Dynamics of different molecules adsorbed in porous media |
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Authors: | S Mitra V S Kamble A K Tripathi N M Gupta R Mukhopadhyay |
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Institution: | (1) Solid State Physics Division, Bhabha Atomic Research Centre, 400 085 Mumbai, India;(2) Applied Chemistry Division, Bhabha Atomic Research Centre, 400 085 Mumbai, India |
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Abstract: | We present in this paper a comparative study on the dynamics of benzene, cyclohexane, and methanol molecules, confined in
the pores of MCM-41 molecular sieve and HZSM-5 zeolite. The quasi-elastic neutron scattering (QENS) measurements revealed
that the physical state of these adsorbed molecules depended not only on the structural characteristics of the host matrix
but also on the chemical properties, such as dipole moment, of the guest molecules. Thus, while no motion was observed in
the time-scale of 10−10−10−12 s in the case of methanol, the larger size benzene and cyclohexane molecules are found to perform six-fold and three-fold
jump rotation, respectively, when adsorbed inside the cages of HZSM-5 at room temperature. At the same time, all the three
molecules are found to undergo a translational motion inside the pores of MCM-41 molecular sieves, the value of diffusion
constant being the lowest in case of methanol because of its higher polarity. Translationl motion of the guest molecules inside
the pores of MCM-41 can be satisfactorily described by Chudley-Eliott fixed jump length diffusion and accordingly the residence
time, jump length and diffusion constant are estimated. |
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Keywords: | Porous materials diffusion neutron scattering |
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