Showing papers in "Journal of Physical Chemistry C in 2011"
TL;DR: Graphene and graphitic carbon nitride composite photocatalysts were prepared by a combined impregnation−chemical reduction strategy involving polymerization of melamine in the presence of graphene oxide (precursors) and hydrazine hydrate (reducing agent), followed by thermal treatment at 550 °C under flowing nitrogen as mentioned in this paper.
Abstract: Graphene and graphitic carbon nitride (g-C3N4) composite photocatalysts were prepared by a combined impregnation−chemical reduction strategy involving polymerization of melamine in the presence of graphene oxide (precursors) and hydrazine hydrate (reducing agent), followed by thermal treatment at 550 °C under flowing nitrogen. The resulting graphene/g-C3N4 composite photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, UV−visible spectrophotometry, nitrogen adsorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The transient photocurrent response was measured for several on−off cycles of intermittent irradiation. The effect of graphene content on the rate of visible-light photocatalytic hydrogen production was studied for a series of graphene−graphitic carbon nitride composite samples containing Pt as a cocatalyst in methanol aqueous solutions. This study shows that graphene sheets a...
1,660 citations
TL;DR: In this article, a combination of high-resolution in situ X-ray photoemission and Xray absorption spectroscopies was used to monitor the deoxygenation process and comprehensively evaluate the electronic structure of graphene oxide thin films at different stages of the thermal reduction process.
Abstract: Despite the recent developments in graphene oxide due to its importance as a host precursor of graphene, the detailed electronic structure and its evolution during the thermal reduction remain largely unknown, hindering its potential applications. We show that a combination of high-resolution in situ X-ray photoemission and X-ray absorption spectroscopies offer a powerful approach to monitor the deoxygenation process and comprehensively evaluate the electronic structure of graphene oxide thin films at different stages of the thermal reduction process. It is established that the edge plane carboxyl groups are highly unstable, whereas carbonyl groups are more difficult to remove. The results consistently support the formation of phenol groups through reaction of basal plane epoxide groups with adjacent hydroxyl groups at moderate degrees of thermal activation (∼400 °C). The phenol groups are predominant over carbonyl groups and survive even at a temperature of 1000 °C. For the first time, a drastic increase...
1,265 citations
TL;DR: In this paper, the authors used density functional theory (DFT) to demonstrate that the oxygen reduction reaction (ORR) on N-doped graphene is a direct fourelectron pathway, which is consistent with the experimental observations.
Abstract: Graphene and its derivatives are attractive for electrocatalytical application in fuel cells because of their unique structures and electronic properties. The electrocatalytical mechanism of nitrogen doped graphene in acidic environment was studied by using density functional theory (DFT). The simulations demonstrate that the oxygen reduction reaction (ORR) on N-doped graphene is a direct four-electron pathway, which is consistent with the experimental observations. The energy calculated for each ORR step shows that the ORR can spontaneously occur on the N-graphene. The active catalytical sites on single nitrogen doped graphene are identified, which have either high positive spin density or high positive atomic charge density. The nitrogen doping introduces asymmetry spin density and atomic charge density, making it possible for N-graphene to show high electroncatalytic activities for the ORR.
1,230 citations
TL;DR: In this article, an ultralayered Co3O4 superstructures with high porosity have been synthesized by a facile homogeneous precipitation process under hydrothermal conditions.
Abstract: Ultralayered Co3O4 structures with high porosity have been synthesized by a facile homogeneous precipitation process under hydrothermal conditions. The superstructures consist of well-arranged micrometer length rectangular 2D flakes with high specific surface area, pore volume, and uniform pore size distribution. The electrochemical measurements demonstrate that charge storage occurs in ultralayered Co3O4 due to reversible redox reactions. The charge–discharge study shows that the material is capable of delivering very high specific capacitance of 548 F g–1 at a current density of 8 A g–1 and retains 66% of capacitance at 32 A g–1. The charge–discharge stability measurements show excellent specific capacitance retention capability, ca. 98.5% after 2000 continuous charge–discharge cycles at high current density of 16 A g–1. The exceptional cyclic, structural, and electrochemical stability at higher current rate with ∼100% Coulombic efficiency, and very low ESR value from impedance measurements promise good...
