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1.
Proc Natl Acad Sci U S A ; 117(17): 9194-9201, 2020 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-32295882

RESUMO

Promotion of C-C bonds is one of the key fundamental questions in the field of CO2 electroreduction. Much progress has occurred in developing bulk-derived Cu-based electrodes for CO2-to-multicarbons (CO2-to-C2+), especially in the widely studied class of high-surface-area "oxide-derived" copper. However, fundamental understanding into the structural characteristics responsible for efficient C-C formation is restricted by the intrinsic activity of these catalysts often being comparable to polycrystalline copper foil. By closely probing a Cu nanoparticle (NP) ensemble catalyst active for CO2-to-C2+, we show that bias-induced rapid fusion or "electrochemical scrambling" of Cu NPs creates disordered structures intrinsically active for low overpotential C2+ formation, exhibiting around sevenfold enhancement in C2+ turnover over crystalline Cu. Integrating ex situ, passivated ex situ, and in situ analyses reveals that the scrambled state exhibits several structural signatures: a distinct transition to single-crystal Cu2O cubes upon air exposure, low crystallinity upon passivation, and high mobility under bias. These findings suggest that disordered copper structures facilitate C-C bond formation from CO2 and that electrochemical nanocrystal scrambling is an avenue toward creating such catalysts.

2.
Chem Rev ; 120(2): 1184-1249, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31580651

RESUMO

The surface and interfaces of heterogeneous catalysts are essential to their performance as they are often considered to be active sites for catalytic reactions. With the development of nanoscience, the ability to tune surface and interface of nanostructures has provided a versatile tool for the development and optimization of a heterogeneous catalyst. In this Review, we present the surface and interface control of nanoparticle catalysts in the context of oxygen reduction reaction (ORR), electrochemical CO2 reduction reaction (CO2 RR), and tandem catalysis in three sections. In the first section, we start with the activity of ORR on the nanoscale surface and then focus on the approaches to optimize the performance of Pt-based catalyst including using alloying, core-shell structure, and high surface area open structures. In the section of CO2 RR, where the surface composition of the catalysts plays a dominant role, we cover its reaction fundamentals and the performance of different nanosized metal catalysts. For tandem catalysis, where adjacent catalytic interfaces in a single nanostructure catalyze sequential reactions, we describe its concept and principle, catalyst synthesis methodology, and application in different reactions.

3.
Hua Xi Kou Qiang Yi Xue Za Zhi ; 37(6): 631-635, 2019 Dec 01.
Artigo em Chinês | MEDLINE | ID: mdl-31875442

RESUMO

OBJECTIVE: This study aimed to investigate the value of normalized iodine concentration (NIC), spectral attenuation curve slope (SACS), area under curve (AUC), and iodine concentration difference (ICD) generated from spectral CT in the assessment of parotid gland tumors. METHODS: Ninety-two patients with pathologically confirmed parotid gland tumors underwent arterial phase- and venous phase-enhanced CT in spectral CT. The patients were divided into the pleomor-phic adenoma group (group A), Warthin tumor group (group B), basal cell tumor group (group C), and malignant tumor group (group D). The SACS, AUC, NIC, ICD were measured and analyzed. Statistical analyses were performed by one-way ANOVA, and statistical significance was set at P<0.05. RESULTS: SACS(AP), AUC(AP), and NIC(AP) in group A were lower than those in other groups; SACS(VP) and AUC(VP) in group C were higher than those in other groups; NIC(AP) and NIC(VP) in group D were higher than those in other groups; and ICD in group B was a positive number. The difference in SACS(AP) and AUC(AP) in groups B and C, SACS(VP) and AUC(VP) in groups C and D, and ICD in groups A and C were not statistically significant. By contrast, the diffe-rence between the other groups was statistically significant (P<0.05). The difference in NIC(AP) between groups A and B and groups C and D and the difference in NIC(VP) between groups A and C, groups A and D, and groups B and C were statistically significant (P=0.005, 0.025, 0.002, 0.038, and 0.049, respectively). CONCLUSIONS: Multi-quantitative parameters from spectral CT might be helpful in differentiating various types of parotid gland tumors.


