Additional file 1: Figure S1. of Hybrid Nanomaterials Based on Graphene and Gold Nanoclusters for Efficient Electrocatalytic Reduction of Oxygen

UV-visible absorbance spectrum of PVP-AuNCs. Figure S2. Representative TEM images of PVP-AuNCs and their size distribution histogram. Figure S3. Representative TEM images of RGO. Figure S4. Representative TEM images with different magnitudes for nanocomposite of RGO/AuNCs (1:1). Figure S5. CV measurements of nanocomposites with different AuNCs loadings in O2-saturated 0.1 M KOH at a scanning rate of 10 mV/s. (DOC 16377 kb

Metal Nickel Foam as an Efficient and Stable Electrode for Hydrogen Evolution Reaction in Acidic Electrolyte under Reasonable Overpotentials

Acidic electrolytes are advantageous for water electrolysis in the production of hydrogen as there is a large supply of H⁺ ions in the solution. In this study, with the applied overpotential larger than the equilibrium potential of Ni⁰/Ni²⁺, Ni foam as HER electrode exhibits excellent and stable HER activity with an onset potential of −84 mV (vs RHE), a high current density of 10 mA cm^–2 at −210 mV (vs RHE), and prominent electrochemical durability (longer than 5 days) in acidic electrolyte. The results presented herein may has potential large-scale application in hydrogen energy production

Porous Carbon-Supported Gold Nanoparticles for Oxygen Reduction Reaction: Effects of Nanoparticle Size

Porous carbon-supported gold nanoparticles of varied sizes were prepared using thiolate-capped molecular Au₂₅, Au₃₈, and Au₁₄₄ nanoclusters as precursors. The organic capping ligands were removed by pyrolysis at controlled temperatures, resulting in good dispersion of gold nanoparticles within the porous carbons, although the nanoparticle sizes were somewhat larger than those of the respective nanocluster precursors. The resulting nanocomposites displayed apparent activity in the electroreduction of oxygen in alkaline solutions, which increased with decreasing nanoparticle dimensions. Among the series of samples tested, the nanocomposite prepared with Au₂₅ nanoclusters displayed the best activity, as manifested by the positive onset potential at +0.95 V vs RHE, remarkable sustainable stability, and high numbers of electron transfer at (3.60–3.92) at potentials from +0.50 to +0.80 V. The performance is comparable to that of commercial 20 wt % Pt/C. The results demonstrated the unique feasibility of porous carbon-supported gold nanoparticles as high-efficiency ORR catalysts

Total Water Splitting Catalyzed by Co@Ir Core–Shell Nanoparticles Encapsulated in Nitrogen-Doped Porous Carbon Derived from Metal–Organic Frameworks

Developing bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) toward overall water splitting with high efficiency and robust durability is highly desirable but very challenging. Herein, we report a highly efficient and robust bifunctional electrocatalyst for overall water splitting based on Co@Ir core–shell nanoparticles encapsulated in nitrogen-doped porous carbon derived from metal–organic frameworks. The series of Co@Ir/NC-<i>x</i> samples were prepared through a galvanic replacement of IrCl₃ with Co/NC, which was obtained by calcination of zeolitic imidazolate framework 67 (ZIF-67). In the electrocatalytic characterizations toward OER and HER, Co@Ir/NC-10% exhibited the best performance among the series, with an overpotential of 280 mV at a current density of 10 mA cm^–2 for OER, superior to the benchmark IrO₂ catalyst, and an overpotential of −121 mV at a current density of 10 mA cm^–2 for HER in 1 M KOH. Moreover, Co@Ir/NC-10% also demonstrated markedly higher long-term stability than IrO₂ for OER and superior long-term durability than Pt/C for HER. Finally, the overall water splitting catalyzed by the series of composites was explored and visually observed

Graphitic Nitrogen Is Responsible for Oxygen Electroreduction on Nitrogen-Doped Carbons in Alkaline Electrolytes: Insights from Activity Attenuation Studies and Theoretical Calculations

To date, controversies remain in the unambiguous identification of the active sites in N-doped carbons for oxygen reduction reaction (ORR). In the present study, prolonged potential cycling was conducted on three N-doped carbons in O₂-saturated 0.1 M KOH aqueous solution, where apparent attenuation of the ORR activity was observed, within the context of limiting current and onset potential. The attenuation trend of the limiting current was closely correlated with the diminishing content of graphitic N, as manifested in X-ray photoelectron spectroscopy measurements and Mott–Schottky analysis. In addition, the specific activity per graphitic N was found to be almost invariant within a wide range of potentials during prolonged potential cycling for all three model catalysts, in good agreement with theoretical prediction, whereas no such a correlation was observed with pyrrolic or pyridinic N. Density functional theory calculations showed that the first-electron reduction, which is a rate-determining step for the 4e^– ORR process, on carbon atoms adjacent to graphitic N, exhibited a much smaller Gibbs free-energy change than that on carbons neighboring pyrrolic or pyridinic N. These results strongly suggest that graphitic N is responsible for the ORR activity of N-doped carbons in alkaline electrolytes. Results in the present work may offer a generic, effective paradigm in the determination of catalytic active sites in heteroatom-doped carbons and be exploited as a fundamental framework for the rational design and engineering of effective carbon catalysts

Fluorescence Intensity and Lifetime Cell Imaging with Luminescent Gold Nanoclusters

