Haitao Fu

Bimetallic Ag-Au nanowires: synthesis, growth mechanism, and catalytic properties.

Silver-gold (Ag-Au) bimetallic nanowires were controllably synthesized by a newly developed wet-chemical method at room temperature. The Ag nanowires and Au nanoparticles were sequentially formed by reduction with vanadium oxide (V2O3) nanoparticles so as to form Ag-Au bimetal, in which the Ag nanowires show a diameter of ~20 nm and length up to 10 μm. A few unique features were noted in our new approach: it was rapid (within a few minutes), controllable in shape and size, reproducible, and there was no need for any surface modifiers. The formation and growth mechanisms of these Ag-Au bimetallic nanostructures driven by lattice match and a unique reducing agent (V2O3) have been proposed in this study. Moreover, the application of such bimetallic nanoparticles for catalytic reduction of 4-nitrophenol to 4-aminophenol was performed, and they exhibit catalytic properties superior to those of the Ag nanowires, Au nanoparticles, and Ag-Pd bimetallic nanostructures prepared under the reported conditions. These Ag-Au bimetallic nanoparticles have potential to be highly efficient catalysts for the reduction of 4-nitrophenol. This study may lead to new path for the generation of other bimetallic nanostructures with excellent catalytic efficiency.

Large-surface mesoporous TiO2 nanoparticles: synthesis, growth and photocatalytic performance.

This study demonstrates a facile and effective method to generate mono-dispersed titanium dioxide spheres at ambient conditions. The size of the colloids can be controlled from 60 to 500 nm by optimizing experimental parameters (e.g., concentration, time, and temperature). Anatase TiO(2) can be obtained through titanium glycolate colloids generated in acetone via two ways: water boiling approach and calcination at a high temperature of 500°C. Particle characteristics (shape, size, and size distribution) were measured by advanced techniques, including transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), UV/Vis absorption spectrum, nitrogen gas adsorption and desorption isotherms Brunauer-Emmett-Teller (BET) surface area measurement, and X-ray diffraction technique (XRD). The possible mechanism of nucleation and growth of such colloids was discussed. The role of acetone in the formation and growth of titanium glycolate colloids was also investigated by Fourier transform infrared (FT-IR) spectroscopy. Finally, the photocatalysis performance of such anatase TiO(2) particles was tested and proved to be efficient in degradation of organic dyes (e.g., phenolphthalein and methly orange).

Hybrid Ag@TiO2 core-shell nanostructures with highly enhanced photocatalytic performance.

A new synthetic approach has been developed to prepare silver@titanium dioxide (Ag@TiO2) core-shell nanostructures with controllable size, shape, crystal phase and function at ambient conditions (e.g. in water, ≤100 ° C). This approach shows a few unique features, including short reaction time (a few minutes) for forming core-shell nanostructures, no requirement of high temperature calcinations for generating TiO2 (e.g. at ~100 ° C in our case), tunable TiO2 shell thickness, high yield and good reproducibility. The experimental results show that the Ag@TiO2 core-shell nanostructures exhibit excellent photocatalytic activity compared to the commercial TiO2 (P25) and Ag-doped TiO2 nanocomposite in the degradation of organic dye molecules (e.g. methyl orange) with ultraviolet (UV) irradiation. This could be attributed to the large surface area of TiO2 nanoparticles for maximum harvesting of UV light, mixed anatase and rutile crystalline phases in the TiO2 shell and the effective charge separation between Ag and TiO2 that can reduce the possible recombination of electron-hole (e(-)-h(+)) pairs within TiO2 generated under UV radiation. To further understand the charge separation situation within Ag-TiO2 composites, theoretical simulation (e.g. density functional theory, DFT) was employed in this study. The DFT simulation results indicate that for the Ag@TiO2 core-shell nanostructures, photo-generated electrons transfer readily from the external TiO2 layer to the internal Ag layer with heavy accumulation compared to those doping Ag on TiO2 surfaces, which may reduce the recombination of e(-)-h(+) pairs and thus enhance the photocatalytic efficiency. The findings may open a new strategy to synthesize TiO2-based photocatalysts with highly enhanced efficiency for environmental remediation applications.

Synthesis of V2O5@TiO2 core–shell hybrid composites for sunlight degradation of methylene blue

This study has demonstrated a facile but efficient synthesis method to prepare vanadium oxide@titanium oxide (V2O5@TiO2) core–shell nanostructures using a water bath at mild temperatures (≤100 °C). This method shows a few unique features, including a short reaction time for fabricating core–shell nanostructures, no requirement of high temperature calcination (>500 °C) for TiO2 crystallization, easily tunable TiO2 shell thickness, high yield, and good reproducibility. With characterization using several advanced techniques (TEM, BET, XRD, XPS and UV-vis spectroscopy), the as-prepared V2O5@TiO2 nanocomposites were found to exhibit a large surface area, and a good stability. The experimental results show that the V2O5@TiO2 core–shell composites show a superior sunlight photocatalytic activity compared to the pure TiO2 nanoparticles for the degradation of organic dyes (e.g., methylene blue), probably because of the matched energy bands between V2O5 and TiO2. These findings may bring new insights into the designing of TiO2-based core–shell and other nanocomposites with enhanced photocatalytic efficiencies for environmental remediation.

