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Showing papers in "Journal of Physical Chemistry C in 2012"


Journal ArticleDOI
TL;DR: Using first-principles structure optimization and phonon calculations based on density functional theory, this paper predicted that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures.
Abstract: Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX2) might offer properties superior to those of graphene. So far, only very few MX2 compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. These materials have two-dimensional hexagonal lattices and have top-view appearances as if they consisted of either honeycombs or centered honeycombs. However, their bonding is different from that of graphene; they can be viewed as a positively charged plane of transition-metal atoms sandwiched between two planes of negatively charged oxygen or chalcogen atoms. Electron correlation in transition-metal oxides was treated by including Coulomb repulsion through LDA...

1,152 citations


Journal ArticleDOI
TL;DR: In this paper, the authors introduced a novel approach for quantitatively measuring the percentage of exposed {001} facets in anatase TiO2 by using Raman spectroscopy, which provided a high sensitivity and accuracy for measuring the exposed facets from the micro perspective of molecular bonding with less measurement errors.
Abstract: Controlling the growth of high-activity anatase TiO2 exposed {001} facets improves greatly the adsorption and electronic and photocatalytic properties and has been attractive for various environmental and energy-related applications. In this paper, we introduced a novel approach for quantitatively measuring the percentage of exposed {001} facets in anatase TiO2 by using Raman spectroscopy. Comparing to XRD, Raman peaks originate from the vibration of molecular bonds, that is, vibrational mode Eg and A1g peaks, which are related to different crystal planes. Therefore, it provided a high sensitivity and accuracy for measuring the percentage of the exposed facets from the micro perspective of molecular bonding with less measurement errors. With the photocatalytic experiments, we found that 50% was the optimal percentage of the exposed {001} facets for the highest efficiency, which seemed more reasonable than the value of 70% obtained from XRD.

635 citations


Journal ArticleDOI
TL;DR: In this article, the effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different loadings using platinum as a cocatalyst in methanol aqueous solutions.
Abstract: Novel CdS quantum dot (QD)-coupled graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a chemical impregnation method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different CdS loadings using platinum as a cocatalyst in methanol aqueous solutions. The synergistic effect of g-C3N4 and CdS QDs leads to efficient separation of the photogenerated charge carriers and, consequently, enhances the visible light photocatalytic H2 production activity of the materials. The optimal CdS QD content is determined to be 30 wt %, and the corresponding H2 evolution rate was 17.27 μmol·h–1 under visible light irradiation, ∼9 times that of pure g-C3N4. A possible photocatalytic mechanism of the CdS/g-C3N4 comp...

630 citations


Journal ArticleDOI
TL;DR: In this article, conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANi), and polypyrrole (PPy) were directly coated on the surface of reduced graphene oxide (RGO) sheets via an in situ polymerization process to prepare conducting polymer-RGO nanocomposites with different loadings of the conducting polymer.
Abstract: In this work, conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANi), and polypyrrole (PPy) were directly coated on the surface of reduced graphene oxide (RGO) sheets via an in situ polymerization process to prepare conducting-polymer-RGO nanocomposites with different loadings of the conducting polymers. Experiment results showed that ethanol played an important role in achieving a uniform coating of the polymers on RGO sheets. The electrochemical capacitive properties of the composite materials were investigated by using cycle voltammetry and charge/discharge techniques. The composite consisting of RGO and PANi (RGO-PANi) exhibited a specific capacitance of 361 F/g at a current density of 0.3 A/g. The composites consisting of RGO and PPy (RGO-PPy) and PEDOT (RGO-PEDOT) displayed specific capacitances of 248 and 108 F/g, respectively, at the same current density. More than 80% of initial capacitance retained after 1000 charge/discharge cycles, suggesting a good cycling stability ...

