Guo-Ying Zhang

An in situ gelatin-assisted hydrothermal synthesis of ZnO–reduced graphene oxide composites with enhanced photocatalytic performance under ultraviolet and visible light

A simple route for preparation of ZnO nanosphere–reduced graphene oxide (RGO) composites by an in situ gelatin-assisted hydrothermal synthesis was investigated. The chemical composition, morphology and structural features of the ZnO and ZnO–RGO samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy (XPS), thermogravimatric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption specific surface area measurements (BET) and diffuse reflectance absorption spectroscopy (DRS). The results showed that ZnO nanoparticles were well dispersed on the RGO nanosheets which serve as ZnO nanocrystal growing supports and the morphology controller. It was first found that through controlling the incorporated contents of RGO with the assistance of gelatin in hydrothermal synthesis, the morphology of ZnO, for example nanoflowers, nanorods and nanospheres, could be controlled. The ZnO–RGO composites were used as photocatalysts for degradation of methylene blue (MB) under ultraviolet (UV) and visible light irradiation. The results suggested that RGO improves the MB degradation performance under both UV and visible light irradiation, and the kinetic rate constants were both improved to 3 times higher by RGO incorporation. It was found that the mechanism of photocatalysis for ZnO–RGO composites under visible light irradiation is different from that under UV light. Under UV light, RGO serves as an electron reservoir to capture or shuttle photogenerated electrons from the ZnO and reduces electron–hole pair recombination; while under visible light, RGO behaves as a photosensitizing semiconductor and electron transformer to ZnO. Moreover, the large surface area and excellent electron transport of RGO also have some positive effects on the improvement of the photocatalytic performance of the composites.

Size-controlled synthesis, magnetic property, and photocatalytic property of uniform α-Fe2O3 nanoparticles via a facile additive-free hydrothermal route

A facile and effective hydrothermal process for the controllable synthesis of uniform hematite nanoparticles is presented. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results showed that the products were uniform α-Fe2O3 truncated nanooctahedra bound by 8 highly symmetric quasi-trigonal facets corresponding to a probable Miller index of {102} and the particle size was around 800 nm. The formation mechanism of the products, the effects of the reaction temperature, concentration of reactant, the solvent and the Fe(III) counter ion on the size and morphology of the products were investigated. Through adjusting the concentration of the FeCl3 solution, the size of the particles can be systematically tailored over a wide range from ca. 170 nm to ca. 2 μm. The magnetic properties and visible light photocatalytic properties of the as-obtained α-Fe2O3 products were investigated. The results showed that these α-Fe2O3 nanoparticles displayed ferromagnetic or weak ferromagnetic behavior at room temperature and exhibited a good photocatalytic property for rhodamine B.

Facile room-temperature precipitation strategy for Ag2O/Bi2WO6 heterojunction with high simulated sunlight photocatalytic performance via bi-directed electron migration mechanism

A trace Ag2O modified Bi2WO6 heterojunction was facilely synthesized via a solution precipitation strategy at ambient temperature. The characterizations of composition, morphology, microstructure, UV-vis absorption, photoluminescence, BET, photocurrent and solar simulated photocatalytic behavior were systematically investigated. They showed that besides a few visible nanoparticles, most of the Ag2O phase was inconspicuously distributed on the surface of the Bi2WO6 substrate. The composite photocatalyst exhibited obviously enhanced photocatalytic activity compared with pure Ag2O and Bi2WO6 for degradation of organic contaminants. In particular, the sample of Ag-0.6 wt% presented the best photocatalytic activity with a rate constant 4.8-fold as fast as that of Bi2WO6. Photochemical and photoelectrochemical analysis indicated that the introduction of trace Ag2O effectively broadened the visible-light absorption and inhibited the photogenerated carrier recombination in Bi2WO6. Based on band structure analysis and XPS results of recycled samples, a bi-directed migration mechanism of photogenerated electrons is proposed at the heterostructure interface. The band-gap coupling effect between Ag2O and Bi2WO6 and the electronic effect of trace metallic Ag in situ photoreduced from the self-stabilized Ag2O are believed to play vital roles in the separation and migration of e−/h+ pairs. The work provides some insights into the rational design of hybrid photocatalysts with high performance via multi-path photogenerated carrier migration.

