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Photochemical CO2 reduction using ubiquitous sunlight akin to natural photosynthesis is an effective approach for conversion of renewable energy into useful chemical feedstock. Driven by the need for earth‐abundant, inexpensive, and sustainable photocatalysts with practical applicability, covalent organic frameworks (COFs) have emerged as a new generation of molecularly defined semiconductors with tunable optoelectronic properties. These reticular frameworks with highly ordered, porous and crystalline structures can be tailor‐made by covalently combining organic building blocks to target specific functions. To date, numerous COFs have been reported, which show promising activity for photocatalytic CO2 reduction allowing to derive structure–property–function relationships. In this review, the different reported strategies are comprehensively analyzed and categorized for active site engineering in COF photocatalysts and the synthetic rationale and resulting catalytic activity for each approach are discussed. The recent advancements in terms of tailored photocatalyst design are then critically assessed, aspects of advanced materials characterization are analyzed, and future perspectives and challenges for the field are highlighted. [ABSTRACT FROM AUTHOR]

Local administrations and companies rely on committed and self-reliant employees to achieve their goals. However, there is limited research on how influencing factors such as trust, understanding, and power affect self-managed teams. This study investigates the modes of interaction of these factors on the team structure within self-managed teams in IT departments and service providers of different German public administrations. The research methodology was a quantitative online survey comprising validated items from standardised test procedures to measure the influence factors. A total of 246 data sets were analysed by regression and mediator analysis. The study found significant positive effects of trust and power on understanding and a mediator effect of power on the relationship between trust and understanding. In conclusion, investments in team member empowerment in low-trust environments can be recommended to improve understanding more significantly than in high-trust situations. [ABSTRACT FROM AUTHOR]

A unique feature of metal-organic frameworks (MOFs) in contrast to rigid nanoporous materials is their structural switchabilty offering a wide range of functionality for sustainable energy storage, separation and sensing applications. This has initiated a series of experimental and theoretical studies predominantly aiming at understanding the thermodynamic conditions to transform and release gas, but the nature of sorption-induced switching transitions remains poorly understood. Here we report experimental evidence for fluid metastability and history-dependent states during sorption triggering the structural change of the framework and leading to the counterintuitive phenomenon of negative gas adsorption (NGA) in flexible MOFs. Preparation of two isoreticular MOFs differing by structural flexibility and performing direct in situ diffusion studies aided by in situ X-ray diffraction, scanning electron microscopy and computational modelling, allowed assessment of n-butane molecular dynamics, phase state, and the framework response to obtain a microscopic picture for each step of the sorption process. Switchable porous materials offer adaptive voids mutating in size and shape in response to molecular stimuli. Here authors use PFG NMR to reveal the decisive role of metastable states leading to counterintuitive negative gas adsorption transitions in responsive MOFs. [ABSTRACT FROM AUTHOR]

Adsorption-based phenomena are important in gas separations (1,2), such as the treatment of greenhouse-gas (3) and toxic-gas (4) pollutants, and in water-adsorption-based heat pumps (5) for solar cooling systems. The [...]

Background: The number of publications in supply chain management (SCM) and artificial intelligence (AI) has risen significantly in the last two decades, and their quality and outcomes vary widely. This study attempts to synthesise the existing literature in this research area and summarise the findings regarding barriers, drivers, and social implications of using AI in SCM. Methods: The methodology used for this meta-study is based on Kitchenham and Charters guidelines, resulting in a selection of 44 literature reviews published between 2000 and 2021. Results: As a summary of the results, the main areas of AI in SCM were algorithms, followed by the Internet of Things (IoT). The main barriers to AI adoption in SCM are change management, existing technical limitations, and the acceptance of humans for these techniques. The main drivers of AI in SCM are saving costs and increasing efficiency in combination with reducing time and resources. The main social factor is human–robot collaboration. As a result, there will be a decreased amount of labour needed in the future, impacting many existing jobs, especially in low-income areas. Conclusions: Therefore, it is essential for organisations that implement new technology to start as early as possible to inform the organisation about the changes and help them successfully implement them. It is also important to mention that constant learning and improvement of the employees are critical for adopting and successfully using new AI tools. Before investing in new technology, a solid Return on Investment calculation (ROI) and monitoring costs and value are critical to transforming the business successfully. [ABSTRACT FROM AUTHOR]

