29 research outputs found
Single-Ion Li[superscript +], Na[superscript +], and Mg[superscript 2+] Solid Electrolytes Supported by a Mesoporous Anionic Cu–Azolate Metal–Organic Framework
No full textA novel Cu(II)–azolate metal–organic framework (MOF) with tubular pores undergoes a reversible single crystal to single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts. The stoichiometric transformation between the two phases allows loading of record amounts of charge-balancing Li[superscript +], Na[superscript +], and Mg[superscript 2+] ions for MOFs. Whereas the halide/pseudohalide anions are bound to the metal centers and thus stationary, the cations move freely within the one-dimensional pores, giving rise to single-ion solid electrolytes. The respective Li[superscript +]-, Na[superscript +]-, and Mg[superscript 2+]-loaded materials exhibit high ionic conductivity values of 4.4 × 10[superscript –5], 1.8 × 10[superscript –5], and 8.8 × 10[superscript –7] S/cm. With addition of LiBF[subscript 4], the Li[superscript +] conductivity improves to 4.8 × 10[superscript –4] S/cm. These are the highest values yet observed for MOF solid electrolytes.National Science Foundation (U.S.) (DMR-1645232)National Science Foundation (U.S.). Graduate Research Fellowship Program (Award 1122374)Alfred P. Sloan FoundationCamille & Henry Dreyfus FoundationResearch Corporation for Science Advancemen
Is iron unique in promoting electrical conductivity in MOFs?
No full textIdentifying the metal ions that optimize charge transport and charge density in metal–organic frameworks is critical for systematic improvements in the electrical conductivity in these materials. In this work, we measure the electrical conductivity and activation energy for twenty different MOFs pertaining to four distinct structural families: M2(DOBDC)(DMF)2 (M = Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+); H4DOBDC = 2,5-dihydroxybenzene-1,4-dicarboxylic acid; DMF = N,N-dimethylformamide), M2(DSBDC)(DMF)2 (M = Mn2+, Fe2+; H4DSBDC = 2,5-disulfhydrylbenzene-1,4-dicarboxylic acid), M2Cl2(BTDD)(DMF)2 (M = Mn2+, Fe2+, Co2+, Ni2+; H2BTDD = bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i]dibenzo[1,4]dioxin), and M(1,2,3-triazolate)2 (M = Mg2+, Mn2+, Fe2+, Co2+, Cu2+, Zn2+, Cd2+). This comprehensive study allows us to single-out iron as the metal ion that leads to the best electrical properties. The iron-based MOFs exhibit at least five orders of magnitude higher electrical conductivity and significantly smaller charge activation energies across all different MOF families studied here and stand out materials made from all other metal ions considered here. We attribute the unique electrical properties of iron-based MOFs to the high-energy valence electrons of Fe2+ and the Fe3+/2+ mixed valency. These results reveal that incorporating Fe2+ in the charge transport pathways of MOFs and introducing mixed valency are valuable strategies for improving electrical conductivity in this important class of porous materials
Reversible Capture and Release of Cl₂ and Br₂ with a Redox-Active Metal–Organic Framework
No full textExtreme toxicity, corrosiveness, and volatility pose serious challenges for the safe storage and transportation of elemental chlorine and bromine, which play critical roles in the chemical industry. Solid materials capable of forming stable nonvolatile compounds upon reaction with elemental halogens may partially mitigate these challenges by allowing safe halogen release on demand. Here we demonstrate that elemental halogens quantitatively oxidize coordinatively unsaturated Co(II) ions in a robust azolate metal-organic framework (MOF) to produce stable and safe-to-handle Co(III) materials featuring terminal Co(III)-halogen bonds. Thermal treatment of the oxidized MOF causes homolytic cleavage of the Co(III)-halogen bonds, reduction to Co(II), and concomitant release of elemental halogens. The reversible chemical storage and thermal release of elemental halogens occur with no significant losses of structural integrity, as the parent cobaltous MOF retains its crystallinity and porosity even after three oxidation/reduction cycles. These results highlight a material operating via redox mechanism that may find utility in the storage and capture of other noxious and corrosive gases.National Science Foundation (U.S.) (Award DMR-1452612
Russia Democratic Retreat: The Role of the Conflict in Chechnya, Declining Media Freedom and a Subdued Middle Class
No full textThe fall of the Soviet Union is argued to have brought more freedom to people in the region. However, is Russia really in a better place in 2012 than it was under communism? Drawing on scholarly research, news sources, and firsthand accounts, this paper challenges the popular understanding of Russian politics by arguing that the democratic decline in Russia has eroded many of the social gains of the 1990s. The focus will be on three specific problems with Russian democracy. First, the conflict in Chechnya demonstrates that political and civil rights continue to be violated on a regular basis. Secondly, the regime\u27s muzzling of the media makes evident that it is still willing to violate individual rights to maintain power. Thirdly, due to the central role that middle classes historically have played in the struggle for democratization, the relative absence of middle class involvement in Russian civil society makes holding leaders accountable and defending human rights a Herculean task
Accounting at Culver Military Academy
No full textvii, 34 p.The author describes an internship with the accounting department at Culver Military Academy as the student billing intern. The author performed student billing duties, the camper and student registration process, and importing data via the computer systems. In the second part, the author researched the techniques of fundamental analysis and used the techniques to evaluate two publicly traded golf club manufacturers
High and Reversible Ammonia Uptake in Mesoporous Azolate MetalOrganic Frameworks with Open Mn, Co, and Ni Sites
No full text[Review of the book Taking root: The origins of the Canadian Jewish community by Gerald Tulchinsky]
No full text
High and Reversible Ammonia Uptake in Mesoporous Azolate Metal–Organic Frameworks with Open Mn, Co, and Ni Sites
No full textA series
of new mesoporous metal–organic frameworks (MOFs)
made from extended bisbenzenetriazolate linkers exhibit coordinatively
unsaturated metal sites that are responsible for high and reversible
uptake of ammonia. Isostructural Mn, Co, and Ni materials adsorb 15.47,
12.00, and 12.02 mmol of NH3/g, respectively, at STP. Importantly,
these near-record capacities are reversible for at least three cycles.
These results demonstrate that azolate MOFs are sufficiently thermally
and chemically stable to find uses in recyclable sorption, storage,
and potentially separation of chemically challenging and/or corrosive
gases, especially when designed to exhibit a high density of open
metal sites
