Zhaoke Zheng

Facile in situ synthesis of visible-light plasmonic photocatalysts M@TiO2 (M = Au, Pt, Ag) and evaluation of their photocatalytic oxidation of benzene to phenol

We developed a facile in situ method of preparing noble-metal plasmonic photocatalysts M@TiO2 (M = Au, Pt, Ag). In this method, the UV irradiation of TiO2 powder dispersed in absolute ethanol generates some Ti3+ ions on the surface of TiO2 particles and these Ti3+ ions, upon addition of a noble-metal salt in the dark, reduce the metal cations to deposit metal nanoparticles on the TiO2 surface. This Ti3+-ion-assisted synthesis leads to a homogeneous loading of noble-metal nanoparticles on the surface of TiO2 particles, which allows photocatalytic reactions to take place under visible-light on the whole TiO2 surface. Among the three photocatalysts M@TiO2 (M = Au, Pt, Ag), Au@TiO2 exhibits a high yield (63%) and selectivity (91%) for the oxidation of benzene to phenol in aqueous phenol. For this photocatalytic reaction, our study suggests a mechanism in which the visible-light absorption by the Au nanoparticles causes electron transfer from the Au nanoparticles to the TiO2 particle, and the electron-depleted Au oxidizes phenoxy anions to form phenoxy radicals that oxidize benzene to phenol.

Synthesis of Highly Efficient Ag@AgCl Plasmonic Photocatalysts with Various Structures

By means of a simple ion-exchange process (using different precursors) and a light-induced chemical reduction reaction, highly efficient Ag@AgCl plasmonic photocatalysts with various self-assembled structures-including microrods, irregular balls, and hollow spheres-have been fabricated. All the obtained Ag@AgCl catalysts were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and UV-visible diffuse reflectance spectroscopy. The effect of the different morphologies on the properties of the photocatalysts was studied. The average content of elemental Ag in Ag@AgCl was found to be about 3.2 mol %. All the catalysts show strong absorption in the visible-light region. The obtained Ag@AgCl samples exhibit enhanced photocatalytic activity for the degradation of organic contaminants under visible-light irradiation. The stability of the plasmonic photocatalysts was also investigated in detail.

Hierarchical TiO2 Microspheres: Synergetic Effect of {001} and {101} Facets for Enhanced Photocatalytic Activity

Well-faceted nanocrystals of anatase TiO(2) with specific reactive facets have attracted extraordinary research interest due to their many intrinsic shape-dependent properties. In this work, hierarchical TiO(2) microspheres consisting of anatase nanosheets or decahedrons were synthesized by means of a facile hydrothermal technique; meanwhile, the percentage of {001} facets can be tuned from 82 to 45%. Importantly, by investigating the photo-oxidation reactions for ˙OH radical generation and photoreduction reactions for hydrogen evolution, the TiO(2) microspheres consisting of nano-decahedrons with 45% {001} facets show superior photoreactivity (more than 4.8-times) compared to the nanosheets with 82% {001} facets. By analyzing the results of scanning electron microscopy (SEM), photoluminescence (PL) and first-principles density functional theory (DFT) calculations, a model of charge separation between the well-formed {001} and {101} facets is proposed, and the enhanced photocatalytic efficiency is largely attributed to the efficient separation of photogenerated charges among the crystal facets co-exposed.

Strategic Synthesis of Hierarchical TiO2 Microspheres with Enhanced Photocatalytic Activity

Synthesis and characterization of one-dimensional structures have attracted much attention due to their potential applications in a variety of fields. Among the one-dimensional nanomaterials reported, special attention has been directed to TiO2 due to its unique functional properties such as increased photocorrosion resistance, high photoconversion efficiency, and its suitability as a material for purification of water and air. Recently, hierarchical inorganic materials have attracted significant scientific and technological interest in functional materials synthesis. Such hierarchical structures proved to be very efficient when using them for practical applications such as water treatment, elecACHTUNGTRENNUNGtrodes for lithium batteries, dye-sensitized solar cells, and catalyst supports. More importantly, the hierarchical structure possesses good light-scattering properties which are expected to provide more efficient light harvesting. Thus, for use as a practical catalyst, hierarchical TiO2 materials produced from one-dimensional building blocks are highly desirable. There have been extensive studies to explore approaches to the synthesis of hierarchical materials, such as chemical vapor deposition methods and solution-phase chemical routes. Among them, the assembly of 1D or 2D nanoscale building blocks into 3D hierarchical superstructures is the most common synthetic route. However, this route usually requires catalysts, and expensive and even toxic templates or surfactants to complete the assembly process. Moreover, assembly of 1D building blocks to hierarchical materials with a particular morphology is generally more difficult. Different from the conventional method for hierarchical materials, herein we report that a strategic synthetic method leads to hierarchical TiO2 microspheres (HTM) with a 1D structure. In our synthetic strategy, primary TiO2 microspheres (PTM) were first synthesized by a simple alcohothermal method. Then, under alkali hydrothermal treatment, these primary microspheres (precursors) transformed into HTM with a hierarchical nanotubular structure. After annealing, these HTM samples exhibit a porous dendritic structure. This may provide a facial route to produce hierarchical TiO2 with a particular matrix morphology. The scanning electron microscopy (SEM) images of the PTM precursors show that they have a smooth surface and are produced from TiO2 nanoparticles (Figure 1 a and b). After alkali hydrothermal treatment and acid washing, hierarchical microspheres with diameters in the range of 4–6 mm were formed (Figure 1 c). The higher magnification SEM and TEM images of the HTM sample revealed that the microspheres are produced from TiO2 nanotubes with diameters of 10 nm and lengths of several micrometers (Figure 1 d). These nanotubes wrapped around each other to form mesoporous microspheres. Once exposed to alkali hydrothermal treatment, the Ti O Ti bonds in the TiO2 nanoparticles of the PTM were broken to form Ti O Na. Singleor multilayered titanate nanosheets were formed in situ, then these nanosheets converted into nanotubes, either by scrolling (rolling-up) singlelayer nanosheets or by curving (wrapping) of conjoined nanosheets. More importantly, the as-synthesized HTM sample retains the original sphere morphology of the PTM precursor. Both anatase and titanate contain zigzag ribbons of TiO6 octahedra that share four edges with the others, and the common structural features make the phase transition from anatase to titanate relatively easy. Therefore, the original sphere morphology could be retained. Unlike conventional hierarchical material synthesis, in which it is difficult to control the morphology of the finally assembled material, this method is rather convenient to control the morphology of the hierarchical products by varying the presynthesized precursor. [a] Z. Zheng, Prof. Dr. B. Huang, X. Qin, Prof. X. Zhang State Key Lab of Crystal Materials Shandong University, Jinan 250100 (China) Fax: (+86) 531-8836-5969 E-mail : bbhuang@sdu.edu.cn [b] Prof. Dr. Y. Dai School of Physics Shandong University, Jinan 250100 (China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001280.

