| 1. |
- Abdelhamid, Hani Nasser, et al.
(författare)
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A Fast and Scalable Approach for Synthesis of Hierarchical Porous Zeolitic Imidazolate Frameworks and One-Pot Encapsulation of Target Molecules
- 2017
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 56:15, s. 9139-9146
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Tidskriftsartikel (refereegranskat)abstract
- A trimethylamine (TEA)-assisted synthesis approach that combines the preparation of hierarchical porous zeolitic imidazolate framework ZIF-8 nanoparticles and one-pot encapsulation of target molecules is presented. Two dye molecules, rhodamine B (RhB) and methylene blue (MB), and one protein (bovine serum albumin, BSA) were tested as the target molecules. The addition of TEA into the solution of zinc nitrate promoted the formation of ZnO nanocrystals, which rapidly transformed to ZIF-8 nanoparticles after the addition of the linker 2-methylimidazole (Hmim). Hierarchical porous dye@ZIF-8 nanoparticles with high crystallinity, large BET surface areas (1300–2500 m2/g), and large pore volumes (0.5–1.0 cm3/g) could be synthesized. The synthesis procedure was fast (down to 2 min) and scalable. The Hmim/Zn ratio could be greatly reduced (down to 2:1) compared to previously reported ones. The surface areas, and the mesopore size, structure, and density could be modified by changing the TEA or dye concentrations, or by postsynthetic treatment using reflux in methanol. This synthesis and one-pot encapsulation approach is simple and can be readily scaled up. The photophysical properties such as lifetime and photostability of the dyes could be tuned via encapsulation. The lifetimes of the encapsulated dyes were increased by 3–27-fold for RhB@ZIF-8 and by 20-fold for MB@ZIF-8, compared to those of the corresponding free dyes. The synthesis approach is general, which was successfully applied for encapsulation of protein BSA. It could also be extended for the synthesis of hierarchical porous cobalt-based ZIF (dye@ZIF-67).
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| 2. |
- Bai, Licheng, et al.
(författare)
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Explaining the Size Dependence in Platinum-Nanoparticle-Catalyzed Hydrogenation Reactions
- 2016
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:50, s. 15656-15661
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenation reactions are industrially important reactions that typically require unfavorably high H-2 pressure and temperature for many functional groups. Herein we reveal surprisingly strong size-dependent activity of Pt nanoparticles (PtNPs) in catalyzing this reaction. Based on unambiguous spectral analyses, the size effect has been rationalized by the size-dependent d-band electron structure of the PtNPs. This understanding enables production of a catalyst with size of 1.2 nm, which shows a sixfold increase in turnover frequency and 28-fold increase in mass activity in the regioselective hydrogenation of quinoline, compared with PtNPs of 5.3 nm, allowing the reaction to proceed under ambient conditions with unprecedentedly high reaction rates. The size effect and the synthesis strategy developed herein may provide a general methodology in the design of metal-nanoparticle-based catalysts for a broad range of organic syntheses.
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| 3. |
- Bao, Zijia, et al.
(författare)
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A bimetallic 3D interconnected metal–organic framework with 2D morphology and its derived electrocatalyst for oxygen reduction
- 2023
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 25:13, s. 1869-1873
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Tidskriftsartikel (refereegranskat)abstract
- Metal–organic frameworks (MOFs) are widely used as precursors to generate derivatives for electrocatalysis. However, two-dimensional (2D) MOFs often suffer from the collapse of their 2D structures after being treated at high temperature. Herein, we used the dense ZIF-EC1 as a precursor and doped Co as a secondary metal. The content of Co in ZIF-EC1 can be tuned without changing the crystalline structure. After pyrolysis, the derived carbon-based material maintains the 2D morphology from the parental precursor. The derived ZIF-EC1(ZnCo)-20-900 exhibits the best activity toward the ORR, which is even better than that of Pt/C. This work demonstrates the potential of using a nonporous dense MOF as a precursor and optimizing electrocatalytic ORR activity by tuning the Co content.
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| 4. |
- Bao, Zijia, et al.
