分级多孔结构ZnO微球的制备及其光电性能

采用简单的低温化学溶液沉积方法制备了分级多孔ZnO微球。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电镜(TEM)、N2吸附脱附以及紫外-可见分光光度计(UV-Vis)等对样品进行了表征。结果显示产物为分级多孔结构的ZnO微球,由直径约10~20 nm ZnO颗粒组装而成,比表面积为40 m2.g-1。把多孔ZnO微球用作染料敏化太阳能电池(DSCs)光阳极,结果表明,该光阳极在增强对入射光的散射作用的同时,为染料分子的吸附提供了较大比表面积,从而提高了DSCs的光伏性能。     

Preparation and properties of amorphous titania-coated zinc oxide nanoparticles

Amorphous TiO₂-coated ZnO nanoparticles were prepared by the solvothermal synthesis of ZnO nanoparticles in ethanol and the followed by sol-gel coating of TiO₂ nanolayer. The analyses of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the resultant ZnO nanoparticles were hexagonal with a wurtzite structure and a mean diameter of about 60 nm. Also, after TiO₂ coating, the TEM images clearly indicated the darker ZnO nanoparticles being surrounded by the lighter amorphous TiO₂ layers. The zeta potential analysis revealed the pH dependence of zeta potentials for ZnO nanoparticles shifted completely to that for TiO₂ nanoparticles after TiO₂ coating, confirming the formation of core-shell structure and suggesting the coating of TiO₂ was achieved via the adhesion of the hydrolyzed species Ti-O⁻ to the positively charged surface of ZnO nanoparticles. Furthermore, the analyses of Fourier transform infrared (FTIR) and Raman spectra were also conducted to confirm that amorphous TiO₂ were indeed coated on the surface of ZnO nanoparticles. In addition, the analyses of ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectra revealed that the absorbance of amorphous TiO₂-coated ZnO nanoparticles at 375 nm gradually decreased with an increase in the Ti/Zn molar ratio and the time for TiO₂ coating, and the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO₂ shell.     

SiO2/ZnO复合纳米粒子的制备及表征

采用双注控制沉积法(Controlled Double-Jet Precipitation,CDJP)将反应物添加到含有SiO₂的溶液中,通过直接的表面反应来制备单分散的SiO₂/ZnO复合纳米粒子,并对其进行了表征。透射电镜(TEM)观察表明,SiO₂表面有一层ZnO纳米颗粒或薄层。对复合纳米粒子SiO₂/ZnO进行X射线衍射(XRD)分析,复合颗粒的衍射峰与单独的氧化锌的衍射峰完全一致。能量弥散X射线法(EDX)分析表明,复合颗粒中含有Zn、Si、O元素。荧光光谱表明有ZnO的吸收峰。     

Controlled placement of polystyrene-grafted CdSe nanoparticles in self-assembled block copolymers

Surface functionalization of semiconductor CdSe nanoparticles has been achieved with polystyrene (PS) brushes by “grafting from” technique for further addition to a polystyrene-b-polybutadiene-b-polystyrene (SBS) block copolymer in order to obtain self-assembled composites. For modification of nanoparticle surface 3-glycidoxypropyltrimethoxysilane (GPS) was used at first for the later attachment of the 4,4′-azobis(4-cyanopentanoic acid) azo initiator. Fourier-transform infrared spectroscopy confirmed the presence of GPS and PS on the surface of nanoparticles. Atomic force microscopy was used for morphological characterization of SBS/CdSe nanocomposites. Modification of nanoparticles with PS brushes by radical polymerization improved their affinity with PS block and the dispersion of nanoparticles avoiding agglomeration. CdSe nanoparticle size was measured to be around 2 nm by the use of X-ray diffraction and UV–Vis techniques. Optical properties were characterized using fluorescence measurements.     

Surface-Modified CdS/ZnO Material: Single-Reactor Synthesis and Mechanism of Formation in Aqueous Solution

Method of chemical precipitation from aqueous solutions was used to cover the surface of polycrystalline ZnO nanotubes with a nanostructured CdS layer. The thus synthesized CdS/ZnO composite material was studied by the methods of X-ray diffraction analysis, electron microscopy, and optical spectroscopy. The fundamental time-related aspects of the process of CdS formation on the ZnO surface were examined. It was found that the amount of deposited CdS nanoparticles is independent of the deposition duration. The morphological specific features of ZnO nanotubes are preserved upon a prolonged keeping of ZnO in solution. The photocatalytic activity of CdS/ZnO under visible and UV light was examined in the reaction of hydroquinone oxidation. A possible mechanism of how the CdS/ZnO composite is formed in an aqueous solution in the course of growth of a layer constituted by CdS nanoparticles on the surface of ZnO nanotubes is suggested on the basis of the experimental data. It is demonstrated that the chemical-precipitation method can be used to obtain surface-active composite materials that are photoactive in the visible spectral range.     