Crystal facets controlled synthesis of graphene@TiO2 nanocomposites by a one-pot hydrothermal process

We report a facile and simple way to synthesize graphene@TiO2 nanocomposites with controlled crystal facets by a one-pot hydrothermal process. By controlling the concentrations of the starting materials and reaction times, graphene@TiO2 nanocomposites with various exposed crystal facets can be obtained. The surface states and the growth process of graphene@TiO2 nanocomposites have been studied. Owing to the exposed high-reactive crystal facets and high dispersities of TiO2 nanocrystals on graphene surfaces, the as-prepared sample exhibited enhanced photocatalytic activities over graphene@P25 nanocomposites.

Facile synthesis of SrTiO3 hollow microspheres built as assembly of nanocubes and their associated photocatalytic activity

SrTiO(3) hollow microspheres built by regular nanocubes were synthesized by a general and facile hydrothermal method. The resulting samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. Owing to the special hollow structure, the synthesized SrTiO(3) microspheres exhibit a superior photocatalytic activity in photoreduction of Cr(VI). As anatase and titanate contain common structural features, it makes this in situ phase transition from anatase to titanate relatively easy. Therefore, this method is rather convenient for controlling the morphology of the products by varying the presynthesized anatase TiO(2) precursor.

Facile synthesis of Zn-rich (GaN)1−x(ZnO)x solid solutions using layered double hydroxides as precursors

(GaN)1−x(ZnO)x solid solutions are potential photocatalysts for water splitting and environmental decontamination under visible light. Solid solutions prepared by the traditional method are not effective because of their low Zn content (x < 0.5). Here, we show that Zn-rich solid solutions (∼0.5 < x < ∼0.8) are readily prepared by the nitridation of layered double hydroxides (LDHs) containing Zn2+ and Ga3+ ions, and that the Zn content is easily adjusted by changing the Zn/Ga ratio of the LDH precursors. The band gap of (GaN)1−x(ZnO)x decreases gradually from 2.60 eV at x = 0.46 to 2.37 eV at x = 0.81. The Zn-rich solid solutions absorb strongly above 500 nm, and these solutions loaded with 1 wt% Pt are found to be efficient for photoreducing Cr6+ ions under visible light.

One-step synthesis of AgBr microcrystals with different morphologies by ILs-assisted hydrothermal method

AgBr microcrystals with different morphologies were synthesized by an ionic liquids (ILs)-assisted hydrothermal method. A plausible growth mechanism, and influence of ionic liquids on the morphology of AgBr, were proposed and studied systematically. The samples were characterized by scanning electronic microscopy and X-ray diffraction. The relationship of morphology and photocatalytic activity of samples was studied.

Topotactic transformation of single-crystalline TiOF2 nanocubes to ordered arranged 3D hierarchical TiO2 nanoboxes

3D hierarchical TiO2 nanoboxes, enclosed by six ordered arranged TiO2 nanorod arrays, were prepared via a template-engaged topotactic transformation process from TiOF2 nanocubes. The lattice matching between TiOF2 and anatase TiO2 was regarded as the key for the preferential growth and ordered arrangement of the TiO2 nanorods.

Enhanced photocatalytic H2 production on hierarchical rutile TiO2 microspheres

Hierarchical rutile TiO2 microspheres composed of nanorods have been synthesized by a facile hydrothermal method. The as-synthesized rutile sample shows highly enhanced photocatalytic activity towards H2 production from water. The superior photocatalytic performance can be attributed to the improved crystalline quality, the higher percentage of reductive {110} facets exposed and increased pore sizes for the samples obtained under higher temperatures.