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1.
The hydrogen evolution reaction (HER) on a noble metal surface in alkaline media is more sluggish than that in acidic media due to the limited proton supply. To promote the reaction, it is necessary to transform the alkaline HER mechanism via a multisite catalyst, which has additional water dissociation sites to improve the proton supply to an optimal level. Here, this study reports a top‐down strategy to create a multisite HER catalyst on a nano‐Pd surface and how to further fine‐tune the areal ratio of the water dissociation component to the noble metal surface in core/shell‐structured nanoparticles (NPs). Starting with Pd/Fe 3O 4 core/shell NPs, electrochemical cycling is used to tune the coverage of iron (oxy)hydroxide on a Pd surface. The alkaline HER activity of the core/sell Pd/FeO x (OH) 2?2x NPs exhibits a volcano‐shaped correlation with the surface Fe species coverage. This indicates an optimum coverage level where the rates of both the water dissociation step and the hydrogen formation step are balanced to achieve the highest efficiency. This multisite strategy assigns multiple reaction steps to different catalytic sites, and should also be extendable to other core/shell NPs to optimize their HER activity in alkaline media. 相似文献
2.
The interaction of superoxide radical anion (O 2 ??) with active dicarbonyls (methylglyoxal, glyoxal, and malonic dialdehyde) was studied. It was demonstrated that glyoxal and methylglyoxal inhibited superoxide-dependent accumulation of formazan; however, malonic dialdehyde stimulated this process. The formation of O 2 ?? in these experiments occurred during the decomposition of the SOTS-1 azo initiator. On the other hand, all of the studied dicarbonyls in this system of O 2 ?? generation competed for superoxide with the TIR ON spin trap. These compounds also inhibited luminal-dependent chemiluminescence during the AIBN azo initiator-induced peroxidation of liposomes from the egg phosphatidylcholine. A mechanism for the antiradical and antioxidant effects of the studied dicarbonyls, assuming the production of free radical intermediates in their reactions with O 2 ?? or its protonated form, is proposed. 相似文献
3.
Luciferase-dependent assays, important for biochemical analyses of cytotoxicity and reporter genes, may be perturbed by compounds interfering with the luciferase reaction. We analyzed the impact of different aluminum (Al) species on a luciferase-based assay for determination of cellular adenosine triphosphate. Al 0 nanoparticles (Al 0–NPs) but not Al 2O 3–NPs decreased luminescence, correlated to high absorbance of Al 0–NPs. By contrast, Al ions increased the luminescent signal. Data demonstrate that luciferase-dependent assays can be reciprocally disturbed by Al–NPs or Al ions in a specific manner, depending on the particular Al species. Careful interpretation of data from such experiments is essential in order to obtain conclusive results. 相似文献
4.
Nonprecious metal catalysts (NPMCs) Fe? N? C are promising alternatives to noble metal Pt as the oxygen reduction reaction (ORR) catalysts for proton‐exchange‐membrane fuel cells. Herein, a new modulation strategy is reported to the active moiety Fe? N 4 via a precise “single‐atom to single‐atom” grafting of a Pt atom onto the Fe center through a bridging oxygen molecule, creating a new active moiety of Pt 1? O 2? Fe 1? N 4. The modulated Fe? N? C exhibits remarkably improved ORR stabilities in acidic media. Moreover, it shows unexpectedly high catalytic activities toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with overpotentials of 310 mV for OER in alkaline solution and 60 mV for HER in acidic media at a current density of 10 mA cm ?2, outperforming the benchmark RuO 2 and comparable with Pt/C(20%), respectively. The enhanced multifunctional electrocatalytic properties are associated with the newly constructed active moiety Pt 1? O 2? Fe 1? N 4, which protects Fe sites from harmful species. Density functional theory calculations reveal the synergy in the new active moiety, which promotes the proton adsorption and reduction kinetics. In addition, the grafted Pt 1? O 2? dangling bonds may boost the OER activity. This study paves a new way to improve and extend NPMCs electrocatalytic properties through a precisely single‐atom to single‐atom grafting strategy. 相似文献
5.
