Showing papers in "Journal of Physical Chemistry C in 2013"
TL;DR: In this article, the authors investigate organometal CH3NH3PbX3 and mixed halide CH3 NH 3PbI2X perovskites (X = Cl, Br, I), which are key materials for high efficiency solid-state solar cells.
Abstract: We computationally investigate organometal CH3NH3PbX3 and mixed halide CH3NH3PbI2X perovskites (X = Cl, Br, I), which are key materials for high efficiency solid-state solar cells. CH3NH3PbX3 perovskites exhibited the expected absorption blue shift along the I → Br → Cl series. The mixed halide systems surprisingly showed the CH3NH3PbI3 and the CH3NH3PbI2Cl (or CH3NH3PbI3–xClx) perovskites to have similar absorption onset at ∼800 nm wavelength, whereas CH3NH3PbI2Br absorbs light below ∼700 nm. To provide insight into the structural and electronic properties of these materials, in light of their application as solar cell active layers, we perform periodic DFT calculations on the CH3NH3PbX3 and CH3NH3PbI2X perovskites. We find a good agreement between the calculated band structures and the experimental trend of optical band gaps. For the mixed halide perovskites our calculations show the existence of two different types of structures with different electronic properties, whose relative stability varies by v...
866 citations
TL;DR: In this paper, the temperature dependence of in-plane E2g and out-of-plane A1g Raman modes in high-quality few-layer MoS2 (FLMS) prepared using a high-temperature vapor phase method was investigated using transmission electron microscopy.
Abstract: We report on the temperature dependence of in-plane E2g and out-of-plane A1g Raman modes in high-quality few-layer MoS2 (FLMS) prepared using a high-temperature vapor-phase method. The materials obtained were investigated using transmission electron microscopy. The frequencies of these two phonon modes were found to vary linearly with temperature. The first-order temperature coefficients for E12g and A1g modes were found to be (1.32 and 1.23) × 10–2 cm–1/K, respectively. The thermal conductivity of the suspended FLMS at room temperature was estimated to be ∼52 W/mK.
595 citations
TL;DR: In this paper, the transformation of graphitic carbon nitride (g-C3N4) from nanoplates to nanorods was realized by a simple reflux method.
Abstract: The transformation of graphitic carbon nitride (g-C3N4) from nanoplates to nanorods was realized by a simple reflux method. The photocatalytic activity and the intensity of the photocurrent response of g-C3N4 nanorods under visible light were about 1.5 and 2.0 times those of g-C3N4 nanoplates, respectively. The formation mechanism of g-C3N4 from nanoplates to nanorods was demonstrated that g-C3N4 nanoplates undergo a possible exfoliation and regrowth process and a rolling mechanism of lamellar structure, which is responsible for elimination of the surface defects in the reflux process. During the transformation of g-C3N4 from nanoplates to nanorods, the enhancement of photocatalytic activity and photocurrent intensity in g-C3N4 nanorods was mainly attributed to the increase of active lattice face and elimination of surface defects.
589 citations
TL;DR: In this article, the authors investigated the adsorption and diffusion of lithium on the recently synthesized VS2 monolayer, in comparison with MoS2 and graphite.
Abstract: By means of density functional theory computations, we systematically investigated the adsorption and diffusion of lithium on the recently synthesized VS2 monolayer, in comparison with MoS2 monolayer and graphite. Intrinsically metallic, VS2 monolayer has a higher theoretical capacity (466 mAh/g), a lower or similar Li diffusion barrier as compared to MoS2 and graphite, and has a low average open-circuit voltage of 0.93 V (vs Li/Li+). Our results suggest that VS2 monolayer can be utilized as a promising anode material for Li ion batteries with high power density and fast charge/discharge rates.
553 citations
TL;DR: In this article, the authors investigate the effects of injection of plasmonic carriers from an optically excited metal nanocrystal to a semiconductor contact or to surface molecules.