867 citations
TL;DR: In this article, the role of trapped water and the evolution of oxygen during annealing of reduced graphene oxide (GO) is investigated, and the interactions between randomly arranged nearby oxygen species are found to affect the spectral response (red and blue shifts) and the overall chemistry during the reduction process.
Abstract: Understanding the thermal reduction of graphene oxide (GO) is important for graphene exfoliation, and chemical and morphological modifications. In this process, the role of trapped water and the evolution of oxygen during annealing are still not well-understood. To unravel the complex mechanisms leading to the removal of oxygen in reduced GO, we have performed in situ transmission infrared absorption spectroscopy measurements of GO films upon thermal annealing at 60–850 °C in vacuum (10–3–10–4 Torr). Using cluster-based first-principles calculations, epoxides, ethers (pyrans and furans), hydroxyls, carboxyls, lactols, and various types of ketones and their possible derivatives have been identified from the spectroscopic data. Furthermore, the interactions between randomly arranged nearby oxygen species are found to affect the spectral response (red and blue shifts) and the overall chemistry during annealing. For instance, the initial composition of oxygen species (relative amounts and types of species, su...
767 citations
TL;DR: In this paper, a supercapacitor based on the Hz-reduced graphene oxide dispersions (GH-Hs) exhibited a high specific capacitance of 220 F g-1 at 1 A g−1, and this capacitance can be maintained for 74% as the discharging current density was increased up to 100 A g −1.
Abstract: Graphene hydrogels prepared via hydrothermal reduction of graphene oxide dispersions (GH-Hs) were further reduced with hydrazine (Hz) or hydroiodic acid (HI) to improve their conductivities. The chemically reduced graphene hydrogels possess high conductivities of 1.3–3.2 S m–1, which are 1 order of magnitude higher than that of a GH-H (0.3 S m–1). The supercapacitor based on the Hz-reduced GH-H exhibited a high specific capacitance of 220 F g–1 at 1 A g–1, and this capacitance can be maintained for 74% as the discharging current density was increased up to 100 A g–1. Furthermore, it showed high power density and long cycle life. The high-performances of this supercapacitor make it promising for high rate charge/discharge applications.
678 citations
TL;DR: In this article, the authors systematically studied the three-dimensional self-assembly of GO sheets in aqueous media to form hydrogels and found that the gelation of GO can be promoted by different supramolecular interactions, including hydrogen bonding, π stacking, electrostatic interaction, and coordination.
Abstract: Graphene oxide (GO) has been recognized as a unique two-dimensional building block for various graphene-based supramolecular architectures. In this article, we systematically studied the three-dimensional self-assembly of GO sheets in aqueous media to form hydrogels. The gelation of GO can be promoted by different supramolecular interactions, including hydrogen bonding, π-stacking, electrostatic interaction, and coordination. Furthermore, the lateral dimensions of GO sheets also have strong influences on GO gelation. The resulting GO hydrogels exhibited low critical gelation concentrations and good reversibility upon chemical stimulations. These findings indicate that GO has rich supramolecular properties, and its hydrogels may have a variety of technological applications.
601 citations
TL;DR: In this paper, a composite of P25 and reduced graphene oxide (RGO) was used as photocatalysts for the evolution of hydrogen from alcohol solution under UV-vis irradiation.
Abstract: Nanocomposites of titanium dioxide (P25) and reduced graphene oxide (RGO), which were prepared by several techniques including UV-assisted photocatalytic reduction, hydrazine reduction, and hydrothermal method, were studied as photocatalysts for the evolution of hydrogen from alcohol solution under UV–vis irradiation. The incorporation of RGO into P25 significantly enhanced the photocatalytic activity for H2 evolution, and the P25–RGO composite prepared by the hydrothermal method exhibited the best performance. The optimum mass ratio of P25 to RGO in the composite was 1/0.2. The P25–RGO composite was stable and could be used recyclably, and it could also catalyze the evolution of H2 from pure water. Our characterizations suggested that P25 nanoparticles with diameters of 20–30 nm were dispersed on the RGO sheet in the composite, and the stronger interaction between P25 and RGO provided a better photocatalytic activity. The intimate contact between P25 and RGO was proposed to accelerate the transfer of pho...