624 citations


Journal ArticleDOI
TL;DR: In this article, an effective structural doping approach has been described to modify the photoelectrochemical properties of g-C3N4 by doping with nonmetal (sulfur or phosphorus) impurities.
Abstract: An effective structural doping approach has been described to modify the photoelectrochemical properties of g-C3N4 by doping with nonmetal (sulfur or phosphorus) impurities. Here, the substitutional and interstitial doped models of g-C3N4 systems were constructed with different doped sites, and then their dopant formation energies and electronic properties were performed to study the stability and visible-light photoactivity using first-principles density functional theory, respectively. Our results have identified that an S atom preferentially substitutes for the edge N atom of g-C3N4; however, a P atom preferentially situates the interstitial sites of in-planar of g-C3N4. Furthermore, it is demonstrated that the doping with nonmetal impurities reduces the energy gap to enhance the visible-light absorption of g-C3N4. The increased dispersion of the contour distribution of the HOMO and LUMO brought by doping facilitates the enhancement of the carrier mobility, while the noncoplanar HOMO and LUMO favor the...

568 citations


Journal ArticleDOI
TL;DR: In this article, an in situ Raman spectroscopic investigation has been carried out to identify the composition of the active phase present on the surface of nickel electrodes used for the electrochemical evolution of oxygen.
Abstract: An in situ Raman spectroscopic investigation has been carried out to identify the composition of the active phase present on the surface of nickel electrodes used for the electrochemical evolution of oxygen. The electrolyte in all cases was 0.1 M KOH. A freshly polished Ni electrode oxidized upon immersion in the electrolyte and at potentials approaching the evolution of oxygen developed a layer of γ-NiOOH. Electrochemical cycling of this film transformed it into β-NiOOH, which was observed to be three times more active than γ-NiOOH. The higher activity of β-NiOOH is attributed to an unidentified Ni oxide formed at a potential above 0.52 V (vs Hg/HgO reference). We have also observed that a submonolayer of Ni oxide deposited on Au exhibits a turnover frequency (TOF) for oxygen evolution that is an order of magnitude higher than that for a freshly prepared γ-NiOOH surface and more than 2-fold higher than that for a β-NiOOH surface. By contrast, a similar film deposited on Pd exhibits a TOF that is similar ...

563 citations


Journal ArticleDOI
TL;DR: In this article, a dicyandiamide precursor was used in the preparation of graphitic carbon nitride (g-C3N4) and nitrogen vacancies were introduced to modify the electronic structure and the properties of photoexcited charge carriers.
Abstract: Vacancy defects can play an important role in modifying the electronic structure and the properties of photoexcited charge carriers and consequently the photocatalytic activity of semiconductor photocatalysts. By controlling the polycondensation temperature of a dicyandiamide precursor in the preparation of graphitic carbon nitride (g-C3N4), we introduced nitrogen vacancies in the framework of g-C3N4. These vacancies exert remarkable effects on modifying the electronic structure of g-C3N4 as shown in UV-visible absorption spectra and valence band spectra. Steady and time-resolved fluorescence emission spectra show that, due to the existence of abundant nitrogen vacancies, the intrinsic radiative recombination of electrons and holes in g-C3N4 is greatly restrained, and the population of short-lived and long-lived charge carriers is decreased and increased, respectively. As a consequence, the overall photocatalytic activity of the g-C3N4, characterized by the ability to generate center dot OH radicals, photodecomposition of Rhodamine B, and photocatalytic hydrogen evolution under both UV-visible and visible light, was remarkably improved.

547 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the hydrogen production from an aqueous medium over amino-functionalized Ti(IV) metal-organic framework (Ti-MOF-NH2) under visible-light irradiation.
Abstract: The present article describes the hydrogen production from an aqueous medium over amino-functionalized Ti(IV) metal–organic framework (Ti-MOF-NH2) under visible-light irradiation. Ti-MOF-NH2, which employs 2-amino-benzenedicarboxylic acid as an organic linker, has been synthesized by a facile solvothermal method. Pt nanoparticles as cocatalysts are then deposited onto Ti-MOF-NH2 via a photodeposition process (Pt/Ti-MOF-NH2). The XRD and N2 adsorption measurements reveal the successful formation of a MOF framework structure and its remaining structure after deposition of Pt nanoparticles. The observable visible-light absorption up to ∼500 nm can be seen in the DRUV–vis spectrum of Ti-MOF-NH2, which is associated with the chromophore in the organic linker. Ti-MOF-NH2 and Pt/Ti-MOF-NH2 exhibit efficient photocatalytic activities for hydrogen production from an aqueous solution containing triethanolamine as a sacrificial electron donor under visible-light irradiation. The longest wavelength available for the ...

