Showing papers by "Zhong Chen published in 2013"

Efficient Ag@AgCl Cubic Cage Photocatalysts Profit from Ultrafast Plasmon‐Induced Electron Transfer Processes

Abstract: Photon-coupling and electron dynamics are the key processes leading to the photocatalytic activity of plasmonic metal-semiconductor nanohybrids. To better utilize and explore these effects, a facile large-scale synthesis route to form Ag@AgCl cubic cages with well-defined hollow interiors is carried out using a water-soluble sacrificial salt-crystal-template process. Theoretical calculations and experimental probes of the electron transfer process are used in an effort to gain insight into the underlying plasmonic properties of the Ag@AgCl materials. Efficient utilization of solar energy to create electron-hole pairs is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots and multilight-reflection inside the cage structure. More importantly, an ultrafast electron transfer process (≤150 fs) from Ag nanoparticles to the AgCl surface is detected, which facilitates the charge separation efficiency in this system, contributing to high photocatalytic activity and stability of Ag@AgCl photocatalyst towards organic dye degradation.

Engineered iron-oxide-based nanoparticles as enhanced T1 contrast agents for efficient tumor imaging.

Abstract: We report the design and synthesis of small-sized zwitterion-coated gadolinium-embedded iron oxide (GdIO) nanoparticles, which exhibit a strong T1 contrast effect for tumor imaging through enhanced permeation and retention effect and the ability to clear out of the body in living subjects. The combination of spin-canting effects and the collection of gadolinium species within small-sized GdIO nanoparticles led to a significantly enhanced T1 contrast effect. For example, GdIO nanoparticles with a diameter of ∼4.8 nm exhibited a high r1 relaxivity of 7.85 mM–1·S–1 and a low r2/r1 ratio of 5.24. After being coated with zwitterionic dopamine sulfonate molecules, the 4.8 nm GdIO nanoparticles showed a steady hydrodynamic diameter (∼5.2 nm) in both PBS buffer and fetal bovine serum solution, indicating a low nonspecific protein absorption. This study provides a valuable strategy for the design of highly sensitive iron-oxide-based T1 contrast agents with relatively long circulation half-lives (∼50 min), efficien...

Ag–AgBr/TiO2/RGO nanocomposite for visible-light photocatalytic degradation of penicillin G

Abstract: A novel photocatalytic nanocomposite, Ag–AgBr/TiO2 supported on reduced graphene oxide (Ag–AgBr/TiO2/RGO), was synthesized via a facile solvothermal–photoreduction method using titanium butoxide, cetyltrimethylammonium bromide (CTAB), AgNO3 and graphene oxide (GO), during which the crystallization of TiO2, Ag nanoparticles generation from AgBr decomposition and reduction of GO to RGO were achieved simultaneously. Compared to the single-component (TiO2), two-component (Ag–AgBr, Ag/TiO2 and TiO2/RGO) and three-component (Ag–AgBr/RGO, Ag–AgBr/TiO2 and Ag/TiO2/RGO) nanocomposites, the four-component nanocomposite (Ag–AgBr/TiO2/RGO) exhibited a much higher photocatalytic activity for the degradation of penicillin G (PG) under white light-emitting diode (LED-W) irradiation. This could be attributed to the multiplex phenomena such as the surface plasmon resonance (SPR) effect of Ag nanoparticles, enhanced utilization of visible light assisted by AgBr, efficient electron transfer in the AgBr–Ag–TiO2 nanojunctions and interfacial electron transfer in the RGO sheets. Ag–AgBr/TiO2/RGO could be photoexcited by visible light with wavelengths extending up to ca. 600 nm. In addition, Ag–AgBr/TiO2/RGO possessed good photochemical stability and reusability. The mechanisms for photocatalytic activity and photochemical stability associated with Ag–AgBr/TiO2/RGO are proposed. The degradation of PG in the presence of scavengers for various reactive oxygen species (ROSs) revealed that ˙O2− significantly contributed to the degradation of PG.