594 citations
TL;DR: The core-shell nanocomposites of M@TiO2 (M = Au, Pd, Pt) have been synthesized successfully via a facile hydrothermal treatment of TiF4 precursor and noble metal colloid particles.
Abstract: The core–shell nanocomposites of M@TiO2 (M = Au, Pd, Pt) have been synthesized successfully via a facile hydrothermal treatment of TiF4 precursor and noble metal colloid particles. Their properties were determined by a collection of joint techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectra (XRD), ultraviolet/visible diffuse reflectance spectra (DRS), photoluminescence spectra (PL), and electron spin resonance spectra (ESR). Photocatalytic degradation of Rhodamine B (RhB) in the liquid phase served as a probe reaction to evaluate the activity of the as-prepared M@TiO2 (M = Au, Pd, Pt) core–shell nanocomposites under the irradiation of both visible light and ultraviolet (UV) light. The results reveal that these core–shell nanocomposites possess tunable photoreactivity. It is interesting to find that the incorporation of noble metal core into the shell of TiO2 only contributes to enhancement of...
555 citations
TL;DR: In this paper, the photocatalytic activity of as-prepared N-graphene/CdS for hydrogen production from water under visible light irradiation at λ ≥ 420 nm was investigated.
Abstract: A series of N-doped graphene (N-graphene)/CdS nanocomposites were synthesized by calcination and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, N2 adsorption analysis, ultraviolet–visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of as-prepared N-graphene/CdS for hydrogen production from water under visible light irradiation at λ ≥ 420 nm was investigated. The results show that N-graphene/CdS nanocomposites have a higher photocatalytic activity than pure CdS. Transient photocurrents measured with a photoelectrochemical test device show that the photocurrent of the N-graphene/CdS sample is much increased as compared to the sole CdS. This enhanced photoresponse indicates that the photoinduced electrons in the CdS prefer separately transferring to the N-doped graphene. As a consequence, the radiative recombination of the electron–hole pairs is hampered and the...
543 citations
TL;DR: In this article, a facile chemical bath method was used to synthesize ZnO/BiOI heterostructures, which exhibited high photocatalytic activity in the degradation of methyl orange under visible-light irradiation.
Abstract: In this study, ZnO/BiOI heterostructures were synthesized by a facile chemical bath method at low temperature. Control of the morphology and constituents of the ZnO/BiOI heterostructures was realized by simply tuning the Bi/Zn molar ratios. The resulting ZnO/BiOI heterostructures exhibited high photocatalytic activity in the degradation of methyl orange under visible-light irradiation. The high photocatalytic activity of the ZnO/BiOI heterostructures was first attributed to their high surface area. Surface photovoltage spectroscopy and transient photovoltage measurements revealed that the photoinduced charge-transfer property of p-type BiOI could be improved greatly by coupling with n-type ZnO. The heterojunction at the interface between the BiOI and ZnO could efficiently reduce the recombination of photoinduced electron–hole pairs to increase the lifetime of charge carriers by 15 times and thus enhance the photocatalytic activity of the ZnO/BiOI heterostructures, in addition to the high surface area. Thi...
TL;DR: In this article, a sulfur/carbon composite has been prepared as a cathode for lithium/sulfur batteries, and the effects of seven different liquid electrolytes on the electrochemical performance were investigated using galvanostatic discharge-charge tests on coin cells.