Gamma irradiation route to synthesis of highly re-dispersible natural polymer capped silver nanoparticles

Aqueous dispersions of highly stable, redispersible silver nanoparticles (Ag NPs) were synthesized using gamma radiolysis with gum acacia as a protecting agent. The formation of nanosized silver was confirmed by its characteristic surface plasmon absorption peak at around 405 nm in UV–vis spectra. The size of the silver nanoparticles can be tuned by controlling the radiation dose, ratio of gum acacia to silver ions and also the ionic strength of the medium. Dynamic light scattering (DLS) measurement of the as-synthesized nanoparticles indicated the size less than 3 nm at higher dose of radiation and this also corroborated the size measurement from the width of the corresponding X-ray diffraction (XRD) peak. The face centered cubic (fcc) crystallinity of the nanoparticles was evident from XRD and high resolution transmission electron microscopic (HRTEM) measurements. Fourier transform infra-red (FTIR) spectroscopic data indicate a bonding of Ag NPs with COO^? group of acacia through bridging bidentate linkage.     

Novel Green Route of Synthesis of ZnO Nanoparticles by Using Natural Biodegradable Polymer and Its Application as a Catalyst for Oxidation of Aldehydes

ZnO nanoparticles have been synthesized by using biodegradable natural biopolymer viz. Gum Tragacanth. This single step approach is very cost effective and reproducible. The reaction time and concentration of precursor zinc acetate play a major role in the nature and growth of ZnO nanoparticles. ZnO nanoparticles were characterized by X-ray diffraction, SEM, FTIR, EDAX, UV-visible spectroscopy and TEM. ZnO nanoparticles with 20-30 nm in diameter and hexagonal morphology were found; dispersed uniformly. Raman spectrum shows the mode E₂ high at 437 cm^?1 that is related to the vibration of wurtzite Zn-O bond in crystal structure of ZnO. The space between adjacent lattice fringes is ～ sharp 2.42 Å. UV-visible absorption spectrum shows the sharp absorption band at 308 nm assigned to the intrinsic transition from valance band to conduction band. The ZnO nanoparticles display superior catalytic activity of conversion of aldehyde to acid as compared to bulk-ZnO material, because of high surface area of ZnO nanoparticles. A trace amount of ZnO nanoparticles catalyst required for organic conversion. The ZnO nanoparticles as catalyst are highly stable, recyclable and efficient in its activity.     

Preparation of ZnO nanoparticles by a surfactant-assisted complex sol–gel method using zinc nitrate

This paper presents a surfactant-assisted complex sol–gel method for the controlled preparation of Zinc Oxide (ZnO) nanoparticles using zinc nitrate and citric acid as starting material. ZnO nanoparticles with a pure wurtzite structure were obtained after calcination at 773 K. The effects of the citric acid concentration, the pH, and the surfactants on the average particle size and morphology of the ZnO nanoparticles were investigated using X-ray diffraction and scanning electron microscopy. Well dispersed ZnO nanoparticles with a uniform size distribution were obtained using polyethylene glycol (PEG) 2000 as a surfactant. During sintering, the ZnO nanoparticles revealed isotropic growth below 1,373 K and anisotropic growth above 1,473 K. The particles’ activation energy was calculated to be 140 ± 6 kJ/mol between 773 and 1,373 K.     

梨形核壳结构氧化锌/银亚微米球的制备、表征及光学性能

利用亚锡离子还原银离子生成的金属银沉积在合成的梨形氧化锌表面作为晶种,进一步生长银纳米粒子,制备了梨形的、核壳结构的、单分散的氧化锌/银亚微米球。利用X射线衍射、透射电镜、能量色散X射线谱、紫外可见吸收谱及光致发光谱对所制备样品的形貌、微观结构、组成和光学性能进行了表征。结果表明:(1)样品是由梨形亚微米氧化锌核和银纳米颗粒壳组成;(2)在氧化锌表面的银纳米粒子作为光激发产生的电子捕获剂提高了光产生的载流子的分离效率,在能量没有改变的情况下减少了紫外发射光的强度,淬灭了可见发射光。     

Creating cellulose fibres with excellent UV protective properties using moist CF4 plasma and ZnO nanoparticles