(författare)
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A helical polypyrrole nanotube interwoven zeolitic imidazolate framework and its derivative as an oxygen electrocatalyst
- 2022
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 58:80, s. 11288-11291
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Tidskriftsartikel (refereegranskat)abstract
- A helical polypyrrole nanotube interwoven zeolitic imidazolate framework (ZIF) has been prepared for the first time. After pyrolysis, the helical carbon could act as highly active sites, while the 3D-connected nanoarchitecture contributed to fast charge transfer. The derived carbon material exhibits high activity for the ORR and good performance for a Zn–air battery.
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| 5. |
- Cheung, Ocean, et al.
(författare)
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Nanostructure and pore size control of template-free synthesised mesoporous magnesium carbonate
- 2016
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:78, s. 74241-74249
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Tidskriftsartikel (refereegranskat)abstract
- The structure of mesoporous magnesium carbonate (MMC) first presented in 2013 is investigated using a bottom-up approach. MMC is found to be built from the aggregation of nanoparticles of amorphous MgCO3 and MgO with a coating of amorphous MgCO3. The nanoparticles have dimensions of approximately 2-5 nm as observed using transmission electron microscopy and the aggregation of the particles creates the pore structure of MMC. We further show that the average pore diameter of MMC can be controlled by varying the temperature during the powder formation process and demonstrate that altering the pore size opens the possibility to tune the amorphous phase stabilisation properties that MMC exerts on poorly soluble drug compounds. Specifically, we show the loading and release of the antifungal drug itraconazole using MMC as a drug carrier.
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| 6. |
- Cheung, Ocean, et al.
(författare)
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Nanostructure and pore size control of template-free synthesised mesoporous magnesium carbonate
- 2016
-
Ingår i: RSC Advances. ; 6:78, s. 74241-74249
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of mesoporous magnesium carbonate (MMC) first presented in 2013 is investigated using a bottom-up approach. MMC is found to be built from the aggregation of nanoparticles of amorphous MgCO3 and MgO with a coating of amorphous MgCO3. The nanoparticles have dimensions of approximately 2-5 nm as observed using transmission electron microscopy and the aggregation of the particles creates the pore structure of MMC. We further show that the average pore diameter of MMC can be controlled by varying the temperature during the powder formation process and demonstrate that altering the pore size opens the possibility to tune the amorphous phase stabilisation properties that MMC exerts on poorly soluble drug compounds. Specifically, we show the loading and release of the antifungal drug itraconazole using MMC as a drug carrier.
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| 7. |
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| 8. |
- Cichocka, Magdalena Ola, et al.
(författare)
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A Porphyrinic Zirconium Metal-Organic Framework for Oxygen Reduction Reaction : Tailoring the Spacing between Active-Sites through Chain-Based Inorganic Building Units
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:36, s. 15386-15395
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal-organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm(-2). Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.
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| 9. |
- Ge, Meng, et al.
(författare)
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High-Throughput Electron Diffraction Reveals a Hidden Novel Metal-Organic Framework for Electrocatalysis
- 2021
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 60:20, s. 11391-11397
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Tidskriftsartikel (refereegranskat)abstract
- Metal-organic frameworks (MOFs) are known for their versatile combination of inorganic building units and organic linkers, which offers immense opportunities in a wide range of applications. However, many MOFs are typically synthesized as multiphasic polycrystalline powders, which are challenging for studies by X-ray diffraction. Therefore, developing new structural characterization techniques is highly desired in order to accelerate discoveries of new materials. Here, we report a high-throughput approach for structural analysis of MOF nano- and sub-microcrystals by three-dimensional electron diffraction (3DED). A new zeolitic-imidazolate framework (ZIF), denoted ZIF-EC1, was first discovered in a trace amount during the study of a known ZIF-CO3-1 material by 3DED. The structures of both ZIFs were solved and refined using 3DED data. ZIF-EC1 has a dense 3D framework structure, which is built by linking mono- and bi-nuclear Zn clusters and 2-methylimidazolates (mIm(-)). With a composition of Zn-3(mIm)(5)(OH), ZIF-EC1 exhibits high N and Zn densities. We show that the N-doped carbon material derived from ZIF-EC1 is a promising electrocatalyst for oxygen reduction reaction (ORR). The discovery of this new MOF and its conversion to an efficient electrocatalyst highlights the power of 3DED in developing new materials and their applications.
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| 10. |
- Ge, Meng, et al.
(författare)
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On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks
- 2021
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Ingår i: Faraday discussions. - 1359-6640 .- 1364-5498. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 angstrom), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.