Vanadium pentoxide cathode materials for high-performance lithium-ion batteries enabled by a hierarchical nanoflower structure via an electrochemical process

Abstract: Hierarchical vanadium oxide nanoflowers (V10O24·nH2O) were synthesized via a simple, high throughput method employing a fast electrochemical reaction of vanadium foil in NaCl aqueous solution, followed by an aging treatment at room temperature. During the electrochemical process, the anodic vanadium foil is dissolved in the form of multi-valence vanadium ions into the solution, driven by the applied electrical field. After being oxidized, the VO2+ and VO2+ ions instantly react with the OH− in the electrolyte to form uniformly distributed vanadium oxide nanoparticles at a high solution temperature due to the exothermic nature of the reaction. Finally, nucleation and growth of one dimensional nanoribbons takes place on the surface of the nanoparticles during the aging process to form unique hierarchical V10O24·nH2O nanoflowers. Upon heat treatment, the hierarchical architecture of the vanadium pentoxide nanoflower morphology is maintained. Such a material provides porous channels, which facilitate fast ion diffusion and effective strain relaxation upon Li ion charge–discharge cycling. The electrochemical tests reveal that the V2O5 nanoflowers cathode could deliver high reversible specific capacities with 100% coulombic efficiency, especially at high C rates (e.g., 140 mAh g−1 at 10 C).

Enhanced Photocatalytic Hydrogen Production with Synergistic Two-Phase Anatase/Brookite TiO2 Nanostructures

Abstract: Highly crystalline pure brookite and two-phase anatase/brookite TiO2 nanostructures were synthesized via a simple hydrothermal method with titanium sulfide as the precursors in sodium hydroxide solutions. The control of the phase composition has been demonstrated via solution concentration and reaction time, and the phase transformation mechanism has been elucidated. Photocatalytic activities of the as-synthesized two-phase anatase/brookite TiO2, pure anatase nanoparticles, and pure brookite nanoplates were appraised via photocatalytic hydrogen evolution in aqueous methanol solution. Results have shown that the photocatalytic activity is higher for the two-phase anatase/brookite TiO2 and brookite nanoplates as compared to pure anatase nanoparticles despite the lower surface areas of the two-phase anatase/brookite TiO2 and brookite nanoplates. From the Mott–Schottky analysis, brookite phase is shown to have a more cathodic conduction band edge potential than anatase phase, which leads to more energetically...

Understanding the Role of Nanostructures for Efficient Hydrogen Generation on Immobilized Photocatalysts

Abstract: For the purpose of efficiently utilizing the renewable solar energy, it is of vital importance to understand the key factors that contribute to the performance merits for photocatalysis applications. In this work, we find that anatase titania nanostructures with high efficiency in photoelectrochemical cell (PEC) do not necessarily retain the same good performance when used in direct heterogeneous reaction (DHR). Investigation is carried out to elucidate how the electronic properties of the different nanostructures are correlated with the PEC and DHR efficiencies. Good PEC cell performance is identified to be related to topotactically formed samples with intimately connected particles that facilitate easy charge transfer. Additional benefit for PEC cell is found to be achieved from the vectorial conduction pathway in the pseudo one dimensional structure. On the other hand, high activity of DHR photocatalysis is attributed mainly to the exposed high reactivity crystal facets. The presence of anatase TiO2 {010} facets is identified to enhance electron-hole separation and create specific surface states that facilitate interactions across the semiconductor/electrolyte interfaces.

Three‐Dimensional CdS–Titanate Composite Nanomaterials for Enhanced Visible‐Light‐Driven Hydrogen Evolution

Abstract: 6 ] have been explored in a bid to meet the above-mentioned specifi c requirements. The ingen-ious arrangement of photochemical system 1 (PS1) and PS2 in a confi ned nanospace for photosynthesis of plants and other organisms is one of the reasons for the high effi ciency conversion of solar energy into chemical energy.

Metabolic responses of HeLa cells to silica nanoparticles by NMR-based metabolomic analyses

