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1.
Chem Commun (Camb) ; 2020 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-31994548

RESUMO

The rational manipulation of reaction intermediates is crucial for achieving high-performance heterogeneous catalysis. Herein, using in situ Fourier transform infrared-diffuse reflection (FTIR) analysis, we report that the methanol oxidation reaction (MOR) intermediates can be controlled by precisely tuning the location and content of Ru on the Pt-Ru alloy surface.

2.
ACS Appl Mater Interfaces ; 11(16): 14862-14870, 2019 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-30933467

RESUMO

An effective design for counter electrode (CE) catalytic materials with superior catalytic activity, excellent stability, low cost, and a facile fabrication process is urgently needed for industrialization of dye-sensitized solar cells (DSSCs). Herein, we report a facile in situ method to fabricate transparent CoS1.097 anchored on an N-doped carbon film electrode through sulfurization of a cobalt-metalloporphyrin metal-organic framework thin film on fluorine-doped tin oxide glass. The transparent film as counter electrode in bifacial DSSCs exhibited higher power conversion efficiency (9.11% and 6.64%), respectively, from front and rear irradiation than that of Pt (8.04% and 5.87%). The uniformly dispersed CoS1.097 nanoparticles on an N-doped carbon film provide a large catalytic active area and facilitate the electron transfer, which leads to the excellent catalytic ability of the CoS1.097@N-doped carbon film. In addition, the in situ preparation of the uniform film with a nanosheet structure offers high electrical conductivity and unobstructed access for the diffusion of triiodide to available electroactive sites, resulting in excellent device performance with superior long-term stability over 1000 h under natural conditions.

3.
ACS Nano ; 12(12): 12369-12379, 2018 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-30508382

RESUMO

As one of the most remarkable oxygen evolution reaction (OER) electrocatalysts, metal chalcogenides have been intensively reported during the past few decades because of their high OER activities. It has been reported that electron-chemical conversion of metal chalcogenides into oxides/hydroxides would take place after the OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during the OER for these electrocatalysts, has not been understood yet; therefore a direct observation for the electrocatalytic water oxidation process, especially at nano or even angstrom scale, is urgently needed. In this research, by employing advanced Cs-corrected transmission electron microscopy (TEM), a step by step oxidational evolution of amorphous electrocatalyst CoS x into crystallized CoOOH in the OER has been in situ captured: irreversible conversion of CoS x to crystallized CoOOH is initiated on the surface of the electrocatalysts with a morphology change via Co(OH)2 intermediate during the OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process has also been confirmed by multiple applications of X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (FTIR), and other ex situ technologies. Moreover, on the basis of this discovery, a high-efficiency electrocatalyst of a nitrogen-doped graphene foam (NGF) coated by CoS x has been explored through a thorough structure transformation of CoOOH. We believe this in situ and in-depth observation of structural evolution in the OER measurement can provide insights into the fundamental understanding of the mechanism for the OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for water splitting.

4.
Micromachines (Basel) ; 9(5)2018 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-30424167

RESUMO

In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4'-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au electrodes. For the BPY molecular junction, two sets of conductance were found with values around 10-3.1 G0 (high G) and 10-3.7 G0 (low G). The addition of nitro side-group(s) onto the pyridine ring resulted in lower conductance of 10-3.8 G0 for BPY-N and 10-3.9 G0 for BPY-2N, respectively, which can be attributed to the twist angle of two pyridine rings. Moreover, the steric hindrance of nitro group(s) also affects the contacting configuration of electrode-molecule-electrode. As a consequence, only one set of conductance value was observed for BPY-N and BPY-2N. Our work clearly shows the important role of side-groups on the electron transport of single-molecule junctions.

5.
Materials (Basel) ; 11(10)2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-30275372

RESUMO

Metal⁻organic framework thin film-based dye sensitized solar cell is fabricated with highly oriented, crystalline, and porous Zn-perylene metal-organic framework (MOF) thin film (SURMOF) which is integrated with Bodipy embedded in poly(methyl methacrylate). It has been demonstrated that the photocurrent can be enhanced by a factor of 5 relative to Zn-perylene MOF thin film due to triplet⁻triplet annihilation up-conversion between the Bodipy/PMMA sensitizer and the Zn-perylene MOF thin film acceptor using Co(bpy)32+/3+ as redox mediator.