Abstract: We investigate theoretically the effects of generation and injection of plasmonic carriers from an optically excited metal nanocrystal to a semiconductor contact or to surface molecules. The energy distributions of optically excited hot carriers are dramatically different in metal nanocrystals with large and small sizes. In large nanocrystals, the majority of hot carriers has very small excitation energies, and the excited-carrier distribution resembles the case of a plasmon wave in bulk. For nanocrystal sizes smaller than 20 nm, the carrier distribution extends to larger energies and occupies the whole region EF < e < EF + ℏω. The physical reason for the above behaviors is nonconservation of momentum in a nanocrystal. Because of the above properties, nanocrystals of small sizes are most suitable for designing opto-electronic and photosynthetic devices based on injection of plasmonic electrons and holes. For gold nanocrystals, the optimal sizes for efficient generation of hot carriers with overbarrier ene...
488 citations
TL;DR: In this paper, the dissolution behaviors of Mn and Ni were examined systematically under various conditions such as state of charge (SOC), temperature, storage time, and crystal structure of LNMO.
Abstract: The high-voltage LiNi0.5Mn1.5O4 (LNMO) spinel is a promising candidate for a positive electrode in lithium ion batteries, but LNMO/graphite full-cells display severe capacity fading issues due to Mn dissolution. In this study, the dissolution behaviors of Mn and Ni were examined systematically under various conditions such as state of charge (SOC), temperature, storage time, and crystal structure of LNMO. In addition, surfaces of calendar- or cycle-aged LNMO and graphite electrodes were analyzed by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), or time-of-flight secondary ion mass spectrometry (TOF-SIMS). The chemical composition of aged electrolyte was determined by gas chromatography (GC) analysis after storage of LNMO electrodes under different conditions. It was found that the amounts of dissolved Mn and Ni and diethyl ether, a decomposition product of diethyl carbonate (DEC) in electrolyte, increased with SOC, temperature, and storage time. The decomposition of electr...
487 citations
TL;DR: In this article, the stability of single-layer transition-metal dichalcogenides has been studied and their potential for photocatalytic water splitting has been determined. But the authors focus on the stability and stability of the dichalcanogenides and determine their potential to be used in photocatalysis.
Abstract: Some of the members of the family of single-layer transition-metal dichalcogenides have recently received a lot of attention for their promising electronic properties, with potential applications in electronic devices. In this work, we focus on the stability of the dichalcogenides and determine their potential for photocatalytic water splitting. Using a first-principles design approach, we perform a systematic theoretical study of the dichalcogenides MX2 (M = Nb, Mo, Ta, W, Ti, V, Zr, Hf, and Pt; X = S, Se, and Te). First, we use a van der Waals functional to accurately calculate their formation energies. The results reveal that most MX2 have similar formation energies to those of single-layer MoS2 and WS2, implying the ease of mechanically exfoliating a single-layer MX2 from their layered bulk counterparts. Next, we use the many-body G0W0 approximation to obtain the band structures, finding that about half of the MX2 are semiconductors. We then calculate conduction and valence band edge positions by comb...
460 citations
TL;DR: In this paper, the potential solar-to-fuel conversion efficiency expected in a device with realistic losses is examined, and recent advances with increasing the performance of promising semiconductor electrode materials and highlight how these advances have led to state-of-the-art solar tochemical efficiencies in the 2-3% range in real devices.
Abstract: In order to be economically competitive with simple “brute force” (i.e., PV + electrolyzer) strategies or the production of promising solar fuels, like H2, from fossil fuels, a practical photoelectrochemical device must optimize cost, longevity, and performance. A promising approach that meets these requirements is the combination of stable and inexpensive oxide semiconductor electrodes in a tandem photoelectrochemical device. In this article, we give an overview of the field including an examination of the potential solar-to-fuel conversion efficiency expected in a device with realistic losses. We next discuss recent advances with increasing the performance of promising semiconductor electrode materials and highlight how these advances have led to state-of-the-art solar-to-chemical efficiencies in the 2–3% range in real devices. Challenges for further optimization are further outlined.
