Adsorption Mechanisms for Contaminant Removal in Water Treatment Systems

Adsorption is a widely applied process for removing organic and inorganic contaminants from water. It relies on the accumulation of pollutant molecules at the surface of a solid phase, the adsorbent, through physical and chemical interactions. Adsorbents vary from activated carbons and biochars to zeolites and metal–organic frameworks, each offering distinct surface areas, pore structures and surface chemistries. Key mechanisms include electrostatic attraction, hydrogen bonding, π–π stacking, van der Waals forces and coordination interactions, all of which govern the affinity and capacity for specific contaminants. The design of high-performance adsorbents focuses on maximising accessible surface area, optimising pore size distribution to favour target molecules and introducing functional groups that enhance selectivity. Thermodynamic and kinetic analyses, using models such as the Langmuir and Freundlich isotherms and pseudo-order kinetics, elucidate whether adsorption is monolayer or multilayer and whether it is controlled by chemisorption or physisorption. Recent advances also explore regenerable adsorbent systems, integration with membrane processes and field-deployable column units, underscoring the global significance of adsorption for mitigating emerging pollutants and heavy metals in drinking water and wastewater treatment.

Research from Nature Portfolio

Studies have shown that chemically modified activated carbons can greatly enhance adsorption of ionisable pollutants. For instance, treatment of activated carbon with ferric chloride increased surface oxygen-containing groups and pore volume, resulting in higher adsorption capacities for antibiotic molecules. Adsorption isotherms of such modified carbons often fit both Langmuir and Freundlich models, indicating a combination of monolayer chemisorption and heterogeneous surface interactions. Mechanistic analyses revealed that micropore capture, electrostatic attraction, hydrogen bonding, π–π electron donor–acceptor interactions and coordination bonds collectively contribute to pollutant uptake. Moreover, temperature and pH were found to tune both adsorption capacity and mechanism, favouring adsorption at lower temperatures and neutral pH for many antibiotics, thereby offering guidelines for optimising treatment processes under realistic water chemistry conditions.

Adsorption Mechanisms for Contaminant Removal in Water Treatment Systems publication trend

The graph below shows the total number of articles in adsorption mechanisms for contaminant removal in water treatment systems across all publications each year (not limited to Nature Index journals).

Technical terms

Adsorption isotherm: A mathematical model describing the relationship between pollutant concentration in solution and the amount adsorbed at equilibrium, commonly represented by Langmuir or Freundlich equations.

Pseudo-second-order kinetics: A kinetic model indicating the adsorption rate is proportional to the square of the number of unoccupied sites, often associated with chemisorption.

Metal–organic framework (MOF): A crystalline porous material composed of metal nodes and organic linkers, notable for high surface area and tunable pore chemistry.

Biochar: A carbon-rich adsorbent produced by pyrolysis of biomass, characterised by its porous structure and surface functional groups.

π–π interactions: Attractive forces between aromatic rings of the adsorbent surface and pollutant molecules, enhancing adsorption of aromatic contaminants.

References

1. Advanced adsorbents for ibuprofen removal from aquatic environments: a review. Environmental Chemistry Letters (2023).
2. Mechanistic insights to sorptive removal of four sulfonamide antibiotics from water using magnetite-functionalized biochar. Biochar (2023).
3. Adsorption of pharmaceutical pollutants on ZnCl2-activated biochar from corn cob: Efficiency, selectivity and mechanism. Journal of Bioresources and Bioproducts (2024).
4. Efficient Adsorption of Sulfamethazine onto Modified Activated Carbon: A Plausible Adsorption Mechanism. Scientific Reports (2017).