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Showing papers in "Journal of Physical Chemistry C in 2010"


Journal ArticleDOI
TL;DR: In this paper, the deoxygenation efficiency of graphene oxide suspensions by different reductants (sodium borohydride, pyrogallol, and vitamin C, in addition to hydrazine), as well as by heating the suspensions under alkaline conditions, was compared.
Abstract: The preparation of solution-processable graphene from graphite oxide typically involves a hydrazine reduction step, but the use of such a reagent in the large-scale implementation of this approach is not desirable due to its high toxicity. Here, we compare the deoxygenation efficiency of graphene oxide suspensions by different reductants (sodium borohydride, pyrogallol, and vitamin C, in addition to hydrazine), as well as by heating the suspensions under alkaline conditions. In almost all cases, the degree of reduction attainable and the subsequent restoration of relevant properties (e.g., electrical conductivity) lag significantly behind those achieved with hydrazine. Only vitamin C is found to yield highly reduced suspensions in a way comparable to those provided by hydrazine. Stable suspensions of vitamin C-reduced graphene oxide can be prepared not only in water but also in common organic solvents, such as N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP). These results open the perspective ...

1,269 citations


Journal ArticleDOI
TL;DR: In this article, the authors synthesize cobalt hydroxide, cobalt oxyhydroxide and cobalt oxide nanomaterials through simple soft chemistry, and characterisation of these cobalt-based materials is fully developed, including X-ray diffraction, transmission electron microscopy combined with selected area electron diffraction.
Abstract: Cobalt hydroxide, cobalt oxyhydroxide, and cobalt oxide nanomaterials were synthesized through simple soft chemistry. The cobalt hydroxide displays hexagonal morphology with clear edges 20 nm long. This morphology and nanosize is retained through to cobalt oxide Co3O4 through a topotactical relationship. Cobalt oxyhydroxide and cobalt oxide nanomaterials were synthesized through oxidation and low-temperature calcination from the as-prepared cobalt hydroxide. Characterization of these cobalt-based nanomaterials was fully developed, including X-ray diffraction, transmission electron microscopy combined with selected area electron diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermal gravimetric analysis. Bonding of the divalent cobalt hydroxide from the oxyhydroxide and oxides by studying their high-resolution XPS spectra for Co 2p3/2 and O 1s. Raman spectroscopy of the as-prepared Co(OH)2, CoO(OH), and Co3O4 nanomaterials characterized each material. T...

1,249 citations


Journal ArticleDOI
TL;DR: In this article, a simple hydrothermal route in a Ti(OC4H9)4-HF-H2O mixed solution followed by a photochemical reduction deposition of Pt nanoparticles on TiO2 nanosheets under xenon lamp irradiation is described.
Abstract: Pt/TiO2 nanosheets with exposed (001) facets were fabricated by a simple hydrothermal route in a Ti(OC4H9)4-HF-H2O mixed solution followed by a photochemical reduction deposition of Pt nanoparticles on TiO2 nanosheets under xenon lamp irradiation. The prepared samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption−desorption isotherms, UV−vis diffuse reflectance spectroscopy, and photoluminescence (PL) spectroscopy. Production of •OH radicals on the TiO2 surface was detected by the PL technique using coumarin as a probe molecule. The effects of Pt loading on the rates of photocatalytic hydrogen production of the as-prepared samples in ethanol aqueous solution were investigated and discussed. The results showed that the photocatalytic hydrogen production rates of TiO2 nanosheets from the ethanol aqueous solutions were significantly enhanced by loaded Pt on the TiO2 nanosheets, and the latter with a 2 wt % of deposited Pt exhi...