456 citations
TL;DR: In this paper, the surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated using two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes.
Abstract: The surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated. The investigation utilizes two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes. The first method, transmission electron microscopy with energy dispersive X-ray spectroscopy, allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF6 salt and ethylene carbonate or fluoroethylene carbonate solvent. Capacity retention was significantly better for cells cycled with LiPF6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF6/EC electrolyte the BF-Si SEI continuously grows during the first ...
447 citations
TL;DR: In this article, the surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated using two novel techniques, which are enabled by the use of binder-free graphite anodes.
Abstract: The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF6 electrolytes, the graphite SEI...
412 citations
TL;DR: MoS2/CdS p-n heterojunction films with high photoelectrochemical activity for H2 evolution under visible light were successfully prepared by electrodeposition followed by chemical bath deposition as mentioned in this paper.
Abstract: MoS2/CdS p-n heterojunction films with high photoelectrochemical activity for H2 evolution under visible light were successfully prepared by electrodeposition followed by chemical bath deposition. The films were characterized by X-ray diffraction, scanning electron microscopy, UV–visible absorption, X-ray photoemission spectroscopy, photoluminescence, and photoelectrochemical response. The MoS2/CdS heterostructure shows much higher visible-light photoelectrocatalytic activity and higher stability toward the water splitting than pure CdS film. The MoS2/CdS film with an optimal ratio of 0.14% exhibits the highest photocurrent of 28 mA/cm2 and the highest IPCE of ca. 28% at 420 nm at 0 V vs Ag/AgCl. The critical role of MoS2 in the MoS2/CdS film was investigated. The improved photoelectrochemical performance of the MoS2/CdS heterojunction film was attributed to the visible light absorption enhanced by MoS2 and the formation of a p-n junction between CdS and MoS2, which accelerates the effective separation of...
TL;DR: In this article, the fundamental thermodynamic and kinetic basis for cation exchange reactions in colloidal semiconductor nanocrystals and highlight its synthetic versatility for accessing nanomaterials intractable by direct synthetic methods.
Abstract: The development of nanomaterials for next generation photonic, optoelectronic, and catalytic applications requires a robust synthetic toolkit for systematically tuning composition, phase, and morphology at nanometer length scales. While de novo synthetic methods for preparing nanomaterials from molecular precursors have advanced considerably in recent years, postsynthetic modifications of these preformed nanostructures have enabled the stepwise construction of complex nanomaterials. Among these postsynthetic transformations, cation exchange reactions, in which the cations ligated within a nanocrystal host lattice are substituted with those in solution, have emerged as particularly powerful tools for fine-grained control over nanocrystal composition and phase. In this feature article, we review the fundamental thermodynamic and kinetic basis for cation exchange reactions in colloidal semiconductor nanocrystals and highlight its synthetic versatility for accessing nanomaterials intractable by direct synthet...
TL;DR: In this article, the UV-vis spectra exhibited a strong π-π* transition near 400 nm with a semiconductor-like band edge extending into the visible range, which is assigned to n−π* electronic transitions involving the N lone pairs.
Abstract: Graphitic carbon nitride compounds were prepared by thermal treatment of C–N–H precursor mixtures (melamine C3N6H9, dicyandiamide C2N4H4). This led to solids based on polymerized heptazine or triazine ring units linked by −N═ or −NH– groups. The H content decreased, and the C/N ratio varied between 0.59 and 0.70 with preparation temperatures between 550 and 650 °C due to increased layer condensation. The UV–vis spectra exhibited a strong π–π* transition near 400 nm with a semiconductor-like band edge extending into the visible range. Samples synthesized at 600–650 °C showed an additional absorption near 500 nm that is assigned to n−π* electronic transitions involving the N lone pairs. These are forbidden for planar symmetric s-triazine or heptazine structures but become allowed as increased condensation causes distortion of the polymeric units. Photocatalysis studies showed there was no correlation between the increased visible absorption due to this feature and H2 evolution from methanol used for the ano...