Hematite nanoplates: Controllable synthesis, gas sensing, photocatalytic and magnetic properties

Uniform hematite (α-Fe2O3) nanoplates exposing {001} plane as basal planes have been prepared by a facile solvothermal method under the assistance of sodium acetate. The morphological evolution of the nanoplates was studied by adjusting the reaction parameters including the solvent and the amount of sodium acetate. The results indicated that both the adequate nucleation/growth rate and selective adsorption of alcohol molecules and acetate anions contribute to the formation of the plate-like morphology. In addition, the size of the nanoplates can be adjusted from ca. 180nm to 740nm by changing the reaction parameters. Three nanoplate samples with different size were selected to investigate the gas sensing performance, photocatalytic and magnetic properties. As gas sensing materials, all the α-Fe2O3 nanoplates exhibited high gas sensitivity and stability toward n-butanol. When applied as photocatalyst, the α-Fe2O3 nanoplates show high photodegradation efficiency towards RhB. Both the gas sensing performance and the photocatalytic property of the products exhibit obvious size-dependent effect. Magnetic measurements reveal that the plate-like α-Fe2O3 particles possess good room temperature magnetic properties.

Mild synthesis of {001} facet predominated Bi2O2CO3 clusters with outstanding simulated sunlight photocatalytic activities

Bi2O2CO3 clusters made up of ultrathin nanosheets with predominated {001} facets were facilely synthesized via a template-free hydrothermal strategy at a mild temperature of 60 °C. Na2CO3 dosage and reaction temperature are confirmed to be key parameters to obtain the hydrolysis product of (Bi2O2)2+ from bismuth nitrate and provide a suitable microenvironment for the assembly of nanosheets. The sample exhibits obviously improved photocatalytic activity for the degradation and mineralization of Rhodamine B compared with thicker Bi2O2CO3 plates of less exposed {001} planes, with the reaction rate constant k enhanced by 3.4 fold. Photoluminescence and electrochemical impedance results confirm that the {001} facets are reactive and favorable for the separation and migration of photogenerated carriers, which primarily account for the superior photocatalytic behavior of the Bi2O2CO3 clusters. In addition, the enhanced specific surface area should also contribute to the improved photocatalytic activity. Based on the band edge positions of Bi2O2CO3 and the redox potentials of detected oxidative species, a possible migration mechanism of photogenerated e−/h+ pairs on the surface of Bi2O2CO3 is proposed. This work provides some new insight into the rational design and synthesis of facet-dependent semiconductor photocatalyst under mild conditions.

A {110} facet predominated Bi6O6(OH)3(NO3)3·1.5H2O photocatalyst: selective hydrothermal synthesis and its superior photocatalytic activity for degradation of phenol

A basic bismuth(III) nitrate photocatalyst with the composition of Bi6O6(OH)3(NO3)3·1.5H2O (BBN) was facilely synthesized using a hydrothermal strategy via incomplete hydrolysis of bismuth nitrate. Characterization of the composition, morphology, microstructure, optical absorption, BET surface area, and photocatalytic behavior was systematically explored. The results indicated that BBN architectures built up of multilayered meshing-teeth structures with predominant {110} side facets can be selectively obtained by fine-tuning the reaction parameters. The sample exhibits an obviously superior photocatalytic activity for the degradation of phenol compared with BBN sheets with dominant top {001} planes and commercial P25, with the rate constant k improved by 3.6 and 2.8 fold, respectively. The excellent photocatalytic behavior combined with the rather low BET surface area of 0.0453 m2 g−1 indicate that the highly reactive {110} facets in BBN are responsible for the photocatalysis. The active oxidation species and main intermediates in the phenol/BBN system are ascertained using scavenger experiments and high performance liquid chromatography (HPLC) techniques. Combining the band edge of BBN and the redox potentials of the active species, a possible migration mechanism of photogenerated e−/h+ pairs on the surface of BBN is proposed. This work provides some new insights for the rational design and synthesis of active-facet exposed basic salt photocatalysts with excellent efficiency.

