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| 2. |
- Kumar, Amol, et al.
(author)
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Electrochromism in Isoreticular Metal-Organic Framework Thin Films with Record High Coloration Efficiency
- 2023
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:21, s. 21595-21603
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Journal article (peer-reviewed)abstract
- The power of isoreticular chemistry has been widely exploited to engineer metal–organic frameworks (MOFs) with fascinating molecular sieving and storage properties but is underexplored for designing MOFs with tunable optoelectronic properties. Herein, three dipyrazole-terminated XDIs (X = PM (pyromellitic), N (naphthalene), or P (perylene); DI = diimide) with different lengths and electronic properties are prepared and employed as linkers for the construction of an isoreticular series of Zn-XDI MOFs with distinct electrochromism. The MOFs are grown on fluorine-doped tin oxide (FTO) as high-quality crystalline thin films and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Due to the constituting electronically isolated XDI linkers, each member of the isoreticular thin film series exhibits two reversible one-electron redox events, each at a distinct electrochemical potential. The orientation of the MOFs as thin films as well as their isoreticular nature results in identical cation-coupled electron hopping transport rates in all three materials, as demonstrated by comparable apparent electron diffusion coefficients, Deapp. Upon electrochemical reduction to either the [XDI]•– or [XDI]2– state, each MOF undergoes characteristic changes in its optical properties as a function of linker length and redox state of the linker. Operando spectroelectrochemistry measurements reveal that Zn-PDI@FTO (PDI = perylene diimide) thin films exhibit a record high coloration efficiency of 941 cm2 C–1 at 746 nm, which is attributed to the maximized Faradaic transformations at each electronically isolated PDI unit. The electrochromic response of the thin film is retained to more than 99% over 100 reduction–oxidation cycles, demonstrating the applicability of the presented materials.
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| 3. |
- Li, Jingguo, et al.
(author)
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Experimental manifestation of redox-conductivity in metal-organic frameworks and its implication for semiconductor/insulator switching
- 2023
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- Electric conductivity in metal-organic frameworks (MOFs) follows either a band-like or a redox-hopping charge transport mechanism. While conductivity by the band-like mechanism is theoretically and experimentally well established, the field has struggled to experimentally demonstrate redox conductivity that is promoted by the electron hopping mechanism. Such redox conductivity is predicted to maximize at the mid-point potential of the redox-active units in the MOF, and decline rapidly when deviating from this situation. Herein, we present direct experimental evidence for redox conductivity in fluorine-doped tin oxide surface-grown thin films of Zn(pyrazol-NDI) (pyrazol-NDI=1,4-bis[(3,5-dimethyl)-pyrazol-4-yl]naphthalenediimide). Following Nernstian behavior, the proportion of reduced and oxidized NDI linkers can be adjusted by the applied potential. Through a series of conductivity measurements, it is demonstrated that the MOF exhibits minimal electric resistance at the mid-point potentials of the NDI linker, and conductivity is enhanced by more than 10000-fold compared to that of either the neutral or completely reduced films. The generality of redox conductivity is demonstrated in MOFs with different linkers and secondary building units, and its implication for applications that require switching between insulating and semiconducting regimes is discussed. MOFs that transport electrons by a hopping mechanism are redox conductors. Here authors demonstrate a diagnostic bell-shaped conductivity curve that is centred around the formal potential of the redox active unit in a variety of MOFs.
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| 4. |
- Mendu, Suresh Kumar, et al.
(author)
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Different subtypes of GABA-A receptors are expressed in human, mouse and rat T lymphocytes
- 2012
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:8, s. e42959-
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Journal article (peer-reviewed)abstract
- γ-aminobutyric acid (GABA) is the most prominent neuroinhibitory transmitter in the brain, where it activates neuronalGABA-A receptors (GABA-A channels) located at synapses and outside of synapses. The GABA-A receptors are primarytargets of many clinically useful drugs. In recent years, GABA has been shown to act as an immunomodulatory molecule. Wehave examined in human, mouse and rat CD4+ and CD8+ T cells which subunit isoforms of the GABA-A channels areexpressed. The channel physiology and drug specificity is dictated by the GABA-A receptor subtype, which in turn isdetermined by the subunit isoforms that make the channel. There were 5, 8 and 13 different GABA-A subunit isoformsidentified in human, mouse and rat CD4+ and CD8+ T cells, respectively. Importantly, the γ2 subunit that imposesbenzodiazepine sensitivity on the GABA-A receptors, was only detected in the mouse T cells. Immunoblots andimmunocytochemistry showed abundant GABA-A channel proteins in the T cells from all three species. GABA-activatedwhole-cell transient and tonic currents were recorded. The currents were inhibited by picrotoxin, SR95531 and bicuculline,antagonists of GABA-A channels. Clearly, in both humans and rodents T cells, functional GABA-A channels are expressed butthe subtypes vary. It is important to bear in mind the interspecies difference when selecting the appropriate animal modelsto study the physiological role and pharmacological properties of GABA-A channels in CD4+ and CD8+ T cells and whenselecting drugs aimed at modulating the human T cells function.
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| 5. |
- Mojumder, Abhishek, et al.
