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1.
ACS Nano ; 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31478375

RESUMO

The discovery in 1974 of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is considered a landmark in the history of spectroscopic and analytical techniques. Much experimental and theoretical effort has been spent toward understanding the surface enhanced Raman scattering (SERS) effect, and demonstrating its potential toward various types of ultrasensitive sensing applications in a wide variety of fields. Forty five years later, SERS has blossomed as an extremely rich area of research and technology, but additional efforts are still needed before it can be routinely used as a commercial product. In this Review, prominent authors from all over the world joined efforts to summarize the current state-of-the-art in understanding and using SERS, as well as to propose what can be expected in the near future, in terms of research, applications, and technological development.

2.
Artigo em Inglês | MEDLINE | ID: mdl-31373130

RESUMO

Adsorption plays a critical role in surface and interface processes. Fractional surface coverage and adsorption free energy are two essential parameters of molecular adsorption. However, although adsorption at the solid-gas interface has been well-studied, and some adsorption models were proposed more than a century ago, challenges remain for the experimental investigation of molecular adsorption at the solid-liquid interface. Herein, we report the statistical and quantitative single-molecule measurement of adsorption at the solid-liquid interface by using the single-molecule break junction technique. The fractional surface coverage was extracted from the analysis of junction formation probability so that the adsorption free energy could be calculated by referring to the Langmuir isotherm. In the case of three prototypical molecules with terminal methylthio, pyridyl, and amino groups, the adsorption free energies were found to be 32.5, 33.9, and 28.3 kJ mol-1 , respectively, which are consistent with DFT calculations.

3.
J Am Chem Soc ; 141(35): 13977-13986, 2019 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-31436416

RESUMO

The chemical reactivity and/or the diffusion of Ag atoms or ions during thermal processing can cause irreversible structural damage, hindering the application of Ag nanowires (NWs) in transparent conducting films and other applications that make use of the material's nanoscale properties. Here, we describe a simple and effective method for growing monolayer SnO2 on the surface of Ag nanowires under ambient conditions, which protects the Ag nanowires from chemical and structural damage. Our results show that Sn2+ and Ag atoms undergo a redox reaction in the presence of water. First-principle simulations suggest a reasonable mechanism for SnO2 formation, showing that the interfacial polarization of the silver by the SnO2 can significantly reduce the affinity of Ag to O2, thereby greatly reducing the oxidation of the silver. The corresponding values (for example, before coating: 17.2 Ω/sq at 86.4%, after coating: 19.0 Ω/sq at 86.6%) show that the deposition of monolayer SnO2 enables the preservation of high transparency and conductivity of Ag. In sharp contrast to the large-scale degradation of pure Ag-NW films including the significant reduction of its electrical conductivity when subjected to a series of harsh corrosion environments, monolayer SnO2 coated Ag-NW films survive structurally and retain their electrical conductivity. Consequently, the thermal, electrical, and chemical stability properties we report here, and the simplicity of the technology used to achieve them, are among the very best reported for transparent conductor materials to date.

4.
J Am Chem Soc ; 141(31): 12192-12196, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31328527

RESUMO

Investigating the chemical nature of the adsorbed intermediate species on well-defined Cu single crystal substrates is crucial in understanding many electrocatalytic reactions. Herein, we systematically study the early stages of electrochemical oxidation of Cu(111) and polycrystalline Cu surfaces in different pH electrolytes using in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). On Cu(111), for the first time, we identified surface OH species which convert to chemisorbed "O" before forming Cu2O in alkaline (0.01 M KOH) and neutral (0.1 M Na2SO4) electrolytes; while at the Cu(poly) surface, we only detected the presence of surface hydroxide. Whereas, in a strongly acidic solution (0.1 M H2SO4), sulfate replaces the hydroxyl/oxy species. This results improves the understanding of the reaction mechanisms of various electrocatalytic reactions.

