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1.
J Am Chem Soc ; 142(2): 962-972, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31852179

RESUMO

The pursuit of efficient hydrogenation nanocatalysts with a desirable selectivity toward intricate substrates is state-of-the-art research but remains a formidable challenge. Herein, we report a series of novel PdCdx nanocubes (NCs) for ultraselective hydrogenation reactions with flexible tuning features. Obtaining a desirable conversion level of the substrates (e.g., 4-nitrophenylacetylene (NPA), 4-nitrobenzaldehyde (NBAD), and 4-nitrostyrene (NS)) and competitive selectivity for all potential hydrogenation products have been achieved one by one under optimized hydrogenation conditions. The performance of these PdCdx NCs displays an evident dependence on both the composition and the use of Cd and a need for a distinct hydrogen source (H2 or HCOONH4). Additionally, for the selectivity of hydrogen to be suitably high, the morphology of the NCs has a very well-defined effect. Density functional theory calculations confirmed the variation of adsorption energy for the substrate and hydrogenation products by carefully controlled introduction of Cd, leading to a desirable level of selectivity for all potential hydrogenation products. The PdCdx NCs also exhibit excellent reusability with negligible activity/selectivity decay and structural/composition changes after consecutive reactions. The present study provides an advanced strategy for the rational design of superior hydrogenation nanocatalysts to achieve a practical application for desirable and selective hydrogenation reaction efficiency.

2.
Nano Lett ; 19(10): 6894-6903, 2019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31547661

RESUMO

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd-Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd4Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd4Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd0 sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd4Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

3.
ACS Nano ; 12(11): 11625-11631, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30481970

RESUMO

Exploring high-performance and cost-efficient electrocatalysts with unusual metastable phase offers opportunities for improving the electrochemical hydrogen generation, while it remains a great challenge to achieve them with desirable activity and stability. Herein, we report that the doping engineering in a metastable, hexagonal-close-packed nickel (hcp Ni) electrocatalyst is a largely unrevealed yet important factor in achieving an extremely active and stable electrocatalyst toward alkaline hydrogen evolution reaction (HER). Theoretical predications and experimental results suggest that, while the stability of metastable hcp Ni electrocatalyst can be largely improved via the manganese (Mn) doping due to the lower formation energy and lattice stabilization, the MnO/hcp Ni surface promotes the HER via intrinsic favorable H2O adsorption and fast water dissociation kinetics. Consequently, the Mn-doped hcp Ni electrocatalyst shows a small overpotential of 80 mV at 10 mA/cm2 and a low Tafel slope of 68 mV/dec. The result is even approaching that of the commercial Pt/C, being one of the best reported non-noble metal HER electrocatalysts in alkaline media. Under long-term chronopotentiometry measurement, such electrocatalyst can endure at least 10 h with negligible activity decay and structure change. The present work demonstrates the dimension in boosting the electrocatalysis by doping engineering of metastable electrocatalysts.

4.
Sci Adv ; 4(7): eaap8817, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-30027113

RESUMO

The search for high-performance non-platinum (Pt) electrocatalysts is the most challenging issue for fuel cell technology. Creating bimetallic non-Pt nanocrystals (NCs) with core/shell structures or alloy features has widely been explored as the most effective way for enhancing their electrochemical properties but still suffered from undesirable performance due to the limited interactions between the different components. By addressing the above issue, we report on a new class of active and stable bimetallic non-Pt electrocatalysts with palladium (Pd) icosahedra as the core and nickel (Ni) decorating the surface toward cathodic oxygen reduction reaction (ORR) under alkaline conditions. The optimized Pd6Ni icosahedra with unique interaction between an icosahedral Pd core and surface Ni yield the highest ORR activity with a mass activity of 0.22 A mgPd-1, which is better than those of the conventional Pd6Ni icosahedra with alloy surfaces or Pd-rich surfaces, and even two times higher than that of the commercial Pt/C (0.11 A mgPt-1), representing one of the best non-Pt electrocatalysts. Simulations reveal that the Pd icosahedra decorated with Ni atoms emerged in the subsurface can weaken the interaction between the adsorbed oxygen and Pd (111) facet and enhance the ORR activities due to an obvious shift of d-band center. More significantly, under electrochemical accelerated durability test, the Pd6Ni icosahedra can endure at least 10,000 cycles with negligible activity decay and structural change. The present work demonstrates an important advance in surface tuning of bimetallic NCs as high-performance non-Pt catalysts for catalysis, energy conversion, and beyond.