Abstract: Silica nanoparticles are increasingly used in the biomedical fields due to their excellent solubility, high stability and favorable biocompatibility. However, despite being considered of low genotoxicity, their bio-related adverse effects have attracted particular concern from both the scientific field and the public. In this study, human cervical adenocarcinoma cells (HeLa line) were exposed to 0.01 or 1.0 mg/mL of hydrophilic silica nanoparticles. The H-1 NMR spectroscopy coupled with multivariate statistical analysis were used to characterize the metabolic variations of intracellular metabolites and the compositional changes of the corresponding culture media. At the early stage of silica nanoparticles-exposure, no obvious dose-effect of HeLa cell metabolome was observed, which implied that cellular stress-response regulated the metabolic variations of HeLa cell. Silica nanoparticles induced the increases of lipids including triglyceride, LDL, VLDL and lactate/alanine ratio and the decreases of alanine, ATP, choline, creatine, glycine, glycerol, isoleucine, leucine, phenylalanine, tyrosine, and valine, which involved in membrane modification, catabolism of carbohydrate and protein, and stress-response. Subsequently, a complicated synergistic effect of stress-response and toxicological-effect dominated the biochemical process and metabolic response, which was demonstrated in the reverse changes of some metabolites including acetate, ADP, ATP, choline, creatine, glutamine, glycine, lysine, methionine, phenylalanine and valine between 6 and 48 h post-treatment of silica nanoparticles. The toxicological-effects induced by high-dosage silica nanoparticles could be derived from the elevated levels of ATP and ADP, the utilization of glucose and amino acids and the production of metabolic end-products such as glutamate, glycine, lysine, methionine, phenylalanine, and valine. The results indicated that it is important and necessary to pursue further the physiological responses of silica nanoparticles in animal models and human before their practical use. NMR-based metabolomic analysis helps to understand the biological mechanisms of silica nanoparticles and their metabolic fate, and further, it offers an ideal platform for establishing the bio-safety of existing and new nanomaterials.

Facile and straightforward synthesis of superparamagnetic reduced graphene oxide–Fe3O4 hybrid composite by a solvothermal reaction

Abstract: A superparamagnetic reduced graphene oxide?Fe3O4 hybrid composite (rGO?Fe3O4) was prepared via a facile and straightforward method through the solvothermal reaction of iron (III) acetylacetonate (Fe(acac)3) and graphene oxide (GO) in ethylenediamine (EDA) and water. By this method, chemical reduction of GO as well as the formation of Fe3O4 nanoparticles (NPs) can be achieved in one step. The Fe3O4 NPs are firmly deposited on the surfaces of rGO, avoiding their reassembly to graphite. The rGO sheets prevent the agglomeration of Fe3O4 NPs and enable a uniform dispersion of these metal oxide particles. The size distribution and coverage density of Fe3O4 NPs deposited on rGO can be controlled by varying the initial mass ratio of GO and iron precursor, Fe(acac)3. With an initial mass ratio of GO and Fe(acac)3 of 5:5, the surfaces of rGO sheets are densely covered by spherical Fe3O4 NPs with an average size of 19.9 nm. The magnetic-functionalized rGO hybrid exhibits a good magnetic property and the specific saturation magnetization (Ms) is 13.2?emu?g?1. The adsorption test of methylene blue from aqueous solution demonstrates the potential application of this rGO-Fe3O4 hybrid composite in removing organic dyes from polluted water.

Molecule-Based Water-Oxidation Catalysts (WOCs): Cluster-Size-Dependent Dye-Sensitized Polyoxometalates for Visible-Light-Driven O2 Evolution

Abstract: From atomic level to understand the cluster-size-dependant behavior of dye-sensitized photocatalysts is very important and helpful to design new photocatalytic materials. Although the relationship between the photocatalytic behaviors and particles' size/shape has been widely investigated by theoretical scientists, the experimental evidences are much less. In this manuscript, we successfully synthesized three new ruthenium dye-sensitized polyoxometalates (POM-n, n relate to different size clusters) with different-sized POM clusters. Under visible-light illumination, all three complexes show the stable O2 evolution with the efficient order POM-3 > POM-2 > POM-1. This cluster-size-dependent catalytic behavior could be explained by the different numbers of M = Ot (terminal oxygen) bonds in each individual cluster because it is well-known that Mo = Ot groups are the catalytically active sites for photooxidation reaction. The proposed mechanism of water oxidation for the dye-sensitized POMs is radical reaction process. This research could open up new perspectives for developing new POM-based WOCs.

Anion-Doped NaTaO3 for Visible Light Photocatalysis

Abstract: In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N–N, C–S, P–P, and N–P codoping have been studied. The redopants’ formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H2 and O2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N–N, C–S, and P–P could absorb visible light. However, they can only decompose water into H2 when the valence band edge is above the water oxidation level.

