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1.
Chem Soc Rev ; 48(20): 5207-5241, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31573024

RESUMO

Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes that are vital for improving energy utilization efficiency and mitigating the aggravating global warming challenge. The noble metals such as platinum are generally the most frequently used electrocatalysts to drive these reactions and facilitate the relevant energy conversion processes. The high cost and scarcity of these materials pose a serious challenge for the wide-spread adoption and the sustainability of these technologies in the long run, which have motivated considerable efforts in searching for alternative electrocatalysts with reduced loading of precious metals or based entirely on earth-abundant metals. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts, such as high activity, selectivity, stability, maximized atom utilization efficiency and easy separation from reactants/products. The graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts for various electrochemical energy conversion processes. In this review, we highlight the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities.

2.
Inorg Chem ; 57(10): 6051-6056, 2018 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-29722989

RESUMO

The quaternary compound Cu2ZnSnSe4 (CZTSe), as a typical candidate for both solar cells and thermoelectrics, is of great interest for energy harvesting applications. Materials with a high thermoelectric efficiency have a relatively low thermal conductivity, which is closely related to their chemical bonding and lattice dynamics. Therefore, it is essential to investigate the lattice dynamics of materials to further improve their thermoelectric efficiency. Here we report a lattice dynamic study in a cobalt-substituted CZTSe system using temperature-dependent X-ray absorption fine structure spectroscopy (TXAFS). The lattice contribution to the thermal conductivity is dominant, and its reduction is mainly ascribed to the increment of point defects after cobalt substitution. Furthermore, a lattice dynamic study shows that the Einstein temperature of atomic pairs is reduced after cobalt substitution, revealing that increasing local structure disorder and weakened bonding for each of the atomic pairs are achieved, which gives us a new perspective for understanding the behavior of lattice thermal conductivity.

3.
Chemosphere ; 196: 393-401, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29316465

RESUMO

An understanding of the species of chlorine is crucial in the metropolis-Beijing, which is suffering serious haze pollution with high frequency. Particulate Matters (PMs) with five different sizes were collected in Beijing from July 2009 to March 2016, and characterized non-destructively by X-ray absorption near edge structure spectroscopy. PM<0.2, PM0.2-0.5 and PM>2.5 contributed for the major PMs mass in spring and summer, PM0.5-1.0 and PM1.0-2.5 contributed for the major PMs mass in autumn and winter. The concentrations of the three chlorine species were in the order of inorganic chlorine (Clinorg) > aliphatic chlorine (Clali) > aromatic chlorine (Claro), indicating that Clinorg constituted the primary chlorine fraction and less toxic Clali constituted the primary total organic chlorine (Clali + Claro, abbreviated as Clorg) in the PMs in Beijing. In addition, these three chlorine species exhibited identical seasonal variation in PM2.5: winter > autumn > spring > summer. Wet precipitation is an important factor to result in the lower mass concentrations of these three chlorine species in summer. The temporal variations of both size resolved PM mass concentrations and chlorine species concentrations suggested that the air pollution prevention and control in Beijing has just won initial success.


Assuntos
Poluentes Atmosféricos/análise , Cloro/análise , Pequim , China , Cloro/química , Monitoramento Ambiental/métodos , Tamanho da Partícula , Material Particulado/análise , Estações do Ano , Espectroscopia por Absorção de Raios X/métodos
4.
J Synchrotron Radiat ; 24(Pt 3): 674-678, 2017 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-28452760

RESUMO

A new quick-scanning X-ray absorption fine-structure (QXAFS) system has been established on beamline 1W1B at the Beijing Synchrotron Radiation Facility. As an independent device, the QXAFS system can be employed by other beamlines equipped with a double-crystal monochromator to carry out quick energy scans and data acquisition. Both continuous-scan and trapezoidal-scan modes are available in this system to satisfy the time scale from subsecond (in the X-ray absorption near-edge structure region) to 1 min. Here, the trapezoidal-scan method is presented as being complementary to the continuous-scan method, in order to maintain high energy resolution and good signal-to-noise ratio. The system is demonstrated to be very reliable and has been combined with in situ cells to carry out time-resolved XAFS studies.

5.
J Synchrotron Radiat ; 24(Pt 1): 367-373, 2017 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-28009579

RESUMO

In this report, AI-BL1.0, an open-source Labview-based program for automatic on-line beamline optimization, is presented. The optimization algorithms used in the program are Genetic Algorithm and Differential Evolution. Efficiency was improved by use of a strategy known as Observer Mode for Evolutionary Algorithm. The program was constructed and validated at the XAFCA beamline of the Singapore Synchrotron Light Source and 1W1B beamline of the Beijing Synchrotron Radiation Facility.