5.
ACS Nano ; 12(6): 6245-6251, 2018 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-29763293

RESUMO

The development of electrocatalysts with high activity and stability for oxygen evolution reaction (OER) is critically important, the one being regarded as the bottleneck process of overall water splitting. Herein, we fulfill significant OER improvement in both activity and stability by constructing a class of Ni(OH)2-CeO2 supported on carbon paper (Ni xCe y@CP) with an intimate hydroxide (Ni(OH)2)-oxide (CeO2) interface. Such interface largely promotes the OER activity with a low overpotential of 220 mV at 10 mA cm-2 and a small Tafel slope of 81.9 mV dec-1 in 1 M KOH. X-ray photoelectron spectroscopy analysis shows that the intimate interface induced by the strong electronic interactions between Ni(OH)2 and CeO2 involves the modulation of binding strength between intermediates and catalysts, making a great contribution to the OER enhancement. Importantly, such intimate interface structures can be largely maintained even after a long-time stability test. We have further demonstrated that, when pairing the Ni4Ce1@CP after phosphorization (P-Ni4Ce1@CP), the Ni4Ce1@CP and P-Ni4Ce1@CP assembly is highly active and stable for overall water splitting with a low voltage of 1.68 V at 25 mA cm-2 and negligible stability delay over 30 h of continuous operation, which are much better than the commercial Ir/C and Pt/C.

6.
Small ; 14(16): e1703990, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29533013

RESUMO

Although direct hydrogen (H2 ) oxidation to hydrogen peroxide (H2 O2 ) is considered as a promising strategy for direct H2 O2 synthesis, the desirable conversion efficiency remains formidable challenge. Herein, highly active and selective direct H2 oxidation to H2 O2 is achieved by using hollow Pd-Sn intermetallic nanoparticles (NPs) as the catalysts. By tuning the catalytic solvents and catalyst supports, the efficiency of direct H2 oxidation to H2 O2 can be optimized well with the hollow Pd2 Sn NPs/P25 exhibiting H2 O2 selectivity up to 80.7% and productivity of 60.8 mol kgcat-1 h-1 . In situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption results confirm the different surface atom arrangements between solid and hollow Pd-Sn NPs. X-ray photoelectron spectra results show that the higher efficiency of Pd2 Sn NPs/P25 is due to its higher content of metallic Pd and higher ratio of Snx+ , which benefit H2 O2 production and selectivity.

7.
Small ; 13(22)2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28418193

RESUMO

Carbon dioxide (CO2 ) hydrogenation is an effective strategy for CO2 utilization, while unsatisfied conversion efficiencies remain great challenges. It is reported herein that zigzag Pt-Co nanowires (NWs) with Pt-rich surfaces and abundant steps/edges can perform as highly active and stable CO2 hydrogenation catalysts. It is found that tuning the Pt/Co ratio of the Pt-Co NWs, solvents, and catalyst supports could well optimize the CO2 hydrogenation to methanol (CH3 OH) with the Pt4 Co NWs/C exhibiting the best performance, outperforming all the previous catalysts. They are also very durable with limited activity decays after six catalytic cycles. The diffuse reflectance infrared Fourier transform spectroscopy result of CO2 adsorption shows that the Pt4 Co NWs/C undergoes the adsorption/activation of CO2 by forming appropriate carboxylate intermediates, and thus enhancing the CH3 OH production.

8.
Adv Mater ; 29(7)2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27966229

RESUMO

An ultrathin PtNi NWs mediated strategy to form PtNiPd core-shell NWs is constructed. The combination of 1D structure, high-index bounded surface, and unique core-shell structure with high activity of the PtNi shell results in superior performance toward both the liquid fuel oxidation reactions and oxygen reduction reaction.

9.
J Sep Sci ; 40(4): 971-978, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28012243

RESUMO

Ordered macroporous molecularly imprinted polymers were prepared by a combination of the colloidal crystal templating method and the molecular imprinting technique by using SiO2 colloidal crystal as the macroporogen, quercetin as the imprinting template, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and tetrahydrofuran as the solvent. Scanning electron microscopy and Brunauer-Emmett-Teller measurements show that the ordered macroporous molecularly imprinted polymers have a more regular macroporous structure, a narrower pore distribution and a greater porosity compared with the traditional bulk molecularly imprinted polymers. The kinetic and isothermal adsorption behaviors of the polymers were investigated. The results indicate that the ordered macroporous molecularly imprinted polymers have a faster intraparticle mass transfer process and a higher adsorption capacity than the traditional bulk molecularly imprinted polymers. The ordered macroporous molecularly imprinted polymers were further employed as a sorbent for a solid-phase extraction. The results show that the ordered macroporous molecularly imprinted polymers can effectively separate quercetin from the Gingko hydrolysate.


