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.     

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.     

Growth and characterization of ZnO multipods on functional surfaces with different sizes and shapes of Ag particles

Three-dimensional ZnO multipods are successfully synthesized on functional substrates using the vapor transport method in a quartz tube. The functional surfaces, which include two different distributions of Ag nanoparticles and a layer of commercial Ag nanowires, are coated onto silicon substrates before the growth of ZnO nanostructures. The structures and morphologies of the ZnO/Ag heterostructures are investigated using X-ray diffraction and field emission scanning electron microscopy. The sizes and shapes of the Ag particles affect the growth rates and initial nucleations of the ZnO structures, resulting in different numbers and shapes of multipods. They also influence the orientation and growth quality of the rods. The optical properties are studied by photoluminescence, UV-vis, and Raman spectroscopy. The results indicate that the surface plasmon resonance strongly depends on the sizes and shapes of the Ag particles.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Preparation and optical properties of ZnO@PPEGMA nanoparticles

The poly(poly(ethylene glycol) methyl ether monomethacrylate) (PPEGMA) grafted zinc oxide (ZnO) nanoparticles were successfully prepared via the surface-initiated atom transfer radical polymerizations (ATRP) from the surfaces functionalized ZnO nanoparticles. The 2-bromoisobutyrate (BIB) was immobilized onto the surface of the ZnO nanoparticles through the reaction between 2-bromoisobutyryl bromide (BIBB) and the hydroxyl groups on nanoparticles, serving as the initiator to induce the ATRP of poly(ethylene glycol) monomethacrylate (PEGMA). Well-defined polymer chains were grown from the surfaces to yield hybrid nanoparticles comprised of ZnO cores and PPEGMA polymer shells having multifunctional end groups. The structure and morphology of the nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties of the nanoparticles were investigated by UV-vis absorption spectroscopy and photoluminescence spectroscopy (PL). The results showed that the dispersion and near-band edge (NBE) emission of ZnO nanoparticles could be improved by the grafted PPEGMA polymer segments.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

Synthesis and characterization of TiO2/Ag/polymer ternary nanoparticles via surface-initiated atom transfer radical polymerization

We report on the novel ternary hybrid materials consisting of semiconductor (TiO₂), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO₂-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF₃SO₃ precursor and a NaBH₄ aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO₂ nanoparticles and the in situ formation of Ag nanoparticles within the polymeric chains were confirmed using transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FT-IR spectroscopy also revealed the specific interaction of Ag nanoparticles with the CO groups of POEM brushes. This study presents a simple route for the in situ synthesis of both metal and polymer confined within the semiconductor, producing ternary hybrid inorganic-organic nanomaterials.     

Synthesis, microstructure, and photocatalysis of ZnO/CdS nano-heterostructure

ZnO/CdS nano-heterostructure with flower-like morphology is fabricated by a facile two-step precipitation method for use in photocatalytic degradation of organic dyes. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, and UV-vis spectroscopy, demonstrating that the microstructure of the ZnO/CdS nano-heterostructure is composed of flower-like ZnO modified by CdS nanoparticles. The photocatalytic performance of ZnO/CdS nano-heterostructure is evaluated by the photodegradation of rhodamine B under the simulated sunlight, and the result indicates that the ZnO/CdS nano-heterostructure exhibits an appreciable photocatalytic property, which can be attributed to the extended photo-response range and the increased charge separation rate in the heterostructure.     

Preparation and characterization of SiO2/ZrO2/Ag multicoated microspheres

A new type of multicoated silica/zirconia/silver (SiO₂/ZrO₂/Ag) core-shell composite microspheres is synthesized in this paper. In the process, ZrO₂-decorated silica (SiO₂/ZrO₂) core-shell composites were firstly fabricated by the modification of zirconia on silica microspheres through the hydrolysis of zirconium precursor. Subsequently, on SiO₂/ZrO₂ composite cores, silver nanoparticles were introduced via ultrasonic irradiation and acted as “Ag seeds” for the formation of integrate silver shell by further reduction of silver ions using formaldehyde as reducer. The resulting samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared, energy-dispersive X-ray, and UV-vis spectroscopy, indicating that zirconia and silver layers were successfully coated on the surfaces of silica microspheres.     