TL;DR: In this article, the transport properties of lithium ion conducting glass ceramics represented by the general composition Li1+x−yAlx3+My5+M2−x-y4+(PO4)3 with NASICON-type structure and their stability in contact with lithium metal were investigated.
Abstract: We report on the transport properties of lithium ion conducting glass ceramics represented by the general composition Li1+x–yAlx3+My5+M2–x–y4+(PO4)3 with NASICON-type structure and their stability in contact with lithium metal. In particular, solid electrolyte phases with M = Ge, M = Ti, Ge, and M = Ti, Ta were investigated. AC impedance spectroscopy and DC polarization measurements were applied to determine the conductivity as a function of temperature, and to extract the partial electronic conductivity. The maximum total conductivity at room temperature was found to be about 4 × 10–4 S/cm for the solely Ge containing sample. We demonstrate that the combination of vacuum-based lithium thin film deposition and X-ray photoelectron spectroscopy (XPS) is well suited to study the reactivity of the solid electrolyte membranes in contact with lithium. As a major result, we show that none of the materials investigated is stable in contact with lithium metal, and we discuss the reactive interaction between solid ...
TL;DR: In this article, the authors used 1H nuclear magnetic resonance (NMR) to characterize the nanoporosity of calcium silicate hydrate (C-S-H) in sealed cured pastes as a function of degree of hydration and water to cement ratio.
Abstract: The nanoscale morphology of, and pore water interactions in, calcium silicate hydrate (C–S–H), the active component of cement, remain uncertain. 1H nuclear magnetic resonance (NMR) can fully characterize the nanoporosity of C–S–H in as-prepared material without the need for damaging sample drying. We use NMR to follow the density of C–S–H in sealed cured pastes as a function of degree of hydration (α) and water to cement ratio. We show clear evidence for C–S–H densification. The C–S–H “solid” density, exclusive of gel pore water, slightly decreases from ρx = 2.73 g/cm3 at α ≈ 0.4 to 2.65 g/cm3at α ≈ 0.9 due to an increase in the number of layers in the nanocrystalline aggregates. In the same range, the C–S–H “bulk” density, including gel water, increases from around 1.8 to 2.1 g/cm3. The increase corresponds to a transition from growth of low-density product containing gel pores to higher density product devoid of gel pores. We update Powers’ classical model from 1947. In contrast to the single “hydrate” ...
TL;DR: In this paper, a combination of symmetry arguments and first-principles calculations is used to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials.
Abstract: We use a combination of symmetry arguments and first-principles calculations to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials. We explain the role of octahedral rotations in suppressing ferroelectricity in these materials and show that, as the tolerance factor decreases, rotations alone cannot fully suppress ferroelectricity. Our results show that it is cation displacements (“hidden” in Glazer notation) that accompany the rotations, rather than the rotations themselves, that play the decisive role in suppressing ferroelectricity in these cases. We use the knowledge gained in our analysis of this problem to explain the origin of ferroelectricity in R3c materials such as FeTiO3 and ZnSnO3 and to suggest strategies for the design and synthesis of new perovskite ferroelectrics. Our results have implications not only for the fundamental crystal chemistry of the perovskites but also for the discovery of new functional materials.
TL;DR: In this article, the electromagnetic behavior of the basic unit constituted by a dimer of dielectric nanoparticles made of moderately low-loss high refractive index material is explored and studied through an analytical dipole-dipole model.
