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1.
J Phys Chem Lett ; 13(4): 1063-1068, 2022 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-35075909

RESUMO

The manipulation of conductive nanowires (NWs) on semiconductor platforms provides important insights into the fabrication of nanoscale electronic devices. In this work, we directly observed the electric field-induced phase transitions in atomic Au-NWs self-assembled on Ge(001) surfaces using scanning tunneling microscopy (STM). The tunneling electrons and electric fields underneath a STM tip apex can effectively trigger a phase transition in Au-NWs on Ge(001) surfaces. Such phase transitions are associated with a remarkable atomic rearrangement in the Au-NWs, thereby modifying their band structures. Moreover, directly monitoring the dynamic reconstruction of Au-NWs on Ge(001) surfaces helps us to understand the NWs' intricate atomic configurations and their electronic properties. The spatially controlled phase transition at the nanometer scale using STM shows the possibility of modulating NWs' properties at an atomic scale.

3.
Nanoscale ; 13(25): 11104-11111, 2021 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-34132284

RESUMO

Three-dimensional (3D) TiO2 architectures have attracted significant attention recently as they can improve the electrochemical stability and realize the full potential of TiO2-based anodes in lithium ion batteries. Here, flower-like rutile TiO2 spheres with radially assembled nanorods (c-channels) were fabricated via a simple hydrothermal method. The 3D radial architecture affords massive active sites to fortify the lithium storage. Moreover, the presence of c-channels facilitates electrolyte infiltration and offers facile pathways for efficient Li+ transport. As a result, this flower-like rutile TiO2 anode gives significantly enhanced specific capacities (615 mA h g-1 at 1 C and 386 mA h g-1 at 2 C after 400 cycles) and a superior long-term cyclability (up to 10 000 cycles with a specific capacity of 67 mA h g-1 at 100 C). Kinetic analysis reveals that the enhanced diffusion-controlled and surface capacitive storage leads to the excellent electrochemical behavior. This work not only exhibits the enormous advantages of 3D architectures with c-channels, but also provides access to structural design and crystal phase selection for TiO2-based anode materials.

4.
Environ Sci Technol ; 55(11): 7711-7720, 2021 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-34003010

RESUMO

Hydroxyl radicals (•OH) generated in the photocatalytic process are crucial to the conversion of methane (CH4) to value-added methanol (CH3OH) at room temperature. However, utilizing noble metal-free catalysts and low-energy photons of solar light, such as visible and near-infrared light (vis-NIR), is difficult to provide more electron states to form •OH radicals. Here, we developed FeOOH/Li0.1WO3 core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO3): (1) lithium ions intercalating into the hexagonal tunnels of h-WO3 to form Li0.1WO3 nanorods and (2) using FeOOH-wrapped Li0.1WO3 to obtain FeOOH/Li0.1WO3 core-shell nanorods. Introduction of lithium induces polaron transition in Li0.1WO3, enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when H2O2 is selected as an oxidant favors the generation of more •OH radicals available for CH4 oxidation to CH3OH. Meanwhile, FeOOH with FeIII as an "electron sink" highly improves the separation of photoinduced electrons and holes in Li0.1WO3. Eventually, efficient selective formation of CH4OH is achieved with remarkable generation rates up to ∼342 and ∼160 µmol g-1 at visible light (420-700 nm) and NIR light (≥800 nm), respectively. Our finding opens up new possibilities for developing noble metal-free catalysts for solar energy-driven CH4 conversion to CH3OH under ambient conditions.


Assuntos
Metanol , Nanotubos , Compostos Férricos , Peróxido de Hidrogênio , Luz , Lítio , Metano
5.
ACS Appl Mater Interfaces ; 12(2): 2548-2554, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31850736

RESUMO

Bimetallic Ni-Cu catalysts feature high activity in CO2 hydrogenation. However, the primary surface intermediates during reaction are still elusive, making the understanding of the reaction mechanism inadequate. Herein, taking advantage of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), we focused on the mechanistic exploration of CO2 hydrogenation on the Ni/Cu(100) model catalyst under millibar pressures. We show that CO2 dissociates into CO and atomic oxygen on the Ni/Cu(100) surface and gives rise to the formation of chemisorbed O and nickel oxide (NiO). The CO3* species is formed through the reaction of CO2 with surface oxygen during CO2 activation. With the presence of H2, the conversion of adsorbed CO3* into the formate intermediate, HCOO*, is unambiguously demonstrated by the C 1s and O 1s core-level spectra as well as ultraviolet photoelectron spectroscopy. Based on these observations, we conclude that the CO2 hydrogenation route via CO2 dissociation, the formation of CO3*, the conversion of CO3* to formate, and the ensuing hydrogenation of formate to methanol on the Ni-Cu catalyst are feasible.