Assuntos
Iodo , Tomografia Computadorizada por Raios X , Diagnóstico Diferencial , Humanos , Glândula Parótida
4.
Hua Xi Kou Qiang Yi Xue Za Zhi ; 37(1): 62-65, 2019 Feb 01.
Artigo em Chinês | MEDLINE | ID: mdl-30854821

RESUMO

OBJECTIVE: This study aims to observe the efficacy of vacuum sealing drainage (VSD) by continuous negative pressure drainage and saline irrigation in the treatment of oral and maxillofacial space infection. METHODS: Retrospective analysis was conducted on 116 cases of maxillofacial space infection, and clinical data were collected to compare the therapeutic effects of routine incision with drainage treatment (traditional treatment group, 58 cases) and VSD treatment (VSD group, 58 cases). RESULTS: The length of hospital stay, white blood cell count, scar length, frequency of dressing change, and pain degree of patients in the VSD group were all lower than those in the traditional treatment group. Moreover, the improvement degree of mouth opening in the VSD groups was better than that in the traditional treatment group (P<0.05). CONCLUSIONS: VSD is a more effective method for the treatment of oral and maxillofacial space infection.


Assuntos
Drenagem , Doenças da Boca , Infecção da Ferida Cirúrgica , Líquidos Corporais , Humanos , Doenças da Boca/terapia , Estudos Retrospectivos , Infecção da Ferida Cirúrgica/terapia , Vácuo
5.
Nano Lett ; 18(11): 6967-6973, 2018 11 14.
Artigo em Inglês | MEDLINE | ID: mdl-30265549

RESUMO

Surface condition plays an important role in the optical performance of semiconductor materials. As new types of semiconductors, the emerging metal-halide perovskites are promising for next-generation optoelectronic devices. We discover significantly improved light-emission efficiencies in lead halide perovskites due to surface oxygen passivation. The enhancement manifests close to 3 orders of magnitude as the perovskite dimensions decrease to the nanoscale, improving external quantum efficiencies from <0.02% to over 12%. Along with about a 4-fold increase in spontaneous carrier recombination lifetimes, we show that oxygen exposure enhances light emission by reducing the nonradiative recombination channel. Supported by X-ray surface characterization and theoretical modeling, we propose that excess lead atoms on the perovskite surface create deep-level trap states that can be passivated by oxygen adsorption.

6.
ACS Nano ; 12(8): 8697-8705, 2018 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-30028589

RESUMO

Pt-based alloys have shown great promise as cathodic catalysts for cost-effective proton-exchange membrane fuel cells. Post-synthesis treatment has been recognized as a critical step to improve the catalytic performance of Pt-based alloys. Here, we present the effects of catalyst processing on the catalytic behavior of Pt-Ni nanoframe electrocatalysts in oxygen reduction reaction. The Pt-Ni nanoframes were made by corroding the Ni-rich phase from solid rhombic dodecahedral particles. A total of three different corrosion procedures were compared. Among them, electrochemical corrosion led to the highest initial specific activity (1.35 mA cm-2 at 0.95 V versus reversible hydrogen electrode) by retaining more Ni in the nanoframes. However, the high activity gradually went down in a subsequent stability test due to continuous Ni loss and concomitant surface reconstruction. On the other hand, the best stability was achieved by a more-aggressive corrosion using oxidative nitric acid. Although the initial activity was compromised, this procedure imparted a less-defective surface, and thus, the specific activity dropped by only 7% over 30 000 potential cycles. These results indicate a delicate trade-off between the activity and stability of Pt-Ni nanoframe electrocatalysts. The obtained understanding of how to balance the activity-stability trade-off via catalyst processing can be generalized to other Pt-based alloys.

