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1.
Nat Commun ; 11(1): 2002, 2020 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-32332731

RESUMO

The development of oxygen evolution reaction (OER) electrocatalysts remains a major challenge that requires significant advances in both mechanistic understanding and material design. Recent studies show that oxygen from the perovskite oxide lattice could participate in the OER via a lattice oxygen-mediated mechanism, providing possibilities for the development of alternative electrocatalysts that could overcome the scaling relations-induced limitations found in conventional catalysts utilizing the adsorbate evolution mechanism. Here we distinguish the extent to which the participation of lattice oxygen can contribute to the OER through the rational design of a model system of silicon-incorporated strontium cobaltite perovskite electrocatalysts with similar surface transition metal properties yet different oxygen diffusion rates. The as-derived silicon-incorporated perovskite exhibits a 12.8-fold increase in oxygen diffusivity, which matches well with the 10-fold improvement of intrinsic OER activity, suggesting that the observed activity increase is dominantly a result of the enhanced lattice oxygen participation.

2.
iScience ; 23(3): 100943, 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-32163897

RESUMO

Rechargeable Zn-ion batteries working with manganese oxide cathodes and mild aqueous electrolytes suffer from notorious cathode dissolution during galvanostatic cycling. Herein, for the first time we demonstrate the dynamic self-recovery chemistry of manganese compound during charge/discharge processes, which strongly determines the battery performance. A cobalt-modified δ-MnO2 with a redox-active surface shows superior self-recovery capability as a cathode. The cobalt-containing species in the cathode enable efficient self-recovery by continuously catalyzing the electrochemical deposition of active Mn compound, which is confirmed by characterizations of both practical coin-type batteries and a new-design electrolyzer system. Under optimized condition, a high specific capacity over 500 mAh g-1 is achieved, together with a decent cycling performance with a retention rate of 63% over 5,000 cycles. With this cobalt-facilitated deposition effect, the battery with low concentration (0.02 M) of additive Mn2+ in the electrolyte (only 12 atom % to the overall Mn) maintains decent capacity retention.

3.
Adv Sci (Weinh) ; 6(10): 1802066, 2019 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-31131190

RESUMO

Iron single atom catalysts (Fe SACs) are the best-known nonprecious metal (NPM) catalysts for the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs), but their practical application has been constrained by the low Fe SACs loading (<2 wt%). Here, a one-pot pyrolysis method is reported for the synthesis of iron single atoms on graphene (FeSA-G) with a high Fe SAC loading of ≈7.7 ± 1.3 wt%. The as-synthesized FeSA-G shows an onset potential of 0.950 V and a half-wave potential of 0.804 V in acid electrolyte for the ORR, similar to that of Pt/C catalysts but with a much higher stability and higher phosphate anion tolerance. High temperature SiO2 nanoparticle-doped phosphoric acid/polybenzimidazole (PA/PBI/SiO2) composite membrane cells utilizing a FeSA-G cathode with Fe SAC loading of 0.3 mg cm-2 delivers a peak power density of 325 mW cm-2 at 230 °C, better than 313 mW cm-2 obtained on the cell with a Pt/C cathode at a Pt loading of 1 mg cm-2. The cell with FeSA-G cathode exhibits superior stability at 230 °C, as compared to that with Pt/C cathode. Our results provide a new approach to developing practical NPM catalysts to replace Pt-based catalysts for fuel cells.

4.
Nat Commun ; 10(1): 2290, 2019 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-31123249

RESUMO

Microbial contribution to gold biogeochemical cycling has been proposed. However, studies have focused primarily on the influence of prokaryotes on gold reduction and precipitation through a detoxification-oriented mechanism. Here we show, fungi, a major driver of mineral bioweathering, can initiate gold oxidation under Earth surface conditions, which is of significance for dissolved gold species formation and distribution. Presence of the gold-oxidizing fungus TA_pink1, an isolate of Fusarium oxysporum, suggests fungi have the potential to substantially impact gold biogeochemical cycling. Our data further reveal that indigenous fungal diversity positively correlates with in situ gold concentrations. Hypocreales, the order of the gold-oxidizing fungus, show the highest centrality in the fungal microbiome of the auriferous environment. Therefore, we argue that the redox interaction between fungi and gold is critical and should be considered in gold biogeochemical cycling.