Assuntos
Impressão Molecular , Polímeros/química , Quercetina/isolamento & purificação , Adsorção , Ginkgo biloba/química , Dióxido de Silício , Extração em Fase Sólida
10.
Small ; 12(33): 4464-70, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27412405

RESUMO

A large-scalable wet-chemical approach to create networked Pt-Pb nanowires (NWs) with tunable compositions is reported. Due to their 3D networked structure, alloy effect, rich defects/steps, and antipoisoning property of Pb, the networked Pt-Pb NWs exhibit the best activity and durability towards ethylene glycol oxidation reaction (EGOR), compared with the networked Pt NWs and Pt/C.

11.
Ying Yong Sheng Tai Xue Bao ; 26(5): 1447-53, 2015 May.
Artigo em Chinês | MEDLINE | ID: mdl-26571664

RESUMO

Correlation analysis between main chemical constituents of tobacco leaves and endogenous harmful components in mainstream cigarette smoke was conducted. Leaf stalk positions exhibited a high relation with endogenous harmful components and hazard index (H). Upper stalk position leaves had greater release of 1-butanone,4-(methylnitrosoamino)-1-(3-pyridinyl)-(NNK), B[a]P, HCN, NH3 and phenol in mainstream cigarette smoke, and a higher hazard index than middle position leaves except for crotonaldehyde, which had greater release from middle position leaves. Different endogenous harmful components in mainstream cigarette smoke presented complicated correlation with main chemical constituents in tobacco. The same type of leaf chemical constituents presented different correlations with various endogenous harmful components in mainstream cigarette smoke. Cigarette hazard index showed significantly positive correlations with contents of nicotine, protein, total nitrogen, major polyphenols and organic acids, while significantly negative correlation with potassium and carbonaceous substances, such as total sugars, reducing sugars and starch. The results suggested that properly increasing potassium content and decreasing nitrogenous constituents in cured tobacco leaf may reduce the cigarette hazard index.


Assuntos
Folhas de Planta/química , Fumaça/análise , Tabaco/química , Nicotina , Nitrogênio , Potássio , Fumaça/efeitos adversos
12.
Tumour Biol ; 36(3): 1755-62, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25366141

RESUMO

The low survival rates of cancers are primarily due to late diagnosis and metastasis. Discriminating the metastasis is a crucial factor for prognosis and improving the survival rate of cancer patients. MicroRNAs (miRNAs) can regulate the expression of hundreds of downstream genes, which has a broad effect on the regulation of the whole cell cycle. Accumulating studies have found that the aberrant expression of miRNAs is associated with cancer genesis. The aim of this study is to evaluate the diagnostic value of miRNAs in detecting cancer metastasis. Medline, PubMed, Embase, and CNKI were searched for relevant articles. Sensitivity, specificity, positive and negative likelihood ratio (PLR, NLR) and diagnostic odds ratio (DOR), the summary receiver operator characteristic (SROC) curve and the calculated AUC (area under the SROC curve) were applied to explore the diagnostic accuracy of miRNAs in metastasis. Seven hundred seventy-one metastatic cancer patients and 552 non-metastatic cancer controls from 14 articles were involved in our meta-analysis. A sensitivity of 0.75 (95% confidence interval (CI), 0.72-0.79) and a specificity of 0.80 (95% CI, 0.76-0.84) were observed from metastatic patients and non-metastatic controls in the combined analysis. And the AUC was 0.83 (95% CI, 0.79-0.86). In addition, results from subgroup analyses suggested that a higher diagnostic value for metastasis was acquired in tissue sample other than blood sample (sensitivity, 0.82 versus 0.73; specificity, 0.84 versus 0.79; PLR, 5.0 versus 3.5; NLR, 0.22 versus 0.34; DOR, 23 versus 10; AUC, 0.88 versus 0.80). In summary, this meta-analysis proved the relatively high diagnostic value of miRNA in metastasis, which might be applied as a novel screening tool to detect metastasis along with other biomarkers. We also illustrated that tissue-based miRNAs may have a better diagnostic accuracy than blood-based miRNAs.