Bioinspired TiO 2 Nanostructure Films with Special Wettability and Adhesion for Droplets Manipulation and Patterning

Abstract: Patterned surfaces with special wettability and adhesion (sliding, sticky or patterned superoleophobic surface) can be found on many living creatures. They offer a versatile platform for microfluidic management and other biological functions. Inspired by their precise arrangement of structure and chemical component, we described a facile one-step approach to construct large scale pinecone-like anatase TiO2 particles (ATP) film. The as-prepared ATP film exhibits excellent superamphiphilic property in air, changes to underwater superoleophobicity with good dynamical stability. In addition, erasable and rewritable patterned superamphiphobic ATP films or three-dimensional (3D) Janus surfaces were constructed for a versatile platform for microfluidic management and biomedical applications. In a proof-of-concept study, robust super-antiwetting feet for artificial anti-oil strider at the oil/water interface, novel superamphiphobic surface for repeatable oil/water separation, and multifunctional patterned superamphiphobic ATP template for cell, fluorecent probe and inorganic nanoparticles site-selective immobilization were demonstrated.

Enhanced Li adsorption and diffusion in silicon nanosheets based on first principles calculations

Abstract: First-principles density functional theory calculations are employed to investigate novel ultrathin silicon nanosheets (SiNSs) for their potential application as the anode material for Li-ion batteries. We find that Li has a higher tendency to bind on the surface of SiNS rather than penetrating through inside. The binding energies of Li show a strong dependence on the thickness of the nanosheets. The results suggest that insertion/deinsertion of Li can be controlled by using nanosheets of different thickness. More importantly, we show that there is a large increase of diffusivity in Si nanosheets as compared with the bulk case. In addition, Li diffusion shows strong dependence on the chemical functionalization of SiNSs, in which the diffusion rate is the fastest on H passivated surface as compared with the halogen passivated surfaces. Our results suggest that SiNSs are potential materials for Li-ion battery applications.

Nanoindentation study on the creep resistance of SnBi solder alloy with reactive nano-metallic fillers

Abstract: SnBi alloy is an attractive soldering material for temperature-sensitive electronic devices. With its excellent yield strength and fracture resistance, SnBi alloy has become one of the promising candidates to replace Pb-based solders. However, due to the low melting temperatures of this alloy, the prominent time-dependent deformation at service temperatures hinders its wide applications. In this study, low concentration (no more than 4 wt%) of reactive nano-metallic fillers, i.e., Cu and Ni, have been added into the Sn–58Bi alloy aiming to enhance its creep resistance. The elastic, plastic and creep properties are characterized by nanoindentation constant strain rate (CSR) technique. The addition of the fillers has refined the microstructure of the solder matrix leading to moderate strengthening and hardening. The creep resistance of the Sn–58Bi alloy has been improved with the filler addition. Two regions of stress-dependent creep rates were found in the alloys with and without fillers. An optimum filler concentration for creep resistance enhancement is identified at which there is a balance between the effects of particle pinning and microstructure refinement.

Partial Fourier transform reconstruction for single-shot MRI with linear frequency-swept excitation.

Abstract: A novel image encoding approach based on linear frequency-swept excitation has been recently proposed to overcome artifacts induced by various field perturbations in single-shot echo planar imaging. In this article, we develop a new super-resolved reconstruction method for it using the concepts of local k-space and partial Fourier transform. This method is superior to the originally developed conjugate gradient algorithm in convenience, image quality, and stability of solution. Reduced field-of-view is applied to the phase encoding direction to further enhance the spatial resolution and field perturbation immunity of the image obtained. Effectiveness of this new combined reconstruction method is demonstrated with a series of experiments on biological samples. Two single-shot sequences with different encoding features are tested. The results show that this reconstruction method maintains excellent field perturbation immunity and improves fidelity of the images. In vivo experiments on rat indicate that this solution is favorable for ultrafast imaging applications in which severe susceptibility heterogeneities around the tissue–air or tissue–bone interfaces, motion and oblique plane effects usually compromise the echo planar imaging image quality. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

Understanding the metabolic fate and assessing the biosafety of MnO nanoparticles by metabonomic analysis

