic GO adsorbents with ion selectivities were developed.•Magnetite nanoclusters were grown in-situ on GO oxygenous groups.•Crown ethers as ligands were covalently grafted via linkers on GO backbone.•Magnetic GO tethered with 12CE4 was highly effective and selective towards Li+.•Wide selection of CE decorated magnetic GOs were fabricated for various applications. Metal ions (Mn+) in water are considered as environmental pollutants, as industrial impurities or as potential secondary sources for valuable metals. Increasing generation of complex feed streams has raised the need for more specialized adsorbents that could preferentially capture the target Mn+. While graphene oxide (GO) is an effective adsorbent, its indiscriminate sequestration negatively affects its selectivity. To meet the growing demand for more Mn+-selective materials, GO adsorbents with dual features of ion recognition and magnetic responsiveness were developed. The bi-functional GOs were fabricated by in-situ nucleation of Fe3O4 nanoclusters on GO oxygenous groups and by direct grafting of ethynylbenzene linkers on its backbone, which served as tethering sites for the macrocyclic crown ether (CEs) ligands with tunable Mn+ affinities (i.e. CE@Fe3O4-rGO). As proof-of-concept, 12CE4@Fe3O4-rGO was proven highly selective for Li+ capture, achieving α = 367–14,513 against Na+, K+, Mg2+, Ca2+ in seawater. Its Langmuir-type Li+ adsorption achieved nearly ~100% 12CE4 utilization (1.03 mmol g−1 CE loading). Its pseudo-second uptake rate demonstrated its rapid Li+ capture. 12CE4@Fe3O4-rGO is water-dispersible, magnetically retrievable, and recyclable with consistent Li+ uptake performance. By replacing the CEs with aza15CE5, aza18CE6 and dibenzo-24CE8, three more types of CE@Fe3O4-rGOs (1.24–1.71 mmol CE g−1) were successfully synthesized with varying affinities towards heavy metals, radionuclides and alkali metal ions. These findings highlight the versatility of the proposed technique in producing a wide selection of CE@Fe3O4-rGOs which can be used for selective Mn+ capture in various application for water decontamination, salts removal, and resource recovery.