Hydrothermal synthesis and characterization of micro/nanostructured ZnSn(OH)6/ZnO composite architectures

Micro/nanostructured ZnSn(OH)₆/ZnO composite architectures were synthesized through a simple one‐step hydrothermal method. Phase structure and morphology of the products were characterized by using X‐ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). ZnSn(OH)₆ microcubes and ZnO nanorods with uniform size were interconnected to form the micro/nanostructured architectures. ZnO nanorods preferentially grow at edges and corners of the microcubes. Morphology of the products was susceptible to concentration of the reactants. With increasing reactant concentration, the ZnO nanorods grown on the surfaces of ZnSn(OH)₆ microcubes disappeared. Meanwhile, the smooth surfaces of the ZnSn(OH)₆ microcubes become coarsened and were etched to spherical outlines. Growth mechanism of the micro/nanostructured ZnSn(OH)₆/ZnO composite architectures was discussed and thermal decomposition properties of the micro/nanostructured ZnSn(OH)₆/ZnO composite architectures at high temperature were examined. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of ZnSn(OH)6 regular octahedrons by a simple hydrothermal process

ZnSn(OH)₆ regular octahedrons were successfully synthesized through a simple hydrothermal method using an aqueous solution containing ZnO flower‐like structures, SnCl₄·5H₂O, and NaOH. Phase structure, morphology and microstructure of the samples were investigated by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Parameters in preparation process such as the ratios of Sn⁴⁺/OH^‐, the molar ratio of Zn/Sn and reaction time were discussed. Results show that the obtained samples are comprised of ZnSn(OH)₆ regular octahedrons with about 2 μm in side length and ZnSn(OH)₆ urchins‐like structures. ZnSn(OH)₆ urchins‐like structures preferentially grow on the edges and corners of regular octahedrons. Morphology of the products is susceptible to the ratios of Sn⁴⁺/OH^‐. A relatively low concentration of OH^‐ is favored to obtain ZnSn(OH)₆ regular octahedrons with urchins‐like structures on the surface, while a high concentration of OH^‐ results in a handful of regular octahedrons without urchins‐like structures on the surface. When the molar ratio of Zn/Sn changes to 1:2 or 2:1, the edges and corners of regular octahedrons become coarse and urchins‐like structures disappear from the surface. More urchins‐like structures form on the surface of regular octahedrons and the edges and corners of regular octahedrons become coarsened with the increase of reaction time. Moreover, the possible mechanism for ZnSn(OH)₆ regular octahedrons is discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

Microwave hydrothermal synthesis and photocatalytic properties of ZnWO4 nanorods

Cd²⁺‐doped ZnWO₄ nanorods have been synthesized at 200 °C with microwave hydrothermal method, using Zn(NO₃)₂·6H₂O, Na₂WO₄·2H₂O and CdCl₂ as raw materials. The effects of Cd²⁺ doping contents on the structure and morphology of the product were studied. The results show that Cd²⁺ doping into the crystal lattice of ZnWO₄ nanopowder makes the powder orientationally grow along (010), (110) and (200) crystal planes to form the nanorods. The bigger Cd²⁺ doping contents are, the more obviously ZnWO₄ nanorods grow. Meanwhile, the nanopowder is gradually transformed from monoclinic phase into the orthogonal phase. As the charge transference medium between the interfaces, Cd²⁺ restrains the combination of holes and electrons. After doped, the photocatalytic properties of ZnWO₄ nanorods are increased. When Cd²⁺ doping content is 20%, the Cd²⁺‐doped ZnWO₄ nanorods showed the highest degradation rate up to 98% in 2 h.     

Sm,C掺杂改性纳米TiO2及其可见光催化性能研究

通过溶胶-凝胶法制备了Sm、C分别单掺杂和共掺杂纳米TiO2光催化剂,采用XRD、FESEM、TEM、XPS、UV-Vis-DRS、PL、Nano-sizer纳米粒度分析仪等对样品进行表征,以光催化降解亚甲基蓝(MB)作为评价模型,研究了不同样品对MB的光催化降解效果.结果表明,Sm单掺杂抑制了TiO2从锐钛矿向金红石的相转变,抑制晶粒长大,C的单掺杂则促进了TiO2的相转变,Sm或(和)C的掺杂均能细化TiO2晶粒,拓展TiO2在可见光区的光谱响应范围,降低光生e-/h+对的复合几率.Sm、C的掺杂均能有效提高TiO2的光催化活性,且共掺杂时存在协同效应,当n(Sm)∶n(C)∶n(Ti)=0.01∶0.3∶1、热处理温度500 ℃时,Sm/C-TiO2样品在普通日光灯下催化降解MB的一级表观速率常数是相同条件下纯TiO2的4.3倍.     