Around 10–15 % of the world's energy consumption is accounted for by the separation and purification of chemicals. Among them is the enrichment and separation of isotopologues which are an essential aspect of modern chemistry. In their recent work, Su et al. demonstrate the separation of water isotopologues by responsive dynamic pore windows in a microporous coordination polymer with unprecedented selectivity based on an elegant mechanism. [ABSTRACT FROM AUTHOR]

Herein we demonstrate mesoporous frameworks interacting with carbon dioxide leading to stimulated structural contractions and massive out‐of‐equilibrium pressure amplification well beyond ambient pressure. Carbon dioxide, a non‐toxic and non‐flammable working medium, is promising for the development of pressure‐amplifying frameworks for pneumatic technologies and safety systems. The strong interaction of the fluid with the framework even contracts DUT‐46, a framework hitherto considered as non‐flexible. Synchrotron‐based in situ PXRD/adsorption experiments reveal the characteristic contraction pressure for DUT‐49 pressure amplification in the range of 350–680 kPa. The stimulated framework contraction expels 1.1 to 2.4 mmol g−1 CO2 leading to autonomous pressure amplification in a pneumatic demonstrator system up to 428 kPa. According to system level estimations even higher theoretical pressure amplification may be achieved between 535 and 1011 kPa. [ABSTRACT FROM AUTHOR]

Molecules in gas and liquid states, as well as in solution, exhibit significant and random Brownian motion. Molecules in the solid-state, although strongly immobilized, can still exhibit significant intramolecular dynamics. However, in most framework materials, these intramolecular dynamics are driven by temperature, and therefore are neither controlled nor spatially or temporarily aligned. In recent years, several examples of molecular machines that allow for a stimuli-responsive control of dynamical motion, such as rotation, have been reported. In this contribution, we investigate the local and global properties of a Lennard-Jones (LJ) fluid surrounding a molecular motor and consider the influence of cooperative and non-directional rotation for a molecular motor-containing pore system. This study uses classical molecular dynamics simulations to describe a minimal model, which was developed to resemble known molecular motors. The properties of an LJ liquid surrounding an isolated molecular motor remain mostly unaffected by the introduced rotation. We then considered an arrangement of motors within a one-dimensional pore. Changes in diffusivity for pore sizes approaching the length of the rotor were observed, resulting from rotation of the motors. We also considered the influence of cooperative motor directionality on the directional transport properties of this confined fluid. Importantly, we discovered that specific unidirectional rotation of altitudinal motors can produce directed diffusion. This study provides an essential insight into molecular machine-containing frameworks, highlighting the specific structural arrangements that can produce directional mass transport. [ABSTRACT FROM AUTHOR]

Unusual adsorption phenomena, such as breathing and negative gas adsorption (NGA), are rare and challenge our thermodynamic understanding of adsorption in deformable porous solids. In particular, NGA appears to break the rules of thermodynamics in these materials by exhibiting a spontaneous release of gas accompanying an increase in pressure. This anomaly relies on long-lived metastable states. A fundamental understanding of this process is desperately required for the discovery of new materials with this exotic property. Interestingly, NGA was initially observed upon adsorption of methane at relatively low temperature, close to the respective standard boiling point of the adsorptive, and no NGA was observed at elevated temperatures. In this contribution, we present an extensive investigation of adsorption of an array of gases at various temperatures on DUT-49, a material which features an NGA transition. Experiments, featuring a wide range of gases and vapors at temperatures ranging from 21–308 K, were used to identify for each guest a critical temperature range in which NGA can be detected. The experimental results were complemented by molecular simulations that help to rationalize the absence of NGA at elevated temperatures, and the non-monotonic behavior present upon temperature decrease. Furthermore, this in-depth analysis highlights the crucial thermodynamic and kinetic conditions for NGA, which are unique to each guest and potentially other solids with similar effects. We expect this exploration to provide detailed guidelines for experimentally discovering NGA and related "rule breaking" phenomena in novel and already known materials, and provide the conditions required for the application of this effect, for example as pressure amplifying materials. [ABSTRACT FROM AUTHOR]