Here, we report for the first time the synthesis of bismuth-coated silver nanoparticles in dichroic bismuth glass nanocomposites
by a novel and simple one-step melt quench technique without using any external reducing agent. The metallic silver nanoparticles
(Ag NPs) were generated first, and subsequently, metallic bismuth was deposited on the Ag NPs and formed a thick layer. The
reduction of Bi 3+ to Bi o and subsequently its deposition on the Ag NPs (which were formed earlier than Bi o) in the K 2O–Bi 2O 3–B 2O 3 (KBB) glass system have been explained by their standard reduction potentials. The UV–vis absorption spectra show a prominent
surface plasmon resonance (SPR) absorption band at 575 nm at lower concentrations (up to 0.01 wt%); three bands at 569, 624
and 780 nm at medium concentration (0.02–0.03 wt%); and two weak bands at 619 and 817 nm at highest concentration (0.06 wt%)
of silver. They have been explained by the electrodynamics theories. TEM images reveal the conversion of spheroidal (5–15 nm)
to hexagonal (10–35 nm) shaped Ag NPs with the increase in concentration of silver (up to 0.06 wt%). SAED pattern confirms
the crystalline planes of rhombohedral bismuth and cubic silver. Thermal treatment at 360 °C, which is the glass transformation
temperature ( T
g) of the sample containing lower concentration of silver (0.007 wt%), shows red-shifted SPR band due to increase in size of
NPs. Whereas the sample containing higher concentration (0.06 wt%) of silver under similar treatment exhibited changes in
SPR spectral profile happened due to conversion to spherical NPs from hexagonal shape and reduction in size (10–20 nm) of
NPs after heat treatment for 65 h. HRTEM images corroborate the different orientations of the NPs. FESEM images reveal hexagonal
disk like structure having different orientations. Dichroic nature of the nanocomposites has been explained with the size
and shape of Ag nanoparticles. We believe that this work will create new avenues in the area of nanometal–glass hybrid nanocomposites
and the materials have significant applications in the field of optoelectronics and nanophotonics. 相似文献
6.
A novel S 2O 3 2? luminescent sensor (Cu 2+- p-CPIP) was developed and the presence of S 2O 3 2? caused an obvious fluorescence enhancement at 420 nm upon excitation at 330 nm, which could be distinguished with the naked eye under a UV lamp. Remarkably, the compound exhibited excellent selective and sensitive response to S 2O 3 2? over other common anions with a micromolar limit of detection (0.442 μM) in DMSO/H 2O (v/v, 1:1) buffer. The absorbance intensity and the color of Cu 2+- p -CPIP solution changed gradually with the increase of S 2O 3 2? concentration. The proposed method was applied to the determination of S 2O 3 2? in milk samples and the recoveries were 97.5–105 %. The preparation of Cu 2+- p -CPIP exhibited the quick, simple and facile advantages. The results showed that Cu 2+- p -CPIP can be a good candidate for simple, rapid and sensitive colorimetric detection of S 2O 3 2? in aqueous solution. 相似文献
7.
The authors report that a marine Shewanella sp. CNZ-1 is capable of producing Au NPs under various conditions. Results showed that initial concentration of Au(III), pH values and electron donors affected nucleation of Au NPs by CNZ-1, resulting in different apparent color of the as-obtained bio-Au NPs, which were further characterized by UV-Vis, TEM, XRD, and XPS analyses. Mechanism studies revealed that Au(III) was first reduced to Au(I) and eventually reduced to EPS-coated Au 0 NPs. FTIR and FEEM analyses revealed that some amides and humic acid-like matters were involved in the production of bio-Au NPs through CNZ-1 cells. In addition, the authors also found that the catalytic activity of bio-Au NPs for 4-nitrophenol (4-NP) reduction could be enhanced by various metal ions (Ca 2+, Cu 2+, Co 2+, Fe 2+, Fe 3+, Ni 2+, Sr 2+, and Cr 3+) and metal oxides (Fe 3O 4, Al 2O 3, and SiO 2), which is beneficial for their further practical application. The maximum zero-order rate constant k 1 and first-order rate constant k2 of all metal ions/oxides supplemented systems can reach 99.65 mg/(L .min) and 2.419 min −1, which are 11.3- and 12.6-fold higher than that of control systems, respectively. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2727, 2019. 相似文献
8.
