Rapid synthesis, characterization and optical properties of TiO2 coated ZnO nanocomposite particles by a novel microwave irradiation method

A novel and rapid microwave method was used to prepare TiO₂ coated ZnO nanocomposite particles. The resulted particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Results show that ZnO nanoparticles were coated with 6-10 nm amorphous TiO₂ layers. In addition, zeta potential analysis demonstrated the presence of TiO₂ layer on the surface of ZnO nanoparticles. Photoluminescence (PL) spectroscopy and UV-visible spectroscopy were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnO nanoparticles, the TiO₂ coated ZnO nanoparticles showed enhanced UV emission. The UV-visible diffuse reflectance study revealed the significant UV shielding characteristics of the nanocomposite particles. Moreover, amorphous TiO₂ coating effectively reduced the photocatalytic activity of ZnO nanoparticles as evidenced by the photodegradation of Orange G with uncoated and TiO₂ coated ZnO nanoparticles under UV radiation.     

Synthesis of ZnOAl2O3 core-shell nanocomposite materials by fast and facile microwave irradiation method and investigation of their optical properties

Alumina (Al₂O₃) coated ZnO core-shell structures were synthesized by a novel, fast, and facile route utilizing microwave (MW) irradiation to control photocatalytic property of ZnO. The phase analysis and the core–shell structure development were corroborated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The XPS results affirmed that elements on the coated surface were Al and O. Zeta potential analysis predicted the presence of Al₂O₃ layer on ZnO due to almost similar zeta potential curve for pure Al₂O₃ and Al₂O₃ coated ZnO nanoparticles. There was no significant change in band gap energy of ZnO after amorphous Al₂O₃ coating as obtained from derived data of the reflectance spectra but gradual decreasing of reflectance in the visible range, measured by UV–vis spectroscopy, of the prepared core-shell nanoparticle may be due to the coating of amorphous Al₂O₃ on ZnO. The photocatalytic efficiency of ZnO was reduced after amorphous Al₂O₃ layer as confirmed by the photodegradation of methylene blue under UV irradiation.     

The microwave effect on the properties of silica-coated TiO2 fine particles prepared using sol-gel method

The silica coating of TiO₂ fine particle was conducted using microwave assisted sol-gel method and conventional sol-gel method to suppress its photo-catalytic activity. The amount and uniformity of silica coating on TiO₂ surface were characterized by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and zeta potential measurements. XPS and XRF results showed that the presence of catalyst and reaction time were important factors to reach high silica amounts. SEM, TEM, and zeta potential results indicated that dense film coating of SiO₂ layer formed on TiO₂ surface in conventional sol-gel method, whereas the nucleation coating was observed on sample prepared by microwave assisted sol-gel method. When photo-catalytic activities and ultraviolet (UV) shielding abilities of these samples were evaluated, the sample prepared by microwave processing showed higher inhibition of photo-catalytic activity and better UV shielding ability than the sample prepared by conventional method. These results suggested that the coating method significantly affected the photo-catalytic activity and UV shielding ability of coated TiO₂.     

In Situ Synthesis of Silica-Coated Magnetite Nanoparticles by Reverse Coprecipitation Method

Silica-coated magnetite nanoparticles were synthesized by reverse coprecipitation of Fe²⁺ and Fe³⁺ with sodium hydroxide in the presence of sodium silicate solution. Effect of reaction conditions and various amounts of sodium silicate solution on the powder particle characteristics was investigated by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer (LPSA), streaming current potential and vibrating sample magnetometer (VSM) techniques. Also, stability of silica-coated magnetite nanoparticles in the acidic condition has been studied by titration method. FT-IR results revealed that silica chemisorbed on the surface of magnetite nanoparticles by Fe?CO?CSi bonds. Analysis of the XRD patterns confirmed the formation of magnetite having spinel structure in the presence of sodium silicate solution. FE-SEM micrographs revealed that the mean particle size of spherical magnetite decreased from 50 to less than 25?nm by adding sodium silicate solution. Agglomeration declined when the volume ratio of sodium silicate/sodium hydroxide was 0.1. This was attributed to the coating of magnetite nanoparticles by silica. Coating of magnetite by silica prevents the formation of hydrogen bondings between magnetite and water molecules. Further increase in the sodium silicate concentration revealed a reverse effect.     