ZnSn(OH)6/SrSn(OH)6光催化降解甲苯的性能研究

采用简单的共沉淀法制备了新型ZnSn(OH)₆/SrSn(OH)₆复合光催化剂。利用X射线衍射(XRD)、X射线光电子能谱(XPS)、紫外可见-漫反射吸收光谱(UV-Vis)、N₂吸附脱附、扫描电镜(SEM)、透射电镜(TEM)对样品的结构、形貌和光吸收性质进行了表征,并以甲苯为目标污染物对其光催化性能进行评价。结果表明,与纯相SrSn(OH)₆和ZnSn(OH)₆相比,复合材料ZnSn(OH)₆/SrSn(OH)₆的紫外光吸收能力显著增强,光生载流子的复合效率降低,进而增强了其光催化降解甲苯的效率。复合样品ZSH/SSH-10摩尔比为10%对甲苯的降解率达到58%,是SrSn(OH)₆单体的1.35倍。循环使用5次后,ZSH/SSH-10的降解率仍保持51%以上,说明该催化剂具有良好的循环稳定性。     

Doped-metal oxide nanoparticles for use as photocatalysts

Nano-sized doped-metal oxides such as Fe-doped TiO₂, WO₃-doped ZnO and Fe-doped CeO₂ were synthesized by the modified sol-gel/impregnation, flame spray pyrolysis and homogeneous precipitation/impregnation methods respectively. The crystalline phase, particles size, and crystallinity of nano-sized powder were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Specific surface area of the sample was examined by the Brunauer, Emmett and Teller (BET) adsorption–desorption of nitrogen gas. The photocatalytic activity of Fe-doped TiO₂, WO₃/ZnO, Fe-doped CeO₂ nanoparticles was examined by studying the mineralization of methanol, sucrose, glucose, oxalic acid and formic acid under UV and visible light irradiations in a pyrex spiral photoreactor. It was found that doped metal oxides could improve the photocatalytic activity of the pure metal oxides.     

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.     

Synthesis and characterization of simonkolleite nanodisks and their conversion into ZnO nanostructures

Simonkolleite (Zn₅(OH)₈Cl₂·2H₂O) nanodisks with a width of 40 nm have been successfully synthesized via a hydrothermal method using zinc chloride and ammonia as the starting materials. The conversion mechanisms from simonkolleite nanodisks to ZnO spindles under hydrothermal condition and to ZnO nanotablets under solid phase transformation were discussed respectively. The simonkolleite nanodisks obviously occur in hydrothermal system with the combination of a lower alkalinity, lower temperature (<363 K), a higher NH₄⁺ ions concentration and in existence of Cl^‐ anion. The morphologies, crystal phases and photoluminescence properties of as‐synthesized samples were investigated by field emission scanning electron microscopy, powder X‐ray diffractometer and fluorescence spectrophotometer. The photocatalytic activities of these as‐synthesized samples in the degradation of methyl orange have been demonstrated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

FTIR,powder XRD,TEM and dielectric studies of pure and zinc doped nano‐hydroxyapatite

Hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ or HAP, is an important bio‐material, which is having application in bone implants and dentistry. In the present study, zinc doped nano‐hydroxyapatite (Zn‐HAP) was synthesized via chemical precipitation route using surfactant mediated approach. The doping of zinc was confirmed by EDAX. The powder X‐ray diffraction (XRD) pattern revealed the typical hydroxyapatite pattern with broadening and extra peaks were observed for higher concentration. The average crystallite size was calculated by applying the Scherrer's formula to powder XRD pattern and was found in the range of 16 to 33 nm. The morphology of synthesized nano‐particles was also confirmed using TEM. FTIR spectroscopy was used to confirm the presence of various bonds. The dielectric study was carried out at room temperature within the frequency range from 10² Hz to 10⁷ Hz and the variations of dielectric constant with frequency of applied field as well as with the concentration of zinc were studied. It was found that as the concentration of zinc increased the dielectric constant increased. The variations of dielectric loss and a.c. conductivity with frequency of applied field were studied. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mixed metal oxide nanocomposites derived from layered double hydroxides as photocatalysts for C.I. Basic Blue 3 degradation under UV light