In this Minireview, we discuss the fundamental chemistry of soft porous crystals (SPCs) by characterizing their common structural features and the resulting structural softness and transitions. In particular, we focus on the recently emerging properties based on metastable transitions and those arising from local dynamics. By comparing the resulting adsorption properties to those of commonly applied rigid adsorbents, we highlight the potential of SPCs to revolutionize adsorption‐based technologies, considering our current understanding of the thermodynamic and kinetic aspects. We provide brief outlines for the experimental and computational characterization of such phenomena and offer an outlook toward next‐generation SPCs likely to be discovered in the next decade. [ABSTRACT FROM AUTHOR]

In diesem Kurzaufsatz wird die Chemie von verformbaren porösen Kristallen (SPCs) anhand von Struktureigenschaften und deren Auswirkungen auf die Verformbarkeit und den daraus resultierenden Strukturübergang diskutiert. Besonders Eigenschaften, die auf metastabilen Übergangszuständen basieren oder durch lokale dynamische Funktionalität hervorgerufen werden, sind hierbei von Interesse. Unterschiede in den Adsorptionseigenschaften rigider poröser Materialien und denen von SPCs auf Grundlage etablierter thermodynamischer und kinetischer Aspekte zeigen das Anwendungspotenzial dieser Materialien für Adsorptionstechniken auf. Die Charakterisierung dieser Eigenschaften und die daraus resultierenden Phänomene werden dabei in den Mittelpunkt gerückt, und abschließend wird ein Ausblick auf die nächste Generation verformbarer poröser Kristalle gegeben. [ABSTRACT FROM AUTHOR]

Selective 13C-labelling of carboxylate carbons in the linker molecules of flexible metal–organic frameworks (MOFs) makes solid-state NMR spectroscopy very powerful to investigate solvent-induced local structural changes as demonstrated by 13C and 1H NMR spectroscopy on the pillared layer MOF DUT-8(Ni). Selective identification of polar solvent–node interactions becomes feasible. [ABSTRACT FROM AUTHOR]

The pressure dependence of the 129Xe chemical shift in the metal–organic frameworks (MOFs) UiO-66 and UiO-67 (UiO – University of Oslo) has been investigated using both theory and experiment. The resulting chemical shift isotherms were analyzed with a theoretical approach based on model systems (as proposed by K. Trepte, J. Schaber, S. Schwalbe, F. Drache, I. Senkovska, S. Kaskel, J. Kortus, E. Brunner and G. Seifert, Phys. Chem. Chem. Phys., 2017, 19, 10020–10027) and experimental 129Xe NMR measurements at different pressures. All investigations were carried out at T = 237 K while the pressure range was chosen according to the maximum pressure at which Xe liquifies (p0 = 1.73 MPa or 17.3 bar), thus 0 ＜ p≤p0. The theoretically predicted chemical shift isotherms agree well with the experimental ones. Additionally, a comparison of the chemical shift isotherms with volumetric adsorption isotherms was carried out to determine the similarities and differences of both isotherms. [ABSTRACT FROM AUTHOR]

A flexible, yet very stable metal-organic framework (DUT-98, Zr6O4(OH)4(CPCDC)4(H2O)4, CPCDC=9-(4-carboxyphenyl)-9 H-carbazole-3,6-dicarboxylate) was synthesized using a rational supermolecular building block approach based on molecular modelling of metal-organic chains and subsequent virtual interlinking into a 3D MOF. Structural characterization via synchrotron single-crystal X-ray diffraction (SCXRD) revealed the one-dimensional pore architecture of DUT-98, envisioned in silico. After supercritical solvent extraction, distinctive responses towards various gases stimulated reversible structural transformations, as detected using coupled synchrotron diffraction and physisorption techniques. DUT-98 shows a surprisingly low water uptake but a high selectivity for pore opening towards specific gases and vapors (N2, CO2, n-butane, alcohols) at characteristic pressure resulting in multiple steps in the adsorption isotherm and hysteretic behavior upon desorption. [ABSTRACT FROM AUTHOR]

