A facile scalable two-step approach based on a low-temperature aqueous electrodeposition and a solid-state crystal phase transformation process was developed to grow rhombus-shaped ZnO nanorod arrays which showed markedly improved hydrogen storage capacity.

Tetragonal perovskite structure PbTiO3 donut-like particles have been synthesized by a hydrothermal method in strong alkaline environment using lead nitrate (Pb(NO3)2) as the lead source and TiCl4 as the titanium source. The as-prepared particles were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), and it was indicated that the phase composition and particles shapes were influenced by the reaction temperature and reaction time. Based on the morphologies and phase evolutions as a function of reaction temperature or reaction time, a mechanism for the growth of the donut-like PbTiO3 particles was proposed to involve nucleation, agglomeration, phase in situ conversion, dissolution, and recrystallization. The spherical particles were formed by primary nucleation of PbTi0.8O2.6 followed by agglomeration into platelets. Then, the platelet PbTi0.8O2.6 particles in situ converted into Pb2Ti2O6 particles. Under the effects of temperature, pressure (autogenous pressure), and high solution pH value, the platelet Pb2Ti2O6 particles dissolved from its center of surface and recrystallized to form PbTiO3 nano-particles which adhered to its edges. Finally, the monocrystal donut-like PbTiO3 particles were formed as the dissolution of Pb2Ti2O6 particles completed.Tetragonal perovskite structure PbTiO3 donut-like particles have been synthesized by a hydrothermal method in strong alkaline environment. The as-prepared particles were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Based on the morphologies and phase evolutions as a function of reaction temperature or reaction time, a mechanism for the growth of the donut-like PbTiO3 particles was proposed to involve nucleation, agglomeration, phase in situ conversion, dissolution, and recrystallization.

Vertically aligned arrays of ZnO nanorod (ZNR) were rapidly synthesized on ITO glass without needing a pre-prepared seed layer of ZnO via a hexamethylenetetramine (HMT)-assisted electrodeposition route. The effect of HMT on the ZNR electrodeposition process was investigated by the cyclic voltammetric curve and the current–time curve. An electrodeposition growth model based on the capping effect of HMT–4H was proposed. The as-synthesized ZNRs possess single crystalline, a wurtzite crystal structure with markedly preferential growth orientation along [0001] direction determined by transmission electron microscopy and powder X-ray diffraction. As compared with the electrodeposited ZnO film without HMT assistance, the ZNR arrays showed the high transmittance (90%) in the visible wavelength range and the blue-shift of the band gap energy. Moreover, the presence of an optical-phonon E2 (high) at 437.3 cm−1 in Raman spectrum and strong ultraviolet emission at 376 nm but weak defect-related deep level emission in the room temperature photoluminescence spectrum also indicated that such ZNR arrays are of good crystal quality. More importantly, the rapid synthesis of ZNRs could provide the feasibility for preparation of ZnO nanotubes within a shorter time by a subsequent electrochemical dissolution process.

This study introduces a cost-effective electrodeposition route for preparation of highly oriented and well-defined ZnO nano/micro-scale structures on indium tin oxide (ITO) glass substrates without a traditionally pre-prepared layer of ZnO seeds. It was demonstrated that the addition of KCl, NaCl, and ethylenediamine (EDA) and the hydrolysis of hexamethylenetetramine (HMT) pose the difference in growth rates between ZnO {101¯0} prismatic planes and (0 0 0 1) end plane and lead to the formation of highly oriented ZnO rods, flower-like ZnO bundles, nanowire arrays or hexagonal plates. The effect of different Cl− sources on the array manner of ZnO plates and the effect of concentration of EDA on the aspect ratio of ZnO rods were investigated, respectively. Electrodeposition potential plays an important role in the preferential growth orientation of ZnO crystals on the substrates without a traditionally pre-prepared layer of ZnO seeds. Room temperature photoluminescence (PL) properties of different ZnO structures were also investigated. In addition, different procreation manner on the (0 0 0 1) growing end planes for ZnO rods and nanowire arrays were observed. On the basis of observation, several growth mechanisms, such as layer-by-layer procreation manner for ZnO nanowires, are suggested.

Molten salt synthesis (MSS) is an effective method to prepare anisotropic shaped single crystals. In this study strontium titanate (SrTiO3) (ST) platelet crystals were successfully synthesized based on Sr3Ti2O7 (S3T2) platelet precursor in MSS process. The objective is to identify the formation mechanism of SrTiO3 platelet crystals based on Sr3Ti2O7 platelet precursor. During the synthesis process of Sr3Ti2O7 and SrTiO3 crystals, the final sizes are strongly influenced by the sorts of alkali chloride medium. Sr3Ti2O7 and SrTiO3 crystals with 30–50 μm in edge length and ∼2 μm in thickness are obtained in KCl medium. The conversion of SrTiO3 platelet crystals from Sr3Ti2O7 platelet precursor is a topochemical process, including diffusion of Sr and O atoms, and reconstruction of SrTiO3 blocks. In the topochemical process, TiO2 is the driving force of diffusion of Sr and O atoms from SrO layer in Sr3Ti2O7, which reacts with dissociative Sr2+ and O2− to form SrTiO3 in different positions: deposited at interior pores and surface of Sr3Ti2O7, and dispersed in molten salt medium.

ZnO rod arrays were directly grown on In2O3/Sn (ITO)-coated glass substrates without needing a preprepared ZnO seed layer by aqueous chemical growth (ACG) using an equimolar aqueous solution of Zn(NO3)2·6H2O and C6H12N4. By further varying the substrates such as glass, Pt/glass, and Au/glass, other assembly patterns of ZnO architectures (rodlike, flowerlike, urchinlike, and stelliform crystals) were also obtained. The possible growth mechanisms for different assembly patterns dependent on the substrate were proposed. It was revealed that both the inherent highly anisotropic structure of ZnO and the surface energy minimization of different substrates play crucial roles in determining final morphologies of ZnO architectures. In addition, the photoluminescence (PL) properties of ZnO architectures on various substrates were investigated at room temperature.

Large-scale and dense ZnO thin films with novel petal-like architectures were directly electrodeposited on the Au/ITO glass substrates from aqueous solution of Zn(NO3)2 and HMTA at a low temperature of 70 °C for the first time. Scanning electron microscopic (SEM) investigation revealed that the Au/ITO glass substrates are fully covered with densely distributed ZnO petal-like architectures. X-ray powder diffraction (XRD) pattern indicated that as-prepared unique films are highly crystalline and wurtzite hexagonal phase with extremely preferred orientation along [0001] direction. The optical band gap energy was found to be 3.85 eV for ZnO film with petal-like architectures on the Au/ITO substrate. Moreover, a strong and sharp ultraviolet (UV) emission at 386 nm but very weak defect-related deep level emission (DLE) in the room temperature photoluminescence (PL) spectrum also indicated that as-grown films are of good crystal quality. The possible growth mechanism for the novel petal-like architectures suggested that both the inherent highly anisotropic structure of ZnO and large lattice mismatch between ZnO and Au played crucial roles in determining final surface microstructures of the products.

A facile scalable two-step approach based on a low-temperature aqueous electrodeposition and a solid-state crystal phase transformation process was developed to grow rhombus-shaped ZnO nanorod arrays which showed markedly improved hydrogen storage capacity.