6.
ACS Synth Biol ; 8(2): 445-454, 2019 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-30616338

RESUMO

The filamentous fungus Fusarium fujikuroi is well-known for its production of natural plant growth hormones: a series of gibberellic acids (GAs). Some GAs, including GA1, GA3, GA4, and GA7, are biologically active and have been widely applied in agriculture. However, the low efficiency of traditional genetic tools limits the further research toward making this fungus more efficient and able to produce tailor-made GAs. Here, we established an efficient CRISPR/Cas9-based genome editing tool for F. fujikuroi. First, we compared three different nuclear localization signals (NLS) and selected an efficient NLS from histone H2B (HTBNLS) to enable the import of the Cas9 protein into the fungal nucleus. Then, different sgRNA expression strategies, both in vitro and different promoter-based in vivo strategies, were explored. The promoters of the U6 small nuclear RNA and 5S rRNA, which were identified in F. fujikuroi, had the highest editing efficiency. The 5S rRNA-promoter-driven genome editing efficiency reached up to 79.2%. What's more, multigene editing was also explored and showed good results. Finally, we used the developed genome editing tool to engineer the metabolic pathways responsible for the accumulation of a series GAs in the filamentous fungus F. fujikuroi, and successfully changed its GA product profile, from GA3 to tailor-made GA4 and GA7 mixtures. Since these mixtures are more efficient for agricultural use, especially for fruit growth, the developed strains will greatly improve industrial GA production.


Assuntos
Sistemas CRISPR-Cas/genética , Fungos/genética , Fungos/metabolismo , Fusarium/genética , Fusarium/metabolismo , Giberelinas/metabolismo , Edição de Genes/métodos , Genoma Fúngico/genética
7.
Chemistry ; 25(46): 10965-10970, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-24687884

RESUMO

Uniform mesoporous anatase hollow spheres with high crystallinity have been fabricated by an efficient method, in which biocompatible ethanedioic acid acts as the chelating agent during the Ostwald ripening process. The combination of high crystallinity, large surface area, and mesoporosity leads to an excellent photocatalytic activity. In solar water splitting, the hollow spheres exhibit remarkably enhanced photocatalytic performance that is 1.4 times of P25.

8.
J Phys Condens Matter ; 30(48): 485402, 2018 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-30406769

RESUMO

2D materials such as MXenes have garnered attention in a wide field of applications ranging from energy to environment to medical. Properties of 2D materials can be tailored via alloying and in some cases, solid-solutions (disordered alloys) are formed. To predict the disordered alloy properties via first-principles, the model structure needs to imitate the random arrangements of alloyants and yet remains computationally tractable. Using density functional theory and the cluster expansion method, we investigate the accuracy of using of special quasirandom structures (SQSs) for predicting disordered 2D alloy properties, evaluating the effect of SQS supercell size on the prediction quality of formation energies, elastic properties, and structural parameters. We illustrate the findings with 5 different disordered binary [Formula: see text] MXene alloy systems (where M = Ti and M' = Zr, Hf, V, Nb, or Ta), demonstrating that SQSs around 6-8 times the primitive cell (N = 6-8) are sufficient to attain convergence in the property predictions versus supercell size. For formation energies, SQSs with N > 4 are found to reproduce the formation energies of the fully disordered phase within ~2.5 meV. For the simulation of the experimentally-synthesized TiNbCO2, we find convergence in structural parameters and elastic tensors at N ~ 6. We traced the convergence of the predictions to the convergence in the band structure-related properties via analysis of the electronic densities-of-states and the projected crystal overlap Hamilton population. Our findings suggest that modest sized SQSs would reproduce the properties of disordered MXene alloys. The results should help guide the investigations of structure-property relationships in other disordered 2D materials as well.

9.
ACS Appl Mater Interfaces ; 10(46): 39879-39889, 2018 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-30353717

RESUMO

Combining both density functional theory and the cluster expansion method, we investigate 3 binary MXene alloy systems of semiconducting Ti2CO2, Zr2CO2, and Hf2CO2, where the transition metals substitute one another (i.e., Ti2(1- x)Zr2 xCO2, Ti2(1- x)Hf2 xCO2, and Zr2(1- x)Hf2 xCO2). We show that this group of MXene alloys forms the solid-solution phase across all compositions. Special quasirandom structures are generated to model the solid-solution phase of these alloys, using which we demonstrate how their structural, mechanical, electronic, and optical properties are tuned via stoichiometry engineering. These alloys exhibit outstanding mechanical strength and stability. They possess indirect band gaps of 1.25-1.80 eV. For Ti2(1- x)Zr2 xCO2 and Ti2(1- x)Hf2 xCO2, they display higher absorbance in the solar spectrum than their constituent Zr2CO2 and Hf2CO2, respectively. Most of the MXene alloys also show appropriately aligned band edges for water splitting. We predict the Ti2(1- x)Zr2 xCO2 alloy with x = 0.2778 to be the most promising water-splitting photocatalyst among the MXenes studied here, outperforming its constituents, Ti2CO2 and Zr2CO2, when solar absorbance performance and band-edge alignments are simultaneously considered. This work demonstrates that alloying can be used to effectively tune photocatalytic performance.