1,058 citations


Journal ArticleDOI
Stefanie Wunder1, Frank Polzer1, Yan Lu1, Yu Mei1, Matthias Ballauff1 
TL;DR: In this article, a study on the catalytic reduction of 4-nitrophenol by sodium borohydride in the presence of metal nanoparticles is presented, where the nanoparticles are embedded in spherical polyelectrolyte brushes.
Abstract: We present a study on the catalytic reduction of 4-nitrophenol by sodium borohydride in the presence of metal nanoparticles. The nanoparticles are embedded in spherical polyelectrolyte brushes, which consist of a polystyrene core onto which a dense layer of cationic polyelectrolyte brushes are grafted. The average size of the nanoparticles is approximately 2 nm. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy could be explained in terms of the Langmuir−Hinshelwood model: The borohydride ions transfer a surface-hydrogen species in a reversible manner to the surface. Concomitantly 4-nitrophenol is adsorbed and the rate-determining step consists of the reduction of nitrophenol by the surface-hydrogen species. The apparent reaction rate can therefore be related to the total surface S of the nanoparticles, to the kinetic constant k related to the rate-determining step, and to the adsorption constants KNip and KBH4 of nitrophenol and of borohydride, respectively. In...

1,047 citations


Journal ArticleDOI
TL;DR: In this article, the density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides with hydrazine or heat treatment.
Abstract: The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

1,033 citations


Journal ArticleDOI
TL;DR: In this article, a detailed model consisting of a negatively charged Pt(111) slab and solvated protons in up to three water bilayers is considered and reaction energies and activation barriers are determined by using a newly developed computational scheme where the potential can be kept constant during a charge transfer reaction.
Abstract: Density functional theory calculations have been performed for the three elementary steps−Tafel, Heyrovsky, and Volmer−involved in the hydrogen oxidation reaction (HOR) and its reverse, the hydrogen evolution reaction (HER). For the Pt(111) surface a detailed model consisting of a negatively charged Pt(111) slab and solvated protons in up to three water bilayers is considered and reaction energies and activation barriers are determined by using a newly developed computational scheme where the potential can be kept constant during a charge transfer reaction. We determine the rate limiting reaction on Pt(111) to be Tafel−Volmer for HOR and Volmer−Tafel for HER. Calculated rates agree well with experimental data. Both the H adsorption energy and the energy barrier for the Tafel reaction are then calculated for a range of metal electrodes, including Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co, Ru, Re, W, Mo, and Nb, different facets, and step of surfaces. We compare the results for different facets of the Pt electrode...

923 citations


Journal ArticleDOI
TL;DR: In this paper, a fundamental study of the influence of solvents on the oxygen reduction reaction (ORR) in nonaqueous electrolytes has been carried out for elucidating the mechanism of the oxygen electrode processes in the rechargeable Li−air battery.
Abstract: A fundamental study of the influence of solvents on the oxygen reduction reaction (ORR) in nonaqueous electrolytes has been carried out for elucidating the mechanism of the oxygen electrode processes in the rechargeable Li−air battery. Using either tetrabutylammonium hexafluorophosphate (TBAPF6) or lithium hexafluorophosphate (LiPF6) electrolyte solutions in four different solvents, namely, dimethyl sulfoxide (DMSO), acetonitrile (MeCN), dimethoxyethane (DME), and tetraethylene glycol dimethyl ether (TEGDME), possessing a range of donor numbers (DN), we have determined that the solvent and the supporting electrolyte cations in the solution act in concert to influence the nature of reduction products and their rechargeability. In solutions containing TBA+, O2 reduction is a highly reversible one-electron process involving the O2/O2− couple. On the other hand, in Li+-containing electrolytes relevant to the Li−air battery, O2 reduction proceeds in a stepwise fashion to form O2−, O22−, and O2− as products. Th...