The antioxidant properties of some phenolic Schiff bases in the presence of different reactive particles such as •OH, •OOH, (CH2=CH−O−O•), and -•O2 were investigated. The thermodynamic values, ΔH
BDE, ΔH
IP, and ΔH
PA, were used for this purpose. Three possible mechanisms for transfer of hydrogen atom, concerted proton−electron transfer (CPET), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) were considered. These mechanisms were tested in solvents of different polarity. On the basis of the obtained results it was shown that SET-PT antioxidant mechanism can be the dominant mechanism when Schiff bases react with radical cation, while SPLET and CPET are competitive mechanisms for radical scavenging of hydroxy radical in all solvents under investigation. Examined Schiff bases react with the peroxy radicals via SPLET mechanism in polar and nonpolar solvents. The superoxide radical anion reacts with these Schiff bases very slowly. 相似文献
9.
Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp 3 nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm ?2. The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec ?1) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH) 2 interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH) 2 nanosheets and the COF shows that in the most favorable configuration the Ni(OH) 2 nanosheets are sandwiched between the sp 3 nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions. 相似文献
10.
The use of noble metal nanoparticles (NPs) as reductants in chemiluminescence (CL) has been reported only rarely owing to their high oxidation potentials. Interestingly, nucleophiles could dramatically lower the oxidation potential of Ag NPs, such that in the presence of nucleophiles Ag NPS could be used as reductants to induce the CL emission of luminol, an important CL reagent widely used in forensic analysis for the detection of trace amounts of blood. Although nucleophiles are indispensible in Ag NP‐luminol CL, only inorganic nucleophiles such as Cl ‐, Br ‐, I ‐ and S 2O 32‐ have been shown to be efficient. The effects of organic nucleophiles on CL remain unexplored. In this study, 20 standard amino acids were evaluated as novel organic nucleophiles in Ag NP‐luminol CL. Histidine, lysine and arginine could initiate CL emission; the others could not. It is proposed that the different behaviors of 20 standard amino acids in the CL reactions derive from the interface chemistry between Ag NPs and these amino acids. UV/vis absorption spectra were studied to validate the interface chemistry. In addition, imidazole and histidine were chosen as a model pair to compare the behavior of the monodentate nucleophile with that of the corresponding multidentate nucleophile in Ag NP‐luminol CL. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
Superoxide dismutases (SODs) are metalloproteins that protect cells against oxidative stress by controlling the concentration of superoxide (O 2−) through catalysis of its dismutation. The activity of superoxide dismutases can be mimicked by low-molecular-weight complexes having potential therapeutic applications. This review presents recent strategies for designing efficient SOD mimics, from molecular metal complexes to nanomaterials. Studies of these systems in cells reveal that some SOD mimics, designed to react directly with superoxide, may also indirectly enhance the cellular antioxidant arsenal. Finally, a good understanding of the bioactivity requires information on the cell-penetration, speciation, and subcellular location of the SOD mimics: we will describe recent studies and new techniques that open opportunities for characterizing SOD mimics in biological environments. 相似文献
12.
The O 2-sensitive reduction of high-molecular-weight aromatic azo and nitro dyes by intestinal bacteria appears to be mediated by low-molecular-weight electron carriers with Eo′ = −200 to −350 mV. This process may allow the design of polymeric azo prodrugs for specific release of certain aromatic amines in the colon. 相似文献
13.