6.
Nanoscale ; 8(11): 5857-64, 2016 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-26509240

RESUMO

Crossed Fe2O3 nanosheets supported cobalt oxide nanoparticles on three-dimensionally macroporous nickel foam substrate (xCo/Fe-NF) was designed and successfully prepared through a facile hydrothermal and impregnation route. These catalysts showed high catalytic soot combustion activities under self-capture contact mode. The three-dimensional macroporous structures of Ni foam and the crossed Fe2O3 nanosheets constituted macroporous voids can greatly increase the contact efficiency between soot particulates and catalysts. The interaction between Co and Fe facilitated the activation of the Fe-O bond and increased the amounts of active oxygen species, thus improving the redox property of the catalysts. The 0.6Co/Fe-NF catalyst exhibited the highest turnover frequency (TOF) for soot combustion, which is in good accordance with the largest amount of active oxygen species. Based upon the catalytic performance and multiple characterization results, two reaction pathways for soot oxidation are identified, namely, the direct oxidation by the activated oxygen species via oxygen vacancies and the NOx-aided soot oxidation.

7.
J Synchrotron Radiat ; 22(5): 1147-50, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26289264

RESUMO

Simulations of the periods, split regularities and mirror symmetries of the glitch pattern of a Si(111) crystal along with the azimuthal angles are presented. The glitch patterns of Si(111) double-crystal monochromators (DCMs) are found to be the superposition of the two sets of glitch patterns from the two crystals. The optimal azimuthal orientation ϕ1,2 = [(2n+1)π]/6 (n = 0, ±1, ±2…) for Si(111) DCMs to achieve the least amount of glitches in the hard X-ray region has been suggested.

8.
J Am Chem Soc ; 137(7): 2622-7, 2015 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-25641111

RESUMO

Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in a nonmagnetic MoS2 semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in a 2H-MoS2 ultrathin nanosheet host, which prompts the transformation of the surrounding 2H-MoS2 local lattice into a trigonal (1T-MoS2) phase. 25% 1T-MoS2 phase incorporation in 2H-MoS2 nanosheets can enhance the electron carrier concentration by an order, introduce a Mo(4+) 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 µB/Mo by the exchange interactions between sulfur vacancy and the Mo(4+) 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures.

9.
J Hazard Mater ; 288: 80-8, 2015 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-25698569

RESUMO

Vanadium(V)-doped hexagonal turbostratic birnessites were synthesized and characterized by multiple techniques and were used to remove Pb(2+) from aqueous solutions. With increasing V content, the V(V)-doped birnessites have significantly decreased crystallinity, i.e., the thickness of crystals in the c axis decreases from 9.8 nm to ∼0.7 nm, and the amount of vacancies slightly increases from 0.063 to 0.089. The specific surface areas of these samples increase after doping while the Mn average oxidation sates are almost constant. V has a valence of +5 and tetrahedral symmetry, and exists as oxyanions, including V6O16(2-), and VO4(3-) on birnessite edge sites by forming monodentate corning-sharing complexes. Pb LIII-edge extended X-ray absorption fine structure (EXAFS) spectra analysis shows that, at low V contents (V/Mn≤0.07) Pb(2+) mainly binds with birnessite on octahedral vacancy and especially edge sites whereas at higher V contents (V/Mn>0.07) more Pb(2+) associates with V oxyanions and form vanadinite [Pb5(VO4)3Cl]-like precipitates. With increasing V(V) content, the Pb(2+) binding affinity on the V-doped birnessites significantly increases, ascribing to both the formation of the vanadinite precipitates and decreased particle sizes of birnessite. These results are useful to design environmentally benign materials for treatment of metal-polluted water.


Assuntos
Chumbo/química , Óxidos/química , Compostos de Vanádio/química , Cristalização , Chumbo/isolamento & purificação , Conformação Molecular , Tamanho da Partícula , Soluções , Termodinâmica , Poluentes Químicos da Água/análise , Poluição Química da Água/análise
10.
J Synchrotron Radiat ; 21(Pt 4): 756-61, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24971971

RESUMO

Obtaining sub-10 pm spatial resolution by extended X-ray absorption fine structure (EXAFS) spectroscopy is required in many important fields of research, such as lattice distortion studies in colossal magnetic resistance materials, high-temperature superconductivity materials etc. However, based on the existing EXAFS data analysis methods, EXAFS has a spatial resolution limit of π/2Δk which is larger than 0.1 Å. In this paper a new data analysis method which can easily achieve sub-10 pm resolution is introduced. Theoretically, the resolution limit of the method is three times better than that normally available. The method is examined by numerical simulation and experimental data. As a demonstration, the LaFe1-xCrxO3 system (x = 0, 1/3, 2/3) is studied and the structural information of FeO6 octahedral distortion as a function of Cr doping is resolved directly from EXAFS, where a resolution better than 0.074 Šis achieved.