7.
Nano Lett ; 18(8): 5329-5334, 2018 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-30011211

RESUMO

Reducing the diameter of silver nanowires has been proven to be an effective way to improve their optoelectronic performance by lessening light attenuation. The state-of-the-art silver nanowires are typically around 20 nm in diameter. Herein we report a modified polyol synthesis of silver nanowires with average diameters as thin as 13 nm and aspect ratios up to 3000. The success of this synthesis is based on the employment of benzoin-derived radicals in the polyol approach and does not require high-pressure conditions. The strong reducing power of radicals allows the reduction of silver precursors to occur at relatively low temperatures, wherein the lateral growth of silver nanowires is restrained because of efficient surface passivation. The optoelectronic performance of as-prepared 13 nm silver nanowires presents a sheet resistance of 28 Ω sq-1 at a transmittance of 95% with a haze factor of ∼1.2%, comparable to that of commercial indium tin oxide (ITO).

8.
Nat Mater ; 17(3): 261-267, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29358645

RESUMO

Smart photovoltaic windows represent a promising green technology featuring tunable transparency and electrical power generation under external stimuli to control the light transmission and manage the solar energy. Here, we demonstrate a thermochromic solar cell for smart photovoltaic window applications utilizing the structural phase transitions in inorganic halide perovskite caesium lead iodide/bromide. The solar cells undergo thermally-driven, moisture-mediated reversible transitions between a transparent non-perovskite phase (81.7% visible transparency) with low power output and a deeply coloured perovskite phase (35.4% visible transparency) with high power output. The inorganic perovskites exhibit tunable colours and transparencies, a peak device efficiency above 7%, and a phase transition temperature as low as 105 °C. We demonstrate excellent device stability over repeated phase transition cycles without colour fade or performance degradation. The photovoltaic windows showing both photoactivity and thermochromic features represent key stepping-stones for integration with buildings, automobiles, information displays, and potentially many other technologies.

9.
Nano Lett ; 17(6): 3798-3802, 2017 06 14.
Artigo em Inglês | MEDLINE | ID: mdl-28493720

RESUMO

Conversion of carbon dioxide to C2-C4 hydrocarbons is a major pursuit in clean energy research. Despite tremendous efforts, the lack of well-defined catalysts in which the spatial arrangement of interfaces is precisely controlled hinders the development of more efficient catalysts and in-depth understanding of reaction mechanisms. Herein, we utilized the strategy of tandem catalysis to develop a well-defined nanostructured catalyst CeO2-Pt@mSiO2-Co for converting CO2 to C2-C4 hydrocarbons using two metal-oxide interfaces. C2-C4 hydrocarbons are found to be produced with high (60%) selectivity, which is speculated to be the result of the two-step tandem process uniquely allowed by this catalyst. Namely, the Pt/CeO2 interface converts CO2 and H2 to CO, and on the neighboring Co/mSiO2 interface yields C2-C4 hydrocarbons through a subsequent Fischer-Tropsch process. In addition, the catalysts show no obvious deactivation over 40 h. The successful production of C2-C4 hydrocarbons via a tandem process on a rationally designed, structurally well-defined catalyst demonstrates the power of sophisticated structure control in designing nanostructured catalysts for multiple-step chemical conversions.

10.
J Am Chem Soc ; 139(24): 8329-8336, 2017 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-28551991

RESUMO

Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.

11.
Oncol Lett ; 14(6): 6417-6420, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29375704

RESUMO

In the present case report, a rare bilateral carotid body tumor (CBT) and the imaging and pathological features of a CBT are described. In the present report, a rare case of bilateral carotid body tumor, which developed in the bifurcation of the common carotid artery, and the clinical manifestations, imaging and pathological features of this CBT are summarized. The imaging cannot validate the diagnosis; however, imaging identified that the tumor exhibited an intact envelope. Immunohistochemical staining revealed that the tumor cells were strongly positive for cluster of differentiation 56, Syn and protein S-100, moderately positive for transcription factor E3, negative for cytokeratin and epithelial membrane antigen, and partial cells were weakly positive for Desmir (<5%). In view of the clinical and pathological features of the carotid body tumor, surgery is hypothesized to be the optimal treatment and may enable the tumor to be resected completely. Refined surgical techniques provide the security of safe resection and decrease the risk of complications occurring.

