A facile method to prepare monodispersed ZnO–Ag core-shell microspheres

Monodispersed and core-shell structured ZnO–Ag microspheres were realized by coating the Ag nanoparticles onto the surface of ZnO microspheres via a novel solution method. The obtained materials were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–Vis) absorption measurement. It was shown that face-center-cubic Ag nanoparticles with the mean size of 20 nm were successfully grown on the surface of ZnO microspheres. The absorption band of ZnO–Ag core-shell microspheres showed a large redshift comparing to pure Ag nanoparticles, indicating the strong interfacial interaction between ZnO and Ag. The effects of Ag coating thickness on the structure, morphology and optical absorption of ZnO–Ag core-shell microspheres were investigated. The discussion on the growth process of ZnO–Ag core-shell microspheres revealed the important role of Sn²⁺. This approach was simple, mild and readily scaled up, affording a simple method for the synthesis of size-tunable inorganic-metal core-shell nanostructures.     

Synthesis and characterization of ZnO-Ag core-shell nanocomposites with uniform thin silver layers

This paper presents an investigation on the synthesis and characterization of ZnO-Ag core-shell nanocomposites. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of reduced Ag by formaldehyde formed the ZnO-Ag core-shell nanocomposites. The ZnO-Ag nanocomposites were annealed at different temperature to improve the crystallinity and binding strength of Ag nanoparticles. The morphology, microstructure and optical properties of the ZnO-Ag core-shell nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet-visible (UV-vis) absorption and photoluminescence measurement. It was demonstrated that very small face-center-cubic Ag nanoparticles were coated on the surface of ZnO nanorods. The ultraviolet absorption and surface plasmon absorption band of ZnO-Ag core-shell nanocomposites exhibited some redshifts relative to pure ZnO nanorods and monometallic Ag nanoparticles. The coating of Ag nanocrystals onto the ZnO nanorods completely quenched the photoluminescence. These observations reflected the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. The effect of Ag coating thickness on the morphology and optical properties of ZnO-Ag core-shell nanocomposites was also investigated. Moreover, the growth mechanism of ZnO-Ag core-shell nanocomposites was also proposed and discussed in detail.     

Preparation, optical properties, magnetic properties and thermal stability of core-shell structure cobalt/zinc oxide nanocomposites

Cobalt nanoparticles coated with zinc oxide can form composite spheres with core-shell structure. This coating process was based on the use of silane coupling with agent 3-mercaptopropyltrimethoxysilane (HS-(CH₂)₃Si(OCH₃)₃, MPTS) as a primer to render the cobalt surface vitreophilic, thus it renders cobalt surface compatible with ZnO. X-ray photoelectron spectroscopy (XPS) was used to gain insight into the way in which the MPTS is bound to the surface of the cobalt nanoparticles. The morphological structure, chemical composition, optical properties and magnetic properties of the product were investigated by using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) spectroscope and vibrating sample magnetometer (VSM). It was found that the Co/ZnO core-shell structure nanocomposites exhibited both of favorable magnetism and photoluminescence properties. Results of the thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicated that the thermal stability of cobalt/zinc oxide was better than that of pure cobalt nanoparticles.     

Formation of CdO films from chemically deposited Cd(OH)2 films as a precursor

Formation of cadmium hydroxide at room temperature onto glass substrates from an aqueous alkaline cadmium nitrate solution using a simple soft chemical method and its conversion to cadmium oxide (CdO) by thermal annealing treatment has been studied in this paper. The as-deposited film was given thermal annealing treatment in oxygen atmosphere at 450 °C for 2 h for conversion into cadmium oxide. The structural, surface morphological and optical studies were performed for as-deposited and the annealed films. The structural analyses revealed that as-deposited films consists of mixture of Cd(OH)₂ and CdO, while annealed films exhibited crystalline CdO. From surface morphological studies, conversion of clusters to grains after annealing was observed. The band gap energy was changed from 3.21 to 2.58 eV after annealing treatment. The determination of elementals on surface composition of the core-shell nanoparticles of annealed films was carried out using X-ray photoelectron spectroscopy (XPS).     

