PAM辅助水热法制备形貌可控的ZnO纳米结构(英文)

采用PAM辅助水热法制备了形貌可控的ZnO纳米晶。X射线衍射分析表明,分别以水和丙三醇为溶剂制备的短棒和棒状的ZnO纳米晶是纤锌矿结构。场发射扫描电镜结果显示,短棒状ZnO的直径约200nm,长约1.5μm,而棒状ZnO的直径约100nm,长度约3μm。当ZnO形貌从短棒向棒状转变时,晶体纵横比从7.5转变成30。荧光光谱分析表明,位于400-450nm的紫峰强度随着形貌从短棒向棒状转变时增大,表明更细更长的ZnO一维纳米结构的缺陷越多;位于520-550nm的绿峰强度随着形貌从短棒向棒状转变时增大,表明更细更长的ZnO一维纳米结构的氧空位越多。并对不同溶剂对ZnO纳米晶形貌的影响机制及ZnO纳米晶在水热条件下的生长机理进行了探讨。     

纳米ZnO粉的新水热法制备技术

ZnO粉是用于传感器、压敏电阻、颜料、电子记录器、医用等的重要材料。ZnO粉的制备方法有多种，如溶胶-凝胶法，溶体蒸发分解法、湿化学合成法、气相反应法等。其中水热合成法是比较理想的方法，这种方法广泛用于优质氧化物粉的合成。然而，采用传统的水热法是难以合成ZnO纳米粉的。人们将这种方法适当加以改进，即在指定温度保温一定时间后，打开放气阀，然后降温，就能得到ZnO纳米粉。这种放气水热法的操作程序如下：放压热水法用的高压釜由衬银管的不锈钢制成，釜的容积为213mL，直径30mm，釜的顶部装有一个放气阀和一块气压表，试验…     

ZnO纳米棒的制备及光催化性能研究

采用水热法制备ZnO纳米棒。利用X射线粉末衍射(XRD)仪和透射电镜(TEM)对其结构和形貌分别进行表征,并通过紫外-可见分光光度计分析ZnO纳米棒光降解甲基紫来研究其光催化活性。结果表明,以氢氧化钠和醋酸锌为原料,聚丙烯酰胺为表面活性剂制备得到直径约26nm,长度达400nm的单晶纤锌矿结构的ZnO纳米棒。添加ZnO纳米棒光催化剂时的光降解率为70%,未加ZnO纳米棒的光降解率为30%,表明ZnO纳米棒具有很好的光催化活性。     

微波水热法制备氧化锌纳米粉体及其光催化性能

以ZnSO4·7H2O为原料,NaOH为矿化剂,采用微波水热法成功制备出氧化锌纳米粉体,研究了NaOH浓度对ZnO粉体的物相,形貌以及光催化性能的影响。XRD表明所得粉体均为纯相六方纤锌矿结构的氧化锌,晶粒尺寸介于39~58nm之间;FE-SEM和TEM表明,当NaOH浓度从0.5mol/L逐渐增大到4.0mol/L时,颗粒形貌由碎片状变为层片花状结构。利用300W高压汞灯作为光源,对质量浓度为20mg/L的罗丹明B溶液进行光催化降解实验,在光照120min后,不同矿化剂浓度下制备的氧化锌催化剂对罗丹明B的降解率均接近100%,说明当前条件下制备的ZnO粉体对罗丹明B具有较高的光催化活性。     

微波水热法制备分等级空心球状CdS纳米结构(英文)

以氯化镉和硫代硫酸钠为原料,以乙二胺四乙酸(EDTA)为模板剂,采用微波水热(M-H)法成功制备了空心球状 CdS 纳米结构。采用 X 射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、能量弥散X射线谱(EDS)和高分辨透射电子显微镜(HRTEM)对所制备的CdS 纳米结构进行表征。采用紫外-可见吸收光谱研究所制备的分等级空心球状 CdS 纳米结构的光学性能。结果表明:得到的CdS是具有纤锌矿结构的直径为 400～600nm的分等级空心球状纳米结构,这种结构由30nm左右的纳米颗粒自组装构成。EDTA和微波辐射在分等级空心球状 CdS纳米结构的形成过程中起了重要作用,讨论了这种作用并提出可能的生长机理。所制备的分等级空心球状CdS纳米结构具有较好的蓝光发射性能。     

一种性能优良的ZnO纳米线的水热法生长

以醋酸锌(Zn(CH3COO)2·2H2O)和氢氧化钠(Na(OH)2)作为实验反应前驱物,聚乙二醇(HO(CH2CH2O)13H)作为表面活性剂,采用低温水热法在60 ℃条件下,合成了不同形貌的ZnO纳米线和纳米棒材料,并对样品结构和形貌进行了XRD、SEM等分析.结果显示,ZnO纳米结构都具有六方纤锌矿结构,主要是由单晶纳米棒状组成的"菊花状"ZnO纳米団簇,団簇中的单晶在不同反应条件下合成了线形、尖细、平面等不同形貌,但主要粒子基本为棒状和菊花状.合成方法可作为制备形貌可控的金属氧化物的参考.     