Abstract: A sulfur/carbon composite has been prepared to serve as a cathode for lithium/sulfur batteries. The effects of seven different liquid electrolytes on the electrochemical performance were investigated using galvanostatic discharge–charge tests on coin cells. The electrolytes included ether, sulfone, and carbonate solvents with common lithium salts. It was found that the solvent plays a key role on the electrochemical performance of the lithium/sulfur battery cathode while the lithium salt has no significant effects. Additional characterization, using in situ sulfur K-edge X-ray absorption spectroscopy (XAS), provided insights into the soluble sulfur species in the discharged and charged batteries. We find that the use of low-viscosity ethereal solvents results in a more complete reduction of soluble polysulfides, while soluble polysulfides remained more oxidized in viscous ethereal solvents. Moreover, XAS revealed that reduced sulfur species chemically react with carbonate-based solvents, making this class...
TL;DR: In this article, a bath sonication-assisted exfoliation of hexagonal boron nitride (h-BN) nanosheets was demonstrated to be effective in exfoliating the layered h-BN structures.
Abstract: Hexagonal boron nitride (h-BN) is traditionally considered to be insoluble in water. However, here we demonstrate that water is effective to exfoliate the layered h-BN structures with the assistance of bath sonication, forming “clean” aqueous dispersions of h-BN nanosheets without the use of surfactants or organic functionalization. Besides few-layered h-BN nanosheets, there was also evidence on the presence of monolayered nanosheet and nanoribbon species. Most nanosheets were of reduced lateral sizes, which was attributed to the cutting of parent h-BN sheets induced by the sonication-assisted hydrolysis (evidenced by the ammonia test and spectroscopy results). The hydrolysis effect also assisted in the exfoliation of h-BN nanosheets in addition to the solvent polarity effect. The h-BN nanosheets in such “clean” aqueous dispersions were demonstrated to be conveniently processed via solution methods with retained physical properties. The dispersed h-BN nanosheets in water also exhibited strong affinity tow...
TL;DR: In this paper, a core/shell structure composites were synthesized via an in situ chemical oxidative polymerization method with chloroform as a solvent, thiophene as a reagent, and iron chloride as an oxidant at 0 °C.
Abstract: Novel sulfur/polythiophene composites with core/shell structure composites were synthesized via an in situ chemical oxidative polymerization method with chloroform as a solvent, thiophene as a reagent, and iron chloride as an oxidant at 0 °C. Different ratios of the sulfur/polythiophene composites were characterized by elemental analysis, FTIR, XRD, SEM, TEM, and electrochemical methods. A suitable ratio for the composites was found to be 71.9% sulfur and 18.1% polythiophene as determined by CV and EIS results. Conductive polythiophene acts as a conducting additive and a porous adsorbing agent. It was uniformly coated onto the surface of the sulfur powder to form a core/shell structure, which effectively enhances the electrochemical performance and cycle life of the sulfur cells. The initial discharge capacity of the active material was 1119.3 mA h g−1, sulfur and the remaining capacity was 830.2 mA h g−1 sulfur after 80 cycles. After a rate test from 100 to 1600 mA g−1 sulfur, the cell remained at 811 mA...
TL;DR: In this paper, a self-organized BiOI/TiO2 nanotube arrays (NTs) were prepared by coating biOI on the tube wall of the selforganized TiO2 NTs using a novel impregnating−hydroxylation method.
Abstract: p−n junction BiOI/TiO2 nanotube arrays (NTs) were prepared by coating BiOI on the tube wall of the self-organized TiO2 NTs using a novel impregnating−hydroxylation method. The as-prepared samples w...
TL;DR: In this article, the authors demonstrate the exfoliation of graphene at relatively high concentration in low boiling point solvents such as chloroform and isopropanol, achieving concentrations of up to 0.5 mg/mL.