Properties of carbon and iron modified TiO2 photocatalyst synthesized at low temperature and photodegradation of acid orange 7 under visible light

The nanoparticles of TiO₂ modified with carbon and iron were synthesized by sol-gel followed solvothermal method at low temperature. Its chemical composition and optical absorption were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence emission spectroscopy (PL), UV-vis absorption spectroscopy, and electron paramagnetic resonance (EPR). It was found that carbon and iron modification causes the absorption edge of TiO₂ to shift the visible light region. Fe(III) cation could be doped into the matrix of TiO₂, by which could hinder the recombination rate of excited electrons/holes. Superior photocatalytic activity of TiO₂ modified with carbon and iron was observed for the decomposition of acid orange 7 (AO7) under visible light irradiation. The synergistic effects of carbon and iron in modified TiO₂ nanoparticles were responsible for improving visible light photocatalytic activity.     

Size-dependent visible photoluminescence from ZnO nanoparticles prepared via SiO2 network

This study reports a simple method for the synthesis of different size of wurtzite ZnO nanoparticles in assistance of tetraethyl orthosilicate (TEOS). With the increase of the amount of TEOS added, the average size of ZnO nanoparticles was found decreased from ∼14.6 to ∼1.9 nm by characterization of X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The growth of ZnO nanoparticles is proposed to be controlled by the density of the SiO₂ chain mesh which is determined by TEOS amount in precursor. Ultraviolet–visible (UV–VIS) absorption and photoluminescence (PL) spectra show both shift to higher energy in cut-off edge and in visible emission bands respectively. The electron transition process in the mechanism of the visible emission shift was described and related to quantum size effect in ZnO nanoparticles.     

Modification of the structural and optical properties of tin oxide nanoparticles by Co doping and thermal annealing

Enhancement of the UV photoluminescence emission of sol–gel synthesized tin oxide nanoparticles is achieved by a combination of thermal annealing and Co doping. The UV as well as the defect-related visible photoluminescence are correlated to the structural characteristics and surface Sn(OH)₂ content. The nanoparticle structure, size, crystallinity, and Sn(OH)₂ content are monitored by a combination of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. In the undoped powders, a suitable annealing leads to a significant UV luminescence at around 365 nm. After doping with Co and annealing, the UV emission is further enhanced. The improvement in the UV emission intensity following annealing and Co doping of SnO₂ is demonstrated to be due to a reduction in the hydroxyl content. The defect-related broad visible photoluminescence (～400–650 nm) can be deconvoluted into three bands at around 440 nm (blue), 510 nm (green), and 600 nm (orange). The green emission is related to Sn(OH)₂ determined by Raman spectroscopy. The blue and orange emissions are attributed to oxygen vacancies.     

Tailoring Cu2−xTe quantum-dot-decorated ZnO nanoparticles for potential solar cell applications

Cu_2−xTe QDs on ZnO nanoparticles were synthesized using a successive ionic layer absorption and reaction technique (SILAR) at room temperature. The as-synthesized QDs which were distributively deposited on ZnO nanoparticles surface were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction and high-resolution transmittance microscope (HR-TEM). It revealed that the average diameter of the QDs was ∼2 nm. The synthesized Cu_2−xTe QDs were solely orthorhombic Cu_1.44Te phase. The growth mechanism was supposed that it based on ions deposition. The energy gap of as-synthesized Cu_2−xTe QDs was determined ∼1.1 eV and the smallest energy gap of 0.76 eV was obtained, equal to that of bulk material. Raman spectroscopy and FTIR were also used to study the Cu_2−xTe QDs on ZnO nanoparticles. These characteristics suggest a promising implication for a potential broadband sensitizer of QDSCs.     

Zno纳米粒子在PS中空微反应器中的合成与光学性能

通过种子乳液聚合合成核壳结构的聚甲基丙烯酸甲酯/聚苯乙烯(PMMA/PS)复合微球,通过酸碱溶胀法进一步制备出次微米级的PS中空微球. 将此中空微球作为微反应器,使在ZnO纳米粒子前驱体溶液中溶胀, 最终ZnO纳米粒子在PS中空微球中原位生成. 实验表明, 组成ZnO纳米粒子前驱体溶液的两种组 分(CH₃COO)₂Zn和LiOH的滴加顺序不同对最终生成的ZnO纳米粒子的尺寸和负载效率有很大的影响,但并不改变ZnO纳米粒子的晶型. 复合物的光致发光和UV-Vis吸     

X-ray and electron spectroscopy investigation of the core-shell nanowires of ZnO:Mn

ZnO/ZnO:Mn core-shell nanowires were studied by means of X-ray absorption spectroscopy of the Mn K- and L_2,3-edges and electron energy loss spectroscopy of the O K-edge. The combination of conventional X-ray and nanofocused electron spectroscopies together with advanced theoretical analysis turned out to be fruitful for the clear identification of the Mn phase in the volume of the core-shell structures. Theoretical simulations of spectra, performed using the full-potential linear augmented plane wave approach, confirm that the shell of the nanowires, grown by the pulsed laser deposition method, is a real dilute magnetic semiconductor with Mn²⁺ atoms at the Zn sites, while the core is pure ZnO.     