In this article, luminescent properties of gold nanoclusters (AuNCs) were studied at the single nanoparticle level and also used as novel imaging agents in cell media. Two types of water-soluble AuNCs which were stabilized with a monolayer composed of either mercaptosuccinic acid (MSA) or tiopronin thiolate ligands were synthesized by a chemical reduction reaction. These AuNCs were determined to have an average core diameter of less than 2 nm. On a time-resolved confocal microscope, the emission signals from the single AuNCs were distinctly recordable. The quantum yields of these AuNCs were measured to be ca. 5%. The lifetime of these AuNCs is also much longer than the lifetime of cellular autofluorescence in lifetime cell imaging as well as the lifetime of organic dye Alexa Fluor 488. After being derivatized with polyethylene glycol (PEG) moieties, the AuNCs were uploaded efficiently in the HeLa cells. Fluorescence intensity and lifetime cell images were recorded on the time-resolved confocal microscope in which the emission from the AuNCs was readily differentiated from the cellular autofluorescence background because of their relatively stronger emission intensities and longer lifetimes. These loaded nanoclusters in the cells were observed to widely distribute throughout the cells and especially densely loaded near the cell nucleuses. The AuNCs in the cells were also tested to have a better photostability relative to the organic fluorophores under the same conditions. We thus conclude that the AuNCs have a great potential as novel nanoparticle imaging agents, especially as lifetime imaging agents, in fluorescence imaging applications. We also prospect much broader applications of these AuNCs after further improvements of their luminescence quantum yields

Mesoporous N‑Doped Carbons Prepared with Thermally Removable Nanoparticle Templates: An Efficient Electrocatalyst for Oxygen Reduction Reaction

Thermally removable nanoparticle templates were used for the fabrication of self-supported N-doped mesoporous carbons with a trace amount of Fe (Fe-N/C). Experimentally Fe-N/C was prepared by pyrolysis of poly­(2-fluoroaniline) (P2FANI) containing a number of FeO­(OH) nanorods that were prepared by a one-pot hydrothermal synthesis and homogeneously distributed within the polymer matrix. The FeO­(OH) nanocrystals acted as rigid templates to prevent the collapse of P2FANI during the carbonization process, where a mesoporous skeleton was formed with a medium surface area of about 400 m²/g. Subsequent thermal treatments at elevated temperatures led to the decomposition and evaporation of the FeO­(OH) nanocrystals and the formation of mesoporous carbons with the surface area markedly enhanced to 934.8 m²/g. Electrochemical measurements revealed that the resulting mesoporous carbons exhibited apparent electrocatalytic activity for oxygen reduction reactions (ORR), and the one prepared at 800 °C (Fe-N/C-800) was the best among the series, with a more positive onset potential (+0.98 V vs RHE), higher diffusion-limited current, higher selectivity (number of electron transfer <i>n</i> > 3.95 at +0.75 V vs RHE), much higher stability, and stronger tolerance against methanol crossover than commercial Pt/C catalysts in a 0.1 M KOH solution. The remarkable ORR performance was attributed to the high surface area and sufficient exposure of electrocatalytically active sites that arose primarily from N-doped carbons with minor contributions from Fe-containing species

Assessing the Biocidal Activity and Investigating the Mechanism of Oligo‑<i>p</i>‑phenylene-ethynylenes

A number of oligo-<i>p</i>-phenylene-ethynylenes (OPEs) have exhibited excellent biocidal activity against both Gram-negative and Gram-positive bacteria. Although cell death may occur in the dark, these biocidal compounds are far more effective in the light as a result of their abilities to generate cell-damaging reactive oxygen species. In this study, the interactions of four OPEs with Escherichia coli and Staphylococcus aureus have been investigated. Compared to the OPEs with quaternary ammonium salts (Q-OPE), the OPEs with tertiary ammonium (T-OPE) effectively kill many more bacterial cells under light irradiation, presumably by severe perturbations of the bacterial cell wall and cytoplasmic membrane. According to the findings from this study, such intriguing light-induced antibacterial behavior is probably attributed to the combination of bacterial membrane disruption and the interfacial or intracellular generation of singlet oxygen or other ROS. Singlet oxygen was proved to be formed from irradiation of the OPEs, whereas the varying cell membrane perturbation abilities of OPEs enhance antibacterial activity

Comprehending the role of the S-phase on the corrosion behavior of austenitic stainless steel exposed to H₂S/CO₂-saturated liquid and vapor environments

The corrosion behavior of austenitic stainless steel after low-temperature liquid oxy-nitriding (LON) was investigated by exposing in H2S/CO2-saturated liquid and vapor environments up to 720 h at 60 °C. The corrosion rates before and after LON were compared by the weightlessness method, and the microstructure as well as the corrosion scales were characterized using surface analysis methods. The results indicated that the composite S-phase layer with the outer Fe3O4 layer and the inner nitrogen-rich sublayer could improve the corrosion performance in H2S/CO2-saturated environment. The base material (BM) suffered local corrosion first, which then transformed into uniform corrosion. As a comparison, The LON sample, covered with a thin corrosion product layer, indicated slight local corrosion. The excellent corrosion resistance of the S-phase should be attributed to the blocking effect of the continuous Fe3O4 film as well as the suppression of the atomic mobility by the nitrogen-containing supersaturated solid solution