单晶ZnO六棱锥的PEG400辅助热分解合成及其光致发光性能(英文)

将由Zn(CH3COO)2·2H2O和Na2CO3通过室温研磨反应获得的前驱体在PEG400存在下于240°C热分解获得大量的ZnO六棱锥产物。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)表征产物的晶体结构和形貌。进一步的实验结果表明:PEG400在ZnO六棱锥形成过程中发挥着重要作用,单六棱锥和双六棱锥的结构差异来自于热分解反应。光致发光谱(PL)测试表明:ZnO六棱锥在386nm处展示强的近带隙发射,在550nm处展示较弱的绿光发射。435cm-1处的拉曼振动表明ZnO六棱锥具有良好的晶体质量。     

水热法制备纳米TiO2的可见光波段光催化活性的溶剂效应

采用单乙醇、丙酮、吡啶、二元以及三元混合有机溶剂的有机溶剂水热法合成高分散纳米TiO2粉体,通过XRD,TEM和DTA-TG等手段研究合成的粉体物相与表面吸附特性,以及可见光光催化降解效率.结果表明在颗粒尺寸与晶型差别不大的各种溶剂制备粉体中,含丙酮单元、二元及三元溶剂制备TiO2粉体光催化效率在76%-89%;而单乙醇、乙醇-吡啶二元溶剂制备的光催化效率很低,均在15%以下.分析表明,可见光波段光催化效率与表面吸附物结构、基团与其极性等密切相关碳链结构溶剂中,含中极性羰基的丙酮溶剂吸附的粉体光催化效率,远高于含强极性羟基的单乙醇、乙醇-吡啶溶剂吸附粉体的光催化效率.)     

纳米ZnO的制备及其微波介电性能

用均匀沉淀法合成纳米ZnO粉体。经XRD和SEM分析表明产物为纤锌矿结构，呈球状或类球状。对所得粉体进行高温热处理。分析结果表明：热处理温度达600℃时，ZnO粉体颗粒小且分布均匀，平均粒径26nm。对所得产物在8．2～12．4GHz范围进行电磁参数的测量，表明：纳米ZnO粉体磁损耗很小，属于介电损耗材料，600℃热处理后，粉体与石蜡组成的复合体不仅具有良好的频响特性，且介电常数实、虚部和损耗值都较大。     

Ag+掺杂ZnWO4纳米棒的微波水热法合成及光催化性能

以硝酸锌(Zn(NO3)2·6H2O)、和钨酸钠(Na2WO4·2H2O)作为起始反应物,利用微波水热法在200℃下合成纳米棒状钨酸锌。利用X-射线粉末衍射、场发射扫描电子显微镜、透射电子显微镜及能谱成分图谱等分析手段对纳米棒状钨酸锌粉体进行表征,并对不同Ag+掺杂量的ZnWO4纳米棒的光催化性能进行了研究。结果表明:Ag+成功的掺入ZnWO4纳米棒中;随着Ag+掺杂量的增加ZnWO4纳米棒的颗粒尺寸也不断增大;Ag+掺杂量2%时纳米棒状钨酸锌粉体的光催化性能最优,但是随着掺杂量的逐渐增加光催化性能反而降低。     

Optical properties and photocatalytic activity of Nd-doped ZnO powders

To improve the photocatalytic activity of zinc oxides, ZnO powders doped with different neodymium (Nd) concentrations were prepared via hydrothermal method. X-ray diffraction (XRD) together with X-ray photoelectron spectroscopy (XPS) patterns revealed that Nd atoms were successfully incorporated into the ZnO lattice. XRD pattern also showed some anisotropy of the powders. The photoluminescence (PL) spectrum demonstrated a strong and broad peak in the visible light region, and the intensity of visible light emission was enhanced by Nd-doping. The photocatalytic activity was evaluated by the degradation of methyl orange solution. It is shown that doping of Nd into ZnO induces an increase of the photocatalytic activity and it attains to optimum at 3% (mole fraction) doping concentration. The intense visible light emission and the enhanced photocatalytic activity were explained by the increase in electron hole pairs and induced defects like antisite oxygen O_Zn and interstitial oxygen O_i, due to the doping of Nd.     

