Quantitative structure-property relationships in montmorillonite: Decoupling crystalline coherence from cation exchange capacity through advanced SAXS analysis--颗粒学报PARTICUOLOGY

Oueslati, W. (2026). Quantitative structure-property relationships in montmorillonite: Decoupling crystalline coherence from cation exchange capacity through advanced SAXS analysis. Particuology, 110, 75-95. https://doi.org/10.1016/j.partic.2026.01.010

Quantitative structure-property relationships in montmorillonite: Decoupling crystalline coherence from cation exchange capacity through advanced SAXS analysis

Walid Oueslati^*

a LR19ES20: Ressources, Materials and Ecosystem (RME), Faculty of Sciences of Bizerte, University of Carthage, Bizerte, 7021, Tunisia
b Physics Department, Faculty of Sciences of Bizerte, University of Carthage, Bizerte, 7021, Tunisia

10.1016/j.partic.2026.01.010

Volume 110, March 2026, Pages 75-95

Received 12 November 2025, Revised 30 December 2025, Accepted 8 January 2026, Available online 16 January 2026, Version of Record 22 January 2026.

E-mail: walidoueslati@ymail.com; walid.oueslati@fsb.ucar.tn

Highlights

• Advanced SAXS analysis was applied to montmorillonite samples with controlled defect densities.

• Quantitative extraction of structural parameters (domain size, microstrain, Δd₀₀₁, FWHM) enabled defect mapping at the nanoscale.

• Strong linear correlations (R² = 0.69–0.87) were established between SAXS descriptors and cation exchange capacity (CEC).

• Defect-induced structural disorder enhances interlayer accessibility and electrostatic functionality.

• Combined SAXS–CEC framework provides a predictive model linking nanoscale structure to macroscopic reactivity in clays.

Abstract

Montmorillonite's variable cation exchange capacity (CEC) contradicts the assumption that structural order enhances reactivity. While primary CEC originates from isomorphic substitutions, defect-induced structural degradation enhances CEC through dual pathways: direct creation of edge sites (55 % of enhancement) and indirect effects via increased specific surface area (45 %). We employ integrated SAXS techniques—pair distribution function, Warren-Averbach analysis, and Porod scattering—to establish quantitative structure-CEC relationships. Well-ordered samples exhibit coherent domain sizes of 85 Å, microstrain of 1.2 %, and CEC of 76.2 cmol/kg. Severely degraded samples show domain sizes of 28 Å (67 % reduction), microstrain of 4.5 % (3.8-fold increase), and enhanced CEC of 118.9 cmol/kg (56 % increase). PDF analysis reveals that long-range layer correlations decay from 45 to 18 Å (60 % reduction). Warren-Averbach decomposition demonstrates a transition from size-dominated (78 % contribution) to strain-dominated broadening (69 %), with crossover at 40 % CEC enhancement corresponding to domain sizes of ∼40 Å. Porod analysis (calibrated against glassy carbon standard) demonstrates 2.3 × increase in specific surface area (28–68 m²/g) with interface fractal dimensions evolving from 2.1 (smooth) to 2.7 (rough). Path analysis confirms that defect-induced edge sites contribute 70–80 % of the CEC enhancement, with the remainder attributed to enhanced interlayer accessibility via structural disorder. The established correlations (R² > 0.87) between SAXS-derived structural descriptors and CEC enable predictive modeling and rational optimization of montmorillonite processing for targeted applications in environmental remediation, catalysis, and advanced functional materials.

Graphical abstract

Keywords

Montmorillonite; Small-angle X-ray scattering; Crystal defect; Cation exchange capacity; Warren-Averbach analysis; Structure-property relationship

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