Abstract: Recently, some types of MnO nanoparticle (Mn-NP) with favorable imaging capacity have been developed to improve the biocompatible profile of the existing Mn-based MRI contrast agent Mn-DPDP; however, the overall bio-effects and potential toxicity remain largely unknown. In this study, (1)H NMR-based metabolic profiling, integrated with traditional biochemical analysis and histopathological examinations, was used to investigate the absorption, distribution, metabolism, excretion and toxicity of Mn-NPs as candidates for MRI contrast agent. The metabolic responses in biofluids (plasma and urine) and tissues (liver, spleen, kidney, lung and brain) from rats could be divided into four classes following Mn-NP administration: Mn biodistribution-dependent, time-dependent, dose-dependent and complicated metabolic variations. The variations of these metabolites involved in lipid, energy, amino acid and other nutrient metabolism, which disclosed the metabolic fate and biological effects of Mn-NPs in rats. The changes of metabolic profile implied that the disturbance and impairment of biological functions induced by Mn-NP exposure were correlated with the particle size and the surface chemistry of nanoparticles. Integration of metabonomic technology with traditional methods provides a promising tool to understand the toxicological behavior of biomedical nanomaterials and will result in informed decision-making during drug development.

CuInZnS-decorated graphene nanosheets for highly efficient visible-light-driven photocatalytic hydrogen production

Abstract: Photocatalytic H2 production from water splitting using semiconductor photocatalysts has attracted much attention due to the increasing global energy crisis. In the past few decades, numerous photocatalysts have been proposed, however, it is still a challenge to develop highly active photocatalysts for water splitting under visible light. Here we report a new composite material consisting of Cu0.02In0.3ZnS1.47 (CIZS) nanospheres and reduced graphene oxide (rGO) nanosheets as a highly active photocatalyst for hydrogen evolution under visible light. These composites were prepared through a solvothermal method in which rGO nanosheets served as a supporting material to load CIZS nanospheres. The nanocomposites demonstrated a high H2 production rate of 3.8 mmol h−1 g−1, which is about 1.84 times that of pure CIZS nanospheres under visible-light irradiation. The high H2 production rate arose from the presence of graphene, which served as an electron collector and transporter to efficiently lengthen the lifetime of photogenerated charge carriers from CIZS nanospheres. This study presents an effective approach to synthesize graphene-based nanocomposites in the field of energy conversion.

Improving Photocatalytic H2 Evolution of TiO2 via Formation of {001}–{010} Quasi-Heterojunctions

Abstract: The coexistence of low-index facets with a highly photoactive {001} facet in anatase TiO2 nanocrystals has been recently found beneficial to enhance the photocatalytic performance of TiO2 via a synergistic effect. In this paper, this synergistic effect has been further extended from a single crystal to interconnected nanocrystals with dominating {001} or {010} facet in intact hierarchical TiO2 nanostrucutre. The particles synthesized at the optimal condition showed outstanding photocatalytic hydrogen production of 364.2 μmol·g–1·h–1, which is about four times as much as that of commercial P25 (96.5 μmol·g–1·h–1). Femtosecond transient spectroscopy and density functional theory (DFT) study indicates that effective electron–hole separation takes place within these nanostructures. This new prototype of synergy, which we denote as quasi-heterojunctions, shows that enhanced photocatalytic performance could be derived in the same anatase phase by synthesizing appropriate faceted nanostructures. This work provid...

Junction-Temperature Determination in InGaN Light-Emitting Diodes Using Reverse Current Method

Abstract: A method is presented in this study to determine the junction temperature (Tj) of LED in terms of the relationship between the diode reverse current (IR) and Tj A theoretical model for the dependence of IR on Tj is derived on the basis of the Shockley equation and is validated by our experimental results The method is compared with the conventional forward voltage method, and its advantages have been identified

Optimization Studies of Two-Phosphor-Coated White Light-Emitting Diodes

Abstract: Three-hump InGaN-based white light-emitting diodes (LEDs) precoated with traditional yellow/green phosphors and red-emitting quantum dots (QDs), have been numerically investigated. Under variations of eight correlated color temperatures (CCTs), three wavelengths, two bandwidths, and two peak heights, optimal results of luminous efficacy radiation (LER) and color rendering index (CRI) are identified and retained through filtering off billions of unqualified candidates. These results include LER = 390 lm/W and CRI = 90 [chromaticity difference (Duv)<;0.0054] at CCT = 3000 K. In addition, our photometric and colorimetric sensitivity studies provide the dependence of LER, CRI, CCT, and Duv on LED spectral parameters affected by operating temperatures. Finally, we have discovered that higher instabilities may be induced for cool white LEDs (CCT = 6500 K) than for warm white LEDs (CCT = 3000 K) within the analysis of CCT versus spectral parameters.