10.
Chemistry ; 24(60): 16097-16103, 2018 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-30088685

RESUMO

The in operando monitoring of catalytic intermediates is crucial for understanding the reaction mechanism and for optimizing the reaction conditions to improve the efficiency of the catalytic protocol; however, until now, this has remained a daunting challenge. Herein, we investigated the interaction of CO2 and H2 with the Cu(111) surface in a CO2 hydrogenation model system by using the in operando technique of near-ambient pressure X-ray photoelectron spectroscopy, which is further assisted by ultraviolet photoemission spectroscopy and low-energy electron diffraction (LEED) measurements. These techniques allowed the direct observation of CO2 dissociation into CO+O on the Cu(111) surface and the adsorption of O on the surface at room temperature. The intermediate HCOO- was unambiguously detected in the CO2 +H2 environment, which corroborated the formate pathway for methanol formation on the Cu(111) surface. We further found that O coverage can prevent the build up of graphitic carbon on the Cu surface. By taking advantage of the competitive interplay between Cu-O and graphitic carbon, we have proposed a feasible strategy for inhibition of the formation of graphitic carbon by tuning the CO2 and H2 partial pressures, which may contribute to sustaining the active Cu catalyst under the reaction conditions.

11.
Phys Chem Chem Phys ; 20(16): 11081-11088, 2018 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-29620770

RESUMO

The activation of C-H bonds in terminal alkynyl groups at room temperature was achieved in the reaction of 2,5-diethynyl-1,4-bis(4-bromophenylethynyl)benzene on Ag(111). Scanning tunneling microscopy studies showed the formation of organometallic species, whose stabilization was confirmed by density functional theory calculations, at room temperature as the product of C-H bond activation. The partial conversion of organometallic structures into covalent products of the homocoupling between the terminal alkynes was achieved by further annealing the sample at 420 K. Detached Br adatoms were suggested to play a key role in promoting the C-H bond activation. This proposal was supported by the theoretical study based on a simplified model of the system, showing the weakening of the C-H bond in the alkynyl group by an approaching Br atom. The results provide a new strategy for on-surface C-H bond activation under mild conditions, which register great potential applications in on-surface synthesis and bottom-up preparation of functional nanomaterials.

12.
J Am Chem Soc ; 139(43): 15414-15419, 2017 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-29017322

RESUMO

The synthesis of free-standing two-dimensional titania (2-D TiO2) with a reduced band gap presents complex challenges to synthetic chemists. Here, we report a free-standing 2-D TiO2 sheet synthesized via a one-step solvothermal methodology, with a measured optical onset at ∼1.84 eV. Using first-principles calculations in combination with experiment, we propose that the as-formed 2-D TiO2 sheets are layers of the lepidocrocite TiO2 structure, but with large nonuniform strains consistent with its crumpled morphology. These strains cause a significant change in the quasiparticle band structure and optical absorption spectra, resulting in large absorption in the visible-light region. This narrow band gap 2-D TiO2 can catalyze the formation of singlet oxygen and the degradation of dye pollutants with low-energy photons of solar light. Our work demonstrates that lattice strains intrinsic to 2-D materials, especially its crumpled, free-standing forms, can result in new and useful properties.

13.
Nanoscale ; 9(2): 666-672, 2017 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-27942692

RESUMO

We report a detailed investigation of elementary catalytic decomposition of ammonia on the Pt-Ni-Pt(111) bimetallic surface using in situ near ambient pressure X-ray photoelectron spectroscopy. Under the near ambient pressure (0.6 mbar) reaction conditions, a different dehydrogenation pathway with a reduced activation energy barrier for recombinative nitrogen desorption on the Pt-Ni-Pt(111) bimetallic surface is observed. The unique surface catalytic activity is correlated with the downward shift of the Pt 5d band states induced by the Ni subsurface atoms via charge redistribution of the topmost Pt layer. Our results provide a practical understanding of the unique chemistry of bimetallic catalysts for facile ammonia decomposition under realistic reaction conditions.

