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1.
Nanoscale ; 11(41): 19422-19428, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31393509

RESUMO

In metal-free carbon-fullerene-based or defective graphene-based electrocatalysts, pentagon rings are known to play a key role in boosting catalytic activities for the oxygen reduction reaction (ORR). However, the fundamental chemical mechanism underlying the remarkable catalytic effect of the pentagon rings towards the ORR is still not fully understood. Herein, we perform a comprehensive computational study of the catalytic activities of various carbon fullerenes and fullerene fragment species, all containing pentagon rings, by using the density functional theory (DFT) and computational hydrogen electrode (CHE) methods. We find that more active sites on carbon are associated with more neighbouring pentagon rings and stronger adsorption of the key intermediates of O*, OH* and OOH* for the ORR. Importantly, two C60-based fragments, namely, C60-frag1 and C60-frag2l, show a very high activity towards the ORR, as both yield overpotentials as low as 0.389 and 0.407 V, and entail suitable adsorption free energy of OH* and OOH* species. These desirable chemical properties of fullerene fragments can be attributed to the high-energy HOMO orbitals, induced by the low-symmetry fullerene-fragment structures. Both the number of neighbouring pentagon rings and the degree of overall symmetry of the fragment appear to be the two important factors that can be adjusted for the design of optimal metal-free carbon electrocatalysts towards high ORR activities.

2.
Phys Chem Chem Phys ; 19(6): 4435-4439, 2017 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-28120960

RESUMO

Manipulation of the chemical reactivity of two-dimensional materials is a challenge for advancing various nanotechnologies, ranging from electronics to catalysis. In this study, on the basis of first-principles calculations, we demonstrated that the chemical reactivity of h-BN sheets towards O2 can be significantly enhanced via a metal substrate-mediated charge effect. The chemisorption of O2 molecule on the h-BN sheet deposited on Ni, Co, or Cu substrate were almost spontaneous with negligible energy barrier, distinctly different from that on the freestanding h-BN sheet, which has ultra-high chemical stability. In particular, the enhanced oxidation of h-BN sheet can be confined in the nanoscale region due to the localized electronic states in the h-BN sheet. These findings imply a pathway to selectively oxidize h-BN sheet by patterning the metal substrate.

3.
Angew Chem Int Ed Engl ; 54(19): 5666-71, 2015 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-25756931

RESUMO

Pt(100) facets are generally considered less active for the oxygen reduction reaction (ORR). Reported herein is a unique Pt-branched structure, a multicube, whose surface is mostly enclosed by {100} facets but contains high-index facets at the small junction area between the adjacent cubic components. The synthesis is accomplished by a Ni(2+) -mediated facet evolution from high-index {311} to {100} facets on the frameworks of multipods. Despite the high {100} facet coverage, the Pt multicubes exhibit impressive ORR activity in terms of half-wave potential and current density nearly to the level of the most active Pt-based catalysts, while the durability of catalysts is well retained. The facet evolution creates a set of samples with tunable ratios of high-index to low-index facets. The results reveal that the excellent ORR performance of Pt multicubes is a combined result of active sites by high-index facets and low resistance by flat surface. It is anticipated that this work will offer a new approach to facet-controlled synthesis and ORR catalysts design.

4.
Angew Chem Int Ed Engl ; 54(8): 2425-30, 2015 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-25327587

RESUMO

A Ru(3+)-mediated synthesis for the unique Pd concave nanostructures, which can directly harvest UV-to-visible light for styrene hydrogenation, is described. The catalytic efficiency under 100 mW cm(-2) full-spectrum irradiation at room temperature turns out to be comparable to that of thermally (70 °C) driven reactions. The yields obtained with other Pd nanocrystals, such as nanocubes and octahedrons, are lower. The nanostructures reported here have sufficient plasmonic cross-sections for light harvesting in a broad spectral range owing to the reduced shape symmetry, which increases the solution temperature for the reaction by the photothermal effect. They possess a large quantity of atoms at corners and edges where local heat is more efficiently generated, thus providing active sites for the reaction. Taken together, these factors drastically enhance the hydrogenation reaction by light illumination.

5.
Sci Rep ; 4: 5441, 2014 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-24962006

RESUMO

The CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-BN monolayer support single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2 molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2 molecules synchronously, which is the rate-limiting step with an energy barrier of 0.47 eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43 × 10(5) s(-1)) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29 s(-1)). Further, the quantum BOMD simulation at the temperature of 300 K demonstrates the complete reaction process in real time.

6.
Angew Chem Int Ed Engl ; 53(12): 3205-9, 2014 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-24520003

RESUMO

The charge state of the Pd surface is a critical parameter in terms of the ability of Pd nanocrystals to activate O2 to generate a species that behaves like singlet O2 both chemically and physically. Motivated by this finding, we designed a metal-semiconductor hybrid system in which Pd nanocrystals enclosed by {100} facets are deposited on TiO2 supports. Driven by the Schottky junction, the TiO2 supports can provide electrons for metal catalysts under illumination by appropriate light. Further examination by ultrafast spectroscopy revealed that the plasmonics of Pd may force a large number of electrons to undergo reverse migration from Pd to the conduction band of TiO2 under strong illumination, thus lowering the electron density of the Pd surface as a side effect. We were therefore able to rationally tailor the charge state of the metal surface and thus modulate the function of Pd nanocrystals in O2 activation and organic oxidation reactions by simply altering the intensity of light shed on Pd-TiO2 hybrid structures.

7.
J Am Chem Soc ; 135(8): 3200-7, 2013 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-23391267

RESUMO

In many organic reactions, the O(2) activation process involves a key step where inert ground triplet O(2) is excited to produce highly reactive singlet O(2). It remains elusive what factor induces the change in the electron spin state of O(2) molecules, although it has been discovered that the presence of noble metal nanoparticles can promote the generation of singlet O(2). In this work, we first demonstrate that surface facet is a key parameter to modulate the O(2) activation process on metal nanocrystals, by employing single-facet Pd nanocrystals as a model system. The experimental measurements clearly show that singlet O(2) is preferentially formed on {100} facets. The simulations further elucidate that the chemisorption of O(2) to the {100} facets can induce a spin-flip process in the O(2) molecules, which is achieved via electron transfer from Pd surface to O(2). With the capability of tuning O(2) activation, we have been able to further implement the {100}-faceted nanocubes in glucose oxidation. It is anticipated that this study will open a door to designing noble metal nanocatalysts for O(2) activation and organic oxidation. Another perspective of this work would be the controllability in tailoring the cancer treatment materials for high (1)O(2) production efficiency, based on the facet control of metal nanocrystals. In the cases of both organic oxidation and cancer treatment, it has been exclusively proven that the efficiency of producing singlet O(2) holds the key to the performance of Pd nanocrystals in the applications.


Assuntos
Nanopartículas , Neoplasias/terapia , Oxigênio/metabolismo , Paládio/química , Catálise , Células HeLa , Humanos , Microscopia Eletrônica de Transmissão , Propriedades de Superfície
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