Abstract: One of the problems with solvent exfoliation of graphene is that the best solvents tend to have high boiling points and so are difficult to remove and can present problems for flake deposition and composite formation. Here, we demonstrate the exfoliation of graphene at relatively high concentration in low boiling point solvents such as chloroform and isopropanol. It is possible to achieve concentrations of up to 0.5 mg/mL, just under half that which can be achieved with high boiling point solvents such as N-methyl-pyrrolidone. These dispersions consist of graphene flakes of ∼1 μm length and with a thickness of less than 10 layers (≤5 layers for isopropanol). For both solvents, >75% of the graphene remains dispersed indefinitely. Raman spectroscopy shows the flakes to be relatively defect-free. A significant advantage of low boiling point solvents is that they allow individual flakes to be spray cast onto substrates. Deposited densities of >10 flakes with length >1 μm per 10 μm × 10 μm square have been con...
TL;DR: In this article, the authors compared six typical reduction methods: N2H4·H2O, NaOH, NaBH4, solvothermal, high-temperature, and two-step.
Abstract: Reduced graphene oxide (RGO) is an intriguing nanomaterial with tremendous potential for many applications. Although considerable efforts have been devoted to develop the reduction methods, it still needs further improvement, and how to choose an appropriate one for a specific application is a troublesome problem. In this study, RGOs were prepared by six typical reduction methods: N2H4·H2O, NaOH, NaBH4, solvothermal, high-temperature, and two-step. The samples were systematic compared by four aspects: dispersibility, reduction degree, defect repair degree, and electrical conductivity. On the basis of the comparison, a simple evaluation criterion was proposed for qualitatively judging the quality of RGO. This evaluation criterion would be helpful to understand the mechanism of reduction and design more ideal reduction methods.
TL;DR: In this article, the functionalization of the two-dimensional single-layer MoS2 structure through adatom adsorption and vacancy defect creation was studied based on first-principles plane-wave calculations.
Abstract: Based on first-principles plane-wave calculations, we studied the functionalization of the two-dimensional single-layer MoS2 structure through adatom adsorption and vacancy defect creation. Minimum-energy adsorption sites were determined for 16 different adatoms, each of which gives rise to diverse properties. Bare, single-layer MoS2, which is normally a nonmagnetic, direct-band-gap semiconductor, attains a net magnetic moment upon adsorption of specific transition-metal atoms, as well as silicon and germanium atoms. The localized donor and acceptor states in the band gap expand the utilization of MoS2 in nanoelectronics and spintronics. Specific adatoms, such as C and O, attain significant excess charge upon adsorption onto single-layer MoS2, which might be useful for tribological applications. Each MoS2 triple vacancy created in a single layer of MoS2 gives rise to a net magnetic moment, whereas other vacancy defects related to Mo and S atoms do not influence the nonmagnetic ground state. The present re...
TL;DR: In this paper, the authors proposed the dumbbell-and flower-like Au−Fe3O4 heterostructures by thermal decomposition of the iron−oleate complex in the presence of Au nanoparticles (NPs) have been successfully fabricated using different sizes of Au NPs as the seeds for magnetically recyclable catalysis of p-nitrophenol and 2,4-dinitrophensol reduction.
Abstract: The dumbbell- and flower-like Au−Fe3O4 heterostructures by thermal decomposition of the iron−oleate complex in the presence of Au nanoparticles (NPs) have been successfully fabricated using different sizes of Au NPs as the seeds for magnetically recyclable catalysis of p-nitrophenol and 2,4-dinitrophenol reduction. The heterostructures exhibit bifunctional properties with high magnetization and excellent catalytic activity toward nitrophenol reduction. The epitaxial linkages in dumbbell- and flower-like heterostructures are different, leading to the change in magnetic and catalytic properties of the heterostructured nanocatalysts. The pseudo-first-order rate constants for nitrophenol reduction are 0.63−0.72 min−1 and 0.38−0.46 min−1 for dumbbell- and flower-like Au−Fe3O4 heterostructures, respectively. In addition, the heterostructured nanocatalysts show good separation ability and reusability which can be repeatedly applied for nearly complete reduction of nitrophenols for at least six successive cycles....
TL;DR: In this paper, the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Fe3O4 nanoparticles, and the reduction extent of GO by this process could be comparable to that by conventional methods.
