– Many metal ion separation processes involve complex mixtures with competing ions. While the review discusses functionalization strategies, were there specific studies that quantified COFs’ selectivity when multiple metal ions with similar ionic radii and charges coexist? How do COFs perform in real wastewater or mining leachates compared to controlled lab conditions?
– The review discusses adsorption mechanisms such as electrostatic interactions and coordination bonding, but was there any attempt to link experimental adsorption capacities with theoretical density functional theory (DFT) calculations? Would such an approach help in predicting optimal COF designs for specific metal ions?
– Given the high cost and synthesis complexity of certain COFs, have the authors evaluated any techno-economic analyses for large-scale production? Are there any green or solvent-free synthesis routes discussed that could improve the feasibility of COFs for commercial metal recovery applications?
– COFs are presented as a promising alternative, but how do they compare in efficiency and cost-effectiveness to existing ion-exchange resins, MOFs, or bio-based adsorbents? Are there any hybrid approaches (e.g., COF-membrane composites) explored to enhance separation performance?
Having read both the review and the critical questions raised, I find that while the paper provides a solid theoretical foundation on COFs for metal ion separation, there are notable gaps that warrant further discussion. Below is a scientific response to the key issues raised:
– The review discusses functionalization strategies that enhance COF selectivity, particularly through pore size tuning, ligand coordination, and electrostatic interactions. However, studies specifically quantifying COFs’ selectivity in real-world conditions (e.g., wastewater or mining leachates) remain limited. Metal ion adsorption is often studied in controlled laboratory settings, where the influence of competing ions, pH variations, and organic contaminants is minimized. This raises concerns about COFs’ practical performance in complex matrices. Some recent works have evaluated multi-metal systems with COFs, showing that functionalized COFs can achieve preferential adsorption of specific metal ions, but a systematic comparative analysis against commercial ion-exchange resins and bio-based adsorbents would provide a more realistic assessment of their efficiency.
– The review thoroughly discusses COF adsorption mechanisms, but there is limited integration of theoretical predictions with experimental findings. Density functional theory (DFT) is a powerful tool for modeling COF-metal interactions, binding affinities, and selectivity trends, but adsorption behaviors in real aqueous environments may deviate from theoretical predictions due to factors such as solvent effects, competitive adsorption, and structural rearrangements. Some studies have successfully combined DFT with molecular dynamics simulations to better model hydration effects and ion solvation, but further experimental validation is needed. One possible approach would be to correlate DFT-calculated binding energies with adsorption isotherms and kinetic models, which could refine COF design for targeted metal separation applications.
– The review acknowledges that high synthesis costs and scalability challenges remain obstacles to large-scale COF application, but it lacks a detailed techno-economic analysis. While green synthesis methods, such as mechanochemical and aqueous-phase synthesis, have been proposed to reduce solvent use and processing time, the cost of precursors and functionalization reagents still limits COFs’ large-scale production. Compared to MOFs, ion-exchange resins, and biopolymer-based adsorbents, COFs remain less commercially viable due to their multi-step synthesis and limited industrial adoption. A life-cycle assessment comparing COFs to conventional adsorbents in terms of synthesis energy demand, material longevity, and recyclability would provide a clearer picture of their feasibility.
– COFs are highlighted as promising materials for metal ion separation, but no direct comparative analysis is provided in the review against MOFs, ion-exchange resins, or bio-based adsorbents. While COFs exhibit high chemical stability, tunable porosity, and selective adsorption, existing commercial adsorbents outperform them in cost, scalability, and regeneration efficiency. Some studies have explored COF-membrane composites to enhance separation performance, but these approaches remain in early research stages. A quantitative comparison of adsorption kinetics, capacity, and regeneration cycles between COFs and conventional adsorbents in real industrial settings would be crucial in evaluating their true advantages and trade-offs.