In this research we report synthesis of the heterostructure Mg‐Al‐Zn mixed metal oxide (ZnO/MMO) nanocomposite photocatalysts derived from Zn(OH)₂/Mg‐Al‐layered double hydroxides (ZLDHs) precursors. The obtained samples were characterized by the X‐ray diffraction (XRD), FT‐IR, BET surface area, ICP and TG/DTG methods. The chemical compositions and morphology of the synthesized materials were investigated by the energy dispersive X‐ray analysis (EDX) and the transmission electron microscopy (TEM). The results reveal that at the reaction time 96 h, ZLDH has the highest crystalinity which was confirmed by the X‐ray diffraction spectra. The calcined samples at 500, 600 and 700 °C for 4 h show that the crystallinity of the nanocomposite improves with the increase of calcination temperature. The photocatalytic activities of synthesized nanocomposites were compared for the degradation of C. I. Basic Blue 3 (BB3) dye under UV illumination in aqueous solution. Among the synthesized nanocomposites, ZnO/MMO calcined at 700 °C shows the highest efficiency towards the removal of dye. The effect of UV illumination on the stability of ZnO in ZnO/MMO nanocomposite and pure ZnO was also investigated. The results showed that the photostability of ZnO in ZnO/MMO nanocomposite is increased compared to the pure ZnO.     

Synthesis and characterization of visible light responsive N-TiO2 mixed crystal by a modified hydrothermal process

N doped TiO₂ with anatase and rutile mixed crystal were prepared by using tetrabutyl titanate as the precursor via a modified hydrothermal process and calcination at 320 °C. The microstructure and morphology of samples were characterized by XRD, UV-vis-DRS, FTIR and XPS. The results showed that N-TiO₂ particles were crystallized to anatase and rutile mixed crystal structure; they were presented narrow particle size distribution, and the average particle size was ca. 13.5 nm calculated from XRD results. It was found that the N-doped TiO₂ particles showed strong visible-light absorption and high photocatalytic activity for the mineralization of Rhodamine B under irradiation by visible light (400-500 nm). The high visible-light photocatalytic activity of the obtained N-doped TiO₂ might result from the synergetic effect of nitrogen doping and the mixed lattice structure of N-TiO₂. Possible mechanism of N-TiO₂ mixed crystal formed under hydrothermal conditions was discussed.     

Studies on fabrication of urchin‐like WO3·H2O hollow spheres and their photocatalytic properties

Urchin‐like tungsten oxide hydrate (WO₃ · H₂O) hollow spheres were successfully synthesized via a self‐sacrifice template method at low temperature. The effects of reaction parameters on the preparation were studied in solution. The growth mechanism was also proposed on the basis of experimental results. In addition, the acid amount and temperature have important effects on size control of the as‐obtained samples. The achieved nanoarchitectures have typical diameters of 4–6 μm with nanoflakes of several nanometers at surface. Crystal structure, morphology, and composition of final nanostructures were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Degradation experiments of organic contaminant were also performed on samples of hollow spheres and walnut‐like structures under visible‐light illumination. Hollow sphere sample exhibited better photocatalytic capability than walnut‐like sample. Possible mechanism was studied for WO₃ · H₂O assisted photocatalytic degradation of organic contaminant under visible light.     

CeO2-Bi2O3 nanocomposite: Two step synthesis, microstructure and photocatalytic activity

CeO₂-Bi₂O₃ composite was synthesized via a two-stage process. The precursors were prepared from Ce(NO₃)₃·6H₂O, Bi(NO₃)₃·5H₂O and CO(NH₂)₂ with different molar ratio through the hydrothermal process, and then was completed by carrying out the precursors for 4 h at 600 °C under flowing air atmosphere. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and diffuse reflectance ultraviolet-vis spectra (UV-DRS) were employed to characterize the as-synthesized materials. The results showed that the microstructure and morphology of CeO₂-Bi₂O₃ composite were similar in spite of different inverse proportion. We also investigated improved photocatalytic activity in the case of CeO₂-Bi₂O₃ composite catalyst compared to the catalytic activity of pure Bi₂O₃ or CeO₂ powder. The suppression of charge recombination in the composite CeO₂-Bi₂O₃ catalyst led to higher catalytic activity for the degradation of RhB. The CeO₂ 10%/Bi₂O₃ photocatalyst exhibited maximum photocatalytic activity. The photocatalytic activity is in close relation with the inverse proportion between reactants.     

