Easy and efficient energy storage is one of the problems treated by numerous researchers today. Hydrophobic nanoporous materials can potentially be used as actuators, but also as molecular springs, dampers, or shock absorbers. [1] In this case, the reversible intrusion of a liquid in nonwetting pores at high pressure, a process subject to hysteresis, is used to store or produce mechanical work. Herein, we show the possibility to store mechanical energy using porous metal-organic framework materials (MOFs) in which their flexibility is used instead of nonwetting properties. Indeed, MOFs have found increasing interest over the past few years in potential applications such as gas separation and storage, [2][3][4] liquidphase separation, [5] or drug delivery.[6]One of the unique properties of some of these materials is their high degree of framework flexibility, which has reached 230 % in the case of the MIL-88 series (MIL stands for Materials from Institut Lavoisier). In most cases, the flexibility of these materials has been induced by adsorption of guest species, [7] which produce various types of flexibility. [8,9] One of the most interesting classes of flexible solids are those of the MIL-53 series. These are metal(III) terephthalates built up from chains of corner sharing metal(III) octahedral (M = Al, Cr, Fe, Ga, In, …) and terephthalate groups that delimit one-dimensional microporous pore system.[2] The Al and Cr forms are found in the large pore (LP) form after thermal removal of the guest species, whereas in the presence of various fluids, a narrow pore (NP) form is observed (MIL-53(Cr) NP; space group C2/c; V % 1020 3 ) before re-expansion to the LP form (MIL-53(Cr) LP; space group Imcm; V % 1490 3 ; see Figure 1). In the case of MIL-53(Al), this reversible flexible character has also been observed as being dependent on the temperature [10] with hysteresis between the cooling and heating processes. The transition from LP to NP occurs on cooling in the 125-150 K range whereas that from NP to LP occurs on heating in the range 325-375 K. The presence of these different crystalline states opens the possibility for phase diagrams to be established.Although previous gas adsorption studies have been carried out under various pressures, [4,5,9] to the best of our knowledge, the response of these materials solely under pressure, without any adsorption effect in pores, has not been reported to date. In the recent study of Moggach et al., ZIF-8 samples were submitted to a high hydrostatic pressure that provokes crystal phase transitions, but with the presence of liquid inside pores.[11] Logically, one would expect that a transition from the LP to the NP phase would occur provided a high enough pressure is applied to the MOF phase in question. One reason for this behavior is that the MIL-53 phases are usually synthesized in the form of micrometersized particles and it is not easy to impose a mechanical stress around the particle in a controlled manner. However, the use of mercury porosimetry permits an isostatic press...

This paper demonstrates that nanospace engineering of KOH activated carbon is possible by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. High specific surface areas, porosities, sub-nanometer (<1 nm) and supra-nanometer (1-5 nm) pore volumes are quantitatively controlled by a combination of KOH concentration and activation temperature. The process typically leads to a bimodal pore size distribution, with a large, approximately constant number of sub-nanometer pores and a variable number of supra-nanometer pores. We show how to control the number of supra-nanometer pores in a manner not achieved previously by chemical activation. The chemical mechanism underlying this control is studied by following the evolution of elemental composition, specific surface area, porosity, and pore size distribution during KOH activation and preceding H(3)PO(4) activation. The oxygen, nitrogen, and hydrogen contents decrease during successive activation steps, creating a nanoporous carbon network with a porosity and surface area controllable for various applications, including gas storage. The formation of tunable sub-nanometer and supra-nanometer pores is validated by sub-critical nitrogen adsorption. Surface functional groups of KOH activated carbon are studied by microscopic infrared spectroscopy.

A simple laboratory-scale protocol that enables the evaluation of the effect of adsorbed water on CO uptake is proposed. 45 metal-organic frameworks (MOFs) were compared against reference zeolites and active carbons. It is possible to classify materials with different trends in CO uptake with varying amounts of pre-adsorbed water, including cases in which an increase in CO uptake is observed for samples with a given amount of pre-adsorbed water. Comparing loss in CO uptake between "wet" and "dry" samples with the Henry constant calculated from the water adsorption isotherm results in a semi-logarithmic trend for the majority of samples allowing predictions to be made. Outliers from this trend may be of particular interest and an explanation for the behaviour for each of the outliers is proposed. This thus leads to propositions for designing or choosing MOFs for CO capture in applications where humidity is present.