Solvothermal synthesis of mesoporous slabstone‐like TiO2 and its photodegradation preference in a methyl orange‐rhodamine B mixture solution

Mesoporous slabstone‐like anatase TiO₂ micro‐nanometer composite structure has been successfully synthesized by a facile solvothermal method at 180 °C using polyethylene glycol (PEG) as a structure‐directing agent, followed by calcination at 400 °C for 2 h. The crystal structure and morphology of the product were characterized by XRD, SEM, TEM and HRTEM. Its BET specific surface area was obtained from N₂ adsorption‐desorption isotherm measurement. Rhodamine B (RB) aqueous solution was used to evaluate the photocatalytic activity of the as‐prepared TiO₂ under simulated sunlight irradiation and compared with that of commercial TiO₂ (P25). A RB and methyl orange (MO) coexisting solution was chosen to investigate the photodegradation preference of the slabstone‐like TiO₂ on these two dyes. The results show that the photocatalytic activity of the as‐prepared TiO₂ is much higher than that of P25, and MO is the preferential degradation species in the MO‐RB mixture solution.     

Determination of nucleation parameters and the solid liquid interfacial energy of the KCl‐ethanol‐water system

The kinetic parameters of homogeneous nucleation of KCl in different ethanol‐water solvent mixtures were determined at 25°C from the experimental measurements of the width of the metastable zone at different cooling rates. The ethanol mass ratio in the ethanol water solvent mixture was varied from 0‐0.9 and the metastable zone width for each solvent mixture was measured under the cooling rates of 10, 20 and 30 K/h. The influence of ethanol ratio on the activity coefficient was calculated. It was found that increasing the ethanol ratio in the solvent mixture leads to an increase in the mean molal activity coefficient. The experimental results obtained showed that the increase in the ethanol ratio in the solvent widens the metastable zone for the crystallization of KCl. Also it has inferred from the calculations based on the classical nucleation theory that increasing of the ethanol ratio in the solvent mixture resulted in an increase of the nucleation rate order, increase of the critical size of nuclei and increase of the solid liquid interfacial energy. It has been found that the solid liquid interfacial energy can be good correlated with inversely proportionality to the solubility. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Graphene oxide used as a surfactant to induce the flower‐like ZnO microstructures: growth mechanism and enhanced photocatalytic properties

In this paper, graphene oxide (GO) was used as a temple to induce the formation of flower‐like ZnO microparticals compared with surfactants, such as cetyltrimethylammonium bromide (CTAB) and dodecyl dimethyl betaine (BS‐12). The zinc hydroxide carbonate ((Zn₄(CO₃)(OH)₆,ZHC)) was produced by a hydrothermal reaction. The flower‐like ZnO microparticals were gained by calcining ZHC. In the GO medium, the microparticals were assembled by numerous porous nanosheets from one point (initial nucleus) to flower‐like microparticals finally. The nanosheets of graphene oxide and functional groups were likely to contribute to the formation of the precursor, and some nanosheets were retained in the complex. The growth mechanism of ZHC was also proposed in this paper. The photocatalytic activity of the flower‐like ZnO microparticals was evaluated by photo degradation reaction of rhodamine B (RhB). The peony‐like porous ZnO/rGO compounds showed high photocatalytic activity and better than ZnO microparticals formed in the CTAB and BS‐12. These results indicated that GO could be widely used as a surfactant to induce composite materials with special morphology and photoelectric properties, etc.     

Synthesis of flower‐like zinc oxide and polyaniline with worm‐like morphology and their applications in hybrid solar cells

ZnO with a “flower‐like” morphology was synthesized using a simple microwave assisted hydrothermal method and used as an acceptor material in hybrid solar cells. X‐Ray diffraction and Raman Spectroscopy confirmed the formation of a highly crystalline wurtzite ZnO structure. A highly crystalline and conductive polyaniline with “worm‐like” morphology was synthesized by chemical polymerization of aniline using KH(IO₃)₂ as an oxidant and was used as a donor material for solar cells. The morphology was probed by using scanning and transmission electron microscopy. Polyaniline with worm‐like morphology had a diameter of 160 nm and about 2 µm long. Solar cell device fabricated from PANI/ZnO active bilayer demonstrated a fill factor of about 22.8%. Upon blending PANI with ZnO the fill factor was improved to 25.6% and efficiency by almost 100 fold when PANI:ZnO 1:1 composite was used as an bulk heterogeneous active layer. The fill factor was further improved to 26.4% when device architecture was changed to diffused bilayer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology‐controllable synthesis of ZnO nano‐/micro‐ structures by a solvothermal process in ethanol solution

Flower‐like ZnO nanostructures assembled by nanorods with bimodal size distribution have been synthesized by a solvothermal process in NaOH‐Et system. Various effects of the solvothermal parameters and assistant additives on the morphologies of ZnO nanostructures have been investigated. The directing effect of chloride ions have been observed in the formation of highly symmetrical 3D ZnO nanostructures. A possible mechanism has been proposed to explain the formation of ZnO nanoflowers in NaOH‐Et system. A strong near‐UV emission band centered at around 396 nm is observed in the photoluminescence spectrum of flower‐like ZnO nanostructures, indicating of their high crystal quality.     