Abstract: Dielectric nanoparticles with moderately high refractive index and very low absorption (like Si and Ge in the visible–near-infrared (VIS–NIR) range) show a magnetodielectric behavior that produces interesting far-field coherent effects, like directionality phenomena or field enhancement in the proximity of the particle surface. As in the case of metals, ensembles of two or more dielectric particles can constitute basic elements for developing new spectroscopic tools based on surface field enhancement effects. Here we explore the electromagnetic behavior of the basic unit constituted by a dimer of dielectric nanoparticles made of moderately low-loss high refractive index material. The interactions responsible for the spectral features of the scattered radiation and field enhancement of the dimer are identified and studied through an analytical dipole–dipole model. The fluorescence of a single emitter (either electric or magnetic dipole) located in the dimer gap is also explored by calculating the quantum e...
TL;DR: In this article, the effects of donor and acceptor substitutions and extend the applications of TPE-based materials, three TPE kindred, TTPE, BTPEFN, and BATPEFN, are employed.
Abstract: Luminescent materials with aggregation-induced emission (AIE) property have attracted considerable interests for their promising applications in light-emitting and display devices and fluorescent probes for chemo- and biosensors. Tetraphenylethene (TPE) derivatives are the most attractive species for their notable AIE performance, facile synthesis, and flexible structure modification. To study the effects of donor and acceptor substitutions and extend the applications of TPE-based materials, three TPE kindred, TTPE, BTPEFN, and BATPEFN, are employed. TTPE film displays efficient green fluorescence (λem = 494 nm, ΦF = 100%), evident AIE characteristic (αAIE = 154), and reversible mechanochromism by grinding-fuming: from blue (λem = 472 nm) to green emission (λem = 505 nm). Replacing two phenyls by two cyano (A) groups on the central TPE moiety derives BTPEFN, whose film shows efficient orange fluorescence (λem = 575 nm, ΦF = 100%) and evident AIE (αAIE = 13). The mechanochromic behavior of BTPEFN (from yel...
TL;DR: In this article, a facile, reproducible, and template-free strategy to prepare g-C3N4-Fe3O4 nanocomposites by an in situ growth mechanism was demonstrated.
Abstract: Herein we demonstrate a facile, reproducible, and template-free strategy to prepare g-C3N4–Fe3O4 nanocomposites by an in situ growth mechanism. The results indicate that monodisperse Fe3O4 nanoparticles with diameters as small as 8 nm are uniformly deposited on g-C3N4 sheets, and as a result, aggregation of the Fe3O4 nanoparticles is effectively prevented. The as-prepared g-C3N4–Fe3O4 nanocomposites exhibit significantly enhanced photocatalytic activity for the degradation of rhodamine B under visible-light irradiation. Interestingly, the g-C3N4–Fe3O4 nanocomposites showed good recyclability without loss of apparent photocatalytic activity even after six cycles, and more importantly, g-C3N4–Fe3O4 could be recovered magnetically. The high performance of the g-C3N4–Fe3O4 photocatalysts is due to a synergistic effect including the large surface-exposure area, high visible-light-absorption efficiency, and enhanced charge-separation properties. In addition, the superparamagnetic behavior of the as-prepared g-C...
TL;DR: In this article, the structural properties of clinopyroxene NaScSi2O6 have been investigated using the X-ray powder diffraction refinement, and the luminescence properties of Eu2+ and Eu 2+/Mn2+-activated NaSc SiO6 has been studied to explore the new materials for phosphor-converted white light ultraviolet light-emitting diodes (UV-LEDs).
Abstract: The structural properties of clinopyroxene NaScSi2O6 have been investigated using the X-ray powder diffraction refinement, and the luminescence properties of Eu2+ and Eu2+/Mn2+-activated NaScSi2O6 have been studied to explore the new materials for phosphor-converted white light ultraviolet light-emitting diodes (UV-LEDs). Eu2+ was introduced into the NaScSi2O6 host in the reducing atmosphere, and the preferred crystallographic positions of the Eu2+ ions were determined based on the different structural models of the NaScSi2O6 host. The as-obtained NaScSi2O6:Eu2+ phosphor shows greenish yellow emission with the broad-band peak at 533 nm, and efficient energy transfer (ET) takes place between Eu2+ and Mn2+ in NaScSi2O6, leading to a series of color-tunable phosphors emitting at 533 and 654 nm for the designed NaScSi2O6:Eu2+,Mn2+ phosphors under excitation at 365 nm. The ET mechanism of Eu2+ and Mn2+ has also been evaluated. We have demonstrated that NaScSi2O6:Eu2+ and NaScSi2O6:Eu2+,Mn2+ materials exhibit g...