Abstract: In this paper, we proposed a facile one-step strategy to prepare graphene-Fe3O4 (GN–Fe3O4) nanocomposites under hydrothermal conditions, where the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Fe3O4 nanoparticles. The reduction extent of GO by this process could be comparable to that by conventional methods. A transmission electron microscopy image has shown that the as-formed Fe3O4 nanoparticles with a diameter as small as 7 nm were densely and uniformly deposited on GN sheets, and, as a result, the aggregating of the Fe3O4 nanoparticles was effectively prevented. The GN–Fe3O4 nanocomposites exhibit improved cycling stability and rate performances as a potential anode material for high-performance lithium ion batteries. In addition, the GN–Fe3O4 nanocomposites exhibit a superparamagnetic behavior, making them promising candidates for practical applications in the fields of bionanotechnology/controlled targeted drug delivery.
TL;DR: In this article, a simple method for the removal and collection of oils and organic solvents from the surfaces of water based on superhydrophobic and superoleophilic sponges that were fabricated by solution-immersion processes was presented.
Abstract: The development of a convenient method for the removal (or collection) of oils and organic solvents from water surface is of great significance for water environmental protection, especially for the cleanup of oil spillage on seawater. A major challenge is the fabrication of an oil absorber with high absorption capacity, low cost, scalable fabrication, high selectivity, and excellent recyclability. In this paper, we present a simple method for the removal and collection of oils and organic solvents from the surfaces of water based on superhydrophobic and superoleophilic sponges that were fabricated by solution-immersion processes. The as-prepared sponges fast and selectively absorbed various kinds of oils up to above 13 times the sponges’ weight while completely repelling water through a combination of porous, superhydrophobic, and superoleophilic properties. More interesting, the absorbed oils were readily collected by a simple mechanical squeezing process, and the recovered sponges could be reused in oi...
TL;DR: In this article, the microwave absorption properties in S-band have been obtained due to proper combination of the complex permeability and permittivity resulting from the magnetic nanoparticles and lightweight MWCNTs.
Abstract: Multiwalled carbon nanotubes (MWCNTs)/Fe, MWCNTs/Co, and MWCNTs/Ni nanopowders have been prepared conveniently by a simple chemical method. The excellent microwave absorption properties in S-band have been obtained due to proper combination of the complex permeability and permittivity resulting from the magnetic nanoparticles and lightweight MWCNTs. The frequency of microwave absorption obeys the quarter-wavelength matching model. For the most excellent microwave absorption properties in S-band, it is found that the reflection loss exceeds −20 dB from 2.04 to 3.47 GHz for the absorber thickness between 3.36 and 5.57 mm, and a minimum reflection loss value of −39 dB was observed at 2.68 GHz on a specimen with a matching thickness of 4.27 mm for MWCNTs/Fe. The MWCNTs/Fe/Co/Ni nanopowders all can be a promising candidate for lightweight microwave absorption materials in S-band.
TL;DR: In this article, the atomic, electronic, magnetic, and phonon properties of the one-dimensional honeycomb structure of molybdenum disulfide (MoS2) using the first-principles plane wave method were analyzed.
Abstract: We present our study on atomic, electronic, magnetic, and phonon properties of the one-dimensional honeycomb structure of molybdenum disulfide (MoS2) using the first-principles plane wave method. Calculated phonon frequencies of bare armchair nanoribbon reveal the fourth acoustic branch and indicate the stability. Force constant and in-plane stiffness calculated in the harmonic elastic deformation range signify that the MoS2 nanoribbons are stiff quasi one-dimensional structures, but not as strong as graphene and BN nanoribbons. Bare MoS2 armchair nanoribbons are nonmagnetic, direct band gap semiconductors. Bare zigzag MoS2 nanoribbons become half-metallic as a result of the (2 × 1) reconstruction of edge atoms and are semiconductor for minority spins, but metallic for the majority spins. Their magnetic moments and spin-polarizations at the Fermi level are reduced as a result of the passivation of edge atoms by hydrogen. The functionalization of MoS2 nanoribbons by adatom adsorption and vacancy defect cre...