Surface modification of ZnO nanocrystals

Nano-crystalline ZnO particles were synthesized using alcoholic solutions of zinc acetate dihydrate through a colloidal process. Five types of capping agents: 3-aminopropyl trimethoxysilane (Am), tetraethyl orthosilicate (TEOS), mercaptosuccinic acid (Ms), 3-mercaptopropyl trimethoxysilane (Mp) and polyvinylpyrrolidone (Pv) were added at the first ZnO precipitation time (first PPT) to limit the particle growth. The first three capping agents effectively capped the ZnO nanoparticles and limited the growth of the particles, while the last two capping agents caused agglomeration or larger clusters in the solutions. Particles synthesized were in the size range of 10-30 nm after capping, and grew to 60 and 100 nm in 3 and 6 weeks, respectively, during storage at ambient conditions. Refluxing time was found to only affect the first PPT time. Washing by ethanol and slow drying were very important in converting Zn(OH)₂ into ZnO. XRD analyses revealed single phase ZnO Wurtzite crystal structure. Photoluminescence (PL) spectra showed high-intensity in UV emission and very low intensity in the visible emission, which indicates a good surface morphology of the ZnO nanoparticles with little surface defects. Optical absorption spectra showed a blue shift by the capped ZnO due to the quantum confinement effect by the single crystal size of 5-6 nm as analysed by TEM. Capping effectiveness of each agent is discussed through possible capping mechanism and chemical reaction of each capping agent. This synthesis process is a low cost, high purity, easy to control method using only bio-compatible materials.     

Luminescence studies and formation mechanism of symmetrically dispersed ZnO quantum dots embedded in SiO2 matrix

Surface effects significantly influence the functionality of semiconductor nanocrystals. In the current work we present synthesis of ZnO quantum dots (QD) vis-a-vis symmetrically dispersed ZnO quantum dots embedded in SiO₂ matrix and discussed their optical properties to understand the role of the surface effects. These nanomaterials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared (FTIR), absorption (UV-visible) and photoluminescence (PL) spectroscopy. TEM studies confirm the formation of ZnO nanophosphors inside the SiO₂ matrix in highly symmetrical manner. These symmetrically dispersed ZnO@SiO₂ nanophosphors exhibited enhanced stable emission over uncoated sample and would permit the conjugation of the nanocrystals to biological entities after functionalization. Furthermore, the mechanism behind the formation of symmetrically dispersed ZnO quantum dots embedded in SiO₂ matrix was discussed in detail.     

Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO₂ nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10 wt%) were prepared by a sol–gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1 eV. Photocatalytic results indicated that TiO₂ had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO₂ nanoparticles. Among the samples, Fe-1 wt% doped TiO₂ nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.     

Preparation, characterization and infrared emissivity study of helical polyurethane@SiO2 core-shell composite

Helical polyurethane@SiO₂ (HPU@SiO₂) core-shell composite was prepared after surface modification of SiO₂ nanoparticles. HPU@SiO₂ was characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified SiO₂. HPU@SiO₂ composite exhibits clearly core-shell structure. The ultraviolet absorption and crystallizability of HPU@SiO₂ are changed due to the shell of helical polyurethane, which possesses regular single-handed conformation and inter-chain hydrogen bonds. The infrared emissivity of HPU@SiO₂ was also investigated. The result indicates that the interfacial interactions between organic shell and inorganic core induce the infrared emissivity value being reduced from 0.781 for SiO₂ to 0.503 for HPU@SiO₂.     

A new photoluminescence emission peak of ZnO-SiO2 nanocomposites and its energy transfer to Eu ions

This work reports a new photoluminescence (PL) emission peak at about 402 nm from amorphous ZnO nanoparticles in a silica matrix, and the energy transfer from it to Eu³⁺ ions. The amorphous ZnO-SiO₂ nanocomposites were prepared by the sol-gel method, which is verified by X-ray diffraction (XRD) profiles and FT-IR spectra. The luminescence emission spectra are fitted by four Gauss profiles, two of which at longer wavelength are due to the defects of the material and the others to amorphous ZnO nanoparticles and the Zn-O-Si interface state. With the reduction of Zn/Si ratio and diethanolamine, the relative intensities of visible emission decrease. The weak visible emission is due to the reduction of defects after calcined at high temperature. The new energy state at the Zn-O-Si interface results in strong emission at about 402 nm. When Eu³⁺ ions are co-doped, weak energy transfer from ZnO-SiO₂ nanocomposites to Eu³⁺ emission are observed in the excitation spectra.     