A new low-molecular-weight peptide with phenol oxidase activity, named Pc factor, was isolated and purified from liquid culture of a white-rot basidiomycete Phanerochaete chrysosporium. Its molecular weight was about 600 Da estimated by gel-filtration. Three amino acids Glu, Gly and Val were detected in hydrolysate. Absorption peaks corresponding to amino acids and peptide were observed by UV and IR spectra analysis. And the signal of Cα of amino acid was also detected by 13C-NMR method. Pc factor had high thermostability and remained active in weakly alkalescent pH range. It could chelate Fe 3+ and reduce it to Fe 2+, but no hydroxyl radical HO 9642; could be detected during the reaction process. It could oxidize phenolic lignin-model compounds such as 2,6-dimethoxyphenol (2,6-DMP), 2,2¢-azinobis (3-ethylbenzathiazoline-6-sulfinic acid) (ABTS) and syringaldazine in the absence of Mn 2+ and H 2O 2. These characteristics differed greatly from those of manganese peroxi-dases. The oxidative catalysis of Pc factor can be enhanced by certain metal ions such as Cu 2+ and Mn 2+ etc., and O2 molecule was necessary for this reaction. In summary, Pc factor may function as an electron carrier in this novel oxidation-reduction system. 相似文献
14.
A new low-molecular-weight peptide with phenol oxidase activity, named Pc factor, was isolated and purified from liquid culture
of a white-rot basidiomycete Phanerochaete chrysosporium. Its molecular weight was about 600 Da estimated by gel-filtration. Three amino acids Glu, Gly and Val were detected in hydrolysate.
Absorption peaks corresponding to amino acids and peptide were observed by UV and IR spectra analysis. And the signal of Cα
of amino acid was also detected by 13C-NMR method. Pc factor had high thermostability and remained active in weakly alkalescent pH range. It could chelate Fe 3+ and reduce it to Fe 2+, but no hydroxyl radical HO˙ could be detected during the reaction process. It could oxidize phenolic lignin-model compounds
such as 2,6-dimethoxyphenol (2,6-DMP), 2,2′-azinobis (3-ethylbenzathiazoline-6-sulfinic acid) (ABTS) and syringaldazine in
the absence of Mn 2+ and H 2O 2. These characteristics differed greatly from those of manganese peroxidases. The oxidative catalysis of Pc factor can be
enhanced by certain metal ions such as Cu 2+ and Mn 2+ etc., and O 2 molecule was necessary for this reaction. In summary, Pc factor may function as an electron carrier in this novel oxidation-reduction
system. 相似文献
15.
Nonprecious metal catalysts (NPMCs) Fe?N?C are promising alternatives to noble metal Pt as the oxygen reduction reaction (ORR) catalysts for proton‐exchange‐membrane fuel cells. Herein, a new modulation strategy is reported to the active moiety Fe?N 4 via a precise “single‐atom to single‐atom” grafting of a Pt atom onto the Fe center through a bridging oxygen molecule, creating a new active moiety of Pt 1?O 2?Fe 1?N 4. The modulated Fe?N?C exhibits remarkably improved ORR stabilities in acidic media. Moreover, it shows unexpectedly high catalytic activities toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with overpotentials of 310 mV for OER in alkaline solution and 60 mV for HER in acidic media at a current density of 10 mA cm ?2, outperforming the benchmark RuO 2 and comparable with Pt/C(20%), respectively. The enhanced multifunctional electrocatalytic properties are associated with the newly constructed active moiety Pt 1?O 2?Fe 1?N 4, which protects Fe sites from harmful species. Density functional theory calculations reveal the synergy in the new active moiety, which promotes the proton adsorption and reduction kinetics. In addition, the grafted Pt 1?O 2? dangling bonds may boost the OER activity. This study paves a new way to improve and extend NPMCs electrocatalytic properties through a precisely single‐atom to single‐atom grafting strategy. 相似文献
16.