Formation of ZnO@Cd(OH)2 core-shell nanoparticles by sol-gel method: An approach to modify surface chemistry for stable and enhanced green emission

We report the formation of highly stable and luminescent ZnO@Cd(OH)₂ core-shell nanoparticles by simple introduction of cadmium salt in the initial precursor solution, used to synthesize ZnO nanoparticles by sol-gel route. The cadmium to zinc salt concentration ratio has been also varied to control the growth of ZnO nanoparticles at the smaller particle size. Formation of ZnO@Cd(OH)₂ core-shell nanostructure has been confirmed by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). UV-vis absorption spectroscopy exhibits blue-shift in absorption edge on increasing cadmium concentrations. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO@Cd(OH)₂ nanoparticles in comparison to bare ZnO nanoparticles. It is postulated that Cd(OH)₂ layer at the surface of ZnO nanoparticles prevents the agglomeration of nanoparticles and efficiently assists the trapping of hole at the surface site, a first step necessary for visible emission. The Fourier transform infrared spectroscopy (FTIR) also supports our assumption about surface chemistry.     

Synthesis,characterization and excellent photocatalytic activity of Ag/AgBr/MoO3 composite photocatalyst

A novel composite photocatalyst Ag/AgBr/MoO₃ was successfully synthesized via a simple precipitation method at room temperature. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectroscopy in detail. The photocatalytic activity of the samples was evaluated by monitoring the degradation of rhodamine B (RhB) solution under visible-light irradiation. The results showed that the photocatalytic activity of Ag/AgBr/MoO₃ composite significantly enhanced and the degradation ratio of RhB reached 97.7 % after 15 min only. The excellent photocatalytic activity might be closely related to the large surface area, porosity structure and efficient separation of photoinduced electron–hole pairs. The possible reaction mechanism was also discussed.     

Photocatalytic,sonocatalytic and sonophotocatalytic degradation of Rhodamine B using ZnO/CNTs composites photocatalysts

A series of ZnO nanoparticles decorated on multi-walled carbon nanotubes (ZnO/CNTs composites) was synthesized using a facile sol method. The intrinsic characteristics of as-prepared nanocomposites were studied using a variety of techniques including powder X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM), transmission electron microscope (TEM), scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), Brunauer Emmett Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS). Optical properties studied using UV–Vis diffuse reflectance spectroscopy confirmed that the absorbance of ZnO increased in the visible-light region with the incorporation of CNTs. In this study, degradation of Rhodamine B (RhB) as a dye pollutant was investigated in the presence of pristine ZnO nanoparticles and ZnO/CNTs composites using photocatalysis and sonocatalysis systems separately and simultaneously. The adsorption was found to be an essential factor in the degradation of the dye. The linear transform of the Langmuir isotherm curve was further used to determine the characteristic parameters for ZnO and ZCC-5 samples which were: maximum absorbable dye quantity and adsorption equilibrium constant. The natural sunlight and low power ultrasound were used as an irradiation source. The experimental kinetic data followed the pseudo-first order model in photocatalytic, sonocatalytic and sonophotocatalytic processes but the rate constant of sonophotocatalysis is higher than the sum of it at photocatalysis and sonocatalysis process. The sonophotocatalysis was always faster than the respective individual processes due to the more formation of reactive radicals as well as the increase of the active surface area of ZnO/CNTs photocatalyst. Chemical oxygen demand (COD) of textile wastewater was measured at regular intervals to evaluate the mineralization of wastewater.     

Microstructure and optical properties of ZnO nanoparticles prepared by a simple method

In this investigation, ZnO nanoparticles were prepared by a simple and rapid method. This method is based on the short time solid state milling and calcinations of zinc acetate and citric acid powders. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, photoluminescence and UV-vis spectroscopy. It was shown that the calcination temperature significantly affected the particle size and optical properties of the synthesized ZnO nanoparticles. Calculation based on the XRD data shows that the average sizes of ZnO particles are in agreement with those from TEM images and the size of the particles increases on increasing the calcination temperature. Also the band gap of samples decreased from 3.29 to 3.23 eV on increasing the calcination temperature from 350 to 600 °C. Photoluminescence analyses show that many defects such as interstitial zinc, zinc vacancy and oxygen vacancy are responsible for the observed optical properties.     