Tailoring the characteristics of gating transitions in the porous network, Ni2(ndc)2dabco (ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane), also termed DUT-8(Ni) (DUT = Dresden University of Technology), was achieved by systematically adjusting the critical synthesis parameters. The impact of the starting composition and solvent mixtures in the synthesis was found to critically affect the guest-response properties of the obtained materials. A comprehensive set of physical characterization methods, namely thermal analysis, 1H NMR of digested crystals, solid state 13C NMR, PXRD, SEM, IR and Raman spectroscopy shows that the crystallite size is a crucial factor, determining the differing characteristics such as “gate pressure” and adsorption capacity in the guest-responsive switching behaviour of DUT-8. Crystallites smaller than 500 nm in size retain the open form after removal of the guest molecules resulting in typical “Type Ia” isotherm, whereas crystallites larger than 1 μm transform into the “closed pore” form and therefore can show a characteristic “gate opening” behaviour during gas adsorption. The particle size distribution of DUT-8(Ni) can be tailored by changing the synthesis conditions and consequently the slope of the isotherm at the “gating step” is affected. The in depth analysis of synthesis conditions and switching behaviour is an important step towards a better understanding of the fundamental principles responsible for guest responsive porosity switching in the solid state. [ABSTRACT FROM AUTHOR]

Methane hydrate nucleation and growth in porous model carbon materials illuminates the way towards the design of an optimized solid-based methane storage technology. High-pressure methane adsorption studies on pre-humidified carbons with well-defined and uniform porosity show that methane hydrate formation in confined nanospace can take place at relatively low pressures, even below 3 MPa CH4, depending on the pore size and the adsorption temperature. The methane hydrate nucleation and growth is highly promoted at temperatures below the water freezing point, due to the lower activation energy in ice vs. liquid water. The methane storage capacity via hydrate formation increases with an increase in the pore size up to an optimum value for the 25 nm pore size model-carbon, with a 173% improvement in the adsorption capacity as compared to the dry sample. Synchrotron X-ray powder diffraction measurements (SXRPD) confirm the formation of methane hydrates with a sI structure, in close agreement with natural hydrates. Furthermore, SXRPD data anticipate a certain contraction of the unit cell parameter for methane hydrates grown in small pores. [ABSTRACT FROM AUTHOR]

Exploring the role of surface hydrophilicity of non-precious metal N-doped carbon electrocatalysts in electrocatalysis is challenging. Herein we discover an ultra-hydrophilic non-precious carbon electrocatalyst, showing enhanced catalysis efficiency on both gravimetric and areal basis for oxygen reduction reaction due to a high dispersion of active centres. [ABSTRACT FROM AUTHOR]

Two new mesoporous metal-organic frameworks (DUT-75 and DUT-76) with exceptional ethene uptake were obtained using carbazole dicarboxylate based metal-organic polyhedra as super- molecular building blocks. The compounds have a total pore volume of 1.84 and 3.25 cm³ g-1 and a specific BET surface area of 4081 and 6344 m² g-1, respectively, and high gas uptake at room temperature and high pressure. [ABSTRACT FROM AUTHOR]

Nematic networks with three different concentrations of polar and nonpolar mesogens and the same concentration of a novel cross-linking agent give rise to unusual liquid single crystal elastomers (LSCEs) that are transparent monodomain nematic networks with smectic clusters. The largest spontaneous length change is observed in the sample with 70 mol% of the polar mesogen which also has the highest glass transition temperature and smectic clusters with a slowly increasing but nearly constant layer spacing on cooling from 90° C to 25°C. X-ray scattering intensity from smectic clusters with layer spacings that monotonically increase on cooling first increases to a maximum at T* ~ 60°C corresponding to clusters of about 30 layers. Below T*, the scattering intensity decreases as the number of layers in a cluster decreases. To account for this surprising nonlinear behavior that correlates with nonlinear features of the networks' macroscopic spontaneous shape change and birefringence, a model is proposed where dislocations form in the layers at T*. Below T*, more dislocations form to break down the layer structure. The possibility of dislocation formation at T* independent of mesogenic concentrations is attributed to a conformational change in the crosslinker which is present at the same concentration in the three LSCEs. [ABSTRACT FROM AUTHOR]

A review of the mechanisms that influence the critical behaviour of the nematic monodomain main-chain and side-chain liquid-crystalline elastomers is presented. The crosslinking density, the applied mechanical load and the temperature at which the second crosslinking step takes place are examples of such mechanisms. This knowledge is a powerful tool when the tuning of the critical behaviour and, thus, of the thermo-mechanical response of the elastomers is needed. [ABSTRACT FROM AUTHOR]