CeO2 Nanoparticles Boosted Fe‐N‐C Sites Derived from Dual Metal Organic Frameworks toward Highly Active and Durable Oxygen Reduction Reaction
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Abstract The durability improvement of Fe‐N‐C electrocatalysts toward acidic oxygen reduction reaction (ORR) remains a grand challenge. H 2 O 2 seriously degrades Fe‐N‐C sites, which account for a major origin of the low durability. Herein, the growth of hemin decorated zeolitic imidazole framework (hemin‐ZIF 8) on preformed Ce‐1,3,5‐benzenecarboxylic acid (Ce‐BTC) metal organic frameworks (MOFs) is reported. Interestingly, the resultant dual MOFs appear to be Ce‐BTC nanorods decorated with many hemin‐ZIF 8 dodecahedral nanocrystals, well resembling rice panicles. After pyrolysis, CeO 2 nanoparticles are evenly distributed in carbonized nanorods and abundant Fe‐N‐C sites are embedded in shrunk dodecahedra, labeled as Fe‐N‐C‐CeO 2 . Fe‐N‐C‐CeO 2 exhibits a high ORR activity in terms of a half wave potential (E 1/2 ) of 0.800 V (vs RHE). The high ORR activity is closely correlated with the well exposure of Fe‐N‐C sites. In addition, the presence of CeO 2 leads to a low H 2 O 2 yield of Fe‐N‐C‐CeO 2 (2.3%), much lower than that of Fe‐N‐C (4.3%) by itself in the absence of CeO 2 . After 5000 potential cycling, the E 1/2 of Fe‐N‐C‐CeO 2 degrades 15 mV superior to that of Fe‐N‐C (42 mV). Moreover, a single cell with Fe‐N‐C‐CeO 2 as cathode degrades much slower than that of Fe‐N‐C (28 000 s vs 7200 s) during chronoamperometric measurements.Keywords:
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Abstract The structural, compositional, and morphological features of metal–organic frameworks (MOFs) govern their properties and applications. Construction of hybrid MOFs with complicated structures, components, or morphologies is significant for the development of well‐organized MOFs. An advanced route is reported for construction of atypical hybrid MOFs with unique morphologies and complicated components: 1) MOF‐on‐MOF growth of a 3D zeolitic imidazolate framework (ZIF) on a ZIF‐L template, 2) etching of a part of the 2D ZIF‐L template, and 3) structural transformation of 2D ZIF‐L into 3D ZIF. The formation of core–shell‐type MOF rings and plates is controlled by regulating the three processes. The formation route for the core–shell‐type MOF rings and plates was monitored by tracking changes in morphology, structure, and composition. Carbon materials prepared from the pyrolysis of the core–shell‐type hybrid MOFs displayed enhanced oxygen reduction reaction activities compared to their monomeric counterparts.
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Although hemin is an essential nutrient for the black-pigmented oral bacterium Porphyromonas gingivalis, the mechanisms involved in hemin binding and uptake are poorly defined. In this study, we have examined the binding of hemin and Congo red (CR) to P. gingivalis whole cells and have defined the conditions for maximal binding. Additionally, the accumulation of hemin by P. gingivalis under growing conditions has been characterized. P. gingivalis A7436 was grown under hemin- or iron-deplete conditions (basal medium [BM] or Schaedler broth with dipyridyl [SBD]) or under hemin- or iron-replete conditions (BM with hemin [BMH] or Schaedler broth [SB]), and hemin and CR binding were assessed spectrophotometrically. Binding of hemin by P. gingivalis whole cells was rapid and was observed in samples obtained from cells grown under hemin- and iron-replete and hemin-deplete conditions but was not observed in cells grown under iron limitation. We also found that P. gingivalis whole cells bound more hemin when grown in BMH or SB than cells grown in BM or SBD. Binding of CR by P. gingivalis A7436 was also enhanced when cells were grown in the presence of hemin or when cells were incubated with hemin prior to CR binding. Hemin binding and accumulation were also assessed using [14C]hemin and [59Fe]hemin under growing conditions. Both [14C]hemin and [59Fe]hemin were accumulated by P. gingivalis, indicating that iron and the porphyrin ring were taken into the cell. Binding and accumulation of hemin under growing conditions were also induced by growth of P. gingivalis in hemin-replete media. Hemin accumulation was inhibited by the addition of KCN to P. gingivalis cultures, indicating that active transport was required for hemin uptake. [14C]hemin binding and accumulation were also inhibited by the addition of either cold hemin or protoporphyrin IX. Taken together, these results indicate that P. gingivalis transports the entire hemin moiety into the cell and that the binding and accumulation of hemin are induced by growth of cultures in the presence of hemin.
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Metal Organic Frameworks (MOFs) and Zeolitic Imidazolate Frameworks (ZIFs) are porous crystalline materials comprised of organic units (links) and metal oxide units (secondary building units) with surface areas often exceeding 1000 m 2 /g. These materials are finding increased applications in gas storage, gas separation, and catalysis. In this thesis new MOFs and ZIFs are synthesized to further these applications. Special attention is paid to the synthesis of frameworks, which can be postsynthetically modified with new functionalities including metal centers. Design metrics for postmodification are realized, including pore size, chemical stability, and incorporation of metalation sites in frameworks. Finally, enhancement of gas adsorption across a series of frameworks is investigated.