水热法制备In2O3/ZnO异质结及其高的光催化性能

采用简单的两步水热法合成了不同In₂O₃质量比的In₂O₃/ZnO异质结复合材料．通过X射线衍射仪(XRD)、紫外-可见分光光度计(UV-vis)和扫描电子显微镜(SEM)对复合材料的结构、形貌和性能进行了表征．同时还使用UV-vis分光光度计测试了异质结降解罗丹明B(RhB)的光催化活性．实验结果表明,与纯ZnO和In₂O₃相比,In₂O₃的引入将ZnO的吸收光谱扩展到可见光区域,从而提高了其光生电子和空穴的分离．此外,In₂O₃/ZnO异质结在可见光照射对RhB具有较高的光催化活性．5 wt%-In₂O₃/ZnO异质结对RhB的降解率为84.3%,且具有良好的光催化稳定性．In₂O₃/ZnO异质结复合材料在有机染料废水的降解中有更广阔的应用前景．     

Core/shell structured ZnO/SiO2 nanoparticles: Preparation, characterization and photocatalytic property

ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO₂ layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO₂ nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO₂ core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO₂ nanoparticles with thinner SiO₂ shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment.     

Preparation,characterization and photocatalytic performance of noble metals (Ag,Pd, Pt,Rh) deposited on sponge-like ZnO microcuboids

Novel sponge-like ZnO microcuboids with a hierarchical structure were fabricated via an alcoholic thermal process. Then a series of noble metals (Ag, Pd, Pt, Rh) was loaded onto the microcuboids. The samples obtained were characterized by nitrogen physical adsorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The results show that the ZnO microcuboids have a high surface area and a sponge-like hierarchical structure. Activity tests for the degradation of acid orange II dye showed that the noble metals enhanced the activity of ZnO to different extents. For loading of 0.5 wt.%, the activity enhancement decreased in the order Pd>Ag>Pt>Rh. Co-loading of Pd and Ag had a detrimental effect on activity compared to single loading. The enhanced photocatalytic performance can be attributed to an increase in the rate of separation of photogenerated e^–/h⁺ pairs induced by the noble metals.     

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 of nanometer Bi2WO6 synthesized by sol-gel method and its visible-light photocatalytic activity for degradation of 4BS

Nanometer Bi₂WO₆ catalyst with visible-light responsive was prepared by a sol-gel method in the presence of EDTA. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectrum, Fourier transform infrared (FTIR) spectrum, Brunauer-Emmet-Teller (BET). The UV-vis diffuse reflectance spectrum of the as-prepared sample shows a markedly blue-shift as compared to that of the sample obtained by a solid-state reaction. The as-prepared samples exhibited higher activities than that synthesized by the solid-state reaction for 4BS photodegradation under visible-light irradiation (λ>400 nm) and the sample prepared at 450 °C exhibited the highest photocatalytic activity.     

Enhanced adsorption and visible-light-induced photocatalytic activity of hydroxyapatite modified Ag-TiO2 powders

In order to get a kind of materials with enhanced adsorption and photocatalytic performance, hydroxyapatite modified Ag-TiO₂ powders (Ag-TiO₂-HAP) were prepared by a facile wet chemical strategy. The powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy, N₂ adsorption-desorption measurement (BET), photoluminescence spectroscopy (PL), etc. The photocatalytic activities were evaluated by photocatalytic oxidation decomposition of acetone in air under visible-light illumination. The results showed that the coupled system indicated a highest photocatalytic activity and photochemical stability under visible-light irradiation than all the other catalysts. The intensively improved visible-light-induced photocatalytic activity of the Ag-TiO₂-HAP hybrids could be attributed to its strong absorption in the visible-light region, low recombination rate of the electron-hole pair and large BET specific surface area.     

A novel precursor for synthesis of metallic copper nanocrystals by thermal decomposition approach

[Bis(2-hydroxy-1-naphthaldehydato)copper(II)] complex, as a novel precursor, was employed in thermal decomposition process to synthesize metallic copper nanoparticles using oleylamine (C₁₈H₃₇N) as capping agent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) spectroscopy. The synthesized copper nanoparticles have a fcc structure with average size 20-35 nm.