11.
ACS Nano ; 8(2): 1886-92, 2014 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-24472038

RESUMO

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situ X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca. 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu-Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.

12.
Nanotoxicology ; 8(2): 179-88, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23311584

RESUMO

The release of nanoparticles (NPs) to the environment poses an increasing potential threat to biological systems. This study investigated the phytotoxicity and accumulation of copper oxide (CuO) NPs to Elsholtzia splendens (a Cu-tolerant plant) under hydroponic conditions. The 50% effective concentration (EC50) of CuO NPs to E. splendens was about 480 mg/L, implying the tolerance of E. splendens to CuO NPs. The Cu content in the shoots treated with 1000 mg/L CuO NPs was much higher than those exposed to the comparable 0.5 mg/L soluble Cu and CuO bulk particles. CuO NPs-like deposits were found in the root cells and leaf cells. Cu K-edge X-ray absorption near-edge structure analysis further revealed that the accumulated Cu species existed predominantly as CuO NPs in the plant tissues. All these results suggested that CuO NPs can be absorbed by the roots and translocated to the shoots in E. splendens.


Assuntos
Cobre/metabolismo , Cobre/toxicidade , Lamiaceae/efeitos dos fármacos , Lamiaceae/metabolismo , Nanopartículas Metálicas/toxicidade , Brotos de Planta/efeitos dos fármacos , Adaptação Fisiológica , Cobre/análise , Cobre/química , Lamiaceae/química , Nanopartículas Metálicas/química , Raízes de Plantas/química , Raízes de Plantas/metabolismo
13.
J Synchrotron Radiat ; 21(Pt 1): 165-9, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24365932

RESUMO

A facile heating cell has been designed for in situ transmittance and fluorescence X-ray absorption spectroscopy (XAS) measurements up to 1273 K under vacuum or an inert atmosphere. These high temperatures are achieved using a tantalum heating element by ohmic heating. Because of the small specific heat capacity, the temperature can be changed in a matter of minutes from room temperature to high temperature. Furthermore, a commercial power controller was adapted to provide stable temperature control. The construction of the heat shielding system provides a novel approach to reducing the beam's path length and the cell's size. The cell is inexpensive and easy to build. Its performance was evaluated by in situ XAS measurements of the temperature-dependent structure of ceria nanocrystals. Some preliminary results for the structural mechanism in ceria nanocrystal redox applications are given.

14.
Nanoscale ; 5(24): 12144-9, 2013 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-24177172

RESUMO

Herein, we introduce a specially designed domain-confined macroporous catalyst, namely, the Co3O4 nanocrystals anchored on a TiO2 nanotube array catalyst, which was synthesized by using the mercaptoacetic acid induced surface-grafting method. This catalyst exhibits much better performance for catalytic soot combustion than the conventional TiO2 powder supported one in gravitational contact mode (GMC).


Assuntos
Cobalto/química , Nanotubos/química , Óxidos/química , Fuligem/química , Tioglicolatos/química , Titânio/química , Catálise , Gasolina , Humanos , Nanopartículas Metálicas/química , Propriedades de Superfície , Emissões de Veículos/prevenção & controle
15.
Nanoscale ; 5(23): 11795-800, 2013 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-24122096

RESUMO

Understanding the kinetic mechanism during ligand adsorption on gold nanocrystals is important for designing and fine-tuning their properties and implications. Here, we report a kinetic study on the adsorption process of dodecanethiol ligands on Au nanocrystals of 3.3 nm by an in situ time-resolved X-ray absorption fine structure technique. A two-step process of dodecanethiol adsorption on Au NC surfaces is proposed based on the obtained ligand coverage, which shows a quick increase from 0 to 0.40 within the first 20 min, followed by a much slower increase to the limiting value of 0.94. In-depth analysis suggests that the first stage involves the quick adsorption of dodecanethiol to the corner and edge sites of Au NCs surfaces, leading to remarkable surface Au-Au bond length relaxation (from 2.79 to 2.81 Å) and pronounced gold-to-ligand charge transfer. The second step that corresponds to the much slower adsorption process to the surface facets could be described by the Langmuir kinetics equation with an adsorption rate constant of 0.0132 min(-1) and an initial coverage of 0.41, in good agreement with the initially preferable adsorption of thiols to the most favorable sites.

16.
Proc Natl Acad Sci U S A ; 110(25): 10068-72, 2013 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-23733928

RESUMO

When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.