Weakly ionised gaseous plasma created in a moist tetrafluoromethane gas at a low pressure with an electrodeless radiofrequency discharge was applied to modify the surface properties of cellulose fibres. The plasma was used to increase the adsorption of zinc oxide (ZnO) nanoparticles such that cellulose fibres with good ultraviolet (UV) protective properties could be created. The UV protection factor (UPF) values of the ZnO-functionalised fibres were determined as a function of the plasma treatment time. The chemical and physical surface properties of the plasma-treated fibres were examined using scanning electron microscopy, X-ray photoelectron spectroscopy, and wettability tests. The quantity of zinc on the fibres was determined using inductively coupled plasma mass spectroscopy. The results indicated that 30 s of plasma treatment resulted in ZnO-functionalised samples with lower UPF values than samples without plasma treatment due to the creation of fluorine-rich functional groups on cellulose fibres and the agglomeration of ZnO nanoparticles. The highest UPF values (50+) were obtained when samples were treated with plasma for 10 s. These high UPF values were a result of the increased adsorption of uniformly distributed ZnO nanoparticles caused by fibres surface functionalization and roughening upon plasma treatment. Furthermore, the mechanical properties of textiles treated with moist CF₄ plasma for 10 s were slightly improved.     

A simple CdS nanoparticles cascading approach for boosting N3 dye/ZnO nanoplates DSSCs overall performance

Enhanced photosensitization in presence of CdS nanoparticles is achieved in electrochemically deposited ZnO nanoplates and N3 loaded dye-sensitized solar cells. Chemically embedded CdS nanoparticles act as a sandwiching layer between ZnO nanoplates and dye molecules by overcoming current limiting serious Zn²⁺/dye insulating complex formation and CdS photo-corrosion issues. The X-ray diffraction and the scanning electron microscopy confirm the ZnO with vertically aligned nanoplates, perpendicular to the substrate surface. Amorphous CdS is monitored using electron dispersive X-ray analysis. The low and high resolution transmission electron microscope images confirm the presence of CdS nanoparticles over ZnO nanoplates which later is supported by an increase in optical absorbance and shift in band edge. About 400% increase in solar conversion efficiency with this cascade arrangement is achieved when compared with without CdS which could be fascinating while designing solid state solar cells in presence of suitable p-type layer.     

Ensemble modeling of very small ZnO nanoparticles

The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface.     

Germanium nanoparticles from solvated atoms: synthesis and characterization

Germanium nanoparticles were synthesized by the chemical liquid deposition method (CLD) in which the Ge atoms, produced resistively, were co-deposited with 2-propanol, acetone and tetrahydrofurane vapors to obtain colloidal dispersions. The colloidal dispersions were characterized by UV-vis spectrophotometry, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Infrared Spectroscopy (FTIR) techniques. The Germanium colloids are, in general, kinetically unstable. Strong absorption bands in the UV region suggest that nanoparticles obtained by this procedure exhibit quantum confinement. In the Ge colloids, the particle size distribution is highly sensitive to concentration change. For example, the TEM measurements revealed for the Ge-2-propanol colloid, particle sizes close to 3 nm for a concentration of 10^–3 M and 30 nm for a concentration of 10^–2 M. The HRTEM and SAED showed the high crystallinity of the nanoparticles, and it was possible to observe the typical lattice spaces of a diamond cubic Ge structure. The FTIR studies revealed the Ge-organic nature of the particles surface. Mechanisms and structures have been proposed for surface reactions.     

Preparation of Polycarbonate-ZnO Nanocomposite Films: Surface Investigation after UV Irradiation

Polycarbonate (PC)-ZnO films with different percentages of ZnO were prepared by a solution stirring technique and subjected to ultraviolet (UV; λ = 254 nm) irradiation. Structural parameters of the samples and the effects of UV irradiation on the surface properties of the PC and PC-ZnO nanocomposites were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), water contact angle (WCA) measurements, and a Vickers microhardness (H_V) tester. The XRD patterns of the nanocomposite films were found to show an increase in crystallinity with the increasing ZnO nanoparticles percentage. The WCA was found to be reduced from 90° to 17° after 15 h of UV irradiation, which could be ascribed to the oxidation of the surface of the samples during the irradiation and exposure of the ZnO nanoparticles, a result that is also supported by the obtained XPS data. The microhardness value of the PC-ZnO films including 30 wt.% ZnO enhanced considerably after UV radiation, which can also be attributed to the exposition of the ZnO nanoparticles after photodegradation of the PC superficial layer of the nanocomposite films.     