A fast and facile microwave irradiation method for the synthesis of ZnO@ZrO2 core-shell nanocomposites and the investigation of their optical properties

ZnO@ZrO₂ core-shell nanocomposites (NCs) were prepared by a novel and accessible path employing microwave (MW) irradiation to regulate photocatalytic property of ZnO. The synthesized ZnO@ZrO₂ NCs were further examined to discern their optical and chemical properties by FT-IR, XPS, XRF, XRD, FE-SEM, EDX, TEM, UV–vis, and PL analysis. XPS data analysis confirmed the presence of zirconium and oxygen on the coated surface. An almost similar zeta potential curve was observed for the pure ZrO₂ and ZrO₂ coated ZnO NCs, predicting the presence of the ZrO₂ layer on ZnO. Photoluminescence studies show the enhanced intensity of ZnO@ZrO₂ nanostructure compared to uncoated ZnO. Photocatalytic activity of ZnO could be controlled by the amorphous ZrO₂ layer, which was guaranteed by the photo mineralization of methylene blue under UV irradiation at room temperature.     

Influence of synthetic parameters on the enhanced photocatalytic properties of ZnO nanoparticles for the degradation of organic dyes: a green approach

Herein, we report a green synthetic strategy using aqueous leaves extract of Actinodaphne madraspatna Bedd (AMB) for the synthesis of ZnO NPs. The physical shape, size, thermal stability, surface area, surface composition and chemical state, morphological and optical properties of the synthesized ZnO NPs are well characterized through UV–Visible diffuse reflectance spectroscopy (DRS UV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis–differential thermal analysis (TGA–DTA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photon spectroscopy (XPS). FT-IR spectrum of ZnO NPs showed a characteristic peak at 416.62 cm^?1. Optical studies of prepared ZnO NPs showed the bandgap values are reduced in the range of 3.05 to 2.96 eV. The XRD and TEM data revealed the synthesized ZnO NPs exist in wurtzite crystal structure with crystallite sizes of 18 nm to 68 nm range. The variation in bandgap, surface area and crystallite structure of ZnO NPs would be achieved by changing the experimental parameters. FESEM showed spherical-shaped structure. XPS result confirmed the atomic states of Zn and O. The green synthesized ZnO NPs were examined for the photocatalytic degradation of methylene blue (MB) and acid violet 17 (AV17) dyes under UV light and the rate constants ‘k’ was calculated. It is found that the green synthesized ZnO NPs with reduced bandgap showed enhanced photocatalytic activity with higher rate constant.

     

Studies on nitrogen modified TiO2 photocatalyst prepared in different conditions

Nitrogen modified titania photocatalysts (TiO₂/N) were characterized using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and BET surface area method. The presence of nitrogen in modified photocatalysts has been studied using FT-IR and XPS analyses. The influence of the calcination temperature in the range of 100-350 °C on nanocrystallite as well as particle size of the samples and their photocatalytic activity was investigated. The calcination of TiO₂/N samples caused a growth of the particle size and an increase of their crystallinity. TEM studies present changes of the diameter and shape of TiO₂ particles and nanocrystallites. The XRD and the Raman response of the samples confirmed an increase of the crystallinity of the samples when annealed at higher temperatures.The photocatalytic activity of the modified photocatalysts was determined using the reaction of phenol decomposition. It was shown that phenol decomposition rate was greatly influenced by pH of the solution. The highest phenol degradation using all the modified samples was observed for pH 7.1 which is close to the PZC point established for pristine TiO₂ at pH 6.8.     

An efficient visible light photocatalyst prepared from TiO<Subscript>2</Subscript> and polyvinyl chloride

An efficient visible light photocatalyst has been prepared from TiO₂ nanoparticles and a partly conjugated polymer derived from polyvinyl chloride (PVC). It was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The visible light photocatalytic activity of the as-prepared photocatalyst was evaluated by the photocatalytic degradation of Rhodamine B (RhB) under visible light irradiation. The XPS, FT-IR, and Raman spectra show that the partly conjugated polymer derived from PVC exists on the surface of the TiO₂ nanoparticles. The UV–Vis DRS, XRD, and TEM results reveal that the modification of the partly conjugated polymer can obviously improve the absorbance of the TiO₂ nanoparticles in the range of visible light and hardly affect their size and crystallinity. The visible light photocatalytic activity of the as-prepared TiO₂ nanocomposites is higher than that of commercial TiO₂ (Degussa P25) and comparable with those of visible light photocatalysts reported in the literature. Their visible light photocatalytic stability is also good. The reasons for their excellent visible light photocatalytic activity and the major factors affecting their photocatalytic activity are discussed.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.     

