Selective heavy-metal sequestration and rare-earth element recovery using metal-organic frameworks.

Modern water treatment and resource recovery demand materials that combine high performance with real-world durability. Traditional remediation approaches (e.g., precipitation and coagulation) have drawbacks (e.g., poor selectivity) that can be overcome using adsorption-based strategies. Metal-organic frameworks (MOFs) offer high tunability, high uptake capacities and the potential for regeneration. Translating MOF adsorbents into scalable, reliable technologies requires consistent method reporting and improved mechanistic insight, toward improving long-term stability in realistic water matrices. In this protocol, we describe how to deploy and assess the performance of MOF-based adsorbents for simultaneous heavy-metal sequestration (e.g., Pb(II), Cd(II), Ni(II) and Mn(II)) and rare-earth element recovery (e.g., Nd(III), Y(III) and Dy(III)) from complex water matrices. The workflow is broadly applicable across MOF chemistries and is illustrated using Cu(II)-based frameworks as representative model systems, synthesized at gram scale using commercially available precursors. We stabilize these frameworks through controlled defect engineering (e.g., partial metal substitution) to mitigate hydrolytic degradation and prolong operation time. We further tune morphology (e.g., nanosheets) to enhance surface accessibility and enable recyclability. For industrial applicability, we shape the MOFs into macrobeads via a green process. The procedure comprises: (i) MOF synthesis; (ii) comprehensive pre-adsorption characterization to assess crystallinity, porosity, morphology and composition using powder X-ray diffraction, nitrogen adsorption-desorption, scanning electron microscopy and inductively coupled plasma optical emission spectrometry; (iii) mechanistic adsorption assessment with kinetic, isotherm, thermodynamic, pH and selectivity analyses; (iv) regeneration and recovery workflows; and (v) deployment considerations in complex aqueous matrices, including industrial effluents, saline waters and e-waste leachates. The protocol provides a reproducible framework for implementing MOF-based adsorption technologies in water remediation and circular resource applications.