Studies on optical properties of polycrystalline SnO2:Sb thin films prepared using SnCl2 precursor

Optical properties of spray deposited antimony (Sb) doped tin oxide (SnO₂) thin films, prepared from SnCl₂ precursor, have been studied as a function of antimony doping concentration. The doping concentration was varied from 0‐4 wt.% of Sb. All the films were deposited on microscope glass slides at the optimized substrate temperature of 400 °C. The films are polycrystalline in nature with tetragonal crystal structure. The doped films are degenerate and n‐type conducting. The sheet resistance of tin oxide films was found to decrease from 38.22 Ω/□ for undoped films to 2.17 Ω/□ for antimony doped films. The lowest sheet resistance was achieved for 2 wt.% of Sb doping. To the best of our knowledge, this sheet resistance value is the lowest reported so far, for Sb doped films prepared from SnCl₂ precursor. The transmittance and reflectance spectra for the as‐deposited films were recorded in the wavelength range of 300 to 2500 nm. The transmittance of the films was observed to increase from 42 % to 55 % (at 800 nm) on initial addition of Sb and then it is decreased for higher level of antimony doping. This paper investigates the variation of optical and electrical properties of the as‐deposited films with Sb doping. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

铁、镧共掺杂介孔TiO2微球的制备及光催化性能研究

以钛酸异丙酯为钛源,利用三嵌段共聚物EO106 PO70 EO106(F127)修饰的溶胶-凝胶法合成了La、Fe共掺杂的单分散TiO2介孔微球.并通过X射线衍射(XRD)、场发射扫描电镜(FESEM)、能谱分析(EDX)、透射电镜(TEM)、BET、X射线光电子能谱(XPS)、紫外-可见光漫反射技术对样品的物相组成及微观结构进行了表征,利用紫外光照射降解亚甲基蓝溶液的方法测定其光催化性能.结果表明:与纯TiO2介孔微球相比,La3+的掺入抑制了TiO2晶粒的长大,La3+和Fe3+共掺入TiO2介孔微球的紫外-可见光的吸收带边发生红移,禁带宽度减小;在紫外光照射下,1at;La3+掺杂以及Fe3+、La3+共掺TiO2介孔微球的光催化活性均高于纯TiO2,其中1at;Fe/1at;La-TiO2的光催化性能最好.     

Crystal growth and electric‐property change by rubidium or cesium doping on potassium‐sodium‐niobate

Alkali metals (Na, Rb or Cs) co‐doped with fiber‐ and bulk‐shaped KNbO₃ single crystals were grown using two original methods by means of doping together of small ionic Na and large ionic Rb or Cs into KNbO₃. Single‐phase crystals could be grown with an orthorhombic system at room temperature as well as pure KNbO₃. Piezoelectric and ferroelectric property changes by the co‐doping of Rb or Cs with Na were estimated using d₃₃ values and a polarization‐electric field hysteresis curve in fiber‐ and bulk‐shaped crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,growth and characterization of single crystals of pure and thiourea doped L‐glutamic acid hydrochloride

L(+)Glutamic acid hydrochloride [HOOC (CH₂)₂CH(NH₂) COOH·HCl], a monoamino dicarboxylic acid salt of L‐Glutamic acid was synthesized and the synthesis was confirmed by FTIR analysis. Solubility of the material in water was determined. Pure and Thiourea doped L‐Glutamic acid hydrochloride crystals were grown by low temperature solution growth using solvent evaporation technique. XRD, UV‐Vis‐NIR analyses were carried out for both pure and thiourea doped crystals. The crystals were qualitatively analyzed by EDAX analysis and the presence of thiourea was confirmed. The cell parameters of L‐Glutamic acid hydrochloride have been determined as a = 5.151 Å, b = 11.79 Å, c = 13.35 Å by X‐ray diffraction analysis and it crystallizes in orthorhombic space group P2₁2₁2₁. UV‐Vis‐NIR spectra analysis showed good optical transmission in the entire visible region for both pure and doped crystals. Micro hardness of both pure and doped crystals has been determined using Vickers micro hardness tester. The SHG efficiencies of both pure and doped crystals were determined using Kurtz powder test and pure L‐Glutamic acid hydrochloride crystal was found to possess better efficiency than thiourea doped L‐Glutamic acid hydrochloride crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence and radiation damage in W,Mg, Ca doped Bi4Ge3O12 crystals

Spectral properties and radiation damage in W, Mg and Ca doped Bi₄Ge₃O₁₂ (W:BGO, Mg:BGO, Ca:BGO) crystals before and after thermal treatment and gamma‐ray (γ‐) or ultraviolet (UV) radiation were studied. The absorption and the photoluminescence (PL) spectra of doped BGO crystals in visible region were measured. Before γ or UV radiation, the emission intensity of W:BGO crystal is stronger than that of pure BGO at about 500 nm. After γ radiation (10k Gy), the emission intensities of doped BGO are all weaker than pure BGO under identically condition. However, the emission intensity of W:BGO is stronger than that of pure BGO after UV exposure (10k Gy). Thermal treated (annealed in N₂ at 550 °C for 6 h) W:BGO has shown a much stronger emission intensity than others. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)