520 citations


Journal ArticleDOI
TL;DR: In this article, a change of focus of the current research on ZnO-based DSCs (from morphology to surface control) is suggested and the origin of this striking difference in performance is analyzed and discussed with the perspective of future applications of ZnOs in dye-sensitized solar cells and related devices.
Abstract: ZnO was one of the first metal oxides used in dye-sensitized solar cells (DSCs). It exhibits a unique combination of potentially interesting properties such as high bulk electron mobility and probably the richest variety of nanostructures based on a very wide range of synthesis routes. However, in spite of the huge amount of literature produced in the past few years, the reported efficiencies of ZnO-based solar cells are still far from their TiO2 counterparts. The origin of this striking difference in performance is analyzed and discussed with the perspective of future applications of ZnO in dye-sensitized solar cells and related devices. In this regard, a change of focus of the current research on ZnO-based DSCs (from morphology to surface control) is suggested.

517 citations


Journal ArticleDOI
TL;DR: In this paper, the authors confirm recent reports that cobalt phosphate (Co-Pi) is an efficient water oxidation catalyst for BiVO4 and report an AM1.5 photocurrent of 1.7 mA/cm2 at 1.23 V vs RHE for 100 nm spray-deposited, compact, and undoped biVO4 films with an optimized Co-Pi film thickness of 30 nm.
Abstract: BiVO4 is considered to be a promising photoanode material for solar water splitting applications. Its performance is limited by two main factors: slow water oxidation kinetics and poor charge separation. We confirm recent reports that cobalt phosphate (Co-Pi) is an efficient water oxidation catalyst for BiVO4 and report an AM1.5 photocurrent of 1.7 mA/cm2 at 1.23 V vs RHE for 100 nm spray-deposited, compact, and undoped BiVO4 films with an optimized Co-Pi film thickness of 30 nm. The charge separation of these films depends strongly on light intensity, ranging from 90% at low light intensities to less than 20% at intensities corresponding to 1 sun. These observations indicate that the charge separation efficiency in BiVO4 is limited by poor electron transport and not by the presence of bulk defect states, interface traps, or the presence of a Schottky junction at the back-contact.

499 citations


Journal ArticleDOI
TL;DR: In this article, the positron annihilation lifetime spectroscopy (PALS) was used to characterize the oxygen vacancy associates in hydrogenation-modified TiO2 by using a positron annihilator lifetime spectrograph.
Abstract: This paper introduces a novel method for characterizing the oxygen vacancy associates in hydrogenation-modified TiO2 by using a positron annihilation lifetime spectroscopy (PALS). It was found that a huge number of small neutral Ti3+–oxygen vacancy associates, some larger size vacancy clusters, and a few voids of vacancy associates were introduced into hydrogenated TiO2. The defects blurred the atomic lattice high-resolution transmission electron microscopy (HRTEM) images and brought about the emergence of new Raman vibration. X-ray photoelectron spectroscopy (XPS) measurement indicated that the concentration of oxygen vacancies was 3% in the TiO2 lattice. The photoluminescence (PL) spectroscopy, photocurrent, and degradation of methylene blue indicated that the oxygen vacancy associates introduced by hydrogenation retarded the charge recombination and therefore improved the photocatalytic activity remarkably.

Journal ArticleDOI
TL;DR: In this article, the role of surface adsorption vs pore absorption in Li-S cell capacity retention and cycle life was investigated using nanocrystalline and mesoporous titania additives as polysulfide reservoirs.
Abstract: The possibility of achieving high-energy, long-life storage batteries has tremendous scientific and technological significance. A prime example is the Li–S cell, which can offer a 3–5-fold increase in energy density compared with conventional Li-ion cells, at lower cost. Despite significant recent advances, there are challenges to its wide-scale implementation. Upon sulfur reduction, intermediate soluble lithium polysulfides readily diffuse into the electrolyte, causing capacity fading and poor Coulombic efficiency in the cell. Herein, we increase the capacity retention and cycle life of the Li–S cell through the use of nanocrystalline and mesoporous titania additives as polysulfide reservoirs and examine the role of surface adsorption vs pore absorption. We find that the soluble lithium polysulfides are preferentially absorbed within the pores of the nanoporous titania at intermediate discharge/charge. This provides the major factor in stabilizing capacity although surface binding (adsorption) also plays...