876 citations


Journal ArticleDOI
TL;DR: Titanium dioxide (M-TiO2) was synthesized by standard sol−gel methods and characterized by X-ray diffraction, BET surface area measurement, SEM, and UV−vis diffuse reflectance spectroscopy as mentioned in this paper.
Abstract: Titanium dioxide (M-TiO2), which was doped with 13 different metal ions (ie, silver (Ag+), rubidium (Rb+), nickel (Ni2+), cobalt (Co2+), copper (Cu2+), vanadium (V3+), ruthenium (Ru3+), iron (Fe3+), osmium (Os3+), yttrium (Y3+), lanthanum (La3+), platinum (Pt4+, Pt2+), and chromium (Cr3+, Cr6+)) at doping levels ranging from 01 to 10 at %, was synthesized by standard sol−gel methods and characterized by X-ray diffraction, BET surface area measurement, SEM, and UV−vis diffuse reflectance spectroscopy Doping with Pt(IV/II), Cr(III), V(III), and Fe(III) resulted in a lower anatase to rutile phase transformation (A−R phase transformation) temperature for the resultant TiO2 particles, while doping with Ru(III) inhibited the A−R phase transformation Metal-ion doping also resulted in a red shift of the photophysical response of TiO2 that was reflected in an extended absorption in the visible region between 400 and 700 nm In contrast, doping with Ag(I), Rb(I), Y(III), and La(III) did not result in a red s

709 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported efficient phosphorescence from the crystals of benzophenone and its derivatives with a general formula of (X-C6H4)2C═O (X = F, Cl, Br) as well as methyl 4-bromobenzoate and 4,4′-dibromobiphenyl under ambient conditions.
Abstract: Phosphorescence has rarely been observed in pure organic chromophore systems at room temperature. We herein report efficient phosphorescence from the crystals of benzophenone and its derivatives with a general formula of (X-C6H4)2C═O (X = F, Cl, Br) as well as methyl 4-bromobenzoate and 4,4′-dibromobiphenyl under ambient conditions. These luminogens are all nonemissive when they are dissolved in good solvents, adsorbed on TLC plates, and doped into polymer films, because active intramolecular motions such as rotations and vibrations under these conditions effectively annihilate their triplet excitons via nonradiative relaxation channels. In the crystalline state, the intramolecular motions are restricted by the crystal lattices and intermolecular interactions, particularly C−H···O, N−H···O, C−H···X (X = F, Cl, Br), C−Br···Br−C, and C−H···π hydrogen bonding. The physical constraints and multiple intermolecular interactions collectively lock the conformations of the luminogen molecules. This structural rigi...

656 citations


Journal ArticleDOI
TL;DR: In this paper, the physical adsorption of nanosized plastic beads onto a model cellulose film and two living algal species, Chlorella and Scenedesmus, has been studied.
Abstract: The physical adsorption of nanosized plastic beads onto a model cellulose film and two living algal species, Chlorella and Scenedesmus, has been studied. This adsorption has been found to ubiquitously favor positively charged over negatively charged plastic beads due to the electrostatic attraction between the beads and the cellulose constituent of the model and living systems. Such a charge preference is especially pronounced for Chlorella and Scenedesmus, whose binding with the plastic beads also depended upon algal morphology and motility, as characterized by the Freundlich coefficients. Using a CO2 depletion assay, we show that the adsorption of plastic beads hindered algal photosynthesis, possibly through the physical blockage of light and air flow by the nanoparticles. Our ROS assay further indicated that plastic adsorption promoted algal ROS production. Such algal responses to plastic exposure may have implications on the sustainability of the aquatic food chain.

650 citations


Journal ArticleDOI
TL;DR: In this paper, a carbon nanotubes (CNT)/TiO2 nanocomposite photocatalyst has been prepared by a simple impregnation method, which is used, for the first time, for gas-phase degradation of benzene.
Abstract: A carbon nanotubes (CNT)/TiO2 nanocomposite photocatalyst has been prepared by a simple impregnation method, which is used, for the first time, for gas-phase degradation of benzene. It is found that the as-prepared CNT/TiO2 nanocomposite exhibits an enhanced photocatalytic activity for benzene degradation, as compared with that over commerical titania (Degussa P25). A similar phenomenon has also been found for liquid-phase degradation of methyl orange. The characterization of photocatalysts by a series of joint techniques, including X-ray diffraction, transmission electron microscopy, ultraviolet/visible (UV/vis) diffuse reflectance spectra, and photoluminescence spectra, discloses that CNT has two kinds of crucial roles in enhancement of photocatalytic activity of TiO2. One is to act as an electron reservoir, which helps to trap electrons emitted from TiO2 particles due to irradiation by UV light, therefore hindering electron−hole pairs recombination. The other is to act as a dispersing template or suppo...