5.
Angew Chem Int Ed Engl ; 58(35): 12133-12137, 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31268611

RESUMO

The fundamental understanding of the subtle interactions between molecules and plasmons is of great significance for the development of plasmon-enhanced spectroscopy (PES) techniques with ultrahigh sensitivity. However, this information has been elusive due to the complex mechanisms and difficulty in reliably constructing and precisely controlling interactions in well-defined plasmonic systems. Herein, the interactions in plasmonic nanocavities of film-coupled metallic nanocubes (NCs) are investigated. Through engineering the spacer layer, molecule-plasmon interactions were precisely controlled and resolved within 2 nm. Efficient energy exchange interactions between the NCs and the surface within the 1-2 nm range are demonstrated. Additionally, optical dressed molecular excited states with a huge Lamb shift of ≈7 meV at the single-molecule (SM) level were observed. This work provides a basis for understanding the underlying molecule-plasmon interaction, paving the way for fully manipulating light-matter interactions at the nanoscale.

6.
Nat Commun ; 10(1): 2671, 2019 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-31209216

RESUMO

Plasmon-mediated chemical reactions (PMCRs) constitute a vibrant research field, advancing such goals as using sunlight to convert abundant precursors such as CO2 and water to useful fuels and chemicals. A key question in this burgeoning field which has not, as yet, been fully resolved, relates to the precise mechanism through which the energy absorbed through plasmonic excitation, ultimately drives such reactions. Among the multiple processes proposed, two have risen to the forefront: plasmon-increased temperature and generation of energetic charge carriers. However, it is still a great challenge to confidently separate these two effects and quantify their relative contribution to chemical reactions. Here, we describe a strategy based on the construction of a plasmonic electrode coupled with photoelectrochemistry, to quantitatively disentangle increased temperature from energetic charge carriers effects. A clear separation of the two effects facilitates the rational design of plasmonic nanostructures for efficient photochemical applications and solar energy utilization.

7.
Sci Adv ; 5(6): eaaw3072, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31245539

RESUMO

Oriented external electric fields (OEEFs) offer a unique chance to tune catalytic selectivity by orienting the alignment of the electric field along the axis of the activated bond for a specific chemical reaction; however, they remain a key experimental challenge. Here, we experimentally and theoretically investigated the OEEF-induced selective catalysis in a two-step cascade reaction of the Diels-Alder addition followed by an aromatization process. Characterized by the mechanically controllable break junction (MCBJ) technique in the nanogap and confirmed by nuclear magnetic resonance (NMR) in bottles, OEEFs are found to selectively catalyze the aromatization reaction by one order of magnitude owing to the alignment of the electric field on the reaction axis. Meanwhile, the Diels-Alder reaction remained unchanged since its reaction axis is orthogonal to the electric fields. This orientation-selective catalytic effect of OEEFs reveals that chemical reactions can be selectively manipulated through the elegant alignment between the electric fields and the reaction axis.

8.
Nat Mater ; 18(7): 697-701, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31036960

RESUMO

Solid/liquid interfaces are ubiquitous in nature and knowledge of their atomic-level structure is essential in elucidating many phenomena in chemistry, physics, materials science and Earth science1. In electrochemistry, in particular, the detailed structure of interfacial water, such as the orientation and hydrogen-bonding network in electric double layers under bias potentials, has a significant impact on the electrochemical performances of electrode materials2-4. To elucidate the structures of electric double layers at electrochemical interfaces, we combine in situ Raman spectroscopy and ab initio molecular dynamics and distinguish two structural transitions of interfacial water at electrified Au single-crystal electrode surfaces. Towards negative potentials, the interfacial water molecules evolve from structurally 'parallel' to 'one-H-down' and then to 'two-H-down'. Concurrently, the number of hydrogen bonds in the interfacial water also undergoes two transitions. Our findings shed light on the fundamental understanding of electric double layers and electrochemical processes at the interfaces.

