Adsorption Mechanisms in Layered Double Hydroxide Composites

Layered double hydroxide (LDH) composites combine the positively charged brucite-like layers of mixed metal hydroxides with interlayer anions and often with supporting matrices such as biochar, carbonaceous materials or mineral clays. Their adjustable composition and interlayer spacing enable a variety of adsorption pathways, notably anion exchange, surface complexation, electrostatic attraction and intercalation of target species. In composite form, LDHs benefit from synergistic interactions—π–π stacking, hydrogen bonding and surface precipitation—that enhance affinity for pollutants ranging from heavy-metal ions and oxyanions to organic contaminants. Pore architecture and surface functionalisation govern mass transport and specificity. The result is a versatile platform for water purification, soil remediation and pollution control, where adsorption capacities can reach hundreds to over a thousand milligrams per gram under optimised conditions.

Research from Nature Portfolio

In a recent study, a mesoporous nitrogen-doped composite was synthesised by combining iron-containing Fenton sludge and fly ash via a carbon-thermal route. The resulting material exhibited a high specific surface area and abundant oxygen-containing functional groups, achieving over 80 % removal of hexavalent chromium under alkaline conditions and a maximum adsorption capacity of nearly 394 mg g⁻¹. Adsorption followed a pseudo-second-order kinetic model and was dominated by chemisorption mechanisms involving electron sharing or exchange between Cr(VI) and active sites.

A foundational work demonstrated a one-pot slow pyrolysis approach to coat biochar with calcined Mg-Al LDH. This composite achieved a tetracycline uptake exceeding 1 100 mg g⁻¹ at elevated temperature. The exceptional capacity arose from a combination of interlayer interaction with LDH, π–π stacking between aromatic tetracycline moieties and aromatic biochar domains, and hydrogen bonding to hydroxyl groups on the LDH layers, illustrating the power of host–guest chemistry in LDH-based adsorbents.

Adsorption Mechanisms in Layered Double Hydroxide Composites publication trend

The graph below shows the total number of articles in adsorption mechanisms in layered double hydroxide composites across all publications each year (not limited to Nature Index journals).

Technical terms

Layered double hydroxide (LDH): A class of materials with positively charged mixed-metal hydroxide layers and exchangeable interlayer anions, used as versatile adsorbents.

Anion exchange: A mechanism whereby target anions in solution replace interlayer anions within an LDH structure, facilitating uptake of contaminants.

Surface complexation: Formation of coordination bonds between adsorbate species and surface metal-hydroxide sites on the LDH layers.

Intercalation: Insertion of guest molecules or ions into the interlayer galleries of an LDH, often leading to expanded spacing and enhanced retention.

Electrostatic attraction: Coulombic interaction between charged adsorbent surfaces (or functional groups) and oppositely charged contaminants in solution.

References

1. Ball milled Mg/Al hydroxides modified nitrogen-rich biochar for arsenic removal: performance and governing mechanism. Carbon Research (2023).
2. One-pot synthesis of carbon supported calcined-Mg/Al layered double hydroxides for antibiotic removal by slow pyrolysis of biomass waste. Scientific Reports (2016).
3. Layered Double Hydroxides as Rising-Star Adsorbents for Water Purification: A Brief Discussion. Molecules (2022).
4. Study on adsorption of hexavalent chromium by composite material prepared from iron-based solid wastes. Scientific Reports (2023).
5. MgAl-NO3 LDH: Adsorption Isotherms and Multivariate Optimization for Cr(VI) Removal. Chemistry (2023).
6. Adsorption of Chromate Ions by Layered Double Hydroxide–Bentonite Nanocomposite for Groundwater Remediation. Nanomaterials (2022).