14.
Langmuir ; 32(49): 13046-13053, 2016 12 13.
Artigo em Inglês | MEDLINE | ID: mdl-27951691

RESUMO

Understanding and manipulating the one half-reaction of photoinduced hole-oxidation to oxygen are of fundamental importance to design and develop an efficient water-splitting process. To date, extensive studies on oxygen evolution from water splitting have focused on visible-light harvesting. However, capturing low-energy photons for oxygen evolution, such as near-infrared (NIR) light, is challenging and not well-understood. This report presents new insights into photocatalytic water oxidation using visible and NIR light. WO2-WO3 hybrid nanorods were in situ fabricated using a wet-chemistry route. The presence of metallic WO2 strengthens light absorption and promotes the charge-carrier separation of WO3. The efficiency of the oxygen evolution reaction over noble-metal-free WO2-WO3 hybrids was found to be significantly promoted. More importantly, NIR light (≥700 nm) can be effectively trapped to cause the photocatalytic water oxidation reaction. The oxygen evolution rates are even up to around 220 (λ = 700 nm) and 200 (λ = 800 nm) mmol g-1 h-1. These results demonstrate that the WO2-WO3 material is highly active for water oxidation with low-energy photons and opens new opportunities for multichannel solar energy conversion.

15.
Chem Commun (Camb) ; 52(88): 12944-12947, 2016 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-27747352

RESUMO

Ordered two-dimensional arrays of silver adatoms with tunable metal atom density stabilized by 1,4-diethynyl-2,5-dimethylbenzene, a terminal alkyne, were prepared on Ag(111) and scrutinized by scanning tunneling microscopy and density functional theory calculations. Stabilization of the adatom arrays was attributed to the substrate-mediated electron localizations of the Ag adatom and terminal alkynyl in the molecule.

16.
ACS Omega ; 1(4): 696-705, 2016 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31457157

RESUMO

Two types of out-of-substrate Ag-Ag2O nanoplates were grown on a ZnO substrate through a surfactantless photochemical method. First, the in situ photochemically synthesized Ag-Ag2O nanoparticles further crystallized into nanoplate-like superstructures with rough surfaces and ragged edges. The nanoparticle-mediated crystallization process was governed by a layer-by-layer crystallization mechanism. Our study should help fundamentally understand the formation mechanism of hierarchical nanoparticle superstructures. Under continuous UV illumination, the hundreds of nanometer-sized rough nanoplates (i.e., the nanoplate-like superstructures of nanoparticles) can be transformed into large smooth nanoplates with sizes of up to several micrometers. The out-of-substrate Ag-Ag2O nanoplates/ZnO heterostructures are potentially promising for photocatalytic applications.

17.
Nano Lett ; 15(12): 8091-8, 2015 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-26528623

RESUMO

The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics.

18.
Phys Chem Chem Phys ; 17(40): 27019-26, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26411704

RESUMO

To fully achieve potential applications of the double-decker molecules containing rare earth elements as single-molecule magnets in molecular spintronics, it is crucial to understand the 4f states of the rare earth atoms sandwiched in the double-decker molecules by metal electrodes. In this study, low-temperature scanning tunneling microscopy and spectroscopy were employed to investigate the isolated double-decker DyPc2 molecule adsorbed on Au(111) via its differential conductance measurements. The experimental results revealed that the differential conductance maps acquired at a constant height mode simply depicted the authentic molecular orbitals; moreover, the differential conductance maps achieved at a constant current mode could not directly probe the 4f states of the sandwiched Dy atom. This was consistent with the spectra obtained over the molecule center around the Fermi level, indicative of no Kondo feature. Upon decreasing the tip-molecule distance, the CH-mode images presented high-resolution structure but no information of the 4f states. All results indicated that the Dy atom barely contributed to the tunneling current because of the absence of coupling with the microscope tip, echoing the inaccessibility of the Dy 4f states in the double-decker DyPc2 molecule.

19.
Chem Commun (Camb) ; 51(75): 14195-8, 2015 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-26256051

RESUMO

Adsorption of butadiene monoxide on Si(111)-(7×7) has been scrutinized by high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The experimental results indicate that surface reaction occurs through a [2+2]-like cycloaddition, which is further supported by the DFT studies.

20.
ACS Nano ; 9(6): 6305-14, 2015 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-25990647

RESUMO

Surface reactions of 2,5-diethynyl-1,4-bis(phenylethynyl)benzene on Ag(111), Ag(110), and Ag(100) were systematically explored and scrutinized by scanning tunneling microscopy, molecular mechanics simulations, and density functional theory calculations. On Ag(111), Glaser coupling reaction became dominant, yielding one-dimensional molecular wires formed by covalent bonds. On Ag(110) and Ag(100), however, the terminal alkynes reacted with surface metal atoms, leading to one-dimensional organometallic nanostructures. Detailed experimental and theoretical analyses revealed that such a lattice dependence of the terminal alkyne reaction at surfaces originated from the matching degree between the periodicities of the produced molecular wires and the substrate lattice structures.

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