Journal ArticleDOI
TL;DR: In this article, the geometric and electronic structures of MoO3 and MoO2 have been calculated using the generalized gradient approximation to density functional theory, and the calculated cross-section weighted densities of states are compared with high-resolution X-ray photoemission spectra.
Abstract: The geometric and electronic structures of MoO3 and MoO2 have been calculated using the generalized gradient approximation to density functional theory. The calculated cross-section weighted densities of states are compared with high-resolution X-ray photoemission spectra. There is very good agreement between the calculated structures and those determined previously by X-ray diffraction and between the computed densities of states and the present photoemission measurements. MoO2 is shown to be a metallic material, as is found experimentally, but the Fermi level sits in a distinct trough in the density of states. Satellite peaks found in core photoemission spectra of MoO2 are shown to derive from final state screening effects in this narrow band metallic material.

Journal ArticleDOI
TL;DR: In this article, a one-step template-free approach was used to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on various conducting substrates by using a galvanostatic current method.
Abstract: Vertically aligned conducting polymer nanowire arrays have great potential applications in supercapacitor electrode materials In this paper, we report a facial one-step template-free approach to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on various conducting substrates by using a galvanostatic current method The as-prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode The highest specific capacitance of PANI nanowire arrays was measured as 950 F·g−1 and kept as high as 780 F·g−1 at a large charge−discharge current density (40 A·g−1) Furthermore, the capacitances in several different electrolytes, including HClO4, lithium bis(trifluoromethane sulfonyl) (LiTFSI) aqueous solution and nonsolvent electrolyte ionic liquid, were investigated The results indicated that the orientation of nanostructures could dramatically enhanc

Journal ArticleDOI
TL;DR: Instead of hydrazine, a series of sulfur-containing compounds such as NaHSO3, Na2SO3 and Na2S2O3 were used as reducing agents to reduce graphene oxide to graphene.
Abstract: Instead of hydrazine, a series of sulfur-containing compounds such as NaHSO3, Na2SO3, Na2S2O3, Na2S·9H2O, SOCl2, and SO2, were used as reducing agents to reduce graphene oxide to graphene. Fourier transform infrared spectrometry, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, elemental analysis, and thermogravimetric analysis confirmed the formation of graphene under chemical reduction at 95 °C. The results reveal that the reducing ability of NaHSO3 is comparable to that of hydrazine. This newly found reducing agent is of low toxicity and nonvolatile, which makes the reduction much safer than hydrazine. A possible mechanism of the reduction has been suggested. The electrical conductivity of the graphene paper prepared using a NaHSO3 reducing agent is found to be 6500 S m−1, while it is observed to be 5100 S m−1 for hydrazine-reduced graphene paper. These studies also confirmed that SOCl2 can be a good candidate as a reducing agent to compete with hydrazine.

Journal ArticleDOI
TL;DR: In this paper, three types of MnO2 nanostructures, viz., microsphere/nanosheet core−corona hierarchical architectures, one-dimensional (1D) nanorods, and nanotubes, have been synthesized employing a simple hydrothermal process.
Abstract: In this work, three types of MnO2 nanostructures, viz., microsphere/nanosheet core−corona hierarchical architectures, one-dimensional (1D) nanorods, and nanotubes, have been synthesized employing a simple hydrothermal process. The formation mechanisms have been rationalized. The materials have been thoroughly characterized by X-ray diffraction, Brunauer−Emmett−Teller spectrometry, field-emission scanning electron miscroscopy, energy dispersive spectroscopy, and transmission electron microscopy. The microsphere/nanosheet core−corona hierarchical structures are found to be the layered birnessite-type MnO2, while 1D nanorods and nanotubes are of the α-MnO2 phase. These MnO2 nanostructures are used as a model system for studying the shape/phase-dependent electrocatalytic properties for the oxygen reduction reaction, which have be investigated by cyclic and linear sweep voltammetry. It is found that α-MnO2 nanorods/tubes possess largely enhanced electrocatalytic activity compared to birnessite-type MnO2 core−c...