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| 11. |
- Görbe, Tamás, et al.
(författare)
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Design of a Pd(0)-CalB CLEA Biohybrid Catalyst and Its Application in a One-Pot Cascade Reaction
- 2017
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:3, s. 1601-1605
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Tidskriftsartikel (refereegranskat)abstract
- Herein, a design of a biohybrid catalyst is described, consisting of Pd nanoparticles and a cross-linked network of aggregated lipase B enzyme of Candida antarctica (CalB CLEA) functioning as an active support for the Pd nanoparticles. Both entities of the hybrid catalyst showed good catalytic activity. The applicability was demonstrated in a one-pot reaction, where the Pd-catalyzed cycloisomerization of 4-pentynoic acid afforded a lactone that serves as an acyl donor in a subsequent selective enzymatic kinetic resolution of a set of sec-alcohols. The catalyst proved to be robust and could be recycled five times without a significant loss of activity.
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| 12. |
- Huo, Meiling, et al.
(författare)
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A heteroepitaxially grown two-dimensional metal-organic framework and its derivative for the electrocatalytic oxygen reduction reaction
- 2022
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 10:19, s. 10408-10416
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) metal–organic frameworks (MOFs) have become a hot topic recently due to their high surface area, larger number of exposed active sites, and improved conductivity. Combining different 2D MOFs could introduce new physical and chemical properties. Here, we have synthesized a heteroepitaxially grown 2D zeolitic imidazolate framework with a leaf-like morphology (ZIF-L). ZIF-L has a layer-by-layer dense structure, which possesses a high content of N and metal ions as active sites. ZIF-L-Co is heteroepitaxially grown on ZIF-L-Zn, while ZIF-L-Zn@ZIF-Co has been successfully prepared. After pyrolysis, the heteroepitaxially grown MOF derived ultra-small Co nanoparticle immobilized nitrogen doped carbon (NC) material (HM-Co@NC) exhibits superior oxygen reduction reaction (ORR) activity (Eonset = 0.998 V, E1/2 = 0.905 V) and better stability than Pt/C, achieving well-qualified assemblies for use in rechargeable Zn–air batteries.
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| 13. |
- Jia, Xiaomin, et al.
(författare)
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Single crystal metal-organic framework constructed by vertically self-pillared nanosheets and its derivative for oriented lithium plating
- 2021
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Ingår i: Cuihuà xuébào. - : Elsevier BV. - 0253-9837 .- 1872-2067. ; 42:9, s. 1553-1560
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Tidskriftsartikel (refereegranskat)abstract
- This vertically self-pillared (VSP) structure extends the application range of traditional porous materials with facile mass/ion transport and enhanced reaction kinetics. Here, we prepare a single crystal metal-organic framework (MOF), employing the ZIF-67 structure as a proof of concept, which is constructed by vertically self-pillared nanosheets (VSP-MOF). We further converted VSP-MOF into VSP-cobalt sulfide (VSP-CoS2) through a sulfidation process. Catalysis plays an important role in almost all battery technologies; for metallic batteries, lithium anodes exhibit a high theoretical specific capacity, low density, and low redox potential. However, during the half-cell reaction (Li++e=Li), uncontrolled dendritic Li penetrates the separator and solid electrolyte interphase layer. When employed as a composite scaffold for lithium metal deposition, there are many advantage to using this framework: 1) the VSP-CoS2 substrate provides a high specific surface area to dissipate the ion flux and mass transfer and acts as a pre-catalyst, 2) the catalytic Co center favors the charge transfer process and preferentially binds the Li+ with the enhanced electrical fields, and 3) the VSP structure guides the metallic propagation along the nanosheet 2D orientation without the protrusive dendrites. All these features enable the VSP structure in metallic batteries with encouraging performances.
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| 14. |
- Li, Yunxiang, et al.
(författare)
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De-agglomeration of IZM-2 zeolite crystals by post-synthetic treatment
- 2016
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 225, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- Highly intergrown nanocrystals are commonly observed in zeolite samples, and the densely packed agglomerates may result in small secondary porosity, which restricts the advantage of hierarchical structures. In this work we take IZM-2 zeolite as an example to demonstrate a post-treatment method with diluted hydrofluoric acid solution, which de-agglomerates intergrown zeolite nanocrystals and improves the secondary porosity. The treated samples preserve high crystallinity, similar framework composition and distinctively higher external surface area compared to the agglomerated ones. The results show that this treatment is an effective method for de-agglomeration of intergrown nanocrystals without affecting the original framework.