In the current study, Fe 3O 4 NPs were synthesized and used as catalysts in a sono-Fenton-like process for remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil. The effects of operational variables were studied using central composite design (CCD) optimization approach. Results indicated that the effects of H 2O 2 concentration, Fe 3O 4 NPs dosage, ultrasonic power and pH were significant for pyrene removal as a contaminant model. In optimum experimental conditions, including H 2O 2 concentration of 78 mM, Fe 3O 4 NPs dosage of 18 mM, ultrasonic power of 313 W and pH value of 3.46, the observed pyrene removal was obtained 98.37%, which was verified through the additional experimental tests (99.33%). Pseudo first-order kinetic model was well fitted with the experimental data of pyrene removal with significant coefficient of correlation (R 2: 0.9672). Accordingly, an unwashed real soil sample containing diffident PAHs (pyrene, flurene, acenaphthylene, phenenthrene, chrysene, etc) was subjected to sono-Fenton-like process based on optimized conditions. The obtained findings revealed that the removal (%) ranged between 37.7% and 85.19% for different PAHs. 相似文献
17.
With the ongoing commercialization of nanotechnology products, the increasing use of engineered nanoparticles (NPs) could lead potentially to environmental risks. This study investigated the dynamic influences of three iron-based NPs (Fe 0, Fe 3O 4, and Fe 2O 3) applied into a red soil (RS) and a Wushan soil (WS) with different application rates (2 to 6 g kg ?1) on soil physicochemical properties such as pH, dissolved organic carbon (DOC), available ammonium nitrogen (NH 4 +-N), available phosphorus (AP), and enzymatic activities. The results showed that the addition of Fe 0 NPs increased DOC and available NH 4 +-N, but significantly decreased AP, while Fe 3O 4 and Fe 2O 3 NPs slightly reduced soil pH in both soils and significantly declined available NH 4 +-N in the WS and AP in the RS. No significant difference was observed between the effects of Fe 3O 4 and Fe 2O 3 NPs on soil properties except AP in the RS. All iron-based NPs decreased the activities of urease and acid phosphatase in both soils. The effects on soil physicochemical properties, especially available NH 4 +-N and AP induced by iron-based NPs, varied greatly with soil types. These results implied that cautions should be paid for the environmental application of iron-based NPs, especially iron oxide NPs in soils. 相似文献
18.
AbstractAcinetobacter baumannii is a biofilm forming multidrug resistant (MDR) pathogen responsible for respiratory tract infections. In this study, aluminium oxide nanoparticles (Al 2O 3 NPs) were synthesized and characterized by TEM and EDX and shown to be spherical shaped nanoparticles with a diameter < 10 ?nm. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) for the Al 2O 3 NPs ranged between 125 and 1,000 ?µg ml ?1. Exposure to NPs caused cellular membrane disruption, indicated by an increase in cellular leakage of the contents. Biofilm inhibition was 11.64 to 70.2%, whereas attachment of bacteria to polystyrene surfaces was reduced to 48.8 to 51.9% in the presence of NPs. Nanoparticles also reduced extracellular polymeric substance production and the biomass of established biofilms. The data revealed the non-toxic nature of Al 2O 3 NPs up to a concentrations of 120 ?µg ml ?1 in HeLa cell lines. These results demonstrate an effective and safer use of Al 2O 3 NPs against the MDR A. baumannii by targeting biofilm formation, adhesion and EPS production. 相似文献
19.
Ultrafine PdAg nanoparticles (NPs) are successfully immobilized on zirconia/porous carbon/reduced graphene oxide (ZrO 2/C/rGO) nanocomposite derived from metal organic framework/graphene oxide. Monodispersed PdAg NPs (diameter ≤2.5 nm) can be facilely anchored on the ZrO 2/C/rGO and the aggregation of metal NPs can be avoided utmostly. By virtue of the synergistic effect between metal NPs and support, the resulting PdAg@ZrO 2/C/rGO exhibits excellent activity (turnover frequency, 4500 h ?1 at 333 K) for the dehydrogenation of formic acid. As an effective strategy, it provides an opportunity to immobilize ultrafine metal NPs on metal oxide/porous carbon/reduced graphene oxide, which has tremendous application prospects in various catalytic fields. 相似文献
20.
Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO 2 nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 10 12 W/m 2. Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications. 相似文献
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