TL;DR: In this article, a biogenic synthesis of visible light active Ag-ZnO nanocomposite for photocatalysis and photoelectrode using an electrochemically active biofilm (EAB) was reported.
Abstract: The development of coupled photoactive materials (metal/semiconductor) has resulted in significant advancements in heterogeneous visible light photocatalysis. This work reports the novel biogenic synthesis of visible light active Ag–ZnO nanocomposite for photocatalysis and photoelectrode using an electrochemically active biofilm (EAB). The results showed that the EAB functioned as a biogenic reducing tool for the reduction of Ag+, thereby eliminating the need for conventional reducing agents. The as-prepared Ag–ZnO nanocomposite was characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic experiments showed that the Ag–ZnO nanocomposite possessed excellent visible light photocatalytic activity for the degradation of methyl orange, methylene blue, and 4-nitrophenol. Electrochemical impedance spectroscopy and linear scan voltammetry under dark and visible light irradiation ...
TL;DR: In this article, the authors show that the rate of CO2 conversion per unit surface area is about 10 times higher on 5 nm silver nanoparticles than on bulk silver even though measurements on single crystal catalysts show much smaller variations in rate.
Abstract: Electrochemical conversion of CO2 has been proposed both as a way to reduce CO2 emissions and as a source of renewable fuels and chemicals, but conversion rates need improvement before the process will be practical. In this article, we show that the rate of CO2 conversion per unit surface area is about 10 times higher on 5 nm silver nanoparticles than on bulk silver even though measurements on single crystal catalysts show much smaller variations in rate. The enhancement disappears on 1 nm particles. We attribute this effect to a volcano effect associated with changes of the binding energy of key intermediates as the particle size decreases. These results demonstrate that nanoparticle catalysts have unique properties for CO2 conversion.
TL;DR: This work presents a uniform method for synthesizing pure and bimetallic DENs and demonstrates that their catalytic properties are dependent on the adsorbate’s binding energy.
Abstract: We demonstrate that the reduction of p-nitrophenol to p-aminophenol by NaBH4 is catalyzed by both monometallic and bimetallic nanoparticles (NPs). We also demonstrate a straightforward and precise method for the synthesis of bimetallic nanoparticles using poly(amido)amine dendrimers. The resulting dendrimer encapsulated nanoparticles (DENs) are monodisperse, and the size distribution does not vary with different elemental combinations. Random alloys of Pt/Cu, Pd/Cu, Pd/Au, Pt/Au, and Au/Cu DENs were synthesized and evaluated as catalysts for p-nitrophenol reduction. These combinations are chosen in order to selectively tune the binding energy of the p-nitrophenol adsorbate to the nanoparticle surface. Following the Bronsted-Evans-Polanyi (BEP) relation, we show that the binding energy can reasonably predict the reaction rates of p-nitrophenol reduction. We demonstrate that the measured reaction rate constants of the bimetallic DENs is not always a simple average of the properties of the constituent metals. In particular, DENs containing metals with similar lattice constants produce a binding energy close to the average of the two constituents, whereas DENs containing metals with a lattice mismatch show a bimodal distribution of binding energies. Overall, in this work we present a uniform method for synthesizing pure and bimetallic DENs and demonstrate that their catalytic properties are dependent on the adsorbate's binding energy.