Journal ArticleDOI
TL;DR: In this paper, the catalytic performance of CO on Fe-embedded graphene was investigated by means of first-principles computations, where the Fe atom can be constrained at a vacancy site of graphene with a high diffusion barrier (6.78 eV), and effectively activate the adsorbed O2 molecule.
Abstract: The catalytic oxidation of CO on Fe-embedded graphene was investigated by means of first-principles computations. Fe atom can be constrained at a vacancy site of graphene with a high diffusion barrier (6.78 eV), and effectively activate the adsorbed O2 molecule. The reactions between the adsorbed O2 with CO via both Langmuir−Hinshelwood (LH) and Eley−Rideal (ER) mechanisms were comparably studied. The Fe-embedded graphene shows good catalytic activity for the CO oxidation via the more favorable ER mechanism with a two-step route.

Journal ArticleDOI
TL;DR: In this paper, the synthesis of a graphene/polyaniline (PANI) nanocomposite and its application in the development of a hydrogen (H2) gas sensor was reported.
Abstract: Here we report on the synthesis of a graphene/polyaniline (PANI) nanocomposite and its application in the development of a hydrogen (H2) gas sensor. Using a chemical synthetic route, graphene was prepared and ultrasonicated with a mixture of aniline monomer and ammonium persulfate to form PANI on its surface. The developed material was characterized by scanning electron microscopy (SEM), transmission electron microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. The SEM study revealed that the PANI in the composite has a nanofibrillar morphology. We investigated the H2 gas sensing performance of this material and compare it with that of the sensors based on only graphene sheets and PANI nanofibers. We found that the graphene/PANI nanocomposite-based device sensitivity is 16.57% toward 1% of H2 gas, which is much larger than the sensitivities of sensors based on only graphene sheets and PANI nanofibers.

Journal ArticleDOI
TL;DR: In this article, a photocatalytic reduction of the graphene oxide sheets by the TiO2 nanoparticles in ethanol was shown to increase the graphitized sp2 structure over the disorders in the reduced graphene oxides.
Abstract: TiO2 nanoparticles were physically attached to chemically synthesized single-layer graphene oxide nanosheets deposited between Au electrodes in order to investigate the electrical, chemical, and structural properties of the TiO2/graphene oxide composition exposed to UV irradiation. X-ray photoelectron spectroscopy showed that after effective photocatalytic reduction of the graphene oxide sheets by the TiO2 nanoparticles in ethanol, the carbon content of the reduced graphene oxides gradually decreased by increasing the irradiation time, while no considerable variation was detected in the reduction level of the reduced sheets. Raman spectroscopy indicated that, at first, the photocatalytic reduction resulted in a significant increase in the graphitized sp2 structure over the disorders in the graphene oxides. After that, as the carbon content decreased by UV irradiation, further disorders appeared in the reduced graphene oxide sheets, confirming degradation of the reduced sheets after the photocatalytic redu...

Journal ArticleDOI
TL;DR: In this paper, a reduced graphene oxide/platinum supported electrocatalysts (Pt/RGO) was synthesized by employing a fast and eco-friendly microwave-assisted polyol process, which facilitated the simultaneous reduction of graphene oxide and formation of Pt nanocrystals.
Abstract: Reduced graphene oxide/platinum supported electrocatalysts (Pt/RGO) were synthesized by employing a fast and eco-friendly microwave-assisted polyol process, which facilitated the simultaneous reduction of graphene oxide and formation of Pt nanocrystals. This system was tested for potential use as an anode material through the electrooxidation of methanol. Compared to the commercial carbon-supported Pt electrocatalysts, the Pt/RGO showed an unprecedented CO poisoning tolerance, high electrochemical active surface area, and high catalytic mass activity for methanol oxidation reaction, demonstrated by increases of 110, 134, and 60%, respectively. We found that the high concentration of oxygen functional groups on reduced graphene oxide plays a major role on the removal of carbonaceous species on the adjacent Pt sites, underlining a synergetic effect between the oxygen moieties on graphene support and Pt nanoparticles. The present microwave assisted synthesis of Pt/RGO provides a new path to prepare electroca...