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| 15. |
- Liang, Jie, et al.
(författare)
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A Crystalline Mesoporous Germanate with 48-Ring Channels for CO2 Separation
- 2015
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 54:25, s. 7290-7294
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Tidskriftsartikel (refereegranskat)abstract
- One of the challenges in materials science has been to prepare crystalline inorganic compounds with mesopores. Although several design strategies have been developed to address the challenge, expansion of pore sizes in inorganic materials is more difficult compared to that for metal-organic frameworks. Herein, we designed a novel mesoporous germanate PKU-17 with 3D 48 x 16 x 16-ring channels by introducing two large building units (Ge-10 and Ge-7 clusters) into the same framework. The key for this design strategy is the selection of 2-propanolamine (MIPA), which serves as the terminal species to promote the crystallization of Ge-7 clusters. Moreover, it is responsible for the coexistence of Ge-10 and Ge-7 clusters. To our knowledge, the discovery of PKU-17 sets a new record in pore sizes among germanates. It is also the first germanate that exhibits a good selectivity toward CO2 over N-2 and CH4.
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| 16. |
- Liang, Jie, et al.
(författare)
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CHA-type zeolites with high boron content : Synthesis, structure and selective adsorption properties
- 2014
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 194, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- Borosilicate zeolites with CHA-type framework are synthesized hydrothermally by using N,N,N-trimethylcyclohexylammonium hydroxide as structure directing agent. The use of this cation induces an increase of boron content in the CHA-type zeolites, and the Si/B ratios of the as-synthesized samples is in the range of 11.8-6.9. Rietveld refinements of the calcinated samples reveal a contraction of unit cells with the increase of boron content, and the 8-ring opening window of cha cavity becomes narrower. B-11 MAS NMR shows that all the boron atoms are incorporated into the framework as tetrahedral BO4 units in the as-synthesized samples. The thermal stability of these CHA-type borosilicates decreases with the increase of boron content, and the framework can retain up to 800 degrees C. These borosilicates, with the BET surfaces of 583-632 m(2)/g, show a high adsorption capacity for H-2 at 77 K, 900 mmHg and a preferential adsorption for CO2 at 273 K. This selective adsorption property enables CHA-type borosilicates to be potential materials as CO2 adsorbent.
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| 17. |
- Liang, Zuozhong, et al.
(författare)
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Novel insight into the epitaxial growth mechanism of six-fold symmetrical beta-Co(OH)(2)/Co(OH)F hierarchical hexagrams and their water oxidation activity
- 2018
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 271, s. 526-536
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Tidskriftsartikel (refereegranskat)abstract
- The six-fold symmetry widely presents in both natural and artificial architectures. Understanding the growth mechanism of six-fold symmetrical materials is of fundamental interest and significance. Herein, we report the formation process of beta-Co(OH)(2)/Co(OH)F hierarchical hexagrams with a six-fold symmetrical arrangement. Our results demonstrate that hexagonal beta-Co(OH)(2) plates are first formed under the reaction condition. These hexagonal plates then act as templates for the growth of Co(OH)F nanorods. The intermediate material is therefore composed of plate-like beta-Co(OH)(2) hexagonal cores appended with six rod-like Co(OH)F branches, giving the beta-Co(OH)(2)/Co(OH)F hybrid. After prolonged reaction, the beta-Co(OH)(2) hexagons can be completely converted, leading to authentic six-branched Co(OH)F nanorods as the final product. Consequently, for both intermediate and final materials, the Co(OH)F nanorods are arranged with a six-fold symmetry. Importantly, these Co(OH)F nanorods grow along beta-Co(OH)(2) hexagon edges as lateral branches instead of perpendicular to hexagons. This uncommon epitaxial growth mechanism is considered to be a result of the matching between the b-axis of Co(OH)F crystals and the a-axis of beta-Co(OH)(2) crystals, which is beneficial for the electrocatalysis. The beta-Co(OH)(2)/Co(OH)F hierarchical hexagrams show enhanced water oxidation activity compared to the pure beta-Co(OH)(2) and Co(OH)F.
