Adsorption Mechanisms for Heavy Metal Removal from Aqueous Solutions

Adsorption has emerged as a versatile and cost-effective strategy for extracting toxic heavy metal ions from water. The process involves the accumulation of metal species onto the surface of a solid phase through a combination of physisorption and chemisorption. Key interactions include electrostatic attraction between charged metal ions and surface functional groups, ion exchange with labile cations on the adsorbent, surface complexation via coordinate bonds, π-π stacking in aromatic frameworks and, in some instances, redox transformations that convert metal ions to less soluble forms. Porous materials such as activated carbons, biopolymers, metal–organic frameworks and layered two-dimensional compounds provide high surface areas and tunable pore structures that enhance uptake capacity and selectivity. Adsorption performance is commonly modelled using Langmuir and Freundlich isotherms, while kinetics often follow pseudo-second-order behaviour, indicating that chemisorption can be rate-limiting. Recent advances focus on multifunctional composites that combine high capacity with rapid kinetics, facile regeneration and minimal secondary waste. Such developments are driving large-scale applications in industrial effluents, municipal treatment and contaminated groundwater remediation.

Research from Nature Portfolio

Modified agricultural by-products have been transformed into efficient mercury sorbents by thermal and chemical treatments that introduce thiol and silane functionalities. These low-cost materials exhibit spontaneous adsorption mechanisms, with variations in enthalpy signifying physisorption or endothermic complexation pathways, and surface morphology studies confirm minimal structural degradation after repeated cycles. Electrochemical removal via alloy formation on platinum thin films has demonstrated exceptionally high mercury uptake through in situ formation of a stable intermetallic phase. This method operates across wide pH ranges and yields rapid, selective extraction, with facile electrode regeneration. Separately, hybrid biopolymer–magnetite–graphene oxide sheets have been engineered to remove hexavalent chromium by combining electrostatic attraction, hydrogen bonding and covalent Fe–O–C linkages. These composites not only adsorb Cr(VI) but also catalyse its reduction to Cr(III), enabling simultaneous capture and detoxification with sustained performance over multiple use cycles.

Adsorption Mechanisms for Heavy Metal Removal from Aqueous Solutions publication trend

The graph below shows the total number of articles in adsorption mechanisms for heavy metal removal from aqueous solutions across all publications each year (not limited to Nature Index journals).

Technical terms

Physisorption: Weak, non-specific adsorption driven by van der Waals forces.

Chemisorption: Strong adsorption involving the formation of chemical bonds between adsorbate and surface.

Surface complexation: Coordinate bonding between a metal ion and specific functional groups on an adsorbent.

Ion exchange: Replacement of ions on the adsorbent surface with metal ions from solution.

Adsorption isotherm: Mathematical description of the relationship between solute concentration in solution and adsorbed amount at equilibrium.

Pseudo-second-order kinetics: A kinetic model indicating that chemisorption is rate-controlling, with adsorption rate proportional to the square of available sites.

References

1. Mechanisms of mercury removal from water with highly efficient MXene and silver-modified polyethyleneimine cryogel composite filters. Advanced Composites and Hybrid Materials (2024).
2. Application of covalent organic frameworks and metal–organic frameworks nanomaterials in organic/inorganic pollutants removal from solutions through sorption-catalysis strategies. Carbon Research (2023).
3. Fabrication of chitosan/magnetite-graphene oxide composites as a novel bioadsorbent for adsorption and detoxification of Cr(VI) from aqueous solution. Scientific Reports (2018).
4. Effective removal of mercury from aqueous streams via electrochemical alloy formation on platinum. Nature Communications (2018).
5. Comparative study between adsorption and membrane technologies for the removal of mercury. Separation and Purification Technology (2021).