Journal ArticleDOI
Wenjing Hong1, Hua Bai1, Yuxi Xu1, Zhiyi Yao1, Zhongze Gu1, Gaoquan Shi1 
TL;DR: In this article, positively charged gold nanoparticles (GNPs) with diameters of 2−6 nm were self-assembled onto the surfaces of 1-pyrene butyric acid functionalized graphene (PFG) sheets simply by mixing their aqueous dispersions.
Abstract: Positively charged gold nanoparticles (GNPs) with diameters of 2−6 nm were self-assembled onto the surfaces of 1-pyrene butyric acid functionalized graphene (PFG) sheets simply by mixing their aqueous dispersions. The amount of GNPs assembled on PFG sheets can be easily modulated by controlling the feeding weight ratio of both components. Furthermore, it was found that PFG sheets had a high loading capability of GNPs, and the maximum value was determined to be about 300 times the PFG’s own weight. Glassy carbon (GC) electrodes modified with the composite of GNPs and PFG (GNP−PFG composite) showed strong electrocatalytic activity and high electrochemical stability. A uric acid electrochemical sensor based on the composite modified electrode exhibited rapid response and high sensitivity.

Journal ArticleDOI
TL;DR: In this paper, a facile and efficient method to prepare the composites of SnO2-nanocrystal/graphene-nanosheets was developed on the basis of the reduction of graphene oxide (GO) by Sn2+ ion.
Abstract: To improve the performance of SnO2 as anode materials for lithium battery, a facile and efficient method to prepare the composites of SnO2-nanocrystal/graphene-nanosheets was developed on the basis of the reduction of graphene oxide (GO) by Sn2+ ion. Changing the ratio of Sn2+ and GO led to the morphology changes of SnO2/graphene-nanosheets composite. The performance as anode materials for lithium battery was studied in this report. The results showed that the electrochemical performance of composites was greatly enhanced, indicating that the composites might have a promising future as application in Li-ion battery.

Journal ArticleDOI
TL;DR: ZnO hierarchical microstructures with uniform flower-like morphology were prepared on a large scale through a template-and surfactant-free low-temperature (80 °C) aqueous solution route.
Abstract: ZnO hierarchical microstructures with uniform flower-like morphology were prepared on a large scale through a template- and surfactant-free low-temperature (80 °C) aqueous solution route. The product was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer−Emmett−Teller N2 adsorption−desorption analyses. The flower-like ZnO microstructures are assembled by many interleaving nanosheets which have the uniform thickness of about 10 nm and a well-crystalline structure with dominant surfaces as {2110} planes. Control experiments revealed that the formation of the flower-like ZnO was based on the fast nucleation−growth kinetics. The flower-like ZnO sample shows an enhanced photocatalytic performance compared with the other nanostructured ZnO powders of nanoparticles, nanosheets, and nanorods, which can be attributed to the special structural feature with an open and porous nanostructured surface layer that significantly facilitates the diffusion and ...

Journal ArticleDOI
TL;DR: In this article, Bismuth ferrite (BiFeO3) uniform microcrystals with various morphologies (microspheres and micro/submirocubes) were successfully synthesized by a controlled hydrothermal method.
Abstract: Bismuth ferrite (BiFeO3) uniform microcrystals with various morphologies (microspheres and micro/submirocubes) were successfully synthesized by a controlled hydrothermal method. The resulting microstructures were characterized using X-ray diffraction, scanning/transmission electron microscopies and Raman spectroscopy. Possible formation mechanism for BiFeO3 microcrystals was proposed. UV−vis spectra showed that the optical properties of the microsized BiFeO3 crystals were strongly related to their shape and size. We further demonstrated the useful photocatalytic activity of these regular-shaped structures as determined by degradation of Congo red under visible-light irradiation (λ > 400 nm). Additionally, magnetic responses were observed to be influenced by the morphology of as-synthesized BiFeO3 products, and the ferroelectric performance of BiFeO3 submicrocube was also studied by piezoelectric force microscopy (PFM). Being a multiferroic semiconductor with suitable narrow band gap (∼2.2 eV) and uniform ...

