Controlled synthesis of ZnO nanoparticles from a Zn(II) coordination polymer: Structural characterization,optical properties and photocatalytic activity

A zinc coordination polymer derived from pyridine-2,6-dicarboxylate (PDC), {[Zn₂(PDC)₂]}_n, was successfully prepared via conventional, sonication and microwave-irradiation methods. The composition and characteristics of the obtained coordination polymers (CPs) were investigated by elemental analysis, TGA/DTA, X-ray diffraction and spectroscopic techniques. The so obtained CPs were heat-treated in the air at 600 °C for 2 h to produce ZnO of nanosized particles (NPs). It is of interest to note that the synthesis approach of the precursor greatly affects both the nanoparticle size and the structure of the resulting ZnO NPs. Moreover, the smallest particle size was associated with the sample derived from the ultrasonically prepared precursor. TEM analysis revealed that all samples have sphere-like morphologies. Structural analysis of the prepared ZnO samples was conducted and compared using Rietveld analysis of their PXRD patterns. Optical band gap calculations based on analysis of the UV–vis spectra of ZnO samples using Tauc's power law were achieved. The highest band gap of 3.63 eV was observed for ZnO sample obtained from the ultrasonically prepared precursor. Furthermore, the photocatalytic activity of ZnO NPs for the removal of Eosin Y color was monitored. The highest removal efficiency was recorded for ZnO originated from the ultrasonically synthesized precursor. Enhancement of removal efficiency that reached 98% was attained in only a period of 8 min. Its recycling test showed that it can be reused without structural changes over four cycling experiments.     

Effect of 3D ZnO:Fe morphology on the photocatalytic activity under solar irradiation

Nanoparticles, microsphere, hedgehog sphere-like and flower-like ZnO:Fe photocatalysts were prepared by the hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet/visible absorption spectra (UV?CVis). The results show that the ZnO:Fe photocatalysts with different 3D morphologies are a hexagonal wurtzite structure with space group of p63mc. The pH value of the precursor has a great influence on various morphologies of ZnO:Fe photocatalysts. The flower-like and hedgehog sphere-like ZnO:Fe photocatalysts exhibit the high solar photocatalytic behavior on methylene blue (MB). The ZnO:Fe order of photocatalytic activity is as follows: flower?>?hedgehog sphere?>?microsphere?>?nanoparticle. The flower-like ZnO:Fe is optimal, which exhibits the highest degradation rate of 98% for light time of 5?h.     

Morphology‐controlled Fabrication of SnO2/ZnO Nanocomposites with Enhanced Photocatalytic Performance

In this work, a series of novel SnO₂/ZnO nanocomposites with different morphologies were fabricated via a facile hydrothermal technique followed by calcination in air. The morphological, structural and photocatalytic properties of the SnO₂/ZnO nanocomposites were studied using different methods. The results showed that the synthesized nanocomposites possessed crystal phases of wurtzite hexagonal phase ZnO and tetragonal rutile phase SnO₂. In addition, the morphologies of SnO₂/ZnO nanocomposites strongly depended on the molar ratios of Sn and Zn. Compared with ZnO and SnO₂, the SnO₂/ZnO nanocomposites exhibited considerably higher degradation efficiency for the photodegradation of methylene blue and quinolone antibiotics under mercury lamp irradiation. The SZ‐2 nanospheres exhibited the highest degradation efficiency of 95.81%, which was about 2.63 times higher than that of ZnO nanoparticles. Moreover, the trapping experiments confirmed that ˙OH played the dominant role in MB degradation. Finally, the charge carriers potential transfer pathway and photocatalytic degradation mechanism were put forward. This study provides an economical way to prepare hybrid nanocomposites with controlled morphology for practical applications in the photocatalytic degradation of organic dyes and residual antibiotics.     