Assuntos
Fusarium/metabolismo , Ouro/metabolismo , Hypocreales/metabolismo , Microbiologia do Solo , Solo/química , Ouro/química , Minerais/química , Minerais/metabolismo , Oxirredução , Austrália Ocidental
5.
J Am Chem Soc ; 141(14): 5863-5870, 2019 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-30884944

RESUMO

Electrically insulating objects gain a net electrical charge when brought in and out of contact. This phenomenon-triboelectricity-involves the flow of charged species, but conclusively establishing their nature has proven extremely difficult. Here, we demonstrate an almost linear relationship between a plastic sample's net negative charge and the amount of solution metal ions discharged to metallic particles with a coefficient of proportionality linked to its electron affinity (stability of anionic fragments). The maximum magnitude of reductive redox work is also material dependent: metallic particles grow to a larger extent over charged dielectrics that yield stable cationic fragments (smaller ionization energy). Importantly, the extent to which the sample can act as electron source greatly exceeds the net charging measured in a Faraday pail/electrometer set up, which brings direct evidence of triboeletricity being a mosaic of positive and negative charges rather than a homogeneous ensemble and defines for the first time their quantitative scope in electrochemistry.

6.
Chem Commun (Camb) ; 55(9): 1233-1236, 2019 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-30624439

RESUMO

g-C3N4 crystalline/amorphous lateral-like homostructures were prepared using crystalline g-C3N4 nanosheets as seeds via sequential edge-epitaxy growth. The homojunction effectively separates photogenerated carriers, resulting in high photo- and electro-catalytic activities.

7.
Nat Nanotechnol ; 13(12): 1148-1153, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30297819

RESUMO

Gold nanorods are one of the most widely explored inorganic materials in nanomedicine for diagnostics, therapeutics and sensing1. It has been shown that gold nanorods are not cytotoxic and localize within cytoplasmic vesicles following endocytosis, with no nuclear localization2,3, but other studies have reported alterations in gene expression profiles in cells following exposure to gold nanorods, via unknown mechanisms4. In this work we describe a pathway that can contribute to this phenomenon. By mapping the intracellular chemical speciation process of gold nanorods, we show that the commonly used Au-thiol conjugation, which is important for maintaining the noble (inert) properties of gold nanostructures, is altered following endocytosis, resulting in the formation of Au(I)-thiolates that localize in the nucleus5. Furthermore, we show that nuclear localization of the gold species perturbs the dynamic microenvironment within the nucleus and triggers alteration of gene expression in human cells. We demonstrate this using quantitative visualization of ubiquitous DNA G-quadruplex structures, which are sensitive to ionic imbalances, as an indicator of the formation of structural alterations in genomic DNA.


Assuntos
Núcleo Celular/genética , DNA/química , Quadruplex G , Ouro/metabolismo , Nanotubos , Compostos de Sulfidrila/metabolismo , Núcleo Celular/metabolismo , DNA/genética , Endocitose , Regulação da Expressão Gênica , Ouro/análise , Células HEK293 , Humanos , Células MCF-7 , Nanotubos/análise , Nanotubos/ultraestrutura , Compostos de Sulfidrila/análise
8.
J Colloid Interface Sci ; 530: 556-566, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-30005232

RESUMO

Unreliable energy supply and environmental pollution are two major concerns of the human society in this century. Herein, we report a rational approach on preparation of hierarchically-structured cobalt-carbon composites with tunable properties for a number of applications. A facile hydrothermal treatment of cobalt nitrate and sucrose results in the formation of a metallic cobalt-amorphous carbon composite with cobalt nanospheres anchored homogenously on an amorphous carbon substrate. Tuning the calcination conditions in air will generate either a metallic cobalt-cobalt oxide core-shell structure with magnetism or a fully oxidized Co3O4 composite. The different materials are demonstrated as anodes for lithium-ion batteries (LIBs) and catalysts for advanced oxidation-based wastewater remediation. A fully oxidized composite (FC@CS, fully oxidized Co loaded on carbon spheres) as a LIB anode exhibits superior electrochemical performance, possessing a high reversible capacity, high initial columbic efficiency, outstanding cycling performance and excellent rate capability. The anode performance is superior to most reported Co3O4-based electrodes. Meanwhile, the partially oxidized composite (PC@CS, partially oxidized Co loaded on carbon spheres) functions as an efficient and stable catalyst for removal of phenol via peroxymonosulfate (PMS) activation, which is demonstrated via electron paramagnetic resonance (EPR) and quenching experiments for generation of radicals. More importantly, the recycled PC@CS can be further applied as a LIBs anode after full oxidation regeneration, performing comparably to FC@CS. This FC@CS → PC@CS → FC@CS transformation provides an innovative approach for efficient material synthesis, recycling and application.