The structure and magnetic properties of Cu-doped ZnO prepared by sol-gel method

The Cu-doped ZnO and pure ZnO powders were synthesized by sol-gel method. The structural properties of the samples were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. All the results confirmed that copper ions were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO nanoparticles. The Zn_0.97Cu_0.03O nanoparticles exhibited ferromagnetism at room temperature, as established by the vibrating sample magnetometer analysis.     

Synthesis and Characterization of Ag@TiO2 Core-shell Nanoparticles and TiO2 Nanobubbles

Ag@TiO₂ core-shell structured particles of nano-size dimensions have been successfully prepared via a one-step way, which has proved quite effective in procuring stable colloids. Transmission electron microscopy (TEM) was employed to characterize the core size and the shell thickness, which typically were 20~40 nm and ~2 nm, respectively. X-ray diffraction (XRD) indicated the existence of silver. Optical absorption dependence on core size and synthetic temperature has been explored by UV–Vis absorption spectroscopy. Finally, the interesting titanium dioxide nanobubbles with silver core leached out by a unique means, were studied, which consequently proved the core-shell structure of the prepared nanoparticles, confirming the TEM observation.     

Ex situ synthesis and optical properties of ZnO-PbS nanocomposites

Zinc oxide (ZnO) and lead sulphide (PbS) nanoparticles separately synthesized by a precipitation method were combined by an ex situ route to prepare ZnO-PbS nanocomposites with different molar ratios of ZnO and PbS. The structure and morphology of the ZnO, PbS and ZnO-PbS samples were analyzed with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A UV-vis spectrophotometer was used to collect the absorption and 325 nm He-Cd and 488 nm Ar lasers were used to collect the photoluminescence data from the samples. ZnO nanoparticles showed a broad and stable emission peak at ∼570 nm, while a strongly quantum confined emission from PbS nanoparticles was detected at ∼1344-1486 nm. The ZnO-PbS nanocomposites exhibited dual emission in the visible and near-infrared (NIR) regions that is associated with defects and recombination of excitonic centres in the ZnO and PbS nanoparticles, respectively. The PL intensity of the visible emission from the ZnO-PbS nanocomposite was shown to increase when the ZnO to PbS molar ratio was 5:1 and the emission was almost quenched at molar ratios of 1:1 and 1:5. For different molar ratios of ZnO to PbS, the PL intensity of the NIR emission from the ZnO-PbS nanocomposites was more intense than that of PbS nanoparticles.     

Observation of band gap and surface defects of ZnO nanoparticles synthesized via hydrothermal route at different reaction temperature

The effects of reaction temperature on the average particle size, surface defects and band gap of ZnO nanoparticles have been systematically investigated. The hydrothermal method was employed to synthesize ZnO nanostructures. The nanostructures of the resultant ZnO were studied by means of X-ray diffraction, Transmission Electron Microscopy, Ultraviolet-visible absorption, Raman, Fourier transform Infra-red and Photoluminescence spectroscopy. With increase in the reaction temperature, the peak position of the ultraviolet emission shifts slightly towards the red wavelength and the crystal quality was improved. The prepared ZnO nanoparticles have residual intermediate compound on the surface in the form of an acetate group, which acts as defect centers for the emission of yellow emission. Spectra analyses show that the visible emission depends strongly on the preparation conditions.     

Influence of high-pressure hydrogen treatment on structural and electrical properties of ZnO thin films

ZnO thin films were treated by high-pressure hydrogen (H₂). Scanning electron microscope (SEM) images show that the surface morphology of ZnO films has been changed significantly by H₂ treatment. X-ray diffraction patterns show that the Zn(OH)₂ phases formed after H₂ treatment. The X-ray photoelectron spectroscopy results indicate that H atoms were doped into the surface of ZnO by forming H-O-Zn bond. The phenomenon shows that it is easy to form O-H bond in ZnO rather than H interstitial atom under high-pressure hydrogen circumstance.