12.
J Phys Chem Lett ; 8(2): 319-325, 2017 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-28001072

RESUMO

Cobalt-based catalysts are widely used to produce liquid fuels through the Fischer-Tropsch (FT) reaction. However, the cobalt nanocatalysts can exhibit intriguing size-dependent activity whose origin remains heavily debated. To shed light on this issue, the electronic structures of cobalt nanoparticles with size ranging from 4 to 10 nm are studied using soft X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectroscopies. The RIXS measurements reveal the significant size-dependent d-d excitations, from which we determine that the crystal-field splitting energy 10Dq changes from 0.6 to 0.9 eV when the particle size is reduced from 10 to 4 nm. The finding that larger Co nanoparticles have smaller 10Dq value is further confirmed by the Co L-edge RIXS simulations with atomic multiplet code. Our RIXS results demonstrate a stronger Co-O bond in smaller Co nanoparticles, which brings in further insight into their size-dependent catalytic performance.

13.
J Am Chem Soc ; 138(36): 11568-74, 2016 09 14.
Artigo em Inglês | MEDLINE | ID: mdl-27585650

RESUMO

The concept of tandem catalysis, where sequential reactions catalyzed by different interfaces in single nanostructure give desirable product selectively, has previously been applied effectively in the production of propanal from methanol (via carbon monoxide and hydrogen) and ethylene via tandem hydroformylation. However, the underlying mechanism leading to enhanced product selectivity has remained elusive due to the lack of stable, well-defined catalyst suitable for in-depth comprehensive study. Accordingly, we present the design and synthesis of a three-dimensional (3D) catalyst CeO2-Pt@mSiO2 with well-defined metal-oxide interfaces and stable architecture and investigate the selective conversion of ethylene to propanal via tandem hydroformylation. The effective production of aldehyde through the tandem hydroformylation was also observed on propylene and 1-butene. A thorough study of the CeO2-Pt@mSiO2 under different reaction and control conditions reveals that the ethylene present for the hydroformylation step slows down initial methanol decomposition, preventing the accumulation of hydrogen (H2) and favoring propanal formation to achieve up to 80% selectivity. The selectivity is also promoted by the fact that the reaction intermediates produced from methanol decomposition are poised to directly undergo hydroformylation upon migration from one catalytic interface to another. This synergistic effect between the two sequential reactions and the corresponding altered reaction pathway, compared to the single-step reaction, constitute the key advantages of this tandem catalysis. Ultimately, this in-depth study unravels the principles of tandem catalysis related to hydroformylation and represents a key step toward the rational design of new heterogeneous catalysts.

14.
J Am Chem Soc ; 137(6): 2199-202, 2015 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-25622094

RESUMO

We enclose octahedral silver nanocrystals (Ag NCs) in metal-organic frameworks (MOFs) to make mesoscopic constructs O(h)-nano-Ag⊂MOF in which the interface between the Ag and the MOF is pristine and the MOF is ordered (crystalline) and oriented on the Ag NCs. This is achieved by atomic layer deposition of aluminum oxide on Ag NCs and addition of a tetra-topic porphyrin-based linker, 4,4',4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoic acid (H4TCPP), to react with alumina and make MOF [Al2(OH)2TCPP] enclosures around Ag NCs. Alumina thickness is precisely controlled from 0.1 to 3 nm, thus allowing control of the MOF thickness from 10 to 50 nm. Electron microscopy and grazing angle X-ray diffraction confirm the order and orientation of the MOF by virtue of the porphyrin units being perpendicular to the planes of the Ag. We use surface-enhanced Raman spectroscopy to directly track the metalation process on the porphyrin and map the distribution of the metalated and unmetalated linkers on a single-nanoparticle level.

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