Danzhen Li

Novel approach to enhance photosensitized degradation of rhodamine B under visible light irradiation by the ZnxCd1-xS/TiO2 nanocomposites.

In order to exploit efficient photosensitizers with appropriate electronic states to enhance the transfer of electrons, ZnxCd1-xS/TiO2 nanocomposites were first synthesized by a simple hydrothermal method. The samples were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron spin resonance, and photoluminescence techniques. The results showed that the composite of the two inorganic semiconductors largely enhanced the photosensitized degradation of rhodamine B (RhB) under visible light irradiation (420 nm<λ<800 nm). These photocatalytic reactions were driven mainly by the light absorption of RhB molecules and to a lesser extent by the excitation of ZnxCd1-xS. They were supposed to arise mainly from the electron transferred from the adsorbed dye in its singlet excited state to the conduction band of ZnxCd1-xS and TiO2. Such a heterogeneous photocatalytic reaction has much significance in the degradation of organic pollutants in ordinary photocatalysis.

Low-Temperature and Template-Free Synthesis of ZnIn2S4 Microspheres

Porous ZnIn2S4 microspheres have been successfully synthesized by means of a facile thermal solution method at 353 K. This method was a simple route that involved low temperature, no templates, no catalysts, no surfactants, or organic solvents. Scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, nitrogen sorption analysis, and a UV-vis spectrophotometer were used to characterize the products. The results demonstrated that the microspheres, which were composed of many ZnIn2S4 single crystal nanosheets, underwent the Oswald ripening and self-assembly processes. A morphology formation mechanism has been proposed and discussed. The porous ZnIn2S4 product showed an enhancing visible-light photocatalytic activity for methyl orange degradation. The as-grown architectures may have potential applications in solar energy conversion, environmental remediation, and advanced optical/electric nanodevices.

TiO2 nanotube array-graphene-CdS quantum dots composite film in Z-scheme with enhanced photoactivity and photostability.

The most efficient solar energy utilization is achieved in natural photosynthesis through elaborate cell membrane with many types of molecules ingeniously transferring photogenerated electrons to reactants in a manner similar to the so-called Z-scheme mechanism. However, artificial photosynthetic systems based on semiconductor nanoparticles are inevitably accompanied by undesired non-Z-scheme electron transfer and back reactions, which adversely affect the photoactivity and photostability of the systems. Herein, we report on a novel Z-scheme system with an electrochemically converted graphene (GR) film as the electron mediator interlayer contacted with both TiO2 nanotube (TNT) array and CdS quantum dots (CdS QDs) on two sides. The obtained TiO2 nanotube array-graphene-CdS quantum dots (TNT-GR-CdS) composite film shows higher photoelectric response and photocatalytic activities than other bare TNT, TNT-CdS, TNT-GR, and TNT-CdS-GR. Moreover, compared to TNT-CdS, the activity stability is significantly improved, and the residual amount of Cd element in reaction solution is reduced ∼8 times over TNT-GR-CdS. Various measurements of photoelectrochemistry and radicals reveal that the enhanced photoactivity and photostabilities of TNT-GR-CdS are due to the efficient spatial separation of the photogenerated electron-hole pairs and the restricted photocorrosion of CdS via an efficient Z-scheme mechanism under simulated sunlight.

Sn3O4: a novel heterovalent-tin photocatalyst with hierarchical 3D nanostructures under visible light

Sn3O4 with hierarchical 3D nanostructures was synthesized for the first time by a facile template-free solvothermal method. The heterovalent photocatalyst is highly efficient and stable in the degradation of azo dyes under visible light.

Rapid microwave hydrothermal synthesis of GaOOH nanorods with photocatalytic activity toward aromatic compounds

GaOOH nanorods were synthesized from Ga(NO(3))(3) via a facile microwave hydrothermal method. The obtained sample was characterized by x-ray diffraction, N(2) sorption-desorption, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, electron spin resonance, and x-ray photoelectron spectroscopy. The results revealed that the as-synthesized sample was consisted of rod-like particles. It possessed a surface area of 14.3 m(2) g(-1), and a band gap of 4.75 eV. The photocatalytic property of GaOOH nanorods was evaluated by the degradation of aromatic compounds (such as benzene and toluene) in an O(2) gas stream under ultraviolet (UV) light illumination. The results demonstrated that GaOOH nanorods exhibited superior photocatalytic activity and stability as compared to commercial TiO(2) (P25, Degussa Co.) in both benzene and toluene degradation. In the extended (35 h) reaction test toward benzene, GaOOH maintained a high activity, and no obvious deactivation was observed. A possible mechanism of the photocatalysis over GaOOH is proposed.