9.
Adv Mater ; 30(13): e1706287, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29423964

RESUMO

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1-2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO2 to CO, achieving a turnover frequency (TOF) of 11.7 s-1 at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

10.
ACS Appl Mater Interfaces ; 9(9): 8121-8133, 2017 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-28207229

RESUMO

Rechargeable Zn-air battery is limited by the sluggish kinetics and poor durability of the oxygen catalysts. In this Research Article, a new bifunctional oxygen catalyst has been developed through embedding the ultrafine NiFeO nanoparticles (NPs) in a porous amorphous MnOx layer, in which the NiFeO-core contributes to the high activity for the oxygen evolution reaction (OER) and the amorphous MnOx-shell functions as active phase for the oxygen reduction reaction (ORR), promoted by the synergistic effect between the NiFeO core and MnOx shell. The synergistic effect is related to the electron drawing of NiFeO core from MnOx shell, which decreases the affinity and adsorption energy of oxygen on MnOx shell and significantly increases the kinetics of ORR. The electrocatalytic activity and durability of NiFeO@MnOx depends strongly on the NiFeO:MnOx ratio. NiFeO@MnOx with NiFeO:MnOx weight ratio of 1:0.8 shows the best performance for reversible ORR and OER, with a potential gap (ΔE) of 0.792 V to achieve a current density of 3 mA cm-2 for ORR (EORR=3) and 5 mA cm-2 for OER (EOER=5) in 0.1 M KOH solution. The high activity of the NiFeO@MnOx(1:0.8) has been demonstrated in a Zn-air battery. Zn-air battery fabricated using the NiFeO@MnOx(1:0.8) oxygen electrode shows similar initial performance with that of Pt-Ir/C oxygen electrode but a much better durability under charge and discharge cycles as the result of the structure confinement effect of amorphous MnOx. The results demonstrate NiFeO@MnOx as an effective bifunctional oxygen catalysts for rechargeable metal-air batteries.

12.
Chemistry ; 19(52): 17733-44, 2013 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-24288151

RESUMO

Two N-donor-functionalised ionic liquids (ILs), 1-ethyl-1,4-dimethylpiperazinium bis(trifluoromethylsulfonyl)amide (1) and 1-(2-dimethylaminoethyl)-dimethylethylammonium bis(trifluoromethylsulfonyl)amide (2), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (3). Marked differences in thermal and electrochemical stability were observed between the two tertiary-amine-functionalised salts and the non-functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self-diffusion coefficients (Di ) and molar conductivities (Λ) are higher for the IL with an open-chain cation (2) than that with a cyclic cation (1), but less than that with a non-functionalised, heterocyclic cation (3). The viscosities (η) show the opposite behaviour. The Walden [Λ[proportionality](1/η)(t) ] and Stokes-Einstein [Di /T)[proportionality](1/η)(t) ] exponents, t, are very similar for the three salts, 0.93-0.98 (±0.05); that is, the self-diffusion coefficients and conductivity are set by η. The Di for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13% higher than that of 2. The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D+ +D- ). The Nernst-Einstein deviation parameters (Δ) are such that the mean of the two like-ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3, 1 and 2, respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order D(d)__ < D(d)++ < D(d)+_, as is common for [Tf2N](-) salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti-correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti-correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t~0.95.

13.
Anal Chem ; 85(21): 10495-502, 2013 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-24080025

RESUMO

The ion-to-electron transduction reaction mechanism at the buried interface of the electrosynthesized poly(3-octylthiophene) (POT) solid-contact (SC) ion-selective electrode (ISE) polymeric membrane has been studied using synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), and electrochemical impedance spectroscopy (EIS)/neutron reflectometry (NR). The tetrakis[3,5-bis(triflouromethyl)phenyl]borate (TFPB(-)) membrane dopant in the polymer ISE was transferred from the polymeric membrane to the outer surface layer of the SC on oxidation of POT but did not migrate further into the oxidized POT SC. The TFPB(-) and oxidized POT species could only be detected at the outer surface layer (≤14 Ǻ) of the SC material, even after oxidation of the electropolymerized POT SC for an hour at high anodic potential demonstrating that the ion-to-electron transduction reaction is a surface confined process. Accordingly, this study provides the first direct structural evidence of ion-to-electron transduction in the electropolymerized POT SC ISE by proving TFPB(-) transport from the polymeric ISE membrane to the oxidized POT SC at the buried interface of the SC ISE. It is inferred that the performance of the POT SC ISE is independent of the thickness of the POT SC but is instead contingent on the POT SC surface reactivity and/or electrical capacitance of the POT SC. In particular, the results suggest that the electropolymerized POT conducting polymer may spontaneously form a mixed surface/bulk oxidation state, which may explain the unusually high potential stability of the resulting ISE. It is anticipated that this new understanding of ion-to-electron transduction with electropolymerized POT SC ISEs will enable the development of new and improved devices with enhanced analytical performance attributes.