Journal ArticleDOI
TL;DR: In this paper, a series of new luminescent emission-tunable phosphors Ca2Al3O6F:Ce3+,Tb3+ have been synthesized by a high temperature solid-state reaction.
Abstract: A series of new luminescent emission-tunable phosphors Ca2Al3O6F:Ce3+,Tb3+ have been synthesized by a high temperature solid-state reaction. The UV–vis reflectance, photoluminescence emission and excitation spectra, the lifetime, and the effect of Tb3+ concentration are investigated in detail. The intense green emission is realized in the Ca2Al3O6F:0.08Ce3+,0.05Tb3+ phosphors on the basis of the highly efficient energy transfer from Ce3+ to Tb3+ with an efficiency of over 90%. The energy transfer mechanism from Ce3+ to Tb3+ in the Ca2Al3O6F host was ascribed to the exchange interactions, and the formation of the Ce–Ce clusters and Ce–Tb clusters should be the reason for the high energy transfer efficiency. The critical distance of the energy transfer has also been calculated by the concentration-quenching method. These results indicate that the Ca2Al3O6F:Ce3+,Tb3+ phosphors have potential applications as a near UV-convertible phosphor for white light-emitting diodes because of its broad excitation in the ...

Journal ArticleDOI
Xianjun Du1, Dengsong Zhang1, Liyi Shi1, Ruihua Gao1, Jianping Zhang1 
TL;DR: In this paper, the comparative catalytic activity and coke resistance of Ni/CeO2 nanorods (NR) and nanopolyhedra (NP) were examined in carbon dioxide reforming of methane over Ni/NiO2-NR catalysts and showed that the predominantly exposed planes are the unusually reactive {110 and {100} planes on the CeO2−NR rather than the stable {111} one on the NiO2•NP.
Abstract: The comparative catalytic activity and coke resistance are examined in carbon dioxide reforming of methane over Ni/CeO2 nanorods (NR) and nanopolyhedra (NP). The Ni/CeO2–NR catalysts display more excellent catalytic activity and higher coke resistance compared with the Ni/CeO2–NP. The high resolution transmission electron microscope reveals that the predominantly exposed planes are the unusually reactive {110} and {100} planes on the CeO2–NR rather than the stable {111} one on the CeO2–NP. The prepared samples were also characterized by X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, UV and visible Raman spectra, and oxygen temperature-programmed oxidation. The {110} and {100} planes show great superiority for the anchoring of Ni nanoparticles, which results in the existence of strong metal–support interaction effect (SMSI). The SMSI effect can be helpful to prevent sintering of Ni particles, which benefits to reduce the dea...

Journal ArticleDOI
TL;DR: In this article, the reduced graphene oxide (RGO)-hierarchical ZnO hollow sphere composites are prepared through a simple ultrasonic treatment of the solution containing graphene oxide, Zn(CH3COO)2, DMSO, and H2O.
Abstract: The reduced graphene oxide (RGO)-hierarchical ZnO hollow sphere composites are prepared through a simple ultrasonic treatment of the solution containing graphene oxide (GO), Zn(CH3COO)2, DMSO, and H2O. The GO is reduced to RGO effectively, and the ZnO hollow spheres consisting of nanoparticles are uniformly dispersed on the surface of RGO sheets during the ultrasonic process. The optimum synergetic effect of RGO-ZnO composites is found at a RGO mass ratio of 3.56%, and the photocurrent and photodegradation efficiency on methylene blue of RGO-ZnO composites are improved by five times and 67%, respectively, compared with those of pure ZnO hollow spheres. The enhancements of photocurrent and photocatalytic activity can be attributed to the suppression of charge carriers recombination resulting from the interaction between ZnO and RGO.