TL;DR: In this paper, a single-composition white-emitting phosphor Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ has been synthesized by a high-temperature solid-state reaction.
Abstract: A novel single-composition white-emitting phosphor Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ has been synthesized by a high-temperature solid-state reaction. The spectral overlap between the emission band of Ce3+ and the excitation band of Mn2+, which supports the occurrence of the energy transfer from Ce3+ to Mn2+, has been studied and demonstrated to be a resonant type via a dipole−quadrupole mechanism. Because there was no spectral overlap between the emission spectra of Ce3+ and excitation band of Tb3+ in our study, no energy transfer from Ce3+ to Tb3+ was observed, indicating that Ce3+ and Tb3+ were coexcited. Through effective resonance-type energy transfer and coexcitation, the chromaticity coordinates of Ca3Y(GaO)3(BO3)4:Ce3+,Mn2+,Tb3+ phosphors can be tuned from (0.152, 0.061) for Ca3Y(GaO)3(BO3)4:Ce3+ to (0.562, 0.408) for Ca3Y(GaO)3(BO3)4:Mn2+, and eventually reaching (0.314, 0.573) for Ca3Y(GaO)3(BO3)4:Tb3+. A white light-emitting diode (LED) was fabricated by using the white-emitting single-composition...
TL;DR: In this paper, the liquid−solid phase change enthalpy, crystallization, and thermal conductivity of graphene/1-octadecanol (stearyl alcohol) composite, a nanostructured phase change material, was investigated as a function of graphene content.
Abstract: The liquid−solid phase change enthalpy, crystallization, and thermal conductivity of graphene/1-octadecanol (stearyl alcohol) composite, a nanostructured phase change material, was investigated as a function of graphene content. The thermal conductivity (κ) of the nanocomposite increased by nearly 2.5-fold (∼140% increase) upon ∼4% (by weight) graphene addition while the drop in the heat of fusion (i.e., storage capacity) was only ∼15.4%. The enhancement in thermal properties of 1-octadecanol obtained with the addition of graphene is markedly superior to the effect of other nanofillers such as silver nanowires and carbon nanotubes reported previously in the literature. Boosting the thermal conductivity of organic phase change materials without incurring a significant loss in the heat of fusion is one of the key issues in enabling their practical application as latent heat storage/release units for thermal management and thermal protection.
TL;DR: In this article, metal doping of the metal oxide photoelectrocatalyst, BiVO4, dramatically increases its activity for water oxidation, and the effect of metal doping on the photocurrent was investigated.
Abstract: Metal doping of the metal oxide photoelectrocatalyst, BiVO4, dramatically increases its activity for water oxidation. Scanning electrochemical microscopy (SECM) was used to screen various dopants for their photoelectrochemical performance and to optimize the used dopant material concentrations with this photocatalyst. For example, adding Mo to W-doped BiVO4 enhanced the performance. The photocatalytic activity was examined on larger electrodes by means of photoelectrochemical and electrochemical measurements. The developed photoelectrocatalyst, W- and Mo-doped BiVO4, shows a photocurrent for water oxidation that is more than 10 times higher than undoped BiVO4. Factors that affect performance are discussed, and enhanced separation of excited electron–hole pairs by doping onto the semiconductor is suggested by first-principles density-functional theory (DFT) calculations. Distortion of the crystal structure of monoclinic scheelite-like BiVO4 by addition of W and Mo doping predicted by DFT is also revealed b...
TL;DR: In this paper, a solution-phase photocatalytic reduction of graphene oxide to reduced graphene oxide (RGO) by titanium dioxide (TiO2) nanoparticles produces an RGO-TiO 2 composite that possesses enhanced charge transport properties beyond those of pure TiO2 nanoparticle films.
