RESUMO
Metal-organic frameworks are promising candidates for selective separation processes such as CO2 removal from methane (natural gas sweetening). Framework flexibility, that is, the ability of a MOF lattice to change its structure as a function of parameters like pressure, temperature, and type of adsorbed molecules, is only observed for some special compounds. The main question of our present work is: does framework flexibility influence the adsorption selectivity? As a direct quantitative method to monitor the adsorption of both, carbon dioxide and methane, we make use of high-pressure in situ 13C NMR spectroscopy of 13CO2/13CH4 gas mixtures. This method allows to distinguish between the two gases as well as between adsorbed molecules and the interparticle gas phase. Gas mixture adsorption is studied under isothermal conditions. The selectivity factor for CO2 adsorption from CO2/CH4 mixtures is measured as a function of total gas pressure. The flexible material SNU-9 as well as the flexible and the nonflexible variant of DUT-8(Ni) are compared. Maximum selectivity factors for CO2 are observed for the flexible variant of DUT-8(Ni) in its open, large-pore state. In contrast, the rigid variant of DUT-8(Ni) and SNU-9 especially in its intermediate state exhibits lower adsorption selectivity factors. This observation indicates significant influence of the framework elasticity on the adsorption selectivity.
RESUMO
We report on a simple and effective technique of tuning the colloidal solubility of inorganic-capped CdSe and CdSe/CdS core/shell nanocrystals (NCs) from highly polar to nonpolar media using n-butylamine molecules. The introduction of the short and volatile organic amine mainly results in a modification of the labile diffusion region of the inorganic-capped NCs, enabling a significant extension of their dispersibility and improving the ability to form long-range assemblies. Moreover, the hybrid n-butylamine/inorganic capping can be thermally decomposed under mild heat treatment, making this approach of surface functionalization well-compatible with a low-temperature, solution-processed device fabrication. Particularly, a field-effect transistor-based on n-butylamine/Ga-I-complex-capped 4.5 nm CdSe NC solids shows excellent transport characteristics with electron mobilities up to 2 cm2/(V·s) and a high current modulation value (>104) at a low operation voltage (<2 V).