Magneto-responsive hybrid materials based on cellulose nanocrystals

We fabricated self-standing films of cellulose nanocrystals (CNC) and electrospun composite fibers with CNC and polyvinyl alcohol both with magnetic properties arising from cobalt iron oxide nanoparticles in the CNC matrix. Aqueous dispersions of cobalt-iron oxide nanoparticles (10–80 nm diameter) and CNCs (ca. 150 nm length) were used as precursor systems for the films and composite fibers. The properties of the hybrid material were determined by electron and atomic force microscopy, X-ray diffraction, thermogravimetry and magnetometry. The CNC-inorganic system was ferromagnetic, with a saturation magnetization of ca. 20 emu g^?1 of the magnetic phase. We demonstrate potential applications of the precursor dispersions, including magnetic fluid hyperthermia and highlight possible uses of the CNC-based magneto-responsive systems in biomedical and magneto-optical components.     

Zinc oxide nanostructured platform for electrochemical detection of heavy metals

ZnO nanoparticles (ZnO-NP) were prepared by a facile precipitation technique using di-isopropyl amine as precipitating agent. The morpho-structure and porosity of the as-prepared nano-powder were investigated by FT-IR analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET analysis. By drop-casting, a composite film was deposited to obtain ZnO-NP-Nafion/GCE modified electrode. The modified electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and square wave anodic stripping voltammetry (SWASV) for the detection of Pb²⁺, Cd²⁺, Cu²⁺, and Fe³⁺, and it was successfully applied for the detection of Pb²⁺ and Cu²⁺ in real water samples.     

Co doped ZnO nanowires as visible light photocatalysts

High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10⁻³ min⁻¹ in case of nanoparticles and 4.2·10⁻³ min⁻¹ in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn_0.95Co_0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.     

Synthesis and thermo-physical properties of water-based novel Ag/ZnO hybrid nanofluids

The comparative study on the thermo-physical properties of water-based ZnO nanofluids and Ag/ZnO hybrid nanofluids is reported in the present study. The outer surface of ZnO nanoparticles was modified with a thin coating of Ag nanoparticles by a wet chemical method for improved stability and heat transfer properties. The ZnO and Ag/ZnO nanofluids were prepared with varying volume concentration (??=?0.02–0.1%). The synthesized nanoparticles and nanofluids were characterized with different characterization methods viz., scanning electron microscopy, X-ray diffraction, dynamic light scattering, thermal conductivity measurement, and viscosity measurement. Results show that thermal conductivity of Ag/ZnO hybrid nanofluids is found to be significantly higher compared to ZnO nanofluids. The maximum thermal conductivity an enhancement for Ag/ZnO nanofluid (??=?0.1%) is found to 20% and 28% when it compared with ZnO nanofluid (??=?0.1%) and water, respectively.     

Preparation and characterization of poly(amide-imide)/ZnO nanocomposites containing pendent benzoxazole and benzimidazole segments

In the present investigation, novel poly(amid-imide)/zinc oxide nanocomposites (PAI/ZnO NCs) containing benzoxazole and benzimidazole pendent groups with different amounts of modified zinc oxide nanoparticles (ZnO NPs) were successfully prepared via the ex situ method. Poly(amid-imide) (PAI) was prepared by direct polycondensation of 2-[3,5- bis(N-trimellitimidoyl)phenyl]benzoxazole (DCA) with 5-(2-benzimidazole)-1,3-phenylenediamine (DAMI) and provided the polymeric matrix with well-designed groups. The surface of ZnO NPs was functionalized with 3-aminopropyltriethoxysilane (APS) coupling agent to have a better dispersion and enhancing possible interactions of NPs with functional groups of polymer matrix. The amount of APS bonded to the ZnO surface was determined by thermogravimetric analysis. PAI/ZnO nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM analysis showed that the modified ZnO nanoparticles were homogeneously dispersed in polymer matrix. In addition, TGA data indicated an enhancement of thermal stability of the nanocomposite compared with the neat polymer.     

Effect of annealing on photoluminescence of blue-emitting ZnO nanoparticles by sol–gel method

In this work, we investigated the influence of annealing on the crystallinity, microstructures, and photoluminescence (PL) properties of ZnO nanoparticles prepared by sol–gel method. The annealing was carried out both in air and vacuum. X-ray powder diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used to characterize the crystal structures, diameter, surface morphology, and PL properties of ZnO nanoparticles. It has been found that both the as-grown and annealed ZnO nanoparticles had a hexagonal wurtzite crystal structure, and their average diameter and crystallinity increased with the anneal time and temperature. Pure blue-emitting behavior was observed in all samples. The emission intensity of ZnO nanoparticles was found to be enhanced after annealing, but it was highly dependent on the annealing conditions. Optimal annealing conditions both in air and vacuum were obtained for achieving maximum emission intensity in the ZnO nanoparticles. The dependence of PL properties of the ZnO nanoparticles on the annealing conditions was discussed.