Structural and Dynamical Properties of Guest in Nanoporous Material and of Ionic Liquids

Sharma, Anirban (2017) Structural and Dynamical Properties of Guest in Nanoporous Material and of Ionic Liquids. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Diffusion process is an important phenomenon in different processes like molecular sieving, preferential adsorption, ion exchange, shape-selective catalysis, etc. These processes are generally takes place within microporous solids such as aluminosilicates (zeolites), aluminophosphates or metal organic frameworks. Diffusion process plays an important role also in ionic mobility, solvation, etc which are commonly found in solution. Though are many factors which control diffusivity, size of the diffusing particle has attracted considerable interest in the past. It is reported that self-diffusivity in microporous solids does not vary monotonically on the size of the diffusing particle.One of the central assumption is the force cancellation at the window of microporous materials to explain the existence of anomalous diffusion regime. We examine this issue of force cancellation for a particle moving inside a microporous material exploring the diffusion path and cross-checking the bottleneck associated with diffusion. Conventional wisdom is that the window of a microporous material is the bottleneck for diffusion. Our study reveals that bottleneck for diffusion is always 2.6 to 3.0 Å away from the window plane and depending on the guest size, it lies in different part of the inner surface of α- cage. Window has significant effect in diffusion process only when diffusing particle size is comparable or larger than the window diameter. We show that in the anomalous diffusion regime there is no signature of force cancellation at the window. Window does not play any significant role for the existence of anomalous diffusion regime in microporous materials.

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