Positioning MOFs methods

Frank et al. [168] reported the formation of / -quinone + hydrogen atom via a transition state with a barrier that was estimated at 90 kcal mof and in which the O—O bridge is in para-position (Figure 6.6). Hadad et al. [32] reported a higher barrier of 127 kcal mof for this para-position transition state adduct. From G2M calculations, Tokmakov et al. [180] report a high barrier for this pathway as well (123 kcal mol ). Hadad et al. evaluated the transition state structure and determined the barrier to be around 138 kcal mof. The O—O bridge was found in the meta-position to form Y(C50 ) + CO. The third isomer is the ortho-position transition state structure. This structure was calculated in this work by different computational methods and by Hadad et al. It was found to be at the lowest energy (around 81 kcal mol ). 

Fig. 18 Left. Powder X-ray diffraction patterns of MOF-5 (a), ZnEtJ MOF-5 (b), as ZnO MOF-5 (as synthesized by the wet method) (c), ZnO MOF-5 (after annealing and derived by the wet method) (d), as ZnO MOF-5 (as synthesized by the dry method) (e), ZnO MOF-5 (after annealing and derived by the dry method) (i and ZnO-reference sample obtained from controlled hydrolysis of ZnEt and annealing in air (g). The positions of the characteristic reflections of hexagonal ZnO are marked. Right TEM images of unloaded MOF-5 (a) and ZnO MOF-5 (f, after annealing and derived by the dry method). Reproduced with permission [80]. Copyright 2008 American Chemical Society...

The apparent volume data show that is indeed possible to estimate the position of the CMC based solely on volumetric data. Moreover, compared to other methods (ST, FL, NMR) that are frequently used to estimate CMCs,such analysis also provides some insights concerning the behavior of the solute in the midst of the water molecules. As was mentioned before, the increase in the solutions density is caused by the partial breakup of the hydrogen-bonded network of water molecules due to the intrusion of the solute ions, specially the aliphatic moieties that cause the existence of hydrophobic effects. The small apparent molar volumes of the solutes at the most diluted solutions (around 226cm. mok for [CgCpmJCl solutions below CMC at 298 K (ct Fig. 5.7), as compared to 229cm. moF for pure [CgC imJCl at the same temperature)... 

Falcaro et al. reported how functional ceramic particles can be used as a heterogeneous seed for the nucleation of MOFs [25]. The authors developed a seeding method using a number of different ceramic materials as heterogeneous seeds to spatially control the position as well as the growth rate of MOFs [25,81,82]. 

There are a number of advantages to the seeding methods described here. These typically include low moisture sensitivity, low substrate sensitivity, availability of lithographic methods for positioning nano- and micro-particles, relatively short MOF growth times, and the potential to incorporate functionality within the seeds themselves. 

Fabrication Methods that Require External Control to Position Preformed MOFs... 

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