Synthesis and characterization of polycrystalline ZnO/HZSM-5 nanocomposites

Polycrystalline ZnO/HZSM-5 nanocomposites were synthesized by the impregnation method using a home prepared HZSM-5 zeolite as porous support and Zn(C₅H₇O₂)₂ or Zn(NO₃)₂ as zinc precursors. As-prepared samples were characterized by ICP, XRD, SEM (EDS), TEM (SAED), BET and DRS techniques. A small amount of sub-nanometeric ZnO clusters were introduced into the channels of HZSM-5 zeolite. These ZnO clusters exhibited absorption band onset at about 280 nm, different from ZnO particles at about 370 nm. The significant blue shift possesses high quantum size effect in sub-nanometeric ZnO clusters. SAED and TEM images revealed that the ZnO nanoparticles, supported on the surface of HZSM-5 zeolite, were identified as polycrystalline structure with the particle size of about 20-25 nm. XRD results provided evidence of the strong host-guest interactions between HZSM-5 framework and ZnO structure. The samples prepared by Zn(C₅H₇O₂)₂ were more porous and smaller than those prepared from the Zn(NO₃)₂. This was confirmed by SEM and XRD results.     

Morphology dependent UV photoresponse of Sn-doped ZnO microstructures

In this work, the UV sensing properties of Sn-doped and/or alloyed zinc oxide (ZnO) microstructures with different morphologies were investigated in order to elaborate the high performance UV photodetectors. We have compared two types of morphologies, i.e. Sn-doped ZnO films (ZnO:Sn) and ZnO microtetrapod (T) networks alloyed- and doped-with Sn (ZnO-T:Sn). The UV response (I_UV/I_dark) of ZnO:Sn is about 10³ and 10² for 0.1 and 0.4 at% Sn, respectively. The three-dimensional highly porous ZnO-T:Sn networks demonstrated higher UV response (by two orders of magnitude) and much faster recovery for detection of UV light, which were attributed to the domination of fast processes such as modulation of potential barriers formed at the interface of the tetrapod arms, which are less dependent on adsorbed species. Thus, the UV response for devices with a distance between the pads (interelectrode distance) of about 60, 400, 800 and 1500 μm is 1.7 × 10⁵, 2.4 × 10⁴, 6.7 × 10³ and 925, respectively. All samples demonstrated a sharp increase in photocurrent under illumination with UV light, as well as a fast recovery to the initial electrical baseline. Also, the influence of relative humidity on the rapidity of photodetectors based on ZnO:Sn films and ZnO-T:Sn networks was investigated, confirming a low impact on the rapidity of ZnO-T:Sn networks, with good repeatability and stable electrical baseline, which is very important for effective applications.     

Growth of well-defined ZnO microparticles with additives from aqueous solution

By heating Zn(OH)₂ precursor in aqueous solution to reflux temperature (101 °C), ZnO microparticles with a diversity of well-defined morphologies, including rod-like, nut-like, and rice-like samples, have been successfully synthesized. The shape of the crystallite depends critically on the additive added in the reaction solution. To further understand the effect of the additive on the formation process of ZnO crystallite, scanning electron microscopy analyses of the solid product and concentration measurements of zinc ion remaining in the solution have been made at regular intervals throughout the reaction with and without the addition of sodium dodecyl sulfate (SDS) and triethanolamine (TEA). Results show that SDS and TEA added in the solution remarkably lower the formation rate of ZnO crystallite.     

SbxZn1-xO1+x/2及其壳聚糖复配物的制备和抗菌性能

采用溶胶-凝胶法制备了SbxZn1-xO1+x/2及其壳聚糖的复配物,通过X-射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等表征了样品的物相结构、组成和微观形貌。以大肠杆菌、白色念珠菌和金黄色葡萄球菌为测试菌种,研究了样品的抗菌性能。结果表明,SbxZn1-xO1+x/2的抗菌活性优于纯ZnO,其中x=0.05的样品活性最好;复配物的抗菌活性明显优于单一组分,当Sb0.05Zn0.95O1.025和壳聚糖质量比mSZ/mCS=2时,样品抗菌性能最佳。     

Microwave-assisted and conventional sol-gel preparation of photocatalytically active ZnO/TiO2/glass multilayers

For the first time a combination of microwaves and/or the conventional treatment method was used to dry and heat multilayered sol-gel ZnO/TiO₂/glass structures. Compact or porous TiO₂ films were deposited as a bottom layer, covered with a ZnO film. The structures were characterized by X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscopy (SEM). Only peaks of wurtzite ZnO crystalline phase were registered on the X-Ray diffractograms. The microwave irradiation leads to a formation of poorly crystallized multilayers with very small crystallites and enhanced surface roughness. This results in a better photocatalytic activity of these structures than the structures of the samples treated conventionally. It was established that the morphology of the bottom titania layer affects the reaction of photocatalytic degradation of Malachite Green dye (MG). The structures with the compact bottom TiO₂ films showed higher activities than those on porous TiO₂ films. This study offers an energy saving method of producing ZnO/TiO₂/glass multilayered structures of various morphologies and pronounced photocatalytic properties. The method does not involve any calcination step, normally applied to achieve a good degree of crystallization. This makes the method suitable for protecting substrates of low thermal stability.      