Journal ArticleDOI
TL;DR: In this paper, first-principles calculations were carried out to investigate lithium-dispersed two-dimensional carbon allotropes, viz. graphyne and graphdiyne, for their applications as lithium storage and hydrogen storage materials.
Abstract: Ab initio first-principles calculations were carried out to investigate lithium-dispersed two-dimensional carbon allotropes, viz. graphyne and graphdiyne, for their applications as lithium storage and hydrogen storage materials. The lithiation potentials (vs Li/Li+) and specific capacities in these materials are found to be enhanced considerably as compared to the conventional graphite-based electrode materials. Lithium metal binding to these carbon materials is found to be enhanced considerably and is more than the cohesive energy of lithium. Each lithium atom in these metal-dispersed materials is found to carry nearly one unit positive charge and bind molecular hydrogen with considerably improved adsorption energies. Our calculated hydrogen adsorption enthalpies (−3.5 to −2.8 kcal/mol) are very close to the optimum adsorption enthalpy proposed for ambient temperature hydrogen storage (−3.6 kcal/mol). We have also shown that the band gaps in these planar carbon allotropes can be tuned by varying the numb...

Journal ArticleDOI
TL;DR: In this paper, a well-known gas sensing material SnO2 in combination with reduced graphene oxide was used in heavy metal ions detection for the first time, which could be used for the simultaneous and selective electrochemical detection of ultratrace Cd(II), Pb(II, Cu(II) and Hg(II).
Abstract: A well-known gas sensing material SnO2 in combination with reduced graphene oxide was used in heavy metal ions detection for the first time. This work reports the detailed study on the SnO2/reduced graphene oxide nanocomposite modified glass carbon electrode, which could be used for the simultaneous and selective electrochemical detection of ultratrace Cd(II), Pb(II), Cu(II), and Hg(II) in drinking water. The SnO2/reduced graphene oxide nanocomposite electrode was characterized voltammetrically using redox couples (Fe(CN)63–/4–), complemented with electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) has been used for the detection of Cd(II), Pb(II), Cu(II), and Hg(II). The detection limit (3σ method) of the SnO2/reduced graphene oxide nanocomposite modified GCE toward Cd(II), Pb(II), Cu(II) and Hg(II) is 1.015 × 10–10 M, 1.839 × 10–10 M, 2.269 × 10–10 M, and 2.789 × 10–10 M, respectively, which is very well below the guideline value given by the World Health Organ...

Journal ArticleDOI
TL;DR: In this article, a combined experimental and theoretical study on the vibrational properties of tenorite CuO and paramelaconite Cu4O3 was performed using Raman scattering and infrared absorption spectroscopy.
Abstract: A combined experimental and theoretical study is reported on the vibrational properties of tenorite CuO and paramelaconite Cu4O3. The optically active modes have been measured by Raman scattering and infrared absorption spectroscopy. First-principles calculations have been carried out with the LDA+U approach to account for strong electron correlation in the copper oxides. The vibrational properties have been computed ab initio using the so-called direct method. Excellent agreement is found between the measured Raman and infrared peak positions and the calculated phonon frequencies at the Brillouin zone center, which allows the assignment of all prominent peaks of the Cu4O3 spectra. Through a detailed analysis of the displacement eigenvectors, it is shown that a close relationship exists between the Raman modes of CuO and Cu4O3.

Journal ArticleDOI
TL;DR: In this paper, the polyaniline (PANI)/TiO2 nanocomposites have been successfully synthesized via a hydrothermal method and followed by a low-temperature calcination treatment process.
Abstract: The polyaniline (PANI)/TiO2 nanocomposites have been successfully synthesized via a hydrothermal method and followed by a low-temperature calcination treatment process. We find that such a PANI/TiO2 nanocomposite exhibits higher photocatalytic activity and stability than bare TiO2 and TiO2-xNx toward the liquid-phase degradation of methyl orange (MO) under both UV and visible light (420 nm < λ < 800 nm) irradiation. More noteworthy, the PANI/TiO2 photocatalyst still perform good activity toward MO and 4-chlorophenol (4-CP) under the longer wavelength of light (550 nm < λ < 800 nm). The total organic carbon (TOC) tests show that the mineralization rate of MO and 4-CP over PANI/TiO2 are apparently higher than bare TiO2 under the irradiation of both UV and visible light. The presence of synergic effect between PANI and TiO2 is believed to play an essential role in affecting the photoreactivity. At last, the roles of active species in the photocatalytic process are compared by using different types of active ...