9.
Chem Commun (Camb) ; 55(60): 8824-8827, 2019 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-31140479

RESUMO

A gap-mode configuration was developed for the in situ SERS study of the structure-activity relationship of Au@Pd core-shell nanocatalysts, which show much better performance in the selective oxidation of benzyl alcohol compared to Pd. The in situ SERS results reveal that the tensile strain in the Pd shell could promote the activation of oxygen, thus improving the activity. Such a tensile strain effect decreases with the increase of the Pd shell thickness, leading to a volcano correlation between the activity and the shell thickness.

10.
J Am Chem Soc ; 141(20): 8053-8057, 2019 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-31070906

RESUMO

Surface plasmons (SPs) are able to promote chemical reactions through the participation of the energetic charge carriers produced following plasmons decay. Using p-aminothiophenol (PATP) as a probe molecule, we used surface-enhanced Raman spectroscopy to follow the progress of its transformation, in situ, to investigate systematically the role of hot electrons and holes. The energetic carrier mediated PATP oxidation was found to occur even in the absence of oxygen, and was greatly influenced by the interface region near the gold surface. The observed reaction, which occurred efficiently on Au@TiO2 nanostructures, did not happen on bare gold nanoparticles (NPs) or core-shell nanostructures when a silicon oxide layer blocked access to the gold. Moreover, the product of the PATP oxidation with oxygen on Au@TiO2 nanostructures differed from what was obtained without oxygen, suggesting that the mechanism through which "hot holes" mediated the oxidation reaction was different from that operating with oxygen activated by hot electrons.

11.
Anal Chem ; 91(8): 5316-5322, 2019 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-30912431

RESUMO

Plasmonic "hot spots" play a key role in surface-enhanced Raman scattering (SERS) enabling its ultrahigh surface sensitivity. Thus, precise prediction and control of the location of hot spots in surface nanostructures is of great importance. However, it is difficult to predict the exact location of hot spots due to complex plasmon competition and synergistic effects in three-dimensional (3D) multiparticle surface configurations. In this work, three types of Au@probe@SiO2 core-shell nanoparticles were prepared and a 3D hot spots matrix was assembled via a consecutive layer on layer deposition method. Combined with SERS, distinct probe molecules were integrated into different layers of the 3D multiparticle nanostructure allowing for the hot spots to be precisely located. Importantly, the hot spots could be controlled and relocated by applying different excitation wavelengths, which was verified by simulations and experimental results. This work proposes a new insight and provides a platform for precisely probing and controlling chemical reactions, which has profound implications in both surface analysis and surface plasmonics.

12.
Chem Commun (Camb) ; 55(23): 3379-3382, 2019 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-30820497

RESUMO

We propose programed potential modulation strategies to balance the ion intercalation/deintercalation, surface tailoring and bubbling dispersion processes in the electrochemical exfoliation of graphite, resulting in high-quality graphene with high crystallinity, low oxidation degree, uniform size distribution and few layers.

13.
Anal Chem ; 91(3): 1675-1685, 2019 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-30629409

RESUMO

Electrochemistry and heterogeneous catalysis continue to attract enormous interest. In situ surface analysis is a dynamic research field capable of elucidating the catalytic mechanisms of reaction processes. Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is a nondestructive technique that has been cumulatively used to probe and analyze catalytic-reaction processes, providing important spectral evidence about reaction intermediates produced on catalyst surfaces. In this perspective, we review recent electrochemical- and heterogeneous-catalysis studies using SHINERS, highlight its advantages, summarize the flaws and prospects for improving the SHINERS technique, and give insight into its future research directions.