6.
ACS Appl Mater Interfaces ; 10(10): 8786-8796, 2018 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-29446610

RESUMO

Highly efficient, robust, and cheap water oxidation electrodes are of great significance for large-scale production of hydrogen by electrolysis of water. Here, a self-supported stainless steel (SS) nanocone array coated with a layer of nanoparticulate Ni-Fe oxides/(oxy)hydroxides was fabricated by a facile, low-cost, and easily scalable two-step process. The construction of a nanocone array on the surface of an AISI 304 SS plate by acid corrosion greatly enlarged the specific surface area of the substrate, and the subsequent formation of a layer of Ni-Fe oxides/(oxy)hydroxides featuring the NiFe2O4 spinel phase on the nanocone surface by electrodeposition of [Ni(bpy)3]2+ significantly enhanced the intrinsic activity and the stability of the SS-based electrode. The as-prepared electrode demonstrated superior activity for the oxygen evolution reaction (OER) in 1 M KOH, with 232 and 280 mV overpotentials to achieve 10 and 100 mA cmgeo-2 current densities, respectively. The high activity of the electrode was maintained over 340 h of chronopotentiometric test at 20 mA cmgeo-2, and the electrode also showed good stability over 100 h of electrolysis at high current density (200 mA cm-2). More important for practical application, the used SS-based electrode can be easily regenerated with the original OER activity. The superior activity of this SS-based electrode stems from synergistic combination of high conductivity of the SS substrate, a large electrochemically active surface area of the nanocone array, and a uniformly coated nanoparticulate Ni-Fe oxide/(oxy)hydroxide layer with an optimal Ni/Fe ratio.

7.
Chem Soc Rev ; 46(19): 5730-5770, 2017 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-28682401

RESUMO

Surface-supported metal-organic framework thin films are receiving increasing attention as a novel form of nanotechnology. New deposition techniques that enable the control of the film thickness, homogeneity, morphology, and dimensions with a huge number of metal-organic framework compounds offer tremendous opportunities in a number of different application fields. In response to increasing demands for environmental sustainability and cleaner energy, much effort in recent years has been devoted to the development of MOF thin films for applications in photovoltaics, CO2 reduction, energy storage, water splitting, and electronic devices, as well as for the fabrication of membranes. Although existing applications are promising and encouraging, MOF thin films still face numerous challenges, including the need for a more thorough understanding of the thin-film growth mechanism, stability of the internal and external interfaces, strategies for doping and models for charge carrier transport. In this paper, we review the recent advances in MOF thin films, including fabrication and patterning strategies and existing nanotechnology applications. We conclude by listing the most attractive future opportunities as well as the most urgent challenges.

8.
Beilstein J Nanotechnol ; 8: 892-905, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28503400

RESUMO

To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs), triptycyl thiolates and selenolates with and without methylene spacers on Au(111) surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se-Au binding energy in the investigated SAMs was found to be higher than the S-Au binding energy.

9.
Angew Chem Int Ed Engl ; 55(41): 12683-7, 2016 10 04.
Artigo em Inglês | MEDLINE | ID: mdl-27599895

RESUMO

We have studied the magnetic properties of the SURMOF-2 series of metal-organic frameworks (MOFs). Contrary to bulk MOF-2 crystals, where Cu(2+) ions form paddlewheels and are antiferromagnetically coupled, in this case the Cu(2+) ions are connected via carboxylate groups in a zipper-like fashion. This unusual coupling of the spin 1/2 ions within the resulting one-dimensional chains is found to stabilize a low-temperature, ferromagnetic (FM) phase. In contrast to other ordered 1D systems, no strong magnetic fields are needed to induce the ferromagnetism. The magnetic coupling constants describing the interaction between the individual metal ions have been determined in SQUID experiments. They are fully consistent with the results of ab initio DFT electronic structure calculations. The theoretical results allow the unusual magnetic behavior of this exotic, yet easy-to-fabricate, material to be described in a detailed fashion.

10.
PeerJ ; 4: e2451, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27672506

RESUMO

OBJECTIVE: The skin is an important immunological barrier of the body as well as an optimal route for vaccine administration. Gua Sha, which involves press-stroke treatment of the skin, is an effective folk therapy, widely accepted in East Asia, for various symptoms; however, the mechanisms underlying its therapeutic effects have not been clarified. We investigated the influence of Gua Sha on the immunological features of the skin. METHODS: Gua Sha was performed on BALB/c mice and the effects were evaluated using anatomical, histological, and cytometric methods as well as cytokine determination locally and systemically. The effect on intradermal vaccination was assessed with antigen-specific subtype antibody responses. RESULTS: Blood vessel expansion, erythrocyte extravasation, and increased ratios of immune active cells were observed in the skin tissue following the treatment. Pro-inflammatory cytokines were up-regulated, and immunosuppressive cytokines, down-regulated, in the treated and untreated skin and systemic circulation; no obvious variations were detected in case of anti-inflammatory cytokines. Interestingly, intradermal delivery of a model vaccine following Gua Sha induced about three-fold higher IgG titers with a more Th1-biased antibody subtype profile. CONCLUSION: Gua Sha treatment can up-regulate the innate and adaptive immune functions of the skin and boost the response against intradermal antigens. Thus, Gua Sha may serve as a safe, inexpensive, and independent physical adjuvant for intradermal vaccination.