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| 18. |
- Liang, Zuozhong, et al.
(författare)
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Quasi-single-crystalline CoO hexagrams with abundant defects for highly efficient electrocatalytic water oxidation
- 2018
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 9:34, s. 6961-6968
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Tidskriftsartikel (refereegranskat)abstract
- Defects and structural long-range ordering have been recognized as two crucial characters for advanced electrocatalysts. However, these two features have rarely been achieved together. Herein, we report the preparation of single-crystalline CoO hexagrams and demonstrate their exceptional electrocatalytic properties for water oxidation. The quasi-single-crystalline CoO hexagrams, prepared at the critical phase transition point of -Co(OH)(2)/Co(OH)F hexagrams, possess both abundant oxygen vacancies as defects and structural long-range ordering. The matching between the b-axis of Co(OH)F crystals and the a-axis of -Co(OH)(2) crystals is critical for the formation of the CoO hexagram single crystals. The quasi-single-crystalline CoO hexagrams with abundant defects are highly efficient for water oxidation by delivering a 10 mA cm(-2) current density at a low overpotential of 269 mV in a 1 M KOH aqueous solution.
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| 19. |
- Lin, Junzhong, et al.
(författare)
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Synthesis of hierarchical MCM-22 zeolite via a swelling and pillaring approach
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are type of microporous crystalline material which have been widely used in various aspects of industry, such as separation, adsorption, and catalysis. However, great diffusion limitation can be provoked due to small pore size of mircoporus framework in catalytic reactions. Hierarchical zeolites have been proved to be a successful alternative to solve the diffusion problem. Particularly, the synthesis of hierarchical porous zeolite by swelling and pillaring lamellar MWW zeolitic precursor has been proved as an efficient approach to solve the diffusion limitations in the catalytic reactions. In this work, hierarchical MWW zeolite has been synthesized by swelling and pillaring of lamellar MWW zeolitic precursor (MCM-22) using D4R building units. The synthesis procedure has been carefully studied by various characterization methods, such as PXRD, TEM, N2 adsorption-desorption and etc.
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| 20. |
- Lin, Junzhong, et al.
(författare)
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Titanium incorporated hierarchical porous silicate synthesized using D4R as building blocks
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Hierarchical porous materials as catalyst have provoked great attention recent years considering that it can offer enhanced molecular diffusion and mass transfer during the reaction. Titanium containing hierarchical porous silicate material has been successfully synthesized in present work. Double-four-ring units were used as the basic building blocks to construct the desired material. Both micropores and mesopores were found in the as synthesized material. The local structure of incorporated titanium species was carefully studied using various characterization techniques, such as XPS, UV-vis, XANES and EXAFS. Tetrahedral coordinated titanium can be mostly found in the as synthesized material in this work, the distorted the local structure was further revealed by using EXAFS.
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| 21. |
- Liu, Ben, et al.
(författare)
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A facile synthesis of Fe3C@mesoporous carbon nitride nanospheres with superior electrocatalytic activity
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 8:10, s. 5441-5445
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Tidskriftsartikel (refereegranskat)abstract
- We report a colloidal amphiphile-templating approach to preparing nanosized Fe3C encapsulated within mesoporous nitrogen-doped carbon nanospheres (Fe3C@mCN). The obtained Fe3C@mCN hybrids having a high surface area and ultrafine Fe3C nanocrystals exhibited superior activity and durability for oxygen reduction.
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| 22. |
- Liu, Ben, et al.
