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Zeolites are crystalline aluminosilicates with high porosity and tunable surface properties, widely used as catalysts, adsorbents, and ion exchangers. Their conventional hydrothermal synthesis, however, is energy-intensive and poorly suited for real-time monitoring of the gel-to-crystal transition [1]. In this work, we introduce an alternative, low-energy approach for zeolite synthesis based on osmotic compression of aluminosilicate gels.
By applying a controlled osmotic pressure gradient using polyethylene glycol (PEG) solution across a semi-permeable membrane, water is extracted from the gel, inducing gel shrinkage and subsequent crystallization at room temperature [2]. To probe the kinetics of water transport and gel-to-crystal transformation, we developed a non-invasive time resolved in situ monitoring strategy using ¹H NMR relaxometry.
A custom-designed, 3D-printed miniaturized osmotic cell compatible with NMR measurements enables the real-time acquisition of the transversal relaxation time T₂ relaxation distributions [3]. These distributions provide quantitative information on water populations (free vs. bound) and their evolution during osmotic stress. Our results reveal a clear correlation between gel shrinkage, T₂ decay, and zeolite formation, confirming that proton NMR relaxation is a sensitive probe of structural evolution during osmotic compression.
This methodology establishes a novel, energy-efficient, and physically insightful route for zeolite synthesis and opens prospects for monitoring and controlling phase transitions in colloidal or gel-based materials under osmotic confinement.
Keywords: Low-field NMR, NMR relaxometry, variable-field relaxometry, water dynamics, silicate solutions, colloidal gels, drying, porous media, non-equilibrium processes.
| References | [1] Rodrigues, D.; Keshavarz, B.; Courtois, N.; Ilavskid J.; Mckinley, G.; Poulesquen, A.; Aluminosilicate colloidal gels: from the early age to the crystallization of zeolite. Soft Matter, 2024, 20, pp.5538. https://doi.org/10.1039/d4sm00181h. [2] Keita, C.; Yannick, H.; Salmon, J.B.; Microfluidic osmotic compression of a charge-stabilized colloidal dispersion: Equation of state and collective diffusion coefficient. Physical Review E, 2021, 104 (6), https://doi.org/10.1103/PhysRevE.104.L062601. 3] Maillet, B.; Sidi-Boulenouar, R.; Coussot, P. Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media. Langmuir 2022, 38 (49), 15009–15025. https://doi.org/10.1021/acs.langmuir.2c01918. |
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| Country | France |
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