Facile synthesis, shape evolution and magnetic properties of polyhedral 50-facet Fe3O4 nanocrystals partially enclosed by {311} high-index planes

Magnetite (Fe3O4) polyhedral nanocrystals have been prepared successfully by a simple solvothermal reaction using a mixture of ethylene glycol (EG) and H2O as the solvent without the addition of any surfactants or templates. Based on SEM and TEM characterization, the products were determined to be 50-facet Fe3O4 nanocrystals, 200–300 nm in diameter, enclosed by {100}, {110}, {111}, and high-index {311} facets. The morphological evolution of 50-facet Fe3O4 polyhedra was studied carefully and in detail by adjusting the reaction parameters such as the reaction temperature, the reaction time, the amount of urea, and the volume ratio of EG to H2O in the solvent. The results indicated that an appropriate EG/H2O ratio in the solvent was crucial for the formation of the polyhedral nanocrystals and when the solvent was fixed, the size of the polyhedral nanocrystals could be tuned in a certain range by changing the amount of urea. A possible growth mechanism involving the aggregation and oriented attachment of Fe3O4 seed nanoparticles is proposed on the basis of time-dependent experiments.

Zn(II)-doped γ-Fe2O3 single-crystalline nanoplates with high phase-transition temperature, superparamagnetic property and good photocatalytic property

Zn(II)-doped γ-Fe2O3 single-crystalline porous nanoplates of ca. 15 nm in thickness have been synthesized successfully via a solvothermal process combined with a post calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry analysis (DSC-TG), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results showed that nanoplates have a spindle-like morphology of ca. 200–260 nm in length and ca. 110–150 nm in width. The products showed enhanced maghemite to hematite phase transformation temperature and superparamagnetic property with high saturation magnetization, which may be attributed to the well single-crystalline structure, thin thickness and Zn(II) ion doping. Further experimental results indicated that the phase transformation temperature and the saturation magnetization of the γ-Fe2O3 nanoplates increased with the amount of doped Zn(II) ions. In addition, these nanoplates exhibited good photocatalytic activity for rhodamine B.

Tunable Synthesis of Core-shell α -Fe 2 O 3 /TiO 2 Composite Nanoparticles and Their Visible-light Photocatalytic Activity

Uniform α-Fe2O3/amorphous TiO2 core-shell nanocomposites were prepared via a hydrolysis method and α-Fe2O3/anatase TiO2 core-shell nanocomposites were obtained via a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy. Amorphous TiO2 nanoparticles with diameters of ten to several tens nanometer were formed on the surface of α-Fe2O3 nanoparticles and the coverage density of the secondary TiO2 nanoparticles in the composite can be controlled by varying the concentration of Ti(BuO)4 in the ethanol solution. The visible-light photocatalytic properties of different products towards Rhodamine B(RhB) were investigated. The results show that the α-Fe2O3/amorphous TiO2 exhibits a good photocatalytic property owing to the extension of the light response range to visible light and the efficient separation of photogenerated electrons and holes between α-Fe2O3 and amorphous TiO2.

Synthesis and characterization of heterometallic complexes as nanofibers by a solvothermal route

Micro- and nanosized, long fibers of heterobimetallic complexes, consisting of macrocyclic oxamide complexes (CuL) and transition-metal ions (Mn), have been successfully synthesized by a simple solvothermal approach. The as-prepared products were characterized by scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, energy dispersive X-ray analysis, and magnetic property analysis. The diameter of the fibers can be tuned by changing the proportion of solvent. A possible microsphere to fiber transformation mechanism has been proposed to explain the formation of the products. The thermal properties and magnetic properties of the fibers were investigated, they exhibit obvious size-dependent effects. It is important to note that this solvothermal process is a general approach that can be extended to the fabrication of a series of ultra-long complex nanofibers consisting of different transition-metals.