(author)
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Mitigating the barriers to green procurement adoption : An exploratory study of the Indian construction industry
- 2022
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In: Journal of Cleaner Production. - : Elsevier Science Ltd. - 0959-6526 .- 1879-1786. ; 372
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Journal article (peer-reviewed)abstract
- The construction sector in India is in the governments intense focus on creating a world-class infrastructure balancing environmental conservation. Adopting green procurement practices by mitigating adoption barriers is necessary for Indian construction firms to achieve the goal. However, none of the existing research identified the comprehensive list of barriers, analysed their impacts on green procurement adoption, prioritized the barriers and formulated the solution strategies to mitigate them and maximize green procurement adoption for the Indian construction sector. To bridge this gap, this study has identified barriers, analysed their impact, prioritized the criticality, and developed the solution strategies to alleviate them. Questionnaire surveys and descriptive sta-tistics are first performed for data analysis of the firms based on the firms size and domain of expertise. Later, an analysis of variance (ANOVA) is performed and identified the significant differences in the impact of the barriers on Indian construction firms having different sizes or domains of expertise. The fuzzy best-worst method (FBWM) is then used to identify the most significant barriers as "reduced commitment from higher management ", "lack of management support ", and "perception of higher cost for adhering to green procurement ". Finally, the Delphi technique and assessment of various portals of the Government of India (GOI) have been carried out to identify the solutions to mitigate the barriers. The research results in an original and unique approach to identifying and analysing the critical barriers to green procurement adoption and their impact on different categories of Indian construction firms. It has identified the topmost barriers and then the solution strategies Indian construction firms and GOI need to focus on to embrace green procurement. The procurement managers can identify the top -rated barriers derived from the present study to closely focus and make strategies to eliminate them, helping their organisations adopt green procurement practices. The solution strategies derived from the study may be ready to implement action plans for construction and infrastructure companies of India, environmental and social development of the country, and assisting the GOI in developing and implementing the policy of green pro-curement for the Indian construction industry.
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| 6. |
- Spallacci, Claudia, et al.
(author)
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Fabricating high-purity graphite disk electrodes as a cost-effective alternative in fundamental electrochemistry research
- 2024
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In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14
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Journal article (peer-reviewed)abstract
- Graphite electrodes offer remarkable electrochemical properties, emerging as a viable alternative to glassy carbon (GCE) and other carbon-based electrodes for fundamental electrochemistry research. We report the fabrication and characterization of high-purity graphite disk electrodes (GDEs), made from cost-effective materials and a solvent-free methodology employing readily available laboratory equipment. Analysis of their physical properties via SEM, EDX and XPS reveals no metallic interferences and a notably high porosity, emphasizing their potential. The electrochemical performances of GDEs were found to be comparable to those of GCE. Immobilization of peptides and enzymes, both via covalent coupling and surface adsorption, was used to explore potential applications of GDEs in bioelectrochemistry. Enzyme activity could be addressed both via direct electron transfer and mediated electron transfer mechanism. These results highlight the interesting properties of our GDEs and make them a low-cost alternative to other carbon-based electrodes, with potential for future real-world applications.
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| 7. |
- Suremann, Nina F., 1996-, et al.
(author)
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Molecular Catalysis of Energy Relevance in Metal–Organic Frameworks : From Higher Coordination Sphere to System Effects
- 2023
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In: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 123:10, s. 6545-6611
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Journal article (peer-reviewed)abstract
- The modularity and synthetic flexibility of metal–organic frameworks (MOFs) have provoked analogies with enzymes, and even the term MOFzymes has been coined. In this review, we focus on molecular catalysis of energy relevance in MOFs, more specifically water oxidation, oxygen and carbon dioxide reduction, as well as hydrogen evolution in context of the MOF–enzyme analogy. Similar to enzymes, catalyst encapsulation in MOFs leads to structural stabilization under turnover conditions, while catalyst motifs that are synthetically out of reach in a homogeneous solution phase may be attainable as secondary building units in MOFs. Exploring the unique synthetic possibilities in MOFs, specific groups in the second and third coordination sphere around the catalytic active site have been incorporated to facilitate catalysis. A key difference between enzymes and MOFs is the fact that active site concentrations in the latter are often considerably higher, leading to charge and mass transport limitations in MOFs that are more severe than those in enzymes. High catalyst concentrations also put a limit on the distance between catalysts, and thus the available space for higher coordination sphere engineering. As transport is important for MOF-borne catalysis, a system perspective is chosen to highlight concepts that address the issue. A detailed section on transport and light-driven reactivity sets the stage for a concise review of the currently available literature on utilizing principles from Nature and system design for the preparation of catalytic MOF-based materials.
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| 8. |
- Wrede, Sina, et al.
(author)
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Lateral Electron and Hole Hopping between Dyes on Mesoporous ZrO2 : Unexpected Influence of Solvents with a Low Dielectric Constant
- 2023
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:21, s. 11472-11476
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Journal article (peer-reviewed)abstract
- Lateral intermolecular charge transfer between photosensitizers on metal oxide substrates is important for the understanding on the overall working principles of dye-sensitized systems. Such studies usually concentrate on either hole or electron transfer separately and are conducted in solvents with a high dielectric constant (εs) that are known, however, to show a drastic decrease of the local dielectric constant close to the metal oxide surface. In the present study, both hole and electron hopping between organic donor–acceptor photosensitizers was experimentally investigated on PB6 dye-sensitized mesoporous ZrO2 films. The donor (close to the surface) and acceptor (away from surface) subunit of the PB6 dye were observed to be involved in hole and electron hopping, respectively. Hole and electron transfer kinetics were found to differ remarkably in high-εs solvents, but similar in solvents with εs < 12. This finding indicates that low-εs solvents maintain similar local dielectric constant values close to, and further away from, the semiconductor surface, which is different from the previously observed behavior of high dielectric constant solvents at a metal oxide interface.
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