11.
Opt Express ; 23(11): 13725-33, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-26072745

RESUMO

Monolithic, crystalline and highly oriented coordination network compound (CNC) Prussian blue (PB) thin films have been deposited though different routes on conductive substrates. Characterization of the monolithic thin films reveals a long-term stability, even after many redox cycles the crystallinity as well as the high orientation remain intact during the electrochromic switching process.

12.
Angew Chem Int Ed Engl ; 54(25): 7441-5, 2015 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-25960115

RESUMO

For inorganic semiconductors crystalline order leads to a band structure which gives rise to drastic differences to the disordered material. An example is the presence of an indirect band gap. For organic semiconductors such effects are typically not considered, since the bands are normally flat, and the band-gap therefore is direct. Herein we show results from electronic structure calculations demonstrating that ordered arrays of porphyrins reveal a small dispersion of occupied and unoccupied bands leading to the formation of a small indirect band gap. We demonstrate herein that such ordered structures can be fabricated by liquid-phase epitaxy and that the corresponding crystalline organic semiconductors exhibit superior photophysical properties, including large charge-carrier mobility and an unusually large charge-carrier generation efficiency. We have fabricated a prototype organic photovoltaic device based on this novel material exhibiting a remarkable efficiency.

13.
Phys Chem Chem Phys ; 16(33): 17918-23, 2014 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-25046605

RESUMO

Crystalline, highly orientated surface-anchored MOF thin films, grown on Au substrates, were prepared using liquid-phase epitaxy (LPE). The successful loading of La(3+) ions into the Cu3(BTC)2 (HKUST-1) SURMOFs (surface-mounted metal-organic frameworks) was monitored using X-ray diffraction (XRD). Theoretical calculations using classical force-field based Monte Carlo simulations yield a structure with two La(3+) ions within the large Cu3(BTC)2 pores, in full agreement with experimental results on the composition of these films and the relative intensities of the XRD peaks. Implications of these findings for using MOF thin films for electronic applications are briefly discussed.

14.
Chemistry ; 20(32): 9879-82, 2014 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-24938623

RESUMO

Oriented circular dichroism (OCD) is explored and successfully applied to investigate chiral surface-anchored metal-organic frameworks (SURMOFs) based on camphoric acid (D- and Lcam) with the composition [Cu2(Dcam)(2x)(Lcam)(2-2x)(dabco)]n (dabco = 1,4-diazabicyclo-[2.2.2]-octane). The three-dimensional chiral SURMOFs with high-quality orientation were grown on quartz glass plates by using a layer-by-layer liquid-phase epitaxy method. The growth orientation, as determined by X-ray diffraction (XRD), could be switched between the [001] and [110] direction by using either OH- or COOH-terminated substrates. These SURMOFs were characterized by using OCD, which confirmed the ratio as well as the orientation of the enantiomeric linker molecules. Theoretical computations demonstrate that the OCD band intensities of the enantiopure [Cu2(Dcam)2(dabco)]n grown in different orientations are a direct result of the anisotropic nature of the chiral SURMOFs. Finally, the enantiopure [Cu2(Dcam)2(dabco)]n and [Cu2(Lcam)2(dabco)]n SURMOFs were loaded with the two chiral forms of ethyl lactate [(+)-ethyl-D-lactate and (-)-ethyl-L-lactate)]. An enantioselective enrichment of >60 % was observed by OCD when the chiral host scaffold was loaded from the racemic mixture.


Assuntos
Compostos Organometálicos/química , Dicroísmo Circular , Cristalização , Modelos Moleculares , Estereoisomerismo , Difração de Raios X
15.
Nano Lett ; 14(3): 1526-9, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24512342

RESUMO

We demonstrate the realization of hierarchically organized MOF (metal-organic framework) multilayer systems with pronounced differences in the size of the nanoscale pores. Unusually large values for the lattice constant mismatch at the MOF-MOF heterojunctions are made possible by a particular liquid-phase epitaxy process. The multiheteroepitaxy is demonstrated for the isoreticular SURMOF-2 series [ Liu et al. Sci. Rep. 2012 , 2 , 921 ] by fabricating trilayer systems with lattice constants of 1.12, 1.34, and 1.55 nm. Despite these large (20%) lattice mismatches, highly crystalline, oriented multilayers were obtained. A thorough theoretical analysis of the MOF-on-MOF heterojunction structure and energetics allows us to identify the two main reasons for this unexpected tolerance of large lattice mismatch: the healing of vacancies with acetate groups and the low elastic constant of MOF materials.

