Yanmin Guo

A Full Compositional Range for a (Ga1-x Zn x )(N1-x O x ) Nanostructure: High Efficiency for Overall Water Splitting and Optical Properties

Bulk (Ga1-x Zn x )(N1-x O x ) as a photocatalyst has received increasing attention as a potential solution for the energy shortage challenge; however, its catalytic performance is highly limited by its bulk form. To improve the photochemical potential, the nanoscale form of this multiple-metal oxynitrides is desirable. In this work, a new type of (Ga1-x Zn x )(N1-x O x ) nanostructure is obtained. Its composition can tuned to the full range (0.18 < x < 0.95). The (Ga1-x Zn x )(N1-x O x ) nanostructure exhibits excellent photocatalytic activity for overall water splitting, and the highest quantum efficiency of (Ga1-x Zn x )(N1-x O x ) is as high as 17.3% under visible light irradiation. Using this new type of (Ga1-x Zn x )(N1-x O x ) nanostructure, the narrowing of the bandgap for (Ga1-x Zn x )(N1-x O x ) is not only due to an increase in the valence band maximum, but it is also related to a decrease in the conduction band minimum.

A new type of hybrid nanostructure: complete photo-generated carrier separation and ultrahigh photocatalytic activity

In this work, we obtained a new type of hybrid nanostructure which is formed in the ultrathin shells of mixed metal oxide hollow spheres. This new type of hybrid nanostructure exhibited a complete separation of photo-generated hole–electron pairs and ultrahigh photocatalytic activity which has never been seen before. Using the TiO2/SnO2 hybrid nanostructure as an example, we found that this hybrid nanostructure not only has small grain size and an ultrahigh surface area but is also important for its excellent crystalline compatibility and single-layer distributed arrangement for each nanoheterojunction. Thus, this unique structure leads to complete carrier separation and excellent photocatalytic activity. The typical method has been extended successfully to the synthesis of other hybrid nanostructures. We believe our methodology provides a general route to synthesize the new type of hybrid nanostructure for subsequent applications.

Structural and optical properties of ZnCdO/ZnO multiple quantum wells grown on sapphire substrates using pulsed laser deposition

High quality Zn0.92Cd0.08O/ZnO multiple quantum wells with smooth interfaces have been prepared on c-plane sapphire substrates by pulsed laser deposition. The periodic structure has been characterized by scanning transmission electron microscope and energy dispersive x-ray spectroscopy line scans. The temperature dependent photoluminescence of Zn0.92Cd0.08O/ZnO exhibits an inconspicuous S-shaped property due to a combined effect of the slightly disordered ZnCdO alloy. We can observe both quantum confinement effects and quantum-confinement Stark effect in the quantum wells. We can modulate the well emission energy from 2.90 to 3.085 eV by varying the well thickness at room temperature.

Wavelength tunable photoluminescence of ZnO1-xSx alloy thin films grown by reactive sputtering

ZnO1−xSx alloy thin films with various S contents were deposited on glass substrates by reactive sputtering. The films were grown in high crystalline quality and strong preferential crystallographic orientation. Variations of the lattice constant c followed Vegards law. X-ray photoelectron spectroscopy confirmed the substitution of O by S in ZnO. The composition dependence of the band gap energy in ZnO1−xSx system was investigated and the band gap bowing parameter was estimated to be about 1.46 eV. The incorporation of S led to the expected redshift of the band gap related photoluminescence emission of ZnO1−xSx films up to 320 meV. The results indicate that ZnO1−xSx films could hold the prospect for the development of ZnO based quantum structures.

Iodine‐ion‐induced Size‐tunable Co3O4 Nanowires and the Size‐dependent Catalytic Performance for CO Oxidation

