Dynamics of Confined Reactive Water in Smectite Clay–Zeolite Composites
| Autor: | Michael C. Pitman, Adri C. T. van Duin |
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| Rok vydání: | 2012 |
| Předmět: |
Models
Molecular inorganic chemicals Molecular Conformation Mineralogy Activation energy Neutron scattering Biochemistry Catalysis Diffusion symbols.namesake chemistry.chemical_compound Colloid and Surface Chemistry Magnesium Zeolite Arrhenius equation Models Statistical Chemistry Silicates Temperature Water General Chemistry Hydrogen-Ion Concentration Atmospheric temperature range Silicon Dioxide Silanol Models Chemical Chemical engineering Zeolites symbols Clay Aluminum Silicates Calcium ReaxFF Clay minerals |
| Zdroj: | Journal of the American Chemical Society. 134:3042-3053 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja208894m |
| Popis: | The dynamics of water confined to mesoporous regions in minerals such as swelling clays and zeolites is fundamental to a wide range of resource management issues impacting many processes on a global scale, including radioactive waste containment, desalination, and enhanced oil recovery. Large-scale atomic models of freely diffusing multilayer smectite particles at low hydration confined in a silicalite cage are used to investigate water dynamics in the composite environment with the ReaxFF reactive force field over a temperature range of 300-647 K. The reactive capability of the force field enabled a range of relevant surface chemistry to emerge, including acid/base equilibria in the interlayer calcium hydrates and silanol formation on the edges of the clay and inner surface of the zeolite housing. After annealing, the resulting clay models exhibit both mono- and bilayer hydration structures. Clay surface hydration redistributed markedly and yielded to silicalite water loading. We find that the absolute rates and temperature dependence of water dynamics compare well to neutron scattering data and pulse field gradient measures from relevant samples of Ca-montmorillonite and silicalite, respectively. Within an atomistic, reactive context, our results distinguish water dynamics in the interlayer Ca(OH)(2)·nH(2)O environment from water flowing over the clay surface, and from water diffusing within silicalite. We find that the diffusion of water when complexed to Ca hydrates is considerably slower than freely diffusing water over the clay surface, and the reduced mobility is well described by a difference in the Arrhenius pre-exponential factor rather than a change in activation energy. |
| Databáze: | OpenAIRE |
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