| 1. |
- Beretta, Davide, et al.
(author)
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Thermoelectrics: From history, a window to the future
- 2019
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In: Materials Science and Engineering: R: Reports. - : Elsevier BV. - 0927-796X. ; 138
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Research review (peer-reviewed)abstract
- Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck's observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh's suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed. From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years have provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With increasing demand for sustainable energy conversion technologies, the latter aspect has become crucial for developing thermoelectrics based on abundant and non-toxic materials, which can be processed at economically viable scales, tailored for different ranges of temperature. This includes high temperature applications where a substantial amount of waste energy can be retrieved, as well as room temperature applications where small and local temperature differences offer the possibility of energy scavenging, as in micro harvesters meant for distributed electronics such as sensor networks. While large scale applications have yet to make it to the market, the richness of available and emerging thermoelectric technologies presents a scenario where thermoelectrics is poised to contribute to a future of sustainable future energy harvesting and management. This work reviews the broad field of thermoelectrics. Progress in thermoelectrics and milestones that led to the current state-of-the-art are presented by adopting an historical footprint. The review begins with an historical excursus on the major steps in the history of thermoelectrics, from the very early discovery to present technology. A panel on the theory of thermoelectric transport in the solid state reviews the transport theory in complex crystal structures and nanostructured materials. Then, the most promising thermoelectric material classes are discussed one by one in dedicated sections and subsections, carefully highlighting the technological solutions on materials growth that have represented a turning point in the research on thermoelectrics. Finally, perspectives and the future of the technology are discussed in the framework of sustainability and environmental compatibility. © 2018 Elsevier B.V.
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| 2. |
- Ewald, Johannes, et al.
(author)
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Acid-Cleavable Poly(ethylene glycol) Hydrogels Displaying Protein Release at pH 5
- 2020
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 26:13, s. 2947-2953
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Journal article (peer-reviewed)abstract
- PEG is the gold standard polymer for pharmaceutical applications, however it lacks degradability. Degradation under physiologically relevant pH as present in endolysosomes, cancerous and inflammatory tissues is crucial for many areas. The authors present anionic ring‐opening copolymerization of ethylene oxide with 3,4‐epoxy‐1‐butene (EPB) and subsequent modification to introduce acid‐degradable vinyl ether groups as well as methacrylate (MA) units, enabling radical cross‐linking. Copolymers with different molar ratios of EPB, molecular weights (Mn) up to 10 000 g mol−1 and narrow dispersities (Đ<1.05) were prepared. Both the P(EG‐co‐isoEPB)MA copolymer and the hydrogels showed pH‐dependent, rapid hydrolysis at pH 5–6 and long‐term storage stability at neutral pH (pH 7.4). By designing the degree of polymerization and content of degradable vinyl ether groups, the release time of an entrapped protein OVA‐Alexa488 can be tailored from a few hours to several days (hydrolysis half‐life time t1/2 at pH 5: 13 h to 51 h).
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| 3. |
- Kucheriv, Olesia I., et al.
(author)
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Four‐Step Spin Crossover in a New Cyano‐Bridged Iron‐Silver Coordination Polymer
- 2022
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In: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 28:44
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Journal article (peer-reviewed)abstract
- A new guest-free Hofmann clathrate analogue Fe(2-ethoxypyrazine)2{Ag(CN)2}2 which undergoes a four-step spin crossover during the transition from the low-spin to the high-spin state is reported. At the first step 1/3 of centers become high spin, at the second step another 1/3 of centres become high spin, at the third step spin mixed crystallographic centres are observed, and after the fourth step all centers are high spin.
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| 4. |
- Maslyk, Marcel, et al.
(author)
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Understanding the Stability and Recrystallization Behavior of Amorphous Zinc Phosphate
- 2021
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:4, s. 2636-2647
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Journal article (peer-reviewed)abstract
- Zinc phosphate, an important pigment in phosphate conversion coatings, forms protective films on rubbing surfaces. We have simulated the underlying reactions under shear by ball-milling zinc phosphate and monitored the reaction of hopeite (Zn3(PO4)2·4H2O) and the retarded recrystallization of the amorphous reaction product by powder X-ray diffraction (PXRD) and quantitative infrared (IR) spectroscopy. Abrasion of stainless steel was simulated by addition of pure 57Fe. The results provide insight into the chemistry of phosphate conversion coatings or during battery cycling of metal phosphates and give theoretical guidance for the preparation of amorphous phosphates. Thermal analysis revealed that the release of structural water is a key step during the reaction of hopeite under shear to ball-milled amorphous zinc phosphate. The back-reaction and associated recrystallization kinetics of amorphous zinc phosphate show a classical Langmuir behavior. Fe impurities inhibit the recrystallization of ball-milled amorphous zinc phosphate strongly. 57Fe Mössbauer spectroscopy and PXRD revealed that Fe is oxidized to Fe2+ and Fe3+ during ball-milling and incorporated locally at the tetrahedral and octahedral sites of the structure. Ball-milled amorphous zinc phosphate is metastable as γ-Zn3–xFex(PO4)2. EPR studies showed the incorporation of Fe3+ to be coupled with the formation of Zn2+ vacancies. The Fe3+ defect sites bind water because of their higher Pearson hardness (compared to Fe2+ and Zn2+), thereby reducing water mobility and inhibiting further reactions like the recrystallization to hopeite. Our findings reveal the amorphization mechanism of Zn3(PO4)2·4H2O in stainless steel ball mills at the atomic scale and highlight how the reactivity of amorphous products is affected by impurities associated with the processing method.