室温一步固相反应合成纳米氧化锌的表征、光催化性能及动力学

以七水硫酸锌、氢氧化钠为原料,采用室温一步固相反应合成ZnO纳米粒子,并分别利用X射线衍射分析（XRD）、傅里叶变换红外光谱分析（FTIR）、热重分析（TG）、扫描电子显微分析（SEM）、透射电子显微分析（TEM）、N₂吸附-脱附、紫外可见漫反射光谱分析（UV-Vis DRS）等方法对ZnO纳米粒子进行表征。实验结果表明：不需任何添加剂,室温下可通过一步固相反应合成ZnO纳米粒子,其形成过程首先是ZnSO₄·7H₂O和NaOH充分接触,然后反应形成Zn₄SO₄（OH）₆·5H₂O,最后NaOH的溶解热可使Zn₄SO₄（OH）₆·5H₂O转变为ZnO并逐渐长大形成纳米粒子。同时以甲基橙为降解对象评价了ZnO纳米粒子的光催化活性,实验结果表明：紫外光照射下,该方法合成的ZnO纳米粒子对甲基橙具有较好的光催化活性,且光催化动力学方程符合准一级反应动力学。     

Parameters controlling the photocatalytic performance of ZnO/Hombikat TiO2 composites

Commercial TiO₂ (Hombikat, UV-100) was impregnated with different loadings of zinc nitrate solution and subsequently calcined at different temperatures in order to obtain a stable homogeneous solid composite of ZnO/TiO₂. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), UV-vis and Raman spectroscopy, inductively coupled plasma mass spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS) as well as N₂ adsorption and desorption measurements. Results show that ZnO was incorporated within the TiO₂ crystals and did not form a separate bulky phase or metallic zinc. Moreover, the calcination temperature dramatically modifies the texture properties of the prepared samples compared with original Hombikat TiO₂. The photocatalytic performance of the prepared samples was evaluated by monitoring the degradation of methyl orange dye under black light illumination. Three main parameters were studied; ZnO loading, surface area and initial pH of the methyl orange solution. The variation in ZnO loading appears to have less influence on the catalytic activity than either the surface area or the pH.     

微波诱导燃烧法合成类花状ZnO纳米材料及其晶体结构、荧光性质研究

以硝酸锌[Zn(NO3)2.6H2O]和尿素[CO(NH2)2]作前驱体,通过微波诱导燃烧技术可控合成具有不同形貌的ZnO纳米晶体,并用热重分析和差热分析进行了研究。对各种生长条件:微波功率,辐射时间和尿素/Zn2+物质的量的比对ZnO纳米晶体形貌的影响作了分析。结果表明:尿素/Zn2+物质的量的比对ZnO纳米材料的形貌具有显著影响。X衍射图表明合成的ZnO纳米结构呈六角形。傅里叶变换红外光谱图中400~500 cm-1处明显的峰为Zn-O的振动峰。ZnO纳米结构的发光光谱在366 nm的带边发射,因缺陷又由许多可见光发射峰组成。用扫描电子显微镜、透射电子显微镜、选区电子衍射研究了花状ZnO纳米结构的增长机理。本方法仅需几分钟就获得的了ZnO纳米结构。     

Synthesis and Characterization of β‐Co(OH)2, CuO and ZnO Nanostructures by Solvothermal Method without Any Additive

β‐Co(OH)₂, CuO and ZnO nanostructures with plate‐like, particle‐like and flower‐like morphologies were prepared through the use of simple solvothermal method using of melt salt and 1,10‐phenanthroline as complexing agent and sodium hydroxide. β‐Co(OH)₂ consisted of a plate‐like structure, and the nanoplates size was about 29 nm. The structure was comprised of regular sheets which were assembled together. Furthermore, the as‐obtained β‐Co(OH)₂ nanoplates can be easily converted into Co₃O₄ nanoplates by calcining in air at 500 °C for 2 h. The results indicate that ZnO powder is of hexagonal wurtzite structure and well crystallized with high purity. CuO powder is pure monoclinic‐structured crystalline. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT‐IR) spectra. Possible formation mechanism of the nanostructures is proposed.     