SiO2包覆的羟基磷灰石纳米粒子的制备与性能研究

采用正硅酸乙酯(TEOS)水解法在羟基磷灰石粉体表面包覆SiO2进行表面改性,并通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、红外(FT-IR)、zeta电位和沉降实验等对样品的晶体结构、颗粒形貌进行了表征,结果表明涂层厚度约为3nm,包覆后的纳米粒子在水溶液中的胶体稳定性提高了5倍,SiO2在羟基磷灰石表面的吸附符合异质凝结机制。     

High photocatalytic activity of ZnO-carbon nanofiber heteroarchitectures

One-dimensional ZnO-carbon nanofibers (CNFs) heteroarchitectures with high photocatalytic activity have been successfully obtained by a simple combination of electrospinning technique and hydrothermal process. The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and IR spectrum. The results revealed that the secondary ZnO nanostructures were successfully grown on the primary CNFs substrates without aggregation. And, the coverage density of ZnO nanoparticles coating on the surface of the CNFs could be controlled by simply adjusting the mass ratio of zinc acetate to CNFs in the precursor during the hydrothermal process for the fabrication of ZnO-CNFs heterostructures. The obtained ZnO-CNFs heteroarchitectures showed high photocatalytic property to degrade rhodamine B (RB) because of the formation of heteroarchitectures, which might improve the separation of photogenerated electrons and holes. Moreover, the ZnO-CNFs heteroarchitectures could be easily recycled without the decrease in photocatalytic activity due to their one-dimensional nanostructural property.     

Fabrication of hollow silver spheres by MPTMS-functionalized hollow silica spheres as templates

In this study, we provide a strategy to prepare the hollow silver spheres by accumulating the silver nanoparticles on the surface of 3-mercaptopropyltrimethoxysilane (MPTMS)-functionalized silica as templates, which was accomplished by the chemisorption between silver nanoparticles and thiol groups. Then, the resulting hollow silver spheres were obtained through the chemical wet etching process with 10 M HF solution. In conventional method, the fabrication of hollow silver spheres from core-shell spheres was not easy due to the difficulties in retaining the shell structures during core removal. The method in this paper could overcome this limitation. The major focus of study is on understanding the mechanism of formation of the hollow silver spheres through the self-assembly behavior by chemisorption between silver nanoparticles and thiol groups. The silver-coated silica and hollow silver spheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and X-ray photoelectron spectroscopy (XPS).     

ZnO/Al2O3 coatings for the photoprotection of polycarbonate

ZnO and ZnO/Al₂O₃ thin films were deposited by r.f. magnetron sputtering on polycarbonate (PC) films in order to protect this polymer against photodegradation. The composition, structure and optical properties of the ceramic coatings were characterised. CO₂-plasma treatments were applied to PC in order to improve the coating adhesion. The PC surface energy was characterised by wettability measurements and the chemical bonds were analysed by XPS.It was found that ZnO coatings improve the stability of PC to UV radiations and that an intermediate alumina coating inhibits the photocatalytic oxidation of PC at the PC/ZnO interface. Additionally an external alumina coating brings a high hardness to the coating.     

Preparation and characteristics of core–shell structure cobalt/silica nanoparticles

The silica nanolayer with different thickness was coated on the spherical cobalt nanoparticles (an average diameter of 67 nm) to form core–shell structure by the controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS). This coating process was based on the use of silane coupling agent 3-mercaptopropyltrimethoxysilane (HS-(CH₂)₃Si(OCH₃)₃, MPTS) as a primer to render the cobalt surface vitreophilic, thus rendering cobalt surface compatible with silica. The control over the silica coating layer thickness can be achieved by varying the reaction time. The cobalt nanoparticles and the cobalt coated with silica shell were confirmed by transmission electron microscopy (TEM). 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. Result of the thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicate that the thermal stability of cobalt/silica is better than that of pure cobalt nanoparticles. Magnetic properties of these powders have been evaluated. These cobalt/silica core–shell nanoparticles can be utilized as precursors for making property-tunable magnetic nanoparticles, thin films, and multilayered core–shell structure nanocomposites.     