14.
J Am Chem Soc ; 141(4): 1665-1671, 2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30608680

RESUMO

Perovskite solar cells are strong competitors for silicon-based ones, but suffer from poor long-term stability, for which the intrinsic stability of perovskite materials is of primary concern. Herein, we prepared a series of well-defined cesium-containing mixed cation and mixed halide perovskite single-crystal alloys, which enabled systematic investigations on their structural stabilities against light, heat, water, and oxygen. Two potential phase separation processes are evidenced for the alloys as the cesium content increases to 10% and/or bromide to 15%. Eventually, a highly stable new composition, (FAPbI3)0.9(MAPbBr3)0.05(CsPbBr3)0.05, emerges with a carrier lifetime of 16 µs. It remains stable during at least 10 000 h water-oxygen and 1000 h light stability tests, which is very promising for long-term stable devices with high efficiency. The mechanism for the enhanced stability is elucidated through detailed single-crystal structure analysis. Our work provides a single-crystal-based paradigm for stability investigation, leading to the discovery of stable new perovskite materials.

15.
Angew Chem Int Ed Engl ; 57(50): 16339-16342, 2018 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-30312507

RESUMO

Electrocatalytic CO2 reduction to CO emerges as a potential route of utilizing emitted CO2 . Metal-N-C hybrid structures have shown unique activities, however, the active centers and reaction mechanisms remain unclear because of the ambiguity in true atomic structures for the prepared catalysts. Herein, combining density-functional theory calculations and experimental studies, the reaction mechanisms for well-defined metal-N4 sites were explored using metal phthalocyanines as model catalysts. The theoretical calculations reveal that cobalt phthalocyanine exhibits the optimum activity for CO2 reduction to CO because of the moderate *CO binding energy at the Co site, which accommodates the *COOH formation and the *CO desorption. It is further confirmed by experimental studies, where cobalt phthalocyanine delivers the best performance, with a maximal CO Faradaic efficiency reaching 99 %, and maintains stable performance for over 60 hours.

16.
Chem Commun (Camb) ; 54(77): 10882-10885, 2018 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-30204175

RESUMO

Herein, surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) has been successfully applied in the evaluation of cigarette flavoring quality using monolayer films of Au nanoparticles as substrates. With such a method, even a slight difference in the formula of the essence that cannot be directly identified by SERS can be distinguished.

17.
Anal Chem ; 90(18): 10837-10842, 2018 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-30136575

RESUMO

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO2 NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO2 NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

18.
Angew Chem Int Ed Engl ; 57(35): 11257-11261, 2018 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-29998625

RESUMO

Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (νNC ) was observed, which is consistent with X-ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt-C/Pd-C bonds, leading to improved surface activity towards CO electrooxidation.

19.
Faraday Discuss ; 210(0): 281-287, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-29999067

RESUMO

Recently, the photoelectric effect in metals in electrolyte environments has aroused the interest of researchers. However, direct evidence for surface plasmons-enhanced electrochemical reactions involving classic outer-sphere reactions of reversible redox couples is seldom reported. We used a surface plasmons-active gold-mushroom-array as a working electrode and observed enhanced faradaic current from ferrocenemethanol following illumination with a xenon lamp. The photoelectric current behaved differently in the presence and absence of oxygen in the solution. The preliminary results are discussed with consideration of the possible mechanisms of electron transfer, although they are very complex, due to the lack of direct evidence. Some consideration was also taken of the research on photoelectrochemical reactions on metallic electrodes.

20.
Chem Sci ; 9(22): 5033-5038, 2018 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-29938032

RESUMO

We applied a combination of mechanically controllable break junction (MCBJ) and in situ surface enhanced Raman spectroscopy (SERS) methods to investigate the long-standing single-molecule conductance discrepancy of prototypical benzene-1,4-dithiol (BDT) junctions. Single-molecule conductance characterization, together with configuration analysis of the molecular junction, suggested that disulfide-mediated dimerization of BDT contributed to the low conductance feature, which was further verified by the detection of S-S bond formation through in situ SERS characterization. Control experiments demonstrated that the disulfide-mediated dimerization could be tuned via the chemical inhibitor. Our findings suggest that a combined electrical and SERS method is capable of probing chemical reactions at the single-molecule level.

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