ZnO/BiVO4-V2O5异质结构光生电荷性质及可见光下表面光电流行为

利用水热法合成了花状和球状ZnO微纳材料,并与硝酸铋和偏钒酸铵溶液体系反应构筑了ZnO/BiVO4-V2O5复合体系.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)及X射线衍射(XRD)对材料进行了系统的表征.利用表面光伏(SPV)、表面光电流(SPC)和瞬态光伏(TPV)技术研究了ZnO/BiVO4-V2O5表面光生电荷的产生和传输机制.结果显示该复合材料在可见区产生了良好的光电响应,获得了较高的光生载流子的分离效率,光生电荷的寿命也同时增加.在单色弱可见光(波长500 nm)照射下,复合材料产生良好重复性的表面光电流响应.     

A Synergy of ZnO and ZnWO4 in Composite Nanostructures Deduced from Optical Properties and Photocatalysis

ZnO/ZnWO₄ composite rod-like nanoparticles were synthesized by low-temperature soft solution method at 95 °C with different reaction times (1–120 h), in the presence of non-ionic copolymer surfactant Pluronic F68. Obtained nanoparticles had diameters in the range around 10 nm and length of 30 nm. Optical properties such as reflection and room temperature photoluminescence of obtained samples showed strong dependence on their crystallinity and composition. Photocatalytic activity of ZnO/ZnWO₄ nanopowders was checked using photodegradation of selected dyes as model system. Obtained results were correlated with specific surface area, particle sizes, crystallinity and ZnO/ZnWO₄ ratio of the samples. As crystallinity of ZnWO₄ component in the ZnO/ZnWO₄ increase, photocatalytic activity also increases. The main findings can be explained by charge transfer reactions that follow light absorption by ZnO and ZnWO₄ in nanocomposite.     

Zn<Subscript>0.97</Subscript>M<Subscript>0.03</Subscript>O (M = Co,Fe, and V) pigments: thermal,structural, and optical characterization

Zinc oxide is a widely used white inorganic pigment. Transition metal ions are used as chromophores and originate the ceramic pigments group. In this context, ZnO particles doped with Co, Fe, and V were synthesized by the polymeric precursors method, Pechini method. Differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques were used to accurately characterize the distinct thermal events occurring during synthesis. The TG and DSC results revealed a series of decomposition temperatures due to different exothermal events, which were identified as H₂O elimination, organic compounds degradation and phase formation. The samples were structurally characterized by X-Ray diffractometry revealing the formation of single phase, corresponding to the crystalline matrix of ZnO. The samples were optically characterized by diffuse reflectance measurements and colorimetric coordinates L*, a*, b* were calculated for the pigment powders. The pigment powders presented a variety of colors ranging from white (ZnO), green (Zn_0.97Co_0.03O), yellow (Zn_0.97Fe_0.03O), and beige (Zn_0.97V_0.03O).     

Shape-controlled fabrication of porous ZnO architectures and their photocatalytic properties

In this paper, we report a simple two-step approach to prepare porous octahedron- and rod-shaped ZnO architectures. The morphology of porous ZnO particles can be conveniently tuned by controlling morphologies of the ZnC₂O₄·2H₂O precursor. SEM and TEM characterization results indicate that these porous ZnO architectures are built up by numerous ZnO primary nanoparticles with random attachment. Based on thermogravimetry analysis, we believe that the release of water vapor, CO and CO₂ leads to the formation of high-density pores in shape-controlled particles during the calcination process. Further experimental results indicate that as-prepared porous ZnO particles exhibit good photocatalytic activity due to large surface area.     