(författare)
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Unconventional structural and morphological transitions of nanosheets, nanoflakes and nanorods of AuNP@MnO2
- 2016
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:17, s. 6447-6455
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2-D) layered inorganic materials with ultra-high surface area and mechanical strength have shown impressive photo-/electro-catalytic activities. We herein report a facile synthetic strategy to grow monodispersed 2-D MnO2 nanosheet on an individual gold nanoparticle (AuNP@MnO2 nanosheet), and demonstrate that the strongly interacted AuNP and MnO2 nanosheet could greatly improve the electrocatalytic activity of the MnOx family for electrocatalytic oxygen reduction reactions (ORRs). AuNP@MnO2 nanosheets were prepared using a hydrothermal reduction of KMnO4 by citrate ligands capped on AuNPs. Because of the metastability of the layered MnO2 nanosheets, we observed unconventional structural and morphological transitions of amorphous MnO2 nanosheets to delta-MnO2 nanoflakes, and eventually to alpha-MnO2 nanorods under hydrothermal conditions. The layered MnO2 nanosheets underwent a structural expansion to nanoflakes before the curling and re-folding of layered MnO2 nanosheets occurred. The intermediate states and structural transitions via a layer compression, for the first time, were experimentally recorded at a single-NP scale using electron microscopy. Moreover, we found the electrocatalytic activity of AuNP@MnO2 nanosheets was enhanced roughly 30-40 times, compared to that of pure MnO2 nanosheets and AuNPs. The strong interaction of metal-oxide interfaces (MnO2 nanosheets and AuNPs) was likely responsible for the improved electrocatalytic activity. This interaction of MnO2 and AuNPs was weakened in the course of hydrothermal treatment where partially positively charged Au+ was reduced at elevated temperatures, accompanying with the decrease of ORR activity. This insight into the effect of topological nanostructures and metal-oxide interactions on the electrocatalytic performance of the MnOx family is believed to illustrate an alternative pathway to develop new efficient electrocatalysts.
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| 23. |
- Liu, Kai, et al.
(författare)
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Porous Au-Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis
- 2016
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:6, s. 3675-3681
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of similar to 1.3 x 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.
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| 24. |
- Lv, Hao, et al.
(författare)
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Synthesis and Crystal-Phase Engineering of Mesoporous Palladium-Boron Alloy Nanoparticles
- 2020
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Ingår i: ACS central science. - : American Chemical Society (ACS). - 2374-7943 .- 2374-7951. ; 6:12, s. 2347-2353
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Tidskriftsartikel (refereegranskat)abstract
- Rational design and synthesis of noble metal nanomaterials with desired crystal phases (atomic level) and controllable structures/morphologies (mesoscopic level) are paramount for modulating their physiochemical properties. However, it is challenging to simultaneously explore atomic crystal-phase structures and ordered mesoscopic morphologies. Here, we report a simple synergistic templating strategy for the preparation of palladium-boron (Pd-B) nanoparticles with precisely controllable crystal-phases and highly ordered mesostructures. The engineering of crystal-phase structures at atomic levels is achieved by interstitially inserting metallic B atoms into face-centered cubic mesoporous Pd (fcc-mesoPd) confined in a mesoporous silica template. With the gradual insertion of B atoms, fcc-mesoPd is transformed into fcc-mesoPd(5)B, hcp-mesoPd(2)B with randomly distributed B atoms (hcp-mesoPd(2)B-r), and hcp-mesoPd(2)B with an atomically ordered B sequence (hcp-mesoPd(2)B-o) while preserving well-defined mesostructures. This synergistic templating strategy can be extended to engineer crystal-phase structures with various mesostructures/morphologies, including nanoparticles, nanobundles, and nanorods. Moreover, we investigate the crystal-phase-dependent catalytic performance toward the reduction reaction of p-nitrophenol and find that hcp-mesoPd(2)B-o displays much better catalytic activity. This work thus paves a new way for the synthesis of hcp-Pd2B nanomaterials with mesoscopically ordered structure/morphology and offers new insights of fcc-to-hcp evolution mechanisms which could be applied on other noble metal-based nanomaterials for various targeted applications.
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| 25. |
- Verho, Oscar, et al.
(författare)
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Application of Pd Nanoparticles Supported on Mesoporous Hollow Silica Nanospheres for the Efficient and Selective Semihydrogenation of Alkynes
- 2016
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Ingår i: ChemCatChem. - : Wiley-VCH Verlagsgesellschaft. - 1867-3880 .- 1867-3899. ; 8:4, s. 773-778
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the preparation of a heterogeneous catalyst consisting of 1-2nm sized Pd nanoparticles supported on amino-functionalized mesoporous hollow silica nanospheres and its use for the semihydrogenation of mono- and disubstituted alkynes is reported. By utilizing this Pd nanocatalyst together with the green poisoning agent DMSO, high yields of the desired alkenes could be achieved, while suppressing the degree of over-reduction to alkanes. To our delight, the Pd nanocatalyst displayed remarkable chemoselectivity towards the alkyne moiety, allowing the transformation to be carried out in the presence of other reducible functionalities, such as halogens, carbonyl, and nitro groups.
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