Facile solvothermal synthesis,growth mechanism and thermoelectric property of flower‐like Bi2Te3

Hierarchical flower‐like Bi₂Te₃ was synthesized through a facile solvothermal method. The crystal structure and morphology of the as‐prepared samples were characterized by X‐ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high resolution TEM. The reaction parameters such as reaction time, the amount of glucose, concentration of NaOH and the reaction temperature were systematically investigated. Based on the FESEM observations, a possible mechanism defined as a self‐assembly process accompanied by anisotropic growth mechanism was proposed. Moreover, the thermoelectric properties were measured at the temperature range of 300–600 K. The hierarchical flower‐like Bi₂Te₃ presented good thermoelectrical properties. The maximum ZT value reached up to 0.6 at 600 K, which was higher than that of Bi₂Te₃ nanoparticles.     

Growth of ytterbium tartrate trihydrate crystals in silica and agar‐agar gels and their characterization

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar‐agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar‐agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT‐IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C₄H₄O₆) (C₄H₅O₆).3H₂O. The FT‐IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rapid synthesis of tin-doped indium oxide microcrystals in supercritical water using hydrazine as reducing agent

Tin-doped indium oxide (ITO) microcrystals were successfully synthesized in supercritical water (SCW) using hydrazine (N₂H₄) as a reducing agent. Using a mixture of tin and indium hydroxides prepared at pH = 9.4 as a precursor, ITO microcrystals were synthesized at temperatures 400–450 °C under pressures 25–30 MPa. Synthesizing in SCW effectively shortened the time required to synthesize the ITO microcrystals to below 30 mins. The effect of reducing agents (ethanol, formic acid, and N₂H₄) and reaction conditions on the formation of ITO particles were investigated, and it was found that N₂H₄, which is superior to ethanol and formic acid, played a key role in the doping of the In₂O₃ structure with Sn⁴⁺ to form ITO particles with a blue color. Addition of N₂H₄ possibly depleted the oxygen in the In(Sn)OOH structure, accelerating the formation of cubic In₂O₃ and introduced Sn⁴⁺ into the structure along with the creation of oxygen vacancies. It was also found that the high temperatures and the properties of the SCW, such as ion product, strongly affected the morphology of the ITO particles and the Sn⁴⁺ doping. Based on these results, a mechanism has been proposed for the synthesis of ITO particles under SCW conditions. This study demonstrates that due to the unique properties of SCW, the synthesis of doped oxides in SCW is a plausible alternative method.     

Large‐scale synthesis of submicron gallium oxide hydrate rods and their optical and electrochemical properties

Large‐scale submicron gallium oxide hydrate (GaOOH) rods have been synthesized by a simple hydrothermal process and their optical, electrochemical properties have been analyzed. The diameter of the GaOOH nanorods with good single crystalline structure is 80‐800 nm and length of less than 4 μm. The tips of the GaOOH structures are composed of nanorods with the diameter of less than 10 nm and length of more than 100 nm. Hydrothermal temperature, time and the Ga‐contained starting materials have important roles on the formation and growth of submicron GaOOH rods. The submicron GaOOH rods exhibit good UV‐vis absorption ability. The electrochemical analysis shows that the submicron GaOOH rods have good detecting ability for ascorbic acid and cysteine in PBS and NaCl solution exhibiting promising potential for electrochemical sensing application. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of cationic substitution on lattice constants and optical characterization in solution grown mixed crystals of potassium‐ ammonium zinc chloride

Mixed crystals of potassium‐ammonium zinc chloride in different concentrations were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder x‐ray diffraction studies were carried out on the grown crystals. The comparison between lattice parameters a, b and c are experimentally determined and calculated by Vegad's law. The concentration of K⁺ ions in the crystals was measured by the atomic absorption technique. The crystal morphology changed considerably by increasing K⁺ concentration. The optical absorption coefficient (α) indicated strong influence changing concentration. The optical energy gap was found to decrease with increasing K⁺ concentration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mild hydrothermal synthesis and structures of mixed‐valence iron phosphates: SrFe3(PO4)3 and the interesting Mg2+‐doped AFe3 (PO4)3 (A = Ba,Pb) in Fe2+ site

Series of mixed valence monophosphates AFe_3‐xMg_x(PO₄)₃ [A = Sr(x = 0), Ba(x = 0.6), Pb(x = 0.6)] were synthesized by mild hydrothermal treatment at 210 °C. Refinements of single crystal X‐ray diffraction datas show all these compounds are isostructural. The attempts to make AFe₃(PO₄)₃ (A = Ba, Pb) hydrothermally in the experiment were unsuccessful. However, the Mg‐doped homologues AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb) were synthesized with the addition of MgCO₃ in the reactants as mineralizer. EDS and single crystal X‐ray data refinement indicated that the Mg²⁺ cations were doped in the Fe²⁺ sites of AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb). The influence of the Mg‐doping on the structure and the reason why the Mg doped in the Fe(II) site instead of A site was discussed from the point of view of the bond valence model.