Single Crystals Heterogeneity Impacts the Intrinsic and Extrinsic Properties of Metal–Organic Frameworks

Abstract

over, they are often invasive, [2] require high vacuum, [3] or preclude real-space information, [4] thus preventing in situ studies of materials. These two characterization levels are also reflected in current research efforts, for instance, on metalorganic frameworks (MOFs) that mainly focus on two distinct aspects: molecular structures being tuned and bulk properties being measured. [5] MOF chemists often vary the molecular building units (e.g., installation of a functional group) and examine the corresponding change in the performance of a bulk sample (e.g., gas adsorption isotherm). Alteration of MOF particle properties can be caused twofold: (1) by differences in "extrinsic properties", that is, physical parameters like their particle size, shape, and surface structure, or (2) by variations in "intrinsic properties" ruled by chemical attributes of the framework. These include casual differences in the composition of building blocks, [6] crystallinity, [7] functionalization, [8] and defects, [2] but also designed variations as in multivariate MOFs. The interplay of both kinds of properties determines the overall performance for any application; the mutual impact of intrinsic and extrinsic variations correlated to any change in individual particle properties in situ is challenging to explore in a correlative manner.At present, an enormous characterization gap exists between the study of the crystal structure of a material and its bulk properties. Individual particles falling within this gap cannot be fully characterized in a correlative manner by current methods. The authors address this problem by exploiting the noninvasive nature of optical microscopy and spectroscopy for the correlative analysis of metal-organic framework particles in situ. They probe the intrinsic as well as extrinsic properties in a correlated manner. The authors show that the crystal shape of MIL-88A strongly impacts its optical absorption. Furthermore, the question of how homogeneously water is distributed and adsorbed within one of the most promising materials for harvesting water from humid air, MOF-801, is addressed. The results demonstrate the considerable importance of the particle level and how it can affect the property of the material.

Chemical Synthesis of the Fluorescent, Cyclic Dinucleotides cthGAMP

“…The emission spectrum has a width of more than 200 nm, starting around 380 nm upwards with an emission maximum around 470 nm (Figure 3a). Since excitation sources in the UV and blue spectral range cause high background when being used for imaging cells due to scattering and autofluorescence, we employed two‐photon imaging [19] using a pulsed laser excitation at 774 nm (Supporting Information Figure S5.3a–b). The fluorescence emission of 2’3’‐c th GAMP ( 2 ) in water between 400–650 nm clearly showed a quadratic dependence on the exciting laser power (Supporting Information Figure S5.3c) confirming the nonlinear nature of the two‐photon excitation.…”

Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in MOF-74 Thin Films

“…While traditional techniques like gas sorption and X-ray diffraction are adequate to assess bulk materials, MOF thin films present challenges to assess pore size, pore volume, and specific surface area. , Crystallinity is an important factor in the evaluation of MOF thin film quality. This is because the MOF crystallinity is a crucial parameter in assessing long-range ordering and porosity, and offers insights into structure–property relationships .…”

“…Recently, it has become increasingly evident that the macroscopic structure of MOFs (crystal size, morphology, and shape of crystal aggregates) can play a critical role in defining the overall properties. − In the context of MOF thin films, one of the primary challenges is to achieve properties comparable to, or even better than, those exhibited by the corresponding bulk powders. In other words, MOF thin films should be designed in a manner that their overall performance largely reflects the intrinsic properties of MOFs as dictated by chemical attributes of the framework, namely, constituent building blocks, crystallinity, and functionalization . To this end, a series of Co-MOF-74 and Ni-MOF-74 thin films with good adhesion to the substrate were synthesized by varying the droplet volume of the precursor solution, Table .…”

“…Despite the plethora of fundamental studies, the practical application of MOFs is limited as they are typically obtained as polycrystalline micropowders with very low processability . MOF thin films have the potential to significantly advance energy, catalysis, separations, and chemical/biological sensing applications as they offer possibilities otherwise not feasible with traditional bulk powders. − Therefore, the need for innovative methods to afford MOF thin films that improve the scalability, quality, and generality is necessary. − Indeed, several synthetic techniques have been developed to afford MOF thin films; however, there remain scientific challenges. − As in the case of zeolites, the extrinsic properties such as crystal orientation and microstructure (i.e., film thickness, roughness, particle distribution) may ultimately play a decisive role in the overall performance. − The scientific literature on the study of MOFs as bulk powders is insightful in identifying MOF candidates with significant promise for targeted applications, including kinetic separations . To evaluate the functionality of a thin film, an optical, electrical, or physical signal transduction mechanism is required. − Integration of MOF thin films on a solid surface offers a physical interface for such signal transduction .…”

Single‐Crystal Capacitive Sensors with Micropatterned Electrodes via Space‐Confined Growth of the Metal–Organic Framework HKUST‐1

“…[ 9,10 ] To investigate the intrinsic properties of MOFs, single crystals are ideal platforms that mitigate the impact of defects, impurities, and grain boundaries that exist in polycrystalline films. [ 11,12 ] However, integrating MOF single crystals into devices and interrogating them electrically, either for material characterization or for practical application, is challenging because of the following reasons. First, most MOF single crystals exhibit a polyhedral morphology, which is incompatible with the typically planar architecture of optical and electronic devices.…”