Journal ArticleDOI
TL;DR: In this article, the thermal decomposition of Co3O4 nanoparticles of cobalt-based Prussian blue analogues at different temperatures was used to obtain high discharge capacity of 800, 970, 828, 854, and 651 mAhg.
Abstract: Co3O4 nanoparticles have been prepared by a facile strategy, which involves the thermal decomposition of nanoparticles of cobalt-based Prussian blue analogues at different temperatures. The nanoparticles prepared at 450, 550, 650, 750, and 850 °C exhibited a high discharge capacity of 800, 970, 828, 854, and 651 mAhg–1, respectively, after 30 cycles at a current density of 50 mAg–1. The nanocages produced at 550 °C show the highest lithium storage capacity. It is found that the nanocages display nanosize grains, hollow structure, a porous shell, and large specific surface area. At the temperature higher than 650 °C, the samples with larger grains, better crystallinity, and lower specific surface area can be obtained. It is found that the size, crystallinity, and morphology of nanoparticles have different effects on electrochemical performance. Better crystallinity is able to enhance the initial discharge capacity, while porous structure can reduce the irreversible loss. Therefore, the optimal size, crysta...

Journal ArticleDOI
TL;DR: In this article, the authors report on a systematic study of the effects of interface on the thermal conductivity of highly filled epoxy composites, where six kinds of surface treated and as received AlN particles are used as fillers.
Abstract: The interface between filler and matrix has long been a critical problem that affects the thermal conductivity of polymer composites. The effects of the interface on the thermal conductivity of the composite with low filler loading are well documented, whereas the role of the interface in highly filled polymer composites is not clear. Here we report on a systematic study of the effects of interface on the thermal conductivity of highly filled epoxy composites. Six kinds of surface treated and as received AlN particles are used as fillers. Three kinds of treated AlN are functionalized by silanes, i.e., amino, epoxy, and mercapto group terminated silanes. Others are functionalized by three kinds of materials, i.e., polyhedral oligomeric silsesquioxane (POSS), hyperbranched polymer, and graphene oxide (GO). An intensive study was made to clarify how the variation of the modifier would affect the microstructure, density, interfacial adhesion, and thus the final thermal conductivity of the composites. It was f...

Journal ArticleDOI
TL;DR: In this article, temperature-dependent spectroscopic results were presented to shed some light on the presently unclear fluorescence mechanism of carbon dots, and it was shown that carbon dots exhibit similar temperature behavior as metallic quantum dots (nanoclusters) but are different from inorganic semiconductor quantum dots.
Abstract: Carbon dots are cost-effective, environmental friendly, and biocompatible nanoparticles with many potential applications in optoelectronics and biophotonics. Their dual fluorescence bands were observed and could be attributed to core and surface state emission. We also conduct temperature-dependent fluorescence measurements from cryogenic to room temperatures. The dual emission bands exhibit similar temperature dependence. The strong electron–electron interactions and weak electron–phonon interactions could account for the very broad photoluminescence (PL) band even at 77 K. Our experimental results also suggest that carbon dots exhibit similar temperature behavior as metallic quantum dots (nanoclusters) but are different from inorganic semiconductor quantum dots. Here, for the first time, we present the temperature-dependent spectroscopic results to shed some light on the presently unclear fluorescence mechanism.