Assuntos
Ligas/química , Temperatura Alta , Teste de Materiais/métodos , Metais/química , Alumínio/química , Ouro/química , Níquel/química , Prata/química , Síncrotrons , Estanho/química , Difração de Raios X , Zinco/química
17.
J Synchrotron Radiat ; 20(Pt 2): 243-8, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23412480

RESUMO

In combination with a single-crystal diamond anvil cell (DAC), a polycapillary half-lens (PHL) re-focusing optics has been used to perform high-pressure extended X-ray absorption fine-structure measurements. It is found that a large divergent X-ray beam induced by the PHL leads the Bragg glitches from single-crystal diamond to be broadened significantly and the intensity of the glitches to be reduced strongly so that most of the DAC glitches are efficiently suppressed. The remaining glitches can be easily removed by rotating the DAC by a few degrees with respect to the X-ray beam. Accurate X-ray absorption fine-structure (XAFS) spectra of polycrystalline Ge powder with a glitch-free energy range from -200 to 800 eV relative to the Ge absorption edge are obtained using this method at high pressures up to 23.7 GPa, demonstrating the capability of PHL optics in eliminating the DAC glitches for high-pressure XAFS experiments. This approach brings new possibilities to perform XAFS measurements using a DAC up to ultrahigh pressures.

18.
J Am Chem Soc ; 134(43): 17997-8003, 2012 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-23051636

RESUMO

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters.


Assuntos
Ouro/química , Hexanos/química , Nanopartículas Metálicas/química , Estrutura Molecular , Fatores de Tempo
19.
Environ Sci Technol ; 46(10): 5361-8, 2012 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-22489923

RESUMO

Mercury uptake was induced in two cultivars of Brassica juncea under field conditions using thiosulfate. Analysis was conducted to better understand the mechanism of uptake, speciation of mercury in plants, and redistribution of mercury in the soil. Plant mercury and sulfur concentrations were increased after thiosulfate treatment, and a linear correlation between mercury and sulfur was observed. Mercury may be absorbed and transported in plants as the Hg-thiosulfate complex. The majority of mercury in treated plant tissues (two cultivars) was bound to sulfur in a form similar to ß-HgS (66-94%). Remaining mercury was present in forms similar to Hg-cysteine (1-10%) and Hg-dicysteine (8-28%). The formation of ß-HgS may relate to the transport and assimilation of sulfate in plant tissues. Mercury-thiosulfate complex could decompose to mercuric and sulfate ions in the presence of free protons inside the plasma membrane, while sulfide ions would be produced by the assimilation of sulfate. The concomitant presence of mercuric ions and S(2-) would precipitate ß-HgS. The mercury concentration in the rhizosphere decreased in the treated relative to the nontreated soil. The iron/manganese oxide and organic-bound fractions of soil mercury were transformed to more bioavailable forms (soluble and exchangeable and specifically sorbed) and taken up by plants.


Assuntos
Mercúrio/isolamento & purificação , Mostardeira/efeitos dos fármacos , Mostardeira/metabolismo , Tiossulfatos/farmacologia , Biodegradação Ambiental/efeitos dos fármacos , Biomassa , Fracionamento Químico , China , Análise dos Mínimos Quadrados , Especificidade de Órgãos/efeitos dos fármacos , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/metabolismo , Brotos de Planta/efeitos dos fármacos , Brotos de Planta/metabolismo , Rizosfera , Solo/química , Enxofre/análise , Espectroscopia por Absorção de Raios X
20.
Anal Chem ; 83(20): 7856-62, 2011 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-21805976

RESUMO

Photoreduction is a major obstacle for using the X-ray absorption near-edge structure (XANES) fingerprint to perform metal speciation at the molecular level in biological and environmental samples, especially for metalloproteins. In this study, soft X-ray induced photoreduction was observed in organic Cu(II) compounds during XANES measurements in a third-generation synchrotron source. Next Cu L(3)-edge, O K-edge, and C K-edge XANES spectroscopy, together with the scanning transmission X-ray microscopy (STXM), were used to probe the specific radiation damage processes of Cu acetate with similar local structures to Cu metalloproteins. Breakup of the Cu-Cu bond was hypothesized for the initial photoreduction of Cu acetate. The following radiation damage of Cu acetate produced CuO and an organic Cu(I) compound with a C═C bond, and the further photoreduction of the resulting CuO to Cu metal was also demonstrated. Our results indicated the importance of consideration of photoreduction during soft XANES measurements for the solid state compounds with high valence metals. Reducing the radiation dose to ~0.1 MGy effectively prevented the photoreduction of organic Cu(II) compounds during these measurements. This proposed radiation damage mechanism in Cu acetate may be generally useful in explaining the photoreduction process in Cu metalloproteins.


Assuntos
Cobre/química , Espectroscopia por Absorção de Raios X , Metaloproteínas/química , Compostos Organometálicos/química , Oxirredução , Síncrotrons
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