CO oxidation is one of the most important catalytic reactions owing primarily to its relevance in practical applications in carexhaust emission control, fuel cells, and air purification. Meanwhile, scientifically, it is one of the simplest catalytic reactions and thus is widely used as a model system to understand heterogeneous catalysis. Gold nanoparticles deposited on various metal oxides that show high activity for CO oxidation have aroused tremendous interest since Haruta et al. reported that gold nanoparticles show high activity for CO oxidation. Owing to the high cost of gold-based catalysts, other alternatives would be highly desirable. As an alternative, Co3O4 has been also been considered as a catalyst for CO oxidation. 13, 18, 19] Many groups have tried to control the shape of the catalyst to obtain higher catalytic efficiency, since the activity for CO oxidation strongly depends on the exposed specific crystal planes. 19] Moreover, several groups have synthesized small Co3O4 nanoparticles that displayed much higher catalytic activity, 18] even though there are no specific active planes on the surface of their Co3O4 nanostructures. For instance, Sch th et al. reported small Co3O4 nanoparticles without exposed specific active planes that have much higher activity for CO oxidation than the bulk materials. However, size-dependent chemistry of Co3O4 for catalytic oxidation of CO has been rarely investigated, owing to the uncontrollable size of the Co3O4 nanostructures. In this work, we present a novel synthesis method, which adopts the iodine ions (I ) for the formation of size-tunable Co3O4 nanowires. This method can not only regulate the diameter of nanowires in a wide range from 17 to 150 nm, but also build up a dandelion-like hierarchical structure rapidly. It is observed that I ions played a key role in tuning the dimension of nanowire and promoting the formation of the complex nanostructures. The thinner Co3O4 nanowires with diameter of 15 nm have ultrahigh conversion rate for CO oxidation, which is estimated to be 772 mmol gcat 1 s 1 at 180 8C, and the catalytic performance depends on the size of nanowires. We studied the kinetics of the catalytic reaction of Co3O4 nanowires with different size, which was consistent with the Raman and temperature-programmed desorption curves of oxygen (O2-TPD) experiments. Our results indicate that the major reason of the ultrahigh CO oxidation rate for small size Co3O4 nanowires is the large numbers of weakly bonding oxygen ions on surface edges. So the iodine ions induced synthesis method can directly contribute to improving catalytic performance by controlling the size of nanowires. Shown in Figure 1 are the as-synthesized Co(CO3)0.5(OH)·0.11 H2O nanowires with the addition of NaI. The crystal phase of the as-synthesized product is determined by X-ray diffraction (XRD), with the result shown in Figure 1 a. All the identified peaks can be assigned to pure orthorhombic Co(CO3)0.5(OH)·0.11 H2O. [20] It is clear from the panoramic view (Figure 1 b) that the Co(CO3)0.5(OH)·0.11 H2O nanowires comprise an uniform dandelion-like microsphere and the nanowires are uniform with 4 mm in length. Such a 1 D nanostructure is also revealed under transmission electron microscope (TEM). Under a higher magnification, these nanowires are shown to have a needle-like structure along the axial direction, and the diameter is approximately 17 nm with a smooth surface (Figure 1 c). The exposed crystal surfaces of the nanowires are (0 1 0) and (0 0 1) planes grown along the [1 0 0] direction (Figure 1 d, 1 e). Interestingly, when the samples are synthesized in the absence of NaI, the Co(CO3)0.5(OH)·0.11 H2O nanowires could still be generated with the diameters of 130 nm (Supporting Information, Figure S1 e). Moreover, their arrangement is disordered and the dandelion-like microspheres no longer form (Supporting Information, Figure S1 a). Several template-free methods have been successfully applied to synthesize self-assembled structures of materials. However, to be able to synthesize complex nanostructures of cobalt-based materials, generally high temperature and especially long reaction times are needed. 24, 27] It was, therefore, necessary to develop a simple and effective method that could to synthesize complex cobalt-based nanostructures on a largescale in a short time. In our strategy, the formation of self-assembled Co(CO3)0.5(OH)·0.11 H2O structures is faster and strongly depends on the presence of I ions. Shown in Scheme 1 are the differences between the traditional process and I ions induced self-assembled process and describes how I ions can change the evolution processes to make the growth faster. In the self-assembled evolution reported previously, 27] recrystallization plays a pivotal role in the formation of individual nanocomponents and lateral fusion drives the aggregation of individual nanocomponents in an orderly fashion in the presence [a] Y. Li, Prof. Dr. L. Zhu, Y. Guo, Dr. J. Jiang, L. Hu, Z. Wen, Dr. L. Sun, Prof. Dr. Z. Ye State Key Laboratory of Silicon Materials Department of Materials Science and Engineering Zhejiang University Hangzhou 310027 (P.R. China) Fax: (+ 86) 571-87952625 E-mail : zlp1@zju.edu.cn [b] Y. Li, Prof. Dr. L. Zhu, Y. Guo, Dr. J. Jiang, L. Hu, Z. Wen, Dr. L. Sun, Prof. Dr. Z. Ye Cyrus Tang Center for Sensor Materials and Applications Zhejiang University Hangzhou 310027 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300444.