Journal ArticleDOI
TL;DR: The minimum inhibitory concentration (MIC) of Graphene nanosheets against pathogenic bacteria was evaluated by a micro-dilution method in this article, which showed that 1 μg/mL (against Escherichia coli and Salmonella typhimurium).
Abstract: Graphene nanosheets are highly recognized for their utility toward the development of biomedical device applications. The present study investigated the antibacterial efficiency of graphene nanosheets against four types of pathogenic bacteria. Graphene nanosheets are synthesized by a hydrothermal approach (under alkaline conditions using hydrazine hydrate). UV–vis and X-ray diffraction show a maximum absorbance at 267 nm and appearance of new broad diffraction peak at 26°, which ensures the reduction of graphene oxide into graphene nanosheets. Stretching and bending vibrations of C–C bonds, chemical states, disorder, and defects associated with the graphene nanosheets are evaluated in comparison with graphene oxide. The minimum inhibitory concentration (MIC) of graphene nanosheets against pathogenic bacteria was evaluated by a microdilution method. MICs such as 1 μg/mL (against Escherichia coli and Salmonella typhimurium), 8 μg/mL (against Enterococcus faecalis), and 4 μg/mL (against Bacillus subtilis) su...

Journal ArticleDOI
TL;DR: In this article, the authors report considerable chemical and morphological changes of reaction products in binder-free, vertically aligned carbon nanotube (VACNT) electrodes during Li-O2 battery cycling with a 1,2-dimethoxyethane (DME)-based electrolyte.
Abstract: We report considerable chemical and morphological changes of reaction products in binder-free, vertically aligned carbon nanotube (VACNT) electrodes during Li–O2 battery cycling with a 1,2-dimethoxyethane (DME)-based electrolyte. X-ray absorption near edge structure (XANES) of discharged oxygen electrodes shows direct evidence for the formation of Li2CO3-like species at the interface between VACNTs and Li2O2 but not significantly on the Li2O2 surfaces exposed to the electrolyte. Although Li2O2 and Li2CO3-like species were largely removed upon first charge, the oxidation kinetics became increasingly difficult during Li–O2 cycling, which is accompanied by the accumulation of Li2CO3 in the discharged and charged electrodes as evidenced by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Together, these results indicate that the irreversibility during Li–O2 cycling in DME can be attributed largely to the growth of Li2CO3-like species associated with the reactivity between ...

Journal ArticleDOI
TL;DR: In this article, an oxygen reduction reaction (ORR) catalyst obtained via a heat treatment of polyaniline, iron, and carbon black was characterized at several critical synthesis stages and following heat treatment at various temperatures.
Abstract: This paper summarizes a XANES, XPS, XRD, and Mo study of an oxygen reduction reaction (ORR) catalyst obtained via a heat treatment of polyaniline, iron, and carbon black. The catalyst was characterized at several critical synthesis stages and following heat treatment at various temperatures. The effect of sulfur during the synthesis was also investigated. XANES linear combination fitting (XANES-LCF) was used to determine the speciation of iron using 16 iron standards. The highest ORR activity was measured with a catalyst heat-treated at 900 °C, with the largest Fe−Nx content, as determined by the XANES-LCF, also characterized by the highest microporosity. An absence or a reduction in the amount of a sulfur-based oxidant in the aniline polymerization was found to lead to an increase in the amount of iron carbide formed during the heat treatment and a decrease in the number of Fe−N4 centers, thus attesting to an indirect beneficial role of sulfur in the catalyst synthesis. Using principal component analysis (PCA), a good correlation was found between the ORR activity and the presence of Fe−Nx structures.

Journal ArticleDOI
TL;DR: In this article, the 3-aminopropyltriethoxysilane (APTES) was used in the silanization reaction with silanol-terminated silicon.
Abstract: The use of the coupling agent, 3-aminopropyltriethoxysilane (APTES), in the silanization reaction with silanol-terminated silicon is an important surface modification reaction. Of particular importance is that the terminal amine functionalities of APTES are sufficiently exposed to the gas or liquid phase for further modifications, such as amide coupling reactions. Here, metastable induced electron spectroscopy (MIES) and UV photoelectron spectroscopy (UPS) were used to study the composition of the outermost layer of a silanol-terminated Si surface after silanization with APTES. High-resolution X-ray photoelectron spectroscopy (XPS) was used to validate the attachment of APTES to the surface. Density of States (DOS) calculations were employed for interpreting the MIE spectra. Findings showed that amine functionalities covered only a small fraction of the APTES-modified Si surface.