Self-assembled flower-like microstructure in Zn1-xCdxO nanoparticles

The structural and optical characterization of cadmium-doped zinc oxide nanoparticles synthesized by precipitation method was studied. X-ray diffraction study confirmed the substitution of cadmium dopant without disturbing the basic wurtzite structure of zinc oxide. The average crystalline size, lattice constants and unit cell volume also increased up to 4% of cadmium doping. Energy gaps of the samples were determined from the ultraviolet-visible absorption spectrum as well as Tauc's plot which infers that the energy gap decreases with the increase of cadmium content. Fourier transformation infrared spectrum confirms the cadmium dopant through peak shifting from 485 to 563 cm^?1. Photoluminescence spectrum also defines the cadmium dopant by intensity increase. The broad Raman peak at 437 cm^?1 indicates that the wurtzite structure of zinc oxide is weakened by 5% cadmium doping. Field emission scanning electron microscope study also confirms the existence of particles in nanometer size and it indentifies the microstructure transformation from nanoparticles to jasmine flower-like structure on 5% cadmium doping.     

Growth and photocatalytic activity of ZnO nanosheets stabilized by Ag nanoparticles

The Ag nanoparticles-stabilized ZnO nanosheets were prepared using a liquid-liquid two-phase method with (n-Dodecyl)trimethylammonium bromide (DTAB) as a phase transfer agent at the room temperature. The silver nanoparticles which are conductors with the character of attracting energy can make the ZnO sheets stabilize under the higher energy electrons. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy and fluorescence. The results demonstrate that the silver nanoparticles load on the surface of ZnO sheets and make the ZnO sheets stabilize. Furthermore, the formation mechanism of ZnO sheets stabilized by silver nanoparticles was also proposed and discussed in detail. Moreover, the photocatalysis test shows that the ZnO sheets stabilized by silver nanoparticles exhibit a higher photocatalytic activity than the pure ZnO nanosheets, thereby implying that the Ag/ZnO interfaces promote the separation of photogenerated electron-hole pairs and enhance the photocatalytic activity.     

Single-crystalline heterostructure of ZnO nanowire arrays on large Ag microplates and its photocatalytic activity

This paper presents experimentally a photocatalytic heterogeneous structure of high-density ZnO nanowire (NW) arrays grown on large Ag microplates. First, the dense single-crystalline ZnO NW fabricated using an economical hydrothermal method possess a great reactive surface area because of their high surface-to-volume ratio. In addition, the large Ag microplates synthesized using a simple and competitive growth method serve as an electron reservoir. The heterojunction between ZnO NW and Ag microplates forms a Schottky contact to separate the electrons from the photogenerated excitons in ZnO NW, prolonging the lifetime of excitons and enhancing their photocatalytic capability. The photodegradation experiment employs the methylene blue aqueous solution to reveal a kinetic rate constant of up to 6.60 × 10^?3 min^?1 at a low concentration of the ZnO/Ag heterogeneous structure on the ppm scale, and indicates an outstanding figure of merit of 1.02 × 10^?2 compared with previously reported ZnO/Ag heterogeneous structures.     

Defect mediated photocatalytic activity in shape-controlled ZnO nanostructures

Shape-controlled ZnO nanostructures were synthesized through a facile soft-chemical approach by varying the concentration of OH⁻ ions. X-ray diffraction and Raman spectra reveal the formation of highly crystalline single-phase hexagonal wurtzite nanostructure. It has been observed that the concentration of OH⁻ ions plays an important role in controlling the shape of ZnO nanostructures. TEM micrographs indicate that well-spherical particles of size about 8 nm were formed at lower concentration of OH⁻ ions whereas the higher concentration of OH⁻ ions favor the formation of nanorods of length 30-40 nm. The optical studies confirmed that the band gap and near band edge emission of ZnO nanostructures are strongly dependent on the shape of particles. Furthermore, the decrease in the intensity of green emission as shape of particles changes from sphere to rod indicates the suppressing of defect density, which in turn influences the photocatalytic activity and ferromagnetic-like behavior of ZnO nanostructures.     