Assuntos
Elétrons , Eletrodos Íon-Seletivos , Polímeros/química , Tiofenos/química , Propriedades de Superfície
14.
Phys Chem Chem Phys ; 15(20): 7470-4, 2013 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-23584418

RESUMO

Aluminium electrodeposition is demonstrated from a thermally degraded ionic liquid solution. NMR and voltammetric analyses established that Al(3+) reduction was remarkably similar to that in non-degraded IL solutions suggesting that the electroactive metal-containing species was unaffected by heat treatment. Electron microscopy revealed a significant grain refinement of the deposited metal.


Assuntos
Compostos de Alumínio/química , Líquidos Iônicos/química , Temperatura , Ar , Técnicas Eletroquímicas , Galvanoplastia , Espectroscopia de Ressonância Magnética , Tamanho da Partícula , Propriedades de Superfície , Água/química
15.
Phys Chem Chem Phys ; 15(5): 1364-8, 2013 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-23247387

RESUMO

Resistivities of thin polymer films increase abruptly with decreasing thickness, although the corresponding decline in resistance plateaus below a certain thickness. One can jump to the incorrect conclusion that quantum confinement and surface scattering are responsible for this behaviour, and we highlight the pitfalls of committing such an error.


Assuntos
Polímeros/química , Transporte de Elétrons , Polimetil Metacrilato/química , Teoria Quântica , Propriedades de Superfície
16.
Analyst ; 136(16): 3252-8, 2011 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-21735000

RESUMO

Solid-contact (SC) ion-selective electrodes (ISEs) utilizing thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and plasticized poly(vinylchloride) (PVC) have been produced using a spin casting procedure. This study was carried out with a view of characterizing this popular and well known SC ISE using a series of complementary surface analysis techniques. This work revealed that PEDOT:PSS prevents the separation of an undesirable water layer at the buried interface of this SC ISE due to the high miscibility of water in the hydrophilic PEDOT:PSS layer. The lack of a clearly defined and molecularly sharp buried interface prohibits the formation of a distinct water layer presumably by eliminating sites that promote the accumulation of water. This outcome is important to the chemical sensor community since it provides further insights into the compatibility of sensor components in SC ISEs.

17.
Anal Chem ; 82(14): 6203-7, 2010 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-20557118

RESUMO

This paper reports on three-dimensional synchrotron radiation/Fourier transform-infrared microspectroscopy (SR/FT-IRM) imaging studies of water inclusions at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs). It is our intention to describe a nondestructive method that may be used in surface studies of the buried interfaces of materials, especially multilayers of polymers. Herein, we demonstrate the power of SR/FT-IRM for studying water inclusions at the buried interfaces of SC-ISEs. A poly(methyl methacrylate)-poly(decyl methacyrlate) [PMMA-PDMA] copolymer revealed the presence of micrometer sized inclusions of water at the gold/membrane interface, while a coupling of a hydrophobic solid contact of poly(3-octylthiophene 2,5-diyl) (POT) prevented the accumulation of water at the buried interface. A similar study with a poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate) [PEDOT/PSS] solid contact also revealed an absence of distinct micrometer-sized pools of water; however, there were signs of absorption of water accompanied by swelling of the PEDOT/PSS underlayer, and these membrane zones are enriched with respect to water.


Assuntos
Polímeros/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Síncrotrons , Água/química , Ouro/química , Eletrodos Íon-Seletivos , Tiofenos/química
18.
Anal Chem ; 80(17): 6731-40, 2008 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-18671410

RESUMO

This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modern analytical chemistry (e.g., clinical chemistry using single blood droplets, modern biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem.


Assuntos
Polímeros/química , Água/química , Impedância Elétrica , Eletroquímica , Eletrodos , Interações Hidrofóbicas e Hidrofílicas , Difração de Nêutrons , Nêutrons , Cloreto de Polivinila/química , Espalhamento a Baixo Ângulo , Sensibilidade e Especificidade , Prata/química , Espectrometria de Massa de Íon Secundário , Análise Espectral , Propriedades de Superfície
19.
Phys Chem Chem Phys ; 10(1): 73-6, 2008 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-18075683

RESUMO

This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 A water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs).


Assuntos
Eletrodos Íon-Seletivos , Polímeros/química , Água/química , Membranas Artificiais
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