Journal ArticleDOI
Donge Wang1, Rengui Li1, Jian Zhu1, Jingying Shi1, Jingfeng Han1, Xu Zong1, Can Li1 
TL;DR: In this article, the electrocatalyst cobalt-phosphate (CoPi) was used as a cocatalyst for photocatalytic water splitting under visible light irradiation.
Abstract: The oxygen evolution is kinetically the key step in the photocatalytic water splitting. Cocatalysts could lower the activation potential for O2 evolution. However, the cocatalyst for O2 evolution has been less investigated, and few effective cocatalysts were reported. This paper reports that the O2 evolution rate of photocatalytic water splitting under visible light irradiation can be significantly enhanced when the electrocatalyst cobalt–phosphate (denoted as CoPi) was deposited on BiVO4. The photocurrent density is also greatly enhanced by loading CoPi on BiVO4 electrode, and this enhancement in performance shows the similar trend between the photocatalytic activity and photocurrent density. We also found that this tendency is true for BiVO4 loaded with a series of different electrocatalysts as the cocatalysts. These results demonstrate that an effective electrocatalyst of water oxidation can be also an effective cocatalyst for O2 evolution from photocatalytic water oxidation. By depositing the CoPi as ...

Journal ArticleDOI
TL;DR: In this paper, the authors combine quantitative differential electrochemical mass spectrometry and cyclic voltammetry to probe possible mechanisms and the kinetic overpotentials responsible for discharge and charge in a Li-O2 battery, using C as the cathode and an electrolyte based on dimethoxyethane as the solvent.
Abstract: Quantitative differential electrochemical mass spectrometry and cyclic voltammetry have been combined to probe possible mechanisms and the kinetic overpotentials, responsible for discharge and charge in a Li–O2 battery, using C as the cathode and an electrolyte based on dimethoxyethane as the solvent. Previous spectroscopy experiments (X-ray diffraction, μRaman, IR, XPS) have shown that Li2O2 is the principle product formed during Li–O2 discharge using this electrolyte/cathode combination. At all discharge potentials and charge potentials 4.0 V, the electrochemistry requires significantly more than 2e–/O2, and we take this as evidence for electrolyte decomposition. We find that sequential...

Journal ArticleDOI
TL;DR: In this paper, a high active cocatalyst, limited-layered MoS2 confined on RGO sheets as an alternative of Pt, for hydrogen evolution in dye-sensitized photocatalytic systems was reported.
Abstract: The development of an advanced cocatalyst is critical for improving the efficiency of the photocatalytic hydrogen evolution reaction. Noble metals such as platinum (Pt) have been identified to be the most active cocatalyst for this reaction; however, due to their low-abundance, high cost, their usage in the scale-up setup is impeditive. Here, we report a high active cocatalyst, limited-layered MoS2 confined on RGO sheets as an alternative of Pt, for hydrogen evolution in dye-sensitized photocatalytic systems. Growing a MoS2 cocatalyst on RGO sheets provides more available catalytically edge sites and thus exhibits much higher activity than large aggregated pristine MoS2 particles under visible light irradiation (≥420 nm). The apparent quantum efficiency (AQE) of 24% at 460 nm over an Eosin Y-sensitized MoS2/RGO photocatalyst has been achieved. In addition, the electrical coupling and synergistic effect between MoS2 and RGO sheets greatly facilitate the efficient electron transfer from photoexcited dye to ...

Journal ArticleDOI
TL;DR: In this article, the photocatalytic activity of as-prepared anatase ultrathin TiO2 nanosheets for degradation of methylene blue (MB) under visible-light irradiation at λ ≥ 400 nm was investigated.
Abstract: Tailored synthesis of well-defined anatase TiO2 nanocrystals with a high percentage of reactive facets has attracted widespread attention due to the scientific and technological importance. Here, high-quality nanosized anatase ultrathin TiO2 nanosheets, mainly dominated by {001} facets, were grown on graphene nanosheets by a simple one-pot solvothermal synthetic route. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of as-prepared TiO2/graphene composites for degradation of methylene blue (MB) under visible-light irradiation at λ ≥ 400 nm was investigated. The results show that TiO2/graphene nanocomposites have a higher photocatalytic activity than pure TiO2 and P25. This enhanced photocatalytic activity suggests that the photoinduced electrons in TiO2 pref...