Guest molecules transport

Materials with uniform pore structures offer a wide range of applications, including catalysis, adsorption, and separation. These materials have the benefit ofboth specific pore systems and intrinsic chemical properties [1-3]. The pores in the materials are able to host guest species and provide a pathway for molecule transportation. The skeletal pore walls provide an active and/or affinity surface to associate with guest molecules. According to the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be classified into three main categories based on the diameters of their pores, that is, microporous, mesoporous, and macroporous... 

Rasa M, Meier MAR, Schubert US (2007) Transport of guest molecules by unimolecular micelles evidenced in analytical ultracentrifugation experiments. Macromol Rapid Commun... 

The incorporation of guest molecules can be achieved during their growth or is executed at defect sites and holes via wet chemistry, by surface diffusion and gas-phase transport. Encapsulated fullerenes tend to form chains that are coupled by van der Waals forces. Upon annealing, the encapsulated fullerenes coalesce in the interior of the SWCNTs, resulting in pill-shaped, concentric, endohedral capsules a few nanometers in length [265], The progress of such reactions inside the tubes could be monitored in real time by use of HR-TEM [266],... 

Conversely, a periodic array of anti-dots could modify the electronic properties of a semiconductor. In addition, periodic cavities could be used to selectively adsorb or transport molecules or to perform chemical modification of guest molecules by utilizing electronic or photonic properties of semiconductors. Several studies showed that it was possible irreversibly to bind templating molecules within the semiconductor lattice and through inorganic-organic interactions to modify electronic and photonic properties [59a, b]. 

Analyzing the self-diffusion behavior of guest molecules in a microporous catalyst by the combined application of pulsed-field gradient NMR selfdiffusion techniques reveals the spatial distribution of transport resistances over the catalyst particles. In the case of coke deposits on ZSM-5, the distribution of carbonaceous residues over the crystal was found to be a function of the crystal morphology, the time onstream, and the chemical nature of the coke-producing reactant. In the case of ZSM-5 modified by H3PO4, the spatial distribution of the P compounds over the ZSM-5 crystals can be determined by self-diffusion measurements. Location of transport hindrances in a zeolite framework is based on self-diffusion measurements, in... 

As previously noted (see Section 2.5), the depth reached in a given experiment can, in principle, be approached by the advance of the diffusion layer if the diffusion coefficient for the rate-determining charge transport is known. Then, at short times, only the electrochemical response of the guest molecules externally adsorbed or located in the more external layers of the crystals will be electroactive. At longer times, the observed response will reflect the contribution of molecules located deeper in the host crystals. 

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