Journal ArticleDOI
TL;DR: In this article, perfect mixed 26facet and 18-facet polyhedra of Cu2O microcrystals were successfully synthesized by a hydrothermal process with use of stearic acid as a structure-directing agent.
Abstract: Perfect mixed 26-facet and 18-facet polyhedra of Cu2O microcrystals were successfully synthesized by a hydrothermal process with use of stearic acid as a structure-directing agent. Cu2O octahedra and cubes were also prepared under hydrothermal conditions. The obtained microstructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and UV−vis spectrum. The adsorption and photocatalytic activity of as-prepared 26-facet and 18-facet Cu2O polyhedra for decomposition of methyl orange were investigated and compared to that of octahedra and cubes. The results show that mixed 26-facet and 18-facet polyhedra with dominant {110} facets have a higher adsorption and photocatalytic activity than Cu2O octahedra with dominant {111} surfaces and cubes with {100} surfaces. A higher surface energy and a greater density of the “Cu” dangling bonds on {110} facets of 26-facet and 18-facet polyhedra may be ascribed to its higher catalytic activity. Moreover, a...

Journal ArticleDOI
TL;DR: In this paper, the transformation process of the Mo species loaded on CdS, together with the junctions formed between MoS2 and cdS was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy.
Abstract: Photocatalytic H2 production on MoS2/CdS photocatalysts in the presence of different sacrificial reagents under visible light (λ > 420 nm) has been investigated. The transformation process of the Mo species loaded on CdS, together with the junctions formed between MoS2 and CdS, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. Photocatalytic H2 evolution was optimized for MoS2/CdS catalysts. The 0.2 wt % MoS2/CdS catalyst calcined at 573 K achieves the highest overall activity for H2 evolution, and the 0.2 wt % MoS2/CdS catalyst demonstrates even higher activity than the 0.2 wt % Pt/CdS, irrespective of different sacrificial reagents used. The junctions formed between MoS2 and CdS play an important role in enhancing the photocatalytic activity of MoS2/CdS catalysts. Electrochemical measurements indicate that MoS2 is an excellent H2 evolution catalyst, which is another very important factor responsible for the enhancement of the photocatalytic activity of ...

Journal ArticleDOI
TL;DR: In this paper, the location of copper cations in the zeolite pores and the effect of temperature on these sites and on framework stability were investigated using Rietveld refinement of variable-temperature XRD synchrotron data.
Abstract: Nitrogen oxides (NOx) are a major atmospheric pollutant produced through the combustion of fossil fuels in internal combustion engines. Copper-exchanged zeolites are promising as selective catalytic reduction catalysts for the direct conversion of NO into N2 and O2, and recent reports have shown the enhanced performance of Cu-CHA catalysts over other zeolite frameworks in the NO decomposition of exhaust gas streams. In the present study, Rietveld refinement of variable-temperature XRD synchrotron data obtained for Cu-SSZ-13 and Cu-SSZ-16 is used to investigate the location of copper cations in the zeolite pores and the effect of temperature on these sites and on framework stability. The XRD patterns show that the thermal stability of SSZ-13 is increased significantly when copper is exchanged into the framework compared with the acid form of the zeolite, H-SSZ-13. Cu-SSZ-13 is also more thermally stable than Cu-SSZ-16. From the refined diffraction patterns, the atomic positions of atoms, copper locations a...

