| 1. |
- Chen, Gan, et al.
(författare)
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Effects of Transition Metals on Metal–Octaaminophthalocyanine-Based 2D Metal–Organic Frameworks
- 2023
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Ingår i: ACS Nano. - 1936-0851 .- 1936-086X. ; 17:10, s. 9611-9621
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Tidskriftsartikel (refereegranskat)abstract
- Metal–octaaminophthalocyanine (MOAPc)-based 2D conductive metal–organic frameworks (cMOFs) have shown great potential in several applications, including sensing, energy storage, and electrocatalysis, due to their bimetallic characteristics. Here, we report a detailed metal substitution study on a family of isostructural cMOFs with Co2+, Ni2+, and Cu2+ as both the metal nodes and the metal centers in the MOAPc ligands. We observed that different metal nodes had variations in the reaction kinetics, particle sizes, and crystallinities. Importantly, the electronic structure and conductivity were found to be dependent on both types of metal sites in the 2D cMOFs. Ni-NiOAPc was found to be the most conductive one among the nine possible combinations with a conductivity of 54 ± 4.8 mS/cm. DFT calculations revealed that monolayer Ni-NiOAPc has neither the smallest bandgap nor the highest charge carrier mobility. Hence its highest conductivity stems from its high crystallinity. Collectively, these results provide structure property relationships for MOAPc-based cMOFs with amino coordination units.
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| 2. |
- Chen, Gan, et al.
(författare)
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Valence-Dependent Electrical Conductivity in a 3D Tetrahydroxyquinone-Based Metal-Organic Framework
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:51, s. 21243-21248
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Tidskriftsartikel (refereegranskat)abstract
- Electrically conductive metal-organic frameworks (cMOFs) have become a topic of intense interest in recent years because of their great potential in electrochemical energy storage, electrocatalysis, and sensing applications. Most of the cMOFs reported hitherto are 2D structures, and 3D cMOFs remain rare. Herein we report FeTHQ a 3D cMOF synthesized from tetrahydroxy-1,4-quinone (THQ) and iron(II) sulfate salt. FeTHQexhibited a conductivity of 3.3 +/- 0.55 mS cm(-1) at 300 K, which is high for 3D cMOFs. The conductivity of FeTHQis valence-dependent. A higher conductivity was measured with the as-prepared FeTHQ than with the air-oxidized and sodium naphthalenide-reduced samples.
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| 3. |
- Rao, Qiuhua, et al.
(författare)
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Shear fracture (Mode II) of brittle rock
- 2003
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 40:3, s. 355-375
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Tidskriftsartikel (refereegranskat)abstract
- Mode II fracture initiation and propagation plays an important role under certain loading conditions in rock fracture mechanics. Under pure tensile, pure shear, tension- and compression-shear loading, the maximum Mode I stress intensity factor, K (sub I max) , is always larger than the maximum Mode II stress intensity factor, K (sub II max) . For brittle materials, Mode I fracture toughness, K (sub IC) , is usually smaller than Mode II fracture toughness, K (sub IIC) . Therefore, K (sub I max) reaches K (sub IC) before K (sub II max) reaches K (sub IIC) , which inevitably leads to Mode I fracture. Due to inexistence of Mode II fracture under pure shear, tension- and compression-shear loading, classical mixed mode fracture criteria can only predict Mode I fracture but not Mode II fracture. A new mixed mode fracture criterion has been established for predicting Mode I or Mode II fracture of brittle materials. It is based on the examination of Mode I and Mode II stress intensity factors on the arbitrary plane theta ,K (sub I) (theta ) and K (sub II) (theta ), varying with theta (-180 degrees < or =theta < or =+180 degrees ), no matter what kind of loading condition is applied. Mode I fracture occurs when (K (sub II max) /K (sub I max) )(K (sub IIC) /K (sub IC) ) and K (sub II max) = K (sub IIC) at theta (sub IIC) . The validity of the new criterion is demonstrated by experimental results of shear-box testing. Shear-box test of cubic specimen is a potential method for determining Mode II fracture toughness K (sub IIC) of rock since it can create a favorable condition for Mode II fracture, i.e. K (sub II max) is always 2-3 times larger than K (sub I max) and reaches K (sub IIC) before K (sub I max) reaches K (sub IC) . The size effect on K (sub IIC) for single- and double-notched specimens has been studied for different specimen thickness B, dimensionless notch length a/W (or 2a/W) and notch inclination angle alpha . The test results show that K (sub IIC) decreases as B increases and becomes a constant when B is equal to or larger than W for both the single- and double-notched specimens. When a/W (or 2a/W) increases, K (sub IIC) decreases and approaches a limit. The alpha has a minor effect on K (sub IIC) when alpha is within 65-75 degrees . Specimen dimensions for obtaining a reliable and reproducible value of K (sub IIC) under shear-box testing are presented. Numerical results demonstrate that under the shear-box loading condition, tensile stress around the notch tip can be effectively restrained by the compressive loading. At peak load, the maximum normal stress is smaller than the tensile strength of rock, while the maximum shear stress is larger than the shear strength in the presence of compressive stress, which results in shear failure.
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