Influence of preparation methods on photoluminescence properties of ZnO films on quartz glass

The influence of preparation methods on the photoluminescence properties of ZnO film was studied. Two methods were applied to fabricate ZnO films in a conventional pulsed laser deposition apparatus. One is high temperature （500-700℃） oxidation of the metallic zinc film that is obtained by pulsed laser deposition. The other is pulse laser ablation of Zn target in oxygen atmosphere at low temperature （100-250 ℃）. The photoluminescence property was detected by PL spectrum. The room temperature PL spectra of the ZnO films obtained by oxidation method show single violet luminescence emission centered at 424 nm （or 2.90 eV） without any accompanied deep-level emission and UV emission. The violet emission is attributed to interstitial zinc in the films. Nanostructure ZnO film with c-axis （002） orientation is obtained by pulsed laser deposition. The ZnO film deposited at 200 ℃ shows single strong ultraviolet emission. The excellent UV emission is attributed to the good crystalline quality of the film and low intrinsic defects at such low temperature.     

Synthesis and characteristics of large-scale ZnO rods by wet chemical method

The large-scale ZnO rods of submicrometer were prepared on the bare glass using a wet chemical method under different experimental parameters, such as the reactant concentration and the growth time. The microstructure of the ZnO rods was characterized by X-ray diffractometry（XRD） and field emission scanning electron microscopy （FESEM） with the energy dispersive X-ray spectroscopy（EDX）, and the optical property was investigated by the room-temperature photoluminescence （PL） spectra. XRD and FESEM results show that the wurtzite structure and rod-like ZnO is obtained. The length （3-8 μm） and the diameter （400 nm- 3 μm） vary with the experimental parameters. A strong UV emission at 384 nm and a weak visible yellow-green emission around 570 nm are observed in the PL spectrum. After annealing at 600 ℃ in air, the UV peak intensity increases obviously and the yellow-green peak intensity decreases greatly. The near-band-edge UV emission is attributed to the exciton recombination; the yellow-green emission can be associated with the defect recombination; and some defect complexes may be responsible for the latter emission.     

Hydrothermal synthesis and enhanced photocatalytic activity of hierarchical flower-like Fe-doped BiVO4

Fe-doped BiVO₄ with hierarchical flower-like structure was prepared via a hydrothermal method using sodium dodecyl benzene sulfonate (SDBS) as structure directing agent. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis were applied for characterization of the as-prepared samples. The formation mechanism of flower-like structure was proposed based on the evolution of morphology as a function of hydrothermal time. Fe-doped into substitutional sites of BiVO₄ effectively improved the migration and separation of photogenerated carrier and enhanced the utilization of visible light. Flower-like Fe-doped BiVO₄ showed much higher visible-light-driven photocatalytic efficiency for degradation of methyl blue compared with the pristine BiVO₄. And the sample with a Fe/Bi mole ratio of 2.5% showed the highest photocatalytic efficiency.     

烧结工艺对ZnO压敏陶瓷微观结构与电学性能影响

以ZnO粉末为主要原料,添加TiO2、Bi2O3、MnO2、Co2O3、Sb2O3为组元,在不同烧结温度(1100~1250℃)与保温时间(1.0~2.5h)下制备ZnO压敏陶瓷。采用SEM观察陶瓷形貌,利用压敏电阻直流参数仪测试陶瓷的电学性能,研究烧结温度与保温时间对陶瓷结构和性能的影响。结果表明,随烧结温度升高,压敏电压、漏电流逐渐降低,而非线性系数先减小后增加。制备ZnO压敏陶瓷的适宜烧结温度与保温时间分别为1250℃、1h,压敏电压为17.0V/mm、漏电流为0.014mA、非线性系数为14.2,陶瓷内部晶粒可长大至128.7μm。     

Enhanced photocatalytic activity of new photocatalyst Ag/AgCl/ZnO

A new composite photocatalyst Ag/AgCl/ZnO was fabricated by a two-step synthesis method under the hydrothermal condition. The sample was characterized by XRD, TG-DSC, SEM, TEM, DRS and XPS. The results showed that the samples were composed of Ag, AgCl and ZnO, and the particle size was in the range of 100 nm-1 μm. Methyl orange (MO) was used as a representative dye pollutant to evaluate the photocatalytic activity of Ag/AgCl/ZnO. The photocatalytic activity of Ag/AgCl/ZnO catalyst was higher than that of the pure ZnO catalyst. It was found that the Ag/AgCl/ZnO structure changed to Ag/ZnO gradually after several repeated experiments. However, the photocatalytic ability of the sample was not reduced. Finally, a possible photocatalytic mechanism was proposed.