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| 5. |
- Shylin, Sergii I., et al.
(author)
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1D iron(II)-1,2,4-triazolic chains with spin crossover assembled from discrete trinuclear complexes
- 2022
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In: Dalton Transactions. - Cambridge : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:6, s. 2364-2369
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Journal article (peer-reviewed)abstract
- We report on a molecular cationic iron(II) complex with a 4-amino-1,2,4-triazole ligand and a tetraiodomercurate anion exhibiting an incomplete spin crossover (SCO). The complex exhibits an unusual disordered structure with a linear arrangement of ligand and water molecules that can potentially accommodate up to four iron atoms, but both terminal metal positions have half chemical occupancies, while occupancies of all ligands are full. This corresponds to the crystallisation of disordered trinuclear complexes arranged into 1D supramolecular chains. Iron cations have different N6 or N3O3 coordination environments, leading to the thermally induced SCO in two thirds of the metal centres. This SCO behaviour was characterised by magnetic susceptibility measurements and Mössbauer spectroscopy.
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| 6. |
- Shylin, Sergii I., et al.
(author)
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Hofmann-Like Frameworks Fe(2-methylpyrazine)n[M(CN)2]2 (M = Au, Ag) : Spin-Crossover Defined by the Precious Metal
- 2020
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 59:9, s. 6541-6549
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Journal article (peer-reviewed)abstract
- Hofmann-like cyanometalates constitute a large class of spin-crossover iron(II) complexes with variable switching properties. However, it is not yet clearly understood how the temperature and cooperativity of a spin transition are influenced by their structure. In this paper, we report the synthesis and crystal structures of the metal–organic coordination polymers {FeII(Mepz)[AuI(CN)2]2} ([Au]) and {FeII(Mepz)2[AgI(CN)2]2} ([Ag]), where Mepz = 2-methylpyrazine, along with characterization of their spin-state behavior by variable-temperature SQUID magnetometry and Mössbauer spectroscopy. The compounds are built of cyanoheterometallic layers, which are pillared by the bridging Mepz ligands in [Au] but separated in [Ag]. The complex [Au] exhibits an incomplete stepped spin transition as a function of the temperature with TSCO1 = 170 K and TSCO2 = 308 K for the two subsequent steps. In contrast, the complex [Ag] attains the high-spin state over the whole temperature range. In the crystal structure of [Ag], weak interlayer contacts (Ag−π, Me−π, and Ag–N) are found that may be responsible for an unusual axial elongation of the FeN6 polyhedra. We propose that this structural distortion contributes to the trapping of iron in its high-spin state.
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| 7. |
- Sirenko, Valerii Y., et al.
(author)
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Nature of cyanoargentate bridges defining spin crossover in new 2D Hofmann clathrate analogues
- 2024
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 53:9, s. 4251-4259
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Journal article (peer-reviewed)abstract
- Chemical composition is leading among the numerous factors that determine the spin transition properties of coordination compounds. Classic dicyanometallic bridges {M(CN)2}− are commonly used to build Hofmann-like spin-crossover frameworks, but some extended bridges are also synthetically available. In this paper, we describe a successful synthesis of two very similar spin-crossover frameworks that differ in the cyanometallic bridges involved, namely [Fe(etpz)2{Ag(CN)2}2] (1) and {Fe(etpz)2[Ag2(CN)3][Ag(CN)2]} (2) (where etpz = 2-ethylpyrazine). Magnetic and Mössbauer studies demonstrated the occurrence of abrupt one-step high-spin (HS) ↔ low-spin (LS) transitions for both complexes. The spin transition temperatures are T1/2 ↓ = 233 K and T1/2 ↑ = 243 K for 1 and T1/2 ↓ = 188 K and T1/2 ↑ = 191 K for 2 with thermal hysteresis loops of 10 K for 1 and 3 K for 2. The bridging mononuclear [Ag(CN)2]− units and FeII cations assemble to form infinite 2D layers in the structure of 1. Interestingly, compound 2 forms 2D layers of FeII cations bridged by both binuclear [Ag2(CN)3]− and mononuclear [Ag(CN)2]− units. The structures of 1 and 2 comprise different types of intermolecular interactions including Ag⋯Ag and Ag⋯Netpz, which induce the creation of supramolecular 3D frameworks. The synergy between metallophilic interactions and the spin transition is also confirmed by the variation of Ag⋯Ag distances during spin crossover. The characterization of such analogues allowed us to analyze in detail the effect of the cyanometallic bridge on the structure of new frameworks and on the bistability in Hofmann-like complexes.
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