Wenguang Wang

Nitrogen self-doped nanosized TiO2 sheets with exposed {001} facets for enhanced visible-light photocatalytic activity

Nitrogen self-doped TiO(2) nanosheets with exposed {001} facets (ca. 67%) were synthesized by solvothermal treatment of TiN in a HNO(3)-HF ethanol solution and exhibited much higher visible-light photocatalytic H(2)-production activity than nitrogen doped TiO(2) microcrystallites with exposed {001} facets (ca. 60%) by a factor of 4.1.

Facile synthesis of novel hierarchical graphene–Bi2O2CO3 composites with enhanced photocatalytic performance under visible light

A facile template-free hydrothermal approach is developed to synthesize hierarchical flower-like graphene-Bi(2)O(2)CO(3) microcomposites. The as-prepared samples were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, N(2) adsorption-desorption and UV-visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated towards degradation of Rhodamine B (RhB) under visible light. Compared to hierarchical Bi(2)O(2)CO(3), hierarchical flower-like graphene-Bi(2)O(2)CO(3) microcomposites show enhanced photocatalytic activity. In addition, our results indicate that both the physico-chemical properties and associated photocatalytic activity of graphene-Bi(2)O(2)CO(3) composites are shown to be dependent on graphene loadings. The highest photocatalytic performance can be achieved for the graphene-Bi(2)O(2)CO(3) microcomposites with 1.0 wt% graphene. The underlying mechanism responsible for the formation of graphene-Bi(2)O(2)CO(3) composites and enhanced photoreactivity was discussed. Results from this study illustrate an entirely new approach to fabricate semiconductor composites containing graphene-bismuth with high visible-responsive photocatalytic performance.

Visible‐Light Photocatalytic Activity and Deactivation Mechanism of Ag3PO4 Spherical Particles

Ag(3)PO(4) spherical particles were synthesized by a facile precipitation method using silver nitrate and Na(2) HPO(4) as precursors. The as-prepared samples had a high photocatalytic activity toward Rhodamine B (RhB) degradation under visible-light illumination. With increasing recycling times the photocatalytic activity first increased and then decreased. Based on systematic characterization of particles by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis absorption spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), a possible mechanism responsible for the improvement and subsequent decline of the photocatalytic performance of Ag(3)PO(4) is proposed. Ag(3)PO(4) spherical particles recycled for four times showed the highest photocatalytic activity because, according to our mechanism, Ag nanoparticles deposited on Ag(3)PO(4) acted as electron trapping centers to prevent photogenerated electron-hole pairs from recombination. A further increase in the recycle times decreases the photocatalytic activity owing to the shielding effect by Ag layers on the surface of Ag(3)PO(4). The results presented herein shed new light on the photostability of Ag(3) PO(4) spherical particles and are potentially applicable to other photocatalytically active composites.

Synthesis and Enhanced Photocatalytic Activity of a Hierarchical Porous Flowerlike p–n Junction NiO/TiO2 Photocatalyst

Hierarchical flowerlike β-Ni(OH)(2) superstructures composed of intermeshed nanoflakes are synthesized by hydrothermal treatment with a mixed solution of C(2)H(4)(NH(2))(2), NaOH, and Ni(NO(3))(2). The as-prepared β-Ni(OH)(2) superstructures could be easily changed into NiO superstructures without great morphology change by calcination at 400 °C for 5 h. Furthermore, the TiO(2) nanoparticles can be homogeneously deposited on the surface of NiO superstructures by dispersing β-Ni(OH)(2) powders in Ti(OC(4)H(9))(4)-C(2)H(5)OH mixed solution and then vaporizing to remove the ethanol at 100 °C, and finally calcination at 400 °C for 5 h. The prepared NiO/TiO(2) p-n junction superstructures show much higher photocatalytic activity for photocatalytic degradation of p-chlorophenol aqueous solution than conventional TiO(2) powders and NiO superstructures prepared under the same experimental conditions. An obvious enhancement in the photocatalytic activity can be related to several factors, including formation of hierarchical porous structures, dispersion of TiO(2) particles on the surface of NiO superstructures, and production of a p-n junction. Further results show that NiO/TiO(2) composite superstructures can be more readily separated from the slurry system by filtration or sedimentation after photocatalytic reaction and re-used, compared with conventional powder photocatalysts. After many recycling experiments for the photodegradation of p-chlorophenol, the NiO/TiO(2) composite sample does not exhibit any great activity loss, confirming that NiO/TiO(2) sample is stable and not photocorroded.

Study of TiO2 anatase nano and microstructures with dominant {001} facets for NO oxidation

IntroductionTiO2 anatase nanoplates and hollow microspheres were fabricated by a solvothermal–hydrothermal method using titanium isopropoxide as a titanium precursor and hydrofluoric acid as a capping agent in order to enhance the formation of the {001} crystal facets of the anatase nanocrystals.MethodsThese different morphological structures of TiO2 anatase can be achieved by only changing the solvent, keeping the amount of the precursor and of the capping agent identical during the solvothermal–hydrothermal process.Results and discussionAfter calcination of the samples, the adsorbed fluoride atoms on the {001} crystal facets of the TiO2 anatase nanocrystals were completely removed from their surface according to XPS analysis. The calcined TiO2 anatase structures were higher crystallized and the specific surface area of the catalysts increased, enhancing their photocatalytic activity in comparison to the non-calcined TiO2 anatase structures. All TiO2 anatase samples with adsorbed as well as non-adsorbed fluoride atoms on their {001} crystal facets, exhibited a higher photonic efficiency than Degussa P25, which was used as a reference.ConclusionThe fluoride free TiO2 anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO2 and NO3−.

Template-free synthesis of hierarchical γ-Al2O3 nanostructures and their adsorption affinity toward phenol and CO2

Hierarchical γ-Al2O3 nanostructures with tuneable morphologies including irregular nanoflake assemblies, melon-like nanoflake assemblies, flower-like ellipsoids, hollow core/shell and hollow microspheres were successfully synthesized for the first time via a facile template-free hydrothermal method using aluminium sulfate, aluminium chloride and aluminium nitrate as aluminium sources, respectively, and thiourea as precipitating agent. Their phase structures, morphologies, textural and basic properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), N2 adsorption–desorption and CO2 temperature programmed desorption (CO2-TPD). The results indicate that the thiourea, type of anion in the aluminium source and the molar ratio of thiourea to Al3+ play an essential role in the formation of the aforementioned hierarchical γ-Al2O3. A growth mechanism of chemically induced self-transformation followed by cooperative self-assembly to form hierarchical nanostructures was proposed. In contrast, the γ-Al2O3 hollow core/shell microspheres with average pore size of 14.3 nm obtained from aluminium sulfate show the highest adsorption capacity of 28 mg g−1 towards phenol at 25 °C. However, the hierarchical γ-Al2O3 obtained from aluminium chloride and aluminium nitrate with smaller average pore size of 5.2 nm and 5.4 nm, respectively, is more effective for CO2 capture. This study provides new insights into the design and synthesis of hierarchical nanostructures for environmentally relevant applications.