Synthesis of ZnO crystals with unique morphologies by a low-temperature solvothermal process and their photocatalytic deNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> properties

A series of unique morphologies of ZnO were synthesized by a simple mild solvothermal process using equimolar of Zn(NO₃)₂/Zn(AC)₂–hexamethylenetetramine (HMT) acting as precursors and ethylene glycol (EG) and triethylamine (TEA) as the dispersant and surfactant additive, respectively. When the as-prepared particles were further treated in 0.02 M HMT solution for such a long time as 72 h, screw-like and rose-like crystals with three-dimensional and developed structure could be formed. The deNO _x photocatalytic activity was characterized and the analysis results showed that the modified ZnO crystals possessed a three-dimensionally developed structure and had higher deNO _x photocatalytic activity compared to that of the as-prepared untreated ZnO.     

A study on electrodeposited of ZnO/ZnS heterostructures

ZnO/ZnS heterostructures were synthesized by a two steps electrochemical deposition method. Firstly, ZnS layer was deposited from an aqueous solution containing Na₂S₂O₃ and ZnSO₄ onto indium-doped tin oxide (ITO) coating glass substrate at two deposition potentials. Then, ZnO nanostructures were deposited from an aqueous solution of Zn(NO₃) onto ZnS surface. The as-obtained samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman and UV-visible analysis. The results indicate that the electrodeposition of ZnS layer at ?0.9 V give the best proprieties of ZnO/ZnS heterostructures. Homogeneous and uniform surface of ZnO/ZnS heterostructure was confirmed by AFM images. The XRD patterns indicates a high crystallinity of ZnO/ZnS. A high transmittance of 65% was also noted from UV-Visible spectra and band gap energy as large as 3.6?eV was found.     

微波水热两步法合成高可见光响应Ag2S/ZnO及其光催化性能、机理

在不同的制备条件下,通过微波水热两步法获得了一系列Ag₂S/ZnO光催化剂,采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、扫描电子显微镜(SEM)和N₂吸附-脱附等测试手段对产物结构和形貌进行了表征。结果表明,产物以六方纤锌矿ZnO为主,其晶型结构并未随着反应温度和Ag₂S物质的量的增加而改变。Ag₂S的引入显著增强了光催化剂在可见光区的吸收,使吸收边带发生红移,同时抑制了ZnO(001)晶面的生长。另外,所得产物的形貌随着Ag₂S物质的量的增加从爆米花状转变为少量的柱体颗粒,且BET比表面积经过复合后明显减小。以罗丹明B为目标降解物,研究并比较了一系列Ag₂S/ZnO光催化剂对罗丹明B的光降解性能。结果表明,n_Ag2S/n_ZnO=1:10时,光催化剂在紫外光、可见光和模拟日光的照射下具有最好的光催化效果,优于目前应用最广泛的市售P25。另外,所制备的光催化材料Ag₂S/ZnO经4次循环使用后,其降解效率没有明显下降,表明该催化材料具有一定的光催化稳定性。经捕获实验研究发现,在Ag₂S/ZnO的光催化反应中空穴起主要作用,并根据绝对电负性估算了复合材料Ag₂S/ZnO的能带位置,据此提出了可能的光催化反应机理。     

微波水热两步法合成高可见光响应Ag2S/ZnO及其光催化性能、机理

在不同的制备条件下,通过微波水热两步法获得了一系列Ag₂S/ZnO光催化剂,采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、扫描电子显微镜(SEM)和N₂吸附-脱附等测试手段对产物结构和形貌进行了表征。结果表明,产物以六方纤锌矿ZnO为主,其晶型结构并未随着反应温度和Ag₂S物质的量的增加而改变。Ag₂S的引入显著增强了光催化剂在可见光区的吸收,使吸收边带发生红移,同时抑制了ZnO(001)晶面的生长。另外,所得产物的形貌随着Ag₂S物质的量的增加从爆米花状转变为少量的柱体颗粒,且BET比表面积经过复合后明显减小。以罗丹明B为目标降解物,研究并比较了一系列Ag₂S/ZnO光催化剂对罗丹明B的光降解性能。结果表明,n_Ag2S/n_ZnO为1:10时,光催化剂在紫外光、可见光和模拟日光的照射下具有最好的光催化效果,优于目前应用最广泛的市售P25。另外,所制备的光催化材料Ag₂S/ZnO经4次循环使用后,其降解效率没有明显下降,表明该催化材料具有一定的光催化稳定性。经捕获实验研究发现,在Ag₂S/ZnO的光催化反应中空穴起主要作用,并根据绝对电负性估算了复合材料Ag₂S/ZnO的能带位置,据此提出了可能的光催化反应机理。