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Register a new userRecent advances in the computational chemistry of soft porous crystals
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Added by
Fran\\c{c}ois-Xavier Coudert
Publication date
2018
fields
Physics
and research's language is
English
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Here we highlight recent progress in the field of computational chemistry of nanoporous materials, focusing on methods and studies that address the extraordinary dynamic nature of these systems: the high flexibility of their frameworks, the large-scale structural changes upon external physical or chemical stimulation, and the presence of defects and disorder. The wide variety of behavior demonstrated in soft porous crystals, including the topical class of metal-organic frameworks, opens new challenges for computational chemistry methods at all scales.
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Pulsed-laser deposition (PLD) is one of the most promising techniques for the formation of complex-oxide heterostructures, superlattices, and well-controlled interfaces. The first part of this paper presents a review of several useful modifications of the process, including methods inspired by combinatorial approaches. We then discuss detailed growth kinetics results, which illustrate that true layer-by-layer (LBL) growth can only be approached, but not fully met, even though many characterization techniques reveal interfaces with unexpected sharpness. Time-resolved surface x-ray diffraction measurements show that crystallization and the majority of interlayer mass transport occur on time scales that are comparable to those of the plume/substrate interaction, providing direct experimental evidence that a growth regime exists in which non-thermal processes dominate PLD. This understanding shows how kinetic growth manipulation can bring PLD closer to ideal LBL than any other growth method available today.
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Using infrared spectroscopy combined with ab initio methods we study reactions of H$_2$O and CO inside the confined spaces of Zn-MOF-74 channels. Our results show that, once the water dissociation reaction H$_2$O$;rightarrow;$OH+H takes place at the metal centers, the addition of 40 Torr of CO at 200 $^{circ}$C starts the production of formic acid via OH+H+CO$;rightarrow;$HCO$_2$H. Our detailed analysis shows that the overall reaction H$_2$O+CO$;rightarrow;$HCO$_2$H takes place in the confinement of MOF-74 without an external catalyst, unlike the same reaction on flat surfaces. This discovery has several important consequences: It opens the door to a new set of catalytic reactions inside the channels of the MOF-74 system, it suggests that a recovery of the MOFs adsorption capacity is possible after it has been exposed to water (which in turn stabilizes its crystal structure), and it produces the important industrial feedstock formic acid.
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