TL;DR: In this article, high-efficiency visible-light-driven Ag3PO4/AgI photocatalysts with different mole fractions of AgI have been synthesized via an in-situ anion-exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and UV-vis diffuse reflectance spectrograph (DRS).
Abstract: High-efficiency visible-light-driven Ag3PO4/AgI photocatalysts with different mole fractions of AgI have been synthesized via an in-situ anion-exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and UV–vis diffuse reflectance spectroscopy (DRS). Under visible light (>420 nm), the Ag3PO4/AgI photocatalysts exhibit enhanced photocatalytic activity compared to pure Ag3PO4 or AgI for the degradation of methyl orange and phenol, and the highest activity is reached by the Ag3PO4/AgI hybrid photocatalyst with 20% of AgI. The quenching effects of different scavengers suggest that the reactive h+ and O2•– play the major role in the MO degradation. Detailed X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis reveals that Ag nanoparticles (NPs) form on the surface of Ag3PO4/AgI in the early stage of the photocatalytic oxidation process, thus leading to the transformation from Ag3PO4/AgI to Ag3PO...
TL;DR: In this paper, two novel Bi-based borate photocatalysts Bi4B2O9 and Bi2O2[BO2(OH)] with layered structure have been successfully developed.
Abstract: Through the combination of Bi3+ and a large negative charge ion (BO3)3–, two novel Bi-based borate photocatalysts Bi4B2O9 and Bi2O2[BO2(OH)] with layered structure have been successfully developed. For the first time, the borates were investigated as photocatalysts. They were synthesized by solid-state reaction and hydrothermal method, respectively, and further characterized by XRD, SEM, TEM, HRTEM, and DRS. Bi4B2O9 and Bi2O2[BO2(OH)] possess direct and indirect transition optical band gaps of 3.02 and 2.85 eV, respectively. Density functional calculations revealed that the valence band (VB) and conduction band (CB) of both borates were composed of hybridized states of the O 2p and Bi 6p or 6s orbitals, and a large dispersion was observed in the energy band of Bi2O2[BO2(OH)]. The photodecomposition experiments demonstrated that Bi4B2O9 and Bi2O2[BO2(OH)] can be used as effective photocatalysts under simulated solar irradiation, and Bi2O2[BO2(OH)] exhibits the high photocatalytic activity, which is 2.5 and...
TL;DR: In this paper, a facile solvothermal route to synthesize reduced graphene oxide (RGO) nanosheets combined with surface modified γ-Fe2O3 colloidal nanoparticle clusters was reported.
Abstract: Graphene is highly desirable as an electromagnetic wave (EM) absorber because of its large interface, high dielectric loss, and low density. Nevertheless, the conductive and electromagnetic parameters of pure graphene are too high to meet the requirement of impedance match, which results in strong reflection and weak absorption. In this paper, we report a facile solvothermal route to synthesize reduced graphene oxide (RGO) nanosheets combined with surface-modified γ-Fe2O3 colloidal nanoparticle clusters. The obtained two-dimensional hybrids exhibit a relatively low EM reflection coefficient (RC) and wide effective absorption bandwidth, which are mainly attributed to the unique microstructure of colloidal nanoparticle clusters assembled on RGO. The nanoparticle clusters have more interfaces. The interfacial polarization within nanoparticle clusters and conductivity loss of RGO plays an important role in absorbing EM power. The minimum RC reaches −59.65 dB at 10.09 GHz with a matching thickness of 2.5 mm. T...
TL;DR: In this article, the catalytic capacity of Co-BNNS is attributed to the strong mixing between the cobalt 3d orbitals and oxygen 2p orbitals, which activates the adsorbed molecular or atomic oxygen.