Abstract: Solution-phase photocatalytic reduction of graphene oxide to reduced graphene oxide (RGO) by titanium dioxide (TiO2) nanoparticles produces an RGO-TiO2 composite that possesses enhanced charge transport properties beyond those of pure TiO2 nanoparticle films. These composite films exhibit electron lifetimes up to four times longer than that of intrinsic TiO2 films due to RGO acting as a highly conducting intraparticle charge transport network within the film. The intrinsic UV-active charge generation (photocurrent) of pure TiO2 was enhanced by a factor of 10 by incorporating RGO; we attribute this to both the highly conductive nature of the RGO and to improved charge collection facilitated by the intimate contact between RGO and the TiO2, uniquely afforded by the solution-phase photocatalytic reduction method. Integrating RGO into nanoparticle films using this technique should improve the performance of photovoltaic devices that utilize nanoparticle films, such as dye-sensitized and quantum-dot-sensitized...
TL;DR: In this article, a functionalized graphene oxide Nafion nanocomposites (F-GO/Nafion) are presented as a potential proton exchange membrane (PEM) replacement for high temperature PEM fuel cell applications.
Abstract: Functionalized graphene oxide Nafion nanocomposites (F-GO/Nafion) are presented as a potential proton exchange membrane (PEM) replacement for high temperature PEM fuel cell applications. The GO nanosheets were produced from natural graphite flakes by the modified Hummer’s method and then functionalized by using 3-mercaptopropyl trimethoxysilane (MPTMS) as the sulfonic acid functional group precursor. F-GO/Nafion composite membranes were fabricated by a simplistic solution casting method. Several physicochemical characterization techniques were applied to provide insight into the specific structure and morphology, functional groups, water uptake, and ionic conductivities of the membranes. Proton conductivity and single cell test results demonstrated significant improvements for F-GO/Nafion membranes (4 times) over recast Nafion at 120 °C with 25% humidity.
TL;DR: In this paper, the effect of Ni(OH)2 cluster loading content on the photocatalytic hydrogen production rates of the as-prepared samples in methanol aqueous solution was investigated.
Abstract: Ni(OH)2 cluster-modified TiO2 (Ni(OH)2/TiO2) nanocomposite photocatalysts were fabricated by a simple precipitation method using Degussa P25 TiO2 powder (P25) as support and Ni(NO3)2 as precursor. The effect of Ni(OH)2 cluster loading content on the photocatalytic hydrogen production rates of the as-prepared samples in methanol aqueous solution was investigated. The results showed that the photocatalytic H2-production activity of TiO2 was significantly enhanced by loading Ni(OH)2 clusters. The optimal Ni(OH)2 loading content was found to be 0.23 mol %, giving a H2-production rate of 3056 μmol h−1 g−1 with quantum efficiency (QE) of 12.4%, exceeding that on pure TiO2 by more than 223 times. This high photocatalytic H2-production activity is due to the deposition of Ni(OH)2 clusters on the surface of TiO2. The enhanced mechanism is because the potential of Ni2+/Ni (Ni2+ + 2e− = Ni, Eo = −0.23 V) is slightly lower than conduction band (CB) (−0.26 V) of anatase TiO2, meanwhile higher than the reduction potent...
TL;DR: A magnetite/graphene oxide (M/GO) composite was synthesized via a chemical reaction with a magnetite particle size of 10-15 nm and was developed for the removal of heavy metal ions from aqueous solutions as discussed by the authors.
Abstract: A magnetite/graphene oxide (M/GO) composite was synthesized via a chemical reaction with a magnetite particle size of 10–15 nm and was developed for the removal of heavy metal ions from aqueous solutions. The composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The sorption of Co(II) on the M/GO composite was carried out under various conditions, that is, contact time, sorbent content, pH, ionic strength, foreign ions, and temperature. The sorption isotherms of Co(II) on the M/GO composite could be described well by the Langmuir model. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) calculated from the temperature-dependent isotherms indicated that the sorption reaction of Co(II) on the M/GO composite was an endothermic and spontaneous process. M/GO can be separated and recovered by magnetic separation. Results show that the magnetic M/GO composite is a promising sorbent material for the preconcentration an...