Although, post annealing is an efficient way to annihilate/restructure deficiencies in self-assembly (SA) ZnO nanorods (ZNRs), the detailed investigation about the surface properties of annealed SA-ZNRs is a long standing issue and the major discrepancy is mainly due to single step annealing. We demonstrate the strategic two step annealing process to create reliable structural configuration in SA-ZNRs during the first round of annealing at 800 °C in vacuum (VA process), and create intrinsic defects in the second step of annealing in oxygen rich atmosphere (OA process) to correlate the formation of the defects related to green/orange-red emission. SA-ZNRs annealed in VA-OA processes reveal positive correlations between the oxygen flow rate and formation of oxygen interstitials (Oi) and zinc vacancies (VZn). The OA-VA processes exhibit the relation of residual Oi and additional Vo. According to VA-OA and OA-VA processes, we propose that the green emission in ZnO annealed in oxygen poor/rich condition is mainly due to the formation of Vo/VZn and annealing at oxygen rich condition creates Oi that lead to strong orange-red emission. Rather than O1s, we propose a reliable method by considering the peak shift of Zn2p in XPS to inspect the ZnO matrix, which has good interdependence with the characteristics of PL.

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Nanoparticles of Ni0.2Zn0.6Cu0.2Fe2O4 were prepared by the standard co-precipitation method. The formation of nanocrystalline mixed spinel phase has been confirmed by x-ray diffractograms. The sizes of the nanoparticles were estimated in the range 7–30 nm, which was confirmed by transmission electron microscopy. Thermal variations of the real part of AC magnetic susceptibilities measured from 450 K down to 80 K and Mössbauer effect measurements at room temperature and down to 20 K clearly indicate the presence of superparamagnetic particles in all the samples. Specific saturation magnetizations measured by VSM are found to increase steadily with the increase of average particle size. The coercive field obtained from low frequency measurements shows that in all the samples a small fraction of particles is not relaxed within the measuring time. For samples showing a less dominating superparamagnetic behaviour, AC magnetic susceptibility data showed the expected increase of blocking temperature with increase in particle size. Magnetic anisotropy energy constants of the nanoparticles were estimated from the blocking temperature and the values cannot be directly correlated with their particle sizes.

Abstract:Two-dimensional SnS x (x = 1, 2) nanocrystals are attractive catalysts for photoelectrochemical water splitting as their components are earth abundant and environmentally friendly. We have fabricated SnS thin-film photoelectrodes by spin coating mixed-phase SnS nanocrystals synthesized via a hot-injection technique on glass/Cr/Au substrates. The obtained SnS thin films can be transformed into SnS 2 by introducing structural phase changes via a facile low-vacuum annealing protocol in the presence of sulfur. This sulfurization process enables the insertion of sulfur atoms between layers of SnS and results in the generation of shallow donors that alter the mechanism for water splitting. The SnS 2 thin films are used as stable photocatalysts to drive the oxygen evolution reaction, and the light-current density of 0.195 mA/cm 2 at 0.8 V vs. Ag/AgCl can be achieved due to the high carrier density, lower charge transfer resistance, and a suitable reaction band position. Based on a combination of UV-Vis spectroscopy (ultraviolet and visible spectroscopy), cyclic voltammetry and Mott-Schottky analysis, the band positions and band gaps of SnS and SnS 2 relative to the electrolyte are determined and a detailed mechanism for water splitting is presented. Our results demonstrate the potential of layered tin sulfide compounds as promising photocatalysts for efficient and large-scale water splitting.

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal würtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140-160 nm and a wall of thickness, 40-50 nm. The length of nanorods and nanotubes varies in the narrow range of 500-600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.