Abstract: By means of first-principles computation, metal (Cu, Ag, Au, Pt, Rh, Pd, Fe, Co, and Ir) doped hexagonal boron nitride nanosheets (h-BNNSs) have been systematically investigated. The strong interaction between the metal atoms and defect sites in h-BNNS, such as the boron vacancy and nitrogen edge, suggests that metal doped h-BN nanosheets (M-BNNSs) should be stable under high temperatures. The catalytic activity of Co doped h-BNNS is also investigated by using CO oxidation as a probe, and the calculated low barrier suggests that the Co-BNNS is a viable catalyst for CO oxidation. Based on electronic structure analysis, the catalytic capacity of Co-BNNS is attributed to the strong mixing between the cobalt 3d orbitals and oxygen 2p orbitals, which activates the adsorbed molecular or atomic oxygen.
TL;DR: In this paper, the authors report the light-to-heat energy transfer efficiencies of gold nanoparticles with variable sizes by assessing the temperature profiles of laser-activated particle suspensions in water.
Abstract: We report the light-to-heat energy transfer efficiencies of gold nanoparticles with variable sizes by assessing the temperature profiles of laser-activated particle suspensions in water. Gold nanoparticles with sizes ranging from 5 to 50 nm were synthesized by chemical reduction methods using sodium borohydride, sodium citrate, or hydroquinone as reducing agents. As-synthesized gold nanoparticle solution (1 mL) was loaded into a quartz cuvette and exposed to a CW green laser (532 nm). Heat input into the system by energy transfer from nanoparticles equals heat dissipation at thermal equilibrium. The transducing efficiency was then determined by plotting temperature increase as a function of laser power extinction. The efficiency increases from 0.650 ± 0.012 to 0.803 ± 0.008 as the particle size decreases from 50.09 ± 2.34 to 4.98 ± 0.59 nm, respectively. The results indicate that the photothermal properties of gold nanoparticles are size-tunable, and the variation of efficiency can be correlated to the ab...
TL;DR: In this article, the authors presented the fabrication of TiO2 nanofibers codecorated with Au and Pt nanoparticles through facile electrospinning, which led to remarkably enhanced photocatalytic activities on both hydrogen generation and CO2 reduction.
Abstract: We present the fabrication of TiO2 nanofibers codecorated with Au and Pt nanoparticles through facile electrospinning. The Au and Pt nanoparticles with sizes of 5–12 nm are well-dispersed in the TiO2 nanofibers as evidenced by electron microscopic analyses. The present design of Au/Pt codecoration in the TiO2 nanofibers leads to remarkably enhanced photocatalytic activities on both hydrogen generation and CO2 reduction. This great enhancement is attributed to the synergy of electron-sink function of Pt and surface plasmon resonance (SPR) of Au nanoparticles, which significantly improves charge separation of photoexcited TiO2. Our studies demonstrate that through rational design of composite nanostructures one can harvest visible light through the SPR effect to enhance the photocatalytic activities of semiconductors initiated by UV-light to more effectively utilize the whole solar spectrum for energy conversion.
TL;DR: In this article, the oxidative stability and initial oxidation-induced decomposition reactions of common electrolyte solvents for batteries and electrical double layer capacitors were investigated using quantum chemistry (QC) calculations.
Abstract: The oxidative stability and initial oxidation-induced decomposition reactions of common electrolyte solvents for batteries and electrical double layer capacitors were investigated using quantum chemistry (QC) calculations. The investigated electrolytes consisted of linear (DMC, EMC) and cyclic carbonate (EC, PC, VC), sulfone (TMS), sulfonate, and alkyl phosphate solvents paired with BF4–, PF6–, bis(fluorosulfonyl)imide (FSI–), difluoro-(oxalato)borate (DFOB–), dicyanotriazolate (DCTA–), and B(CN)4– anions. Most QC calculations were performed using the M05-2X, LC-ωPBE density functional and compared with the G4MP2 results where feasible. The calculated oxidation potentials were compared with previous and new experimental data. The intrinsic oxidation potential of most solvent molecules was found to be higher than experimental values for electrolytes even after the solvation contribution was included in the QC calculations via a polarized continuum model. The presence of BF4–, PF6–, B(CN)4–, and FSI– anions...