Journal ArticleDOI
TL;DR: In this article, a three-step process was proposed to construct a crystalline Fe3O4/TiO2 core/shell nanotubes via three-stage process.
Abstract: Fe3O4/TiO2 core/shell nanotubes are fabricated via a three-step process. α-Fe2O3 nanotubes are first obtained, and α-Fe2O3/TiO2 core/shell nanotubes are subsequently fabricated using Ti(SO4)2 as a Ti source by a wet chemical process. The thickness of the amorphous TiO2 shell is about 21 nm. After a H2 deoxidation process, the amorphous TiO2 layer changes into crystalline structures composed of TiO2 nanoparticles with an average diameter of 2.5 nm, and its thickness is decreased to about 18 nm. At the same time, α-Fe2O3 transforms into cubic Fe3O4. Consequently, crystalline Fe3O4/TiO2 core/shell nanotubes can be fabricated through the process above. The measurements of the magnetic properties demonstrate that the Fe3O4/TiO2 core/shell nanotubes exhibit ferromagnetic behavior at room temperature, and the Verwey temperature is about 120 K. The eddy current effect is largely reduced and the anisotropy energy is improved significantly for the core/shell nanotubes due to the presence of the TiO2 shells. The max...

Journal ArticleDOI
TL;DR: In this article, the formations of intrinsic n-type defects, that is, oxygen vacancies and titanium interstitials, in rutile and anatase TiO2 have been compared using GGA+U calculations.
Abstract: The formations of intrinsic n-type defects, that is, oxygen vacancies and titanium interstitials, in rutile and anatase TiO2 have been compared using GGA+U calculations. In both crystal structures, these defects give rise to states in the band gap, corresponding to electrons localized at Ti3+ centers. O vacancy formation in rutile results in two excess electrons occupying 3d orbitals on Ti atoms neighboring the vacancy. Similarly, for anatase, two Ti 3d orbitals are occupied by the excess electrons, with one of these Ti sites neighboring the vacancy, and the second at a next-nearest Ti position. This localization is accompanied by one oxygen moving toward the vacancy site to give a “split vacancy” geometry. A second fully localized solution is also found for anatase, with both occupied Ti sites neighboring the vacancy site. This minimum is 0.05 eV less stable than the split vacancy and is thus expected to be present in experimental samples. A partially delocalized solution corresponding to the split vacan...

Journal ArticleDOI
TL;DR: In this article, the authors used X-ray diffraction, diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM) images to detect the fine dispersion of Cu particles on TiO2 surface.
Abstract: Cu-doped TiO2 with varying amounts of Cu (0.2, 0.3, 0.5, 1, 2, and 5) are prepared by impregnation method and calcined at 350 and 450 °C for 5 h. These catalysts are characterized by X-ray diffraction, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy energy-dispersive X-ray spectroscopy (EDAX), and transmission electron microscopy (TEM). The DRS studies are clearly showing the expanded photo response of TiO2 into the visible region on impregnation of copper ions. TEM images are depicting the fine dispersion of Cu particles on TiO2 surface. XPS studies are showing change in the binding energy values of Ti 2p, O 1s, and Cu 2p, indicating that copper ions are in interaction with TiO2. XPS results are also confirming that the oxidation state of copper is +2 in samples calcined at 350 °C and +1 in samples calcined at 450 °C. EDAX analysis supports the presence of copper species on the surface layers of TiO2. Photocatalytic hydrogen production activity...

Journal ArticleDOI
TL;DR: In this paper, the photocatalytic activity of the ZnO−SnO2 nanofibers for the degradation of rhodamine B (RB) was much higher than that of electrospun ZnOs and SnO2s.
Abstract: One-dimensional ZnO−SnO2 nanofibers with high photocatalytic activity have been successfully synthesized by a simple combination method of sol−gel process and electrospinning technique. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, nitrogen adsorption−desorption isotherm analysis, UV−vis diffuse reflectance (DR), and photoluminescence (PL) spectroscopy were used to characterize the as-synthesized nanofibers. The results indicated that the ZnO−SnO2 nanofibers with diameters of 100−150 nm consisted of wurtzite ZnO and rutile SnO2. The photocatalytic activity of the ZnO−SnO2 nanofibers for the degradation of rhodamine B (RB) was much higher than that of electrospun ZnO and SnO2 nanofibers, which could be attributed to the formation of a ZnO−SnO2 heterojunction in the ZnO−SnO2 nanofibers and the high specific surface area of the ZnO−SnO2 nanofibers. Notably, the ZnO−SnO2 n...