Assuntos
Biomarcadores Tumorais/genética , MicroRNAs/genética , Metástase Neoplásica/genética , Segunda Neoplasia Primária/genética , Humanos , Metástase Neoplásica/diagnóstico , Segunda Neoplasia Primária/diagnóstico , Curva ROC , Sensibilidade e Especificidade
13.
Dalton Trans ; 43(41): 15337-45, 2014 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-25187309

RESUMO

Three multidentate ligands, L1-L3, derived from bis(pyridin-2-ylmethyl)amine (L1) were synthesized. Reaction of these ligands with FeCl3·6H2O in methanol led to the formation of the iron complexes Fe1-Fe3 (Fe1: [FeL1Cl3]; Fe2: [FeL2Cl3]; Fe3: [FeL3Cl3]) in good yields. These complexes have been fully characterized. The structures of complexes Fe1-Fe3 have been determined using X-ray single crystal diffraction analysis. Electrochemical investigation revealed that complex Fe3 partially converts to Fe4 ([FeL3Cl2]PF6) by the replacement of one of its three chlorides with its pendant triazolyl group in solution. Fe4 was also synthesized by dechlorination using AgPF6 as the Cl(-) abstractor and its composition was further confirmed by both elemental analysis and X-ray single crystal diffraction analysis. All four complexes catalyze the direct hydroxylation of benzene to phenol with hydrogen peroxide as an oxidant in a mixed medium of water and acetonitrile. The reactivity of the complexes correlates well with their reduction potentials. The more negative the potential, the more reactive (high conversion rate) the catalysts. These complexes catalyze not only the oxidation of benzene, but also the further oxidation of the product, phenol. In the oxidation, a radical mechanism is certainly involved but an alternative pathway may also exist.

14.
J Sep Sci ; 36(15): 2486-95, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23720441

RESUMO

Sucrose esters (SEs) were successfully extracted from Oriental tobacco leaves using a new methodology based on accelerated solvent extraction followed by hydrophilic-lipophilic balanced cartridge cleanup step. The SEs were detected by HPLC with ion-trap MS detection using an electrospray interface operated in the positive ion mode. This methodology combines the high efficiency of extraction provided by a pressurized fluid and the highly sensitive characterization offered by ion-trap MS. Under the optimized conditions, 14 SEs were first identified among a total of 23 SEs found in Oriental tobacco leaves. Under the same conditions, only four new SEs were extracted by using traditional ultrasound-assisted extraction and liquid-solid extraction methods. The present method might be potentially useful in high-efficiency extraction and sensitive characterization of SEs from complex matrices such as tobacco leaves.


Assuntos
Ésteres/isolamento & purificação , Folhas de Planta/química , Extração em Fase Sólida , Sacarose/isolamento & purificação , Tabaco/química , Cromatografia Líquida de Alta Pressão/instrumentação , Espectrometria de Massas/instrumentação , Extração em Fase Sólida/instrumentação , Solventes/química
15.
Langmuir ; 23(10): 5296-304, 2007 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-17425348

RESUMO

Nearly monodisperse silver nanoparticles have been prepared in a simple oleylamine-liquid paraffin system. Intensive study has found that the formation process of silver nanoparticles could be divided into three stages: growth, incubation, and Ostwald ripening stages. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM have all demonstrated the occurrence of Ostwald ripening, which could result in better control over the size and size distribution of silver nanoparticles. SAXS (small-angle X-ray scattering) results show that the as-obtained silver nanoparticles can self-assemble into ordered arrays. The possible reduction mechanism of silver ions by oleylamine is related to the Ag+-mediated conversion of primary amines to nitriles.

16.
Avian Dis ; 50(1): 59-63, 2006 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-16617983

RESUMO

A recombinant baculovirus was constructed containing an expression cassette with a reporter gene, green fluorescent protein, directed by a constitutive mammalian promoter: a human cytomegalovirus immediate early promoter/enhancer (CMV-IE). High titer virus was prepared with ultracentrifugation. Efficient gene delivery and expression were observed in the virus-treated chicken primary culture, myoblast cells, and whole embryonic fibroblast cells. It was noticed that an addition of sodium butyrate (a selective histone deacetylase inhibitor) to viral transduction medium extremely enhanced the reporter-gene expression. However, there is no effect of presence of trichostatin A observed. To maximize the reporter-gene expression, the baculoviral infection condition was optimized with both cell types. Our approaches demonstrated that recombinant baculovirus could efficiently deliver its genome DNA into chicken primary cells and that CMV-IE, a mammalian-cell-active promoter, was functional in chicken primary cells and could direct a high level of gene expression. Clearly, the recombinant baculovirus provides an alternative means for foreign gene delivery into avian cells.


Assuntos
Baculoviridae/genética , Galinhas/genética , Expressão Gênica , Mioblastos/metabolismo , Animais , Baculoviridae/fisiologia , Células Cultivadas , Técnicas de Transferência de Genes , Engenharia Genética , Vetores Genéticos/genética , Vetores Genéticos/fisiologia , Proteínas de Fluorescência Verde , Transformação Genética
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