TiO2 supported on rod-like mesoporous silica SBA-15: Preparation, characterization and photocatalytic behaviour

TiO₂ nanoparticles have been successfully incorporated in the pores of mesoporous silica SBA-15 with different morphologies by a wet impregnation method. The composites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma (ICP) emission spectroscopy, transmission electron microscopy (TEM), N₂-sorption and UV-Vis diffuse reflectance spectroscopy. The photodegradation of methyl orange (MO) was used to study their photocatalytic property. It is indicated that the morphology of SBA-15 had a great influence on the photocatalytic activity of the composites. When TiO₂/SBA-15 composite was prepared by loading TiO₂ nanoparticles on uniform rod-like SBA-15 of 1 μm length, it showed higher photocatalytic degradation rate than that on less regular but much larger SBA-15 support. This difference was rationalized in terms of the homogeneously distributed and shorter channels of rod-like SBA-15, which favored mass transport and improved the efficient utilization of the pore surface.     

Effect of Fe doping on the photocatalytic activity of ZnO nanoparticles: experimental and theoretical investigations

Pure and Fe doped ZnO nanoparticles were prepared by a facile and cost-effective co-precipitation method. The X-ray diffractograms (XRD) reveal that the grown nanoparticles are hexagonal in structure and the crystallite sizes are in the range of 27–28 nm. The transmission electron microscope (TEM) micrographs confirmed the spherical nature of the grown particles and the Fourier transform-infrared (FT-IR) studies confirmed the presence of Zn–O bonding in the prepared nanoparticles. Additionally, the presence of the constituent elements is confirmed with XPS analysis. The optical bandgap of the prepared nanoparticles are calculated as 3.28, 3.19 and 3.08 eV for ZnO, ZnO–Fe 10 at.% and ZnO–Fe 20 at.%, respectively. The photocatalytic dye degradation efficiency against methylene blue, is 68.52, 73.96, and 87.92, respectively. To validate the photocatalytic activity, a DFT based calculation was performed to measure the band edge positions of the pure and Fe doped ZnO nanostructures, and the obtained results are well supported by the experimental results.     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Facile preparation and electrochemical characterization of graphene/ZnO nanocomposite for supercapacitor applications

Graphene/ZnO nanocomposites were successfully synthesized by microwave-assisted method. The structure, morphology, optical and composition of the obtained samples were characterized using XRD, FT-IR, laser Raman, UV–Vis spectroscopy and XPS analysis. XRD analysis confirmed the presence of graphene/ZnO nanocomposite. FE-SEM image reveals that the homogenous distribution of ZnO nanoparticles on the graphene nanosheets. The electrochemical properties of the graphene/ZnO electrodes were analyzed by cyclic voltammetry and impedance spectroscopy. The results confirmed that the incorporation of ZnO nanoparticles enhanced the capacitive performance of graphene electrode. Graphene/ZnO nanocomposite electrode showed higher capacitance value of 109 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M KCl solution as compared to the graphene electrodes. These results demonstrated the importance and great potential of graphene based composites in the development of high-performance energy-storage systems.     

Structural and photoluminescence properties of Tb-doped CaMoO4 nanoparticles with sequential surface coatings

The crystal structure, surface chemistry and optical properties of Tb-doped CaMoO₄ (CaMoO₄:Tb) nanoparticles and the sequentially coated CaMoO₄:Tb@CaMoO₄ and CaMoO₄:Tb@CaMoO₄@SiO₂ nanostructures have been characterized by X-ray diffraction (XRD), Thermo-gravimetric analysis (TGA), UV–vis absorption (UV–Vis), Fourier- transform infrared spectroscopy (FT-IR), Raman spectroscopy and Photoluminescence spectroscopy. The XRD results indicate that the obtained CaMoO₄:Tb is sheelite tetragonal structure and well crystallized at 150 °C. The particle size increases from 21 to 48 nm by sequential coating of CaMoO₄ and silica formation around the surface of core nanoparticles. These nanocrystals were well-dispersed in aqueous and non-aqueous solvents to form clear colloidal solutions. The colloidal solutions of three samples show well characteristic optical absorption band in UV/Visible region. The surface coating on core particles will significantly influence the structural and photoluminescence properties. The as-prepared core nanoparticles showed high photoluminescence as compared to surface coated core–shell nanoparticles because Tb³⁺ ion located at the particle surface. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices as well as optical bioprobes.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.