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RISS 인기검색어
- 검색키워드
- 저자 : Abroshan, Hadi (검색결과 4 건)
- 무료
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On the structural stability of ionic liquid–IRMOF composites: a computational study
Abroshan, Hadi,Kim, Hyung J. The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.9
<P>The structural stability of isoreticular metal organic frameworks, IRMOF-1 and IRMOF-10, confining ionic liquids (ILs) inside their nano-porous cavities is studied via molecular dynamics (MD) simulations. Imidazolium-and pyridinium-based ILs, including BMI+PF6-, BMI+Br-, BMI+Tf2N-, BMI(+)DCA(-), and BuPy+Tf2N- (BMI+ = 1-butyl-3-methylimidazolium, PF6- = hexafluorophosphate, Br- = bromide, Tf2N- = bis(trifluoromethylsulfonyl)imide, DCA(-) = dicyanamide, and BuPy+ = N-butylpyridinium), at different loadings are considered. It is found that both IRMOFs are structurally unstable and deform dramatically from their crystal structure in the presence of ILs. The interactions between the metallic parts of IRMOFs and IL anions play a major role in structural disruption and collapse of these MOFs. Thus elongated anions such as Tf2N and DCA(-) that can interact with two different metal sites tend to lower IRMOF stability compared to spherical anions such as Br-1 and PF6-. A further analysis via density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations lends support to the MD results regarding structural instability of IRMOFs in the presence of ILs.</P>
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Li, Gao,Abroshan, Hadi,Chen, Yuxiang,Jin, Rongchao,Kim, Hyung J. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.45
<P>The catalytic activity of Au<SUB>25</SUB>(SR)<SUB>18</SUB> nanoclusters (R = C<SUB>2</SUB>H<SUB>4</SUB>Ph) for the aldehyde hydrogenation reaction in the presence of a base, e.g., ammonia or pyridine, and transition-metal ions M<SUP>z+</SUP>, such as Cu<SUP>+</SUP>, Cu<SUP>2+</SUP>, Ni<SUP>2+</SUP> and Co<SUP>2+</SUP>, as a Lewis acid is studied. The addition of a Lewis acid is found to significantly promote the catalytic activity of Au<SUB>25</SUB>(SR)<SUB>18</SUB>/CeO<SUB>2</SUB> in the hydrogenation of benzaldehyde and a number of its derivatives. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry in conjunction with UV–vis spectroscopy confirm the generation of new species, Au<SUB>25-<I>n</I></SUB>(SR)<SUB>18-<I>n</I></SUB> (<I>n</I> = 1–4), in the presence of a Lewis acid. The pathways for the speciation of Au<SUB>24</SUB>(SR)<SUB>17</SUB> from its parent Au<SUB>25</SUB>(SR)<SUB>18</SUB> nanocluster as well as its structure are investigated via the density functional theory (DFT) method. The adsorption of M<SUP><I>z</I>+</SUP> onto a thiolate ligand “SR” of Au<SUB>25</SUB>(SR)<SUB>18</SUB>, followed by a stepwise detachment of “SR” and a gold atom bonded to “SR” (thus an “Au-SR” unit) is found to be the most likely mechanism for the Au<SUB>24</SUB>(SR)<SUB>17</SUB> generation. This in turn exposes the Au<SUB>13</SUB>-core of Au<SUB>24</SUB>(SR)<SUB>17</SUB> to reactants, providing an active site for the catalytic hydrogenation. DFT calculations indicate that M<SUP>z+</SUP> is also capable of adsorbing onto the Au<SUB>13</SUB>-core surface, producing a possible active metal site of a different kind to catalyze the aldehyde hydrogenation reaction. This study suggests, for the first time, that species with an open metal site like adducts [nanoparticle-M]<SUP>(<I>z</I>-1)+</SUP> or fragments Au<SUB>25-<I>n</I></SUB>(SR)<SUB>18-<I>n</I></SUB> function as the catalysts rather than the intact Au<SUB>25</SUB>(SR)<SUB>18</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-45/jacs.5b07716/production/images/medium/ja-2015-07716c_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b07716'>ACS Electronic Supporting Info</A></P>
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Song, Yongbo,Abroshan, Hadi,Chai, Jinsong,Kang, Xi,Kim, Hyung J.,Zhu, Manzhou,Jin, Rongchao American Chemical Society 2017 Chemistry of materials Vol.29 No.7
<P>In this work, we report a new size conversion from [Au-25(SePh)(18)](-) to [Au-23(SePh)(16)](-) nanoclusters under the reductive condition (NaBH4). This novel transformation induced by only reductant has not been reported before in the field of gold nanocluster. The conversion process is studied via MALDI mass spectrometry, and UV-vis spectroscopy. These results demonstrate that the [Au-23(SePh)(16)](-) nanocluster is directly obtained by pulling out two units of 'Au-SeR' from the [Au-25(SePh)(18)](-) nanocluster, which is similar to the 'small molecular' reaction. In order to further understand this novel conversion, DFT calculations were performed, in which, with addition of two H- in the [Au-25(SeH)(18)](-) model, two Au atoms will depart from the structure of the [Au-25(SeH)(18)](-), which is consistent with the experimental results. Furthermore, the as prepared [Au-23(SePh)(16)](-) nanoclusters can be converted into [Au-25(PET)(18)](-) nanocluster (PET = SCH2CH2Ph) with excess PET under the reductive condition, which is quite remarkable due to a stronger bond of Au-Se in comparison to Au-S of the final product. Interestingly, the number of the PET ligands on the surface of the 25-atoms nanocluster can be controlled by the addition of the reductant. Based on these results, a circularly progressive mechanism of ligand exchange is proposed. This may offer a new approach to synthesis of new gold nanoclusters and also have significant contribution for understanding and further exploration of the mechanism of ligand exchange.</P>
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Zhao, Shuo,Jin, Renxi,Abroshan, Hadi,Zeng, Chenjie,Zhang, Hui,House, Stephen D.,Gottlieb, Eric,Kim, Hyung J.,Yang, Judith C.,Jin, Rongchao American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.3
<P>Electrocatalytic water splitting to produce hydrogen comprises the hydrogen and oxygen evolution half reactions (HER and OER), with the latter as the bottleneck process. Thus, enhancing the OER performance and understanding the mechanism are critically important. Herein, we report a strategy for OER enhancement by utilizing gold nanoclusters to form cluster/CoSe2 composites; the latter exhibit largely enhanced OER activity in alkaline solutions. The Au-25/CoSe2 composite affords a current density of 10 mA cm(-2) at small overpotential of, similar to 0.43 V (cf. CoSe2: similar to 0.52 V). The ligand and gold cluster size can also tune the catalytic performance of the composites. Based upon XPS analysis and DFT simulations, we attribute the activity enhancement to electronic interactions between nanocluster and CoSe2, which favors the formation of the important intermediate (OOH) as well as the desorption of oxygen molecules over Au-11/CoSe2 composites in the process of water oxidation. Such an atomic level understanding may provide some guidelines for design of OER catalysts.</P>
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