Synthesis of hierarchical nanosheet-assembled V2O5 microflowers with high sensing properties towards amines

Hierarchical three-dimensional nanosheet-assembled vanadium pentoxide (V2O5) microflowers are successfully synthesized by a hydrothermal method, followed by a high-temperature sintering treatment. Several advanced techniques are used to characterize the morphology and composition of the resulting nanostructures, such as TEM, HRTEM, SEM, XRD, and BET. The HRTEM image shows that the microflowers are assembled from the nanosheets with highly exposed {010} facets, as confirmed by selected area electron diffraction (SAED). According to N2 sorption isothermal studies, the as-prepared V2O5 microflowers show high specific surface area of 61.5 m2 g−1. The formation of the microflowers with assistance of NaHCO3, which may play a critical role in the self-assembly process, may be attributed to a “reproduction mechanism”. The gas sensing performances of both the V2O5 microflowers and the V2O5 nanosheets were evaluated towards several volatile organic compounds (VOCs), such as 1-butylamine, ethanol, acetone, and formaldehyde. The results show that the flower-like structure exhibits a superior sensing response and selectivity towards amines compared to that of the sheet-like structure at an optimum working temperature of ∼300 °C. The high selectivity towards 1-butylamine can be ascribed to the selective oxidation mechanism. This work will help explore vanadium oxides as gas sensors toward volatile organic compounds with high performance.

Comparative study on photocatalytic and bactericidal activity between Ag@TiO 2 core-shell nanoparticles and Ag@TiO 2 surface doped nanostructures

Silver@titanium dioxide (Ag@TiO2) core-shell nanostructures and Ag surface doped TiO2 particles (TiO2@Ag) have been designed and synthesized by sol-gel and hydrothermal methods under mild conditions. These two types of Ag-TiO2 nanocomposites were characterized in terms of their properties. Specifically, the photocatalytic performance and antibacterial behavior of such nanocomposites have been investigated and compared. It was found that the Ag@TiO2 core-shell nanostructures exhibit superior photocatalytic property to the Ag surface doped TiO2 particles under the reported conditions, while the same situation happened in the bactericidal test. This is probably because the Ag cores tend to facilitate charge separation for TiO2, producing greater hydroxyl radicals on the surface of the TiO2 particles. These findings would be useful for the design and synthesis of Ag-TiO2 nanocomposites with desirable photocatalytic and antimicrobial activity for environmental applications.

Preparation of plasmonic porous Au@AgVO3 belt-like nanocomposites with enhanced visible light photocatalytic activity

This study reports a visible light-driven plasmonic photocatalyst of Au deposited AgVO3 nanocomposites prepared by a hydrothermal method, and further in situ modification of Au nanoparticles by a reducing agent of NaHSO3 in an aqueous solution at room temperature. Various characterization techniques, such as SEM, TEM, XRD, EDS, XPS, and Brunauer-Emmett-Teller, were used to reveal the morphology, composition, and related properties. The results show that belt-like AgVO3 nanoparticles with a width of ∼100 nm were successfully synthesized, and Au nanoparticles with controlled sizes (5-20 nm) were well distributed on the surface of the nanobelts. The UV-vis absorption spectra indicate that the decoration of Au nanoparticles can modulate the optical properties of the nanocomposites, namely, red shift occurs with the increase of Au content. The photocatalytic activities were measured by monitoring the degradation of Rhodamine B (RhB) with the presence of photocatalysts under visible light irradiation. The photodegradation results show that AgVO3 nanobelts exhibit good visible light photocatalytic activities with a degradation efficiency of 98% in 50 min and a reaction rate constant of 0.025 min-1 towards 30 ppm RhB. With the modification of Au nanoparticles, photocatalytic activity basically increases with the molar ratio of Au to V. Among the Au@AgVO3 nanocomposites, the 3% (molar ratio) Au decorated AgVO3 nanobelts showed the highest photocatalytic activity, and the k (0.064 min-1) was almost two times higher than that of the pure AgVO3 nanobelts. This can be attributed to several factors including specific surface areas, optical properties, and the energy band structure of the composites under visible light illumination. These findings may be useful for the practical use of visible light-driven photocatalysts with enhanced photocatalytic efficiencies for environmental remediation.

Glycothermal synthesis of urchin-like vanadium pentoxide nanostructure for gas sensing

This study reports a simple but effective glycothermal method for synthesis of urchin-like vanadium pentoxide (V₂O₅) nanostructures for gas sensing. By this method, the V₂O₅ nanostructure was prepared by two steps, involving preparation of precursor, followed by calcinations. The as-prepared precursor particles were rods (200 nm×1 μm) and could assemble into microspheres or urchin-like structures with a diameter of ~3 μm. The V₂O₅ nanoparticles were tested for sensing isopropanol. The microurchin structures show higher gas sensing performance than the nanorods.