A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity

Zinc sulfide-graphene (ZnS-GR) nanocomposites with a high degree of dispersion and high coverage of ZnS quantum dots (QDs) have been synthesized by a facile solvothermal method without any dispersant, during which the formation of ZnS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. ZnS-GR nanocomposites exhibit much higher photoactivity than nanoparticle crystal ZnS (NPC-ZnS) prepared in the absence of graphene (GR), as evaluated by degradation of methylene blue (MB) in the liquid phase under ultraviolet (UV) light. Among them, the ZnS-GR nanocomposite with a 5% mass fraction of GR prepared at 120 ° C has the highest photocatalytic activity. The conversion and mineralization over MB are 96.7% and 57.1% respectively, which is much higher than that of NPC-ZnS. The high photoactivity of ZnS-GR nanocomposites can be ascribed to the integrated effect of an extremely high specific surface area and the excellent electron conductivity of GR and its significant influence on the morphology and structure of the samples. Moreover, it is found that the oxidation of MB is driven mainly by the participation of .OH radicals. Accordingly, a potential photocatalytic mechanism of ZnS-GR nanocomposites in the photocatalytic process has been proposed in this work. It is expected that our work could provide valuable information on the design of metal sulfide decorated GR with excellent properties.

ZnO photonic crystals with enhanced photocatalytic activity and photostability

ZnO photonic crystals (ZnO-PCs) with large area and high quality were prepared by a facile auto-forced impregnation method. The resulting ZnO-PCs exhibited remarkable photocatalytic performance and photocorrosion inhibition compared with porous and commercial nanoparticle ZnO.

One-step preparation of hollow ZnO core/ZnS shell structures with enhanced photocatalytic properties

We report here a facile one-step strategy to prepare hollow ZnO core/ZnS shell structures by microwave irradiation. The growth mechanism of the hollow core/shell structures was investigated in detail. ZnO truncated hexagonal pyramids first form on as-grown precursor flakes and then evolve into ZnO hexagonal twin crystals, which subsequently grow up and dissolve internally. The hollowing progress is firstly controlled by the Kirkendall effect and then undergoes an Ostwald ripening process. Hollow structures and the formation of ZnO/ZnS heterostructure bring enhanced photocatalytic activities to ZnO core/ZnS shell structures. The formed ZnO/ZnS heterostructures also fill the surface defects of ZnO crystals and improve the stability of the photocatalysts by overcoming the photocorrosion effect of a single ZnO photocatalyst under UV light irradiation. Superoxide radicals (O˙−2) are the key active species in the photocatalytic system of degradation of p-chlorophenol over hollow ZnO core/ZnS shell structures. The photocatalysis process has been discussed and a possible mechanism also has been proposed. This work is helpful to controllably construct other hollow core/shell structures, develop ZnO-based photocatalysts without photocorrosion effect and further study the photocatalytic mechanism of similar systems.

Structuring β-Ga2O3 Photonic Crystal Photocatalyst for Efficient Degradation of Organic Pollutants

Coupling photocatalysts with photonic crystals structure is based on the unique property of photonic crystals in confining, controlling, and manipulating the incident photons. This combination enhances the light absorption in photocatalysts and thus greatly improves their photocatalytic performance. In this study, Ga2O3 photonic crystals with well-arranged skeleton structures were prepared via a dip-coating infiltration method. The positions of the electronic band absorption for Ga2O3 photonic crystals could be made to locate on the red edge, on the blue edge, and away from the edge of their photonic band gaps by changing the pore sizes of the samples, respectively. Particularly, the electronic band absorption of the Ga2O3 photonic crystal with a pore size of 135 nm was enhanced more than other samples by making it locate on the red edge of its photonic band gap, which was confirmed by the higher instantaneous photocurrent and photocatalytic activity for the degradation of various organic pollutants under ultraviolet light irradiation. Furthermore, the degradation mechanism over Ga2O3 photonic crystals was discussed. The design of Ga2O3 photonic crystals presents a prospective application of photonic crystals in photocatalysis to address light harvesting and quantum efficiency problems through manipulating photons or constructing photonic crystal structure as groundwork.

Microwave hydrothermal synthesis of calcium antimony oxide hydroxide with high photocatalytic activity toward benzene.

A nanocrystalline CaSb2O5(OH)2 photocatalyst synthesized from CaCl2 and K2H2Sb2O7 was used to degrade benzene in the gas phase for the first time. The obtained sample was characterized by X-ray diffraction, N2 sorption-desorption, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, electron spin resonance, and X-ray photoelectron spectroscopy. The CaSb2O5(OH)2 sample had an average particle size of approximately 8 nm, a specific surface area of 101.8 m2 g(-1), and a band gap of 4.6 eV. Photocatalytic activity of the sample was mainly evaluated by the degradation of benzene in an O2 gas stream under ultraviolet light irradiation. The results demonstrated that the photoactivity of CaSb2O5(OH)2 was higher than that of commercial TiO2 (P25, Degussa Co.). In the photocatalytic degradation of benzene, it finally reached a steady conversion ratio of 29%. CaSb2O5(OH)2 has also exhibited activity toward other aromatic organic compounds. A possible mechanism of photocatalysis over CaSb2O5(OH)2 nanocrystals was proposed.