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This thesis presents the synthesis, properties, and applications of two important classes of metal-organic frameworks (MOFs); lanthanide MOFs and hierarchical porous zeolitic imidazolate frameworks ...
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금속유기구조체(metal-organic frameworks, MOF)는 넓은 비표면적, 규칙적인 구조 및 높게 분산된 금속 성분 등 뛰어난 물리화학적 특성으로 인해 활발한 연구가 이뤄지고 있는 다공성 물질이며, 특히 가스의 흡착, 분리 매체로서 뛰어난 성능이 보고되고 있다. MOF를 이용한 온실가스 이산화탄소의 흡착 연구는 상온 고압 영역에서 이산화탄소 저장 공정과 상온 저압 영역에서 이산화탄소 흡착 공정의 두 범주로 나눌 수 있으며, MOF의 넓은 비표면적 외에도 (1) MOF의 빈 배위결합 자리, (2) MOF의 기능화, (3) MOF의 상호 침투 효과, 및 (4) 이온 교환 효과를 이용한 연구 결과가 보고되고 있다. MOF 물질들은 비교적 낮은 수분 및 열에 대한 안정성이 문제로 제기되고 있으며, 제올라이트 유사 구조체(zeolitic imidazolate frameworks, ZIF) 또는 유기 골격 구조체(covalent organic frameworks, COF) 물질의 이산화탄소 흡착 특성이 거론되고 있다. 본 소고에서는 MOF를 이용한 이산화탄소 흡착에 대한 최근의 연구 결과를 본 연구실의 실험 결과를 중심으로 간략히 소개하고자 한다. Metal organic frameworks (MOFs) are a class of crystalline organic-inorganic hybrid compounds formed by coordination of metal clusters or ions with organic linkers. MOFs have recently attracted intense research interest due to their permanent porous structures, large surface areas and pore volume, high-dispersed metal species, and potential applications in gas adsorption, separation, and catalysis. $CO_2$ adsorption in MOFs has been investigated in two areas of $CO_2$ storage at high pressures and $CO_2$ adsorption at atmospheric pressure conditions. In this short review, $CO_2$ adsorption/separation results using MOFs conducted in our laboratory was explained in terms of four contributing effects; (1) coordinatively unsaturated open metal sites, (2) functionalization, (3) interpenetration/catenation, and (4) ion-exchange. Zeolitic imidazolate frameworks (ZIFs) and covalent organic frameworks (COFs) were also considered as a candidate material.
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A novel porous ZnO@Co3O4 composite is obtained from ZIF-8@ZIF-67 crystals and exhibits a distinguished photocatalytic activity and stability for CO2 reduction.
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Novel metal-organic frameworks (MOFs) based solid catalysts have been synthesized by encapsulating Hemin into the HKUST-1 MOF materials. These have been first applied in the chemiluminescence field with outstanding performance. The functionalized MOFs not only maintain an excellent catalytic activity inheriting from Hemin but also can be cyclically utilized as solid mimic peroxidases in the neutral condition. The synthesized Hemin@HKUST-1 composites have been used to develop practical sensors for H2O2 and glucose with wide response ranges and low detection limits. It was envisioned that catalyst-functionalized MOFs for chemiluminescence sensing would have promising applications in green, selective, and sensitive detection of target analytes in the future.
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Peptide-Mediated Synthesis of Zeolitic Imidazolate Framework-8 with Controllable Morphology and Size
Peptides with a sequence of Nap-Ix-GPLGLAG-R4-NH2 (x = 2, 4, and 6, shorted as I2R4, I4R4, and I6R4) were used as capping agents for the synthesis of zeolitic imidazolate framework-8 (ZIF-8) in water. Peptide addition can significantly inhibit the growth of ZIF-8 crystals. The shape and size of ZIF-8 crystals was related closely to the number of isoleucine (Ile, I) residues as well as concentration of the peptide. The shape of ZIF-8 crystals changes from rhomboid dodecahedron to truncated rhombic dodecahedron to cube with the decreasing number of isoleucine residues from six to two. At a peptide concentration of 1.0 mM, the morphology of ZIF-8 crystals was cubic, truncated rhombic dodecahedron, and typical rhombic dodecahedron in the cases of I2R4, I4R4, and I6R4, respectively. Also, the particle size can be regulated from ca. 1.7 μm to <100 nm by controlling the peptide concentration from 0 to 2.0 mM. This work develops a simple and green method for the synthesis of ZIF-8 crystals with controllable shape and size in water, which shows high potential for biomedical and biological applications.
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High symmetric porous Co3O4 hollow dodecahedra constructed by nanometer-sized building blocks are rationally synthesized by templating against Co-containing zeolitic imidazolate framework-67. The well-defined hollow structure and highly porous framework render these hollow dodecahedra exhibit high specific capacity, excellent cycling stability and superior rate capability when evaluated as an anode material for lithium-ion batteries.
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