16.
J Am Chem Soc ; 136(1): 8-11, 2014 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-24328287

RESUMO

We report the fabrication of 3D, highly porous, covalently bound polymer films of homogeneous thickness. These surface-bound gels combine the advantages of metal-organic framework (MOF) materials, namely, the enormous flexibility and the large size of the maximum pore structures and, in particular, the possibility to grow them epitaxially on modified substrates, with those of covalently connected gel materials, namely, the absence of metal ions in the deposited material, a robust framework consisting of covalent bonds, and, most importantly, pronounced stability under biological conditions. The conversion of a SURMOF (surface-mounted MOF) yields a surface-grafted gel. These SURGELs can be loaded with bioactive compounds and applied as bioactive coatings and provide a drug-release platform in in vitro cell culture studies.


Assuntos
Géis/química , Compostos Organometálicos/química , Bactérias , Química Click , Cobre/química , Reagentes para Ligações Cruzadas/química , Microscopia de Força Atômica , Tamanho da Partícula , Porosidade , Propriedades de Superfície
17.
Langmuir ; 29(51): 15958-64, 2013 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-24283622

RESUMO

In this work, we demonstrate that strain-promoted azide-alkyne cycloaddition (SPAAC) yields virtually complete conversion in the context of the post-synthetic modification (PSM) of metal-organic frameworks (MOFs). We use surface-anchored MOF (SURMOF) thin films, [Zn2(N3-bdc)2(dabco)], grown on modified Au substrates using liquid-phase epitaxy (LPE) as a model system to first show that, with standard click chemistry, presently, the most popular method for rendering additional functionality to MOFs via PSM, quantitative conversion yields, cannot be reached. In addition, it is virtually impossible to avoid contaminations of the product by the cytotoxic Cu(I) ions used as a catalyst, a substantial problem for applications in life sciences. Both problems could be overcome by SPAAC, where a metal catalyst is not needed. After optimization of reaction conditions, conversion yields of nearly 100% could be achieved. The consequences of these results for various applications of PSM-modified SURMOFs in the fields of membranes, optical coatings, catalysis, selective gas separation, and chemical sensing are briefly discussed.


Assuntos
Química Click , Compostos Organometálicos/química , Zinco/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Catálise , Técnicas de Química Sintética , Cobre/química , Corantes Fluorescentes/química , Compostos Organometálicos/síntese química , Molhabilidade
18.
Adv Mater ; 25(33): 4631-5, 2013 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-23813674

RESUMO

Flexible in many aspects: inkjet printing of metal-organic frameworks permits their larger area, high-resolution deposition in any desired pattern, even in the form of gradients or shades. When flexible substrates are used, many applications can be envisioned, such as sensing and capture of hazardous gases for personal safety measures.

19.
Phys Chem Chem Phys ; 15(12): 4130-5, 2013 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-23400238

RESUMO

Surface-enhanced Raman spectroscopy (SERS) benefits from the enhanced electromagnetic field of the localized surface plasmon resonance effect of metallic (especially coinage metals) nanoparticles or nanostructures. The detection sensitivity and reproducibility of SERS measurement appear to be the two critical issues in SERS. To solve the problem associated with traditional nanoparticle aggregates and SERS substrates, we propose in this work single particle SERS. We prepared uniform gold microspheres with controllable size and surface roughness using an etching-assisted seed-mediated method. Single particle dark-field spectroscopy and SERS measurements show that particles with a larger roughness give a stronger SERS signal, but still retain a good reproducibility. This study points to the promising future of the practical application of the single particle SERS technique for trace analysis.

20.
Sci Rep ; 2: 921, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23213357

RESUMO

A novel class of metal organic frameworks (MOFs) has been synthesized from Cu-acetate and dicarboxylic acids using liquid phase epitaxy. The SURMOF-2 isoreticular series exhibits P4 symmetry, for the longest linker a channel-size of 3 × 3 nm(2) is obtained, one of the largest values reported for any MOF so far. High quality, ab-initio electronic structure calculations confirm the stability of a regular packing of (Cu(++))(2)- carboxylate paddle-wheel planes with P4 symmetry and reveal, that the SURMOF-2 structures are in fact metastable, with a fairly large activation barrier for the transition to the bulk MOF-2 structures exhibiting a lower, twofold (P2 or C2) symmetry. The theoretical calculations also allow identifying the mechanism for the low-temperature epitaxial growth process and to explain, why a synthesis of this highly interesting, new class of high-symmetry, metastable MOFs is not possible using the conventional solvothermal process.


Assuntos
Ácidos Carboxílicos/química , Cobre/química , Compostos Organometálicos/química , Biologia Computacional , Cristalografia por Raios X , Modelos Moleculares , Estrutura Molecular
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