Synthesis and photoluminescent properties of silica-coated LaCeF<Subscript>3</Subscript>:Tb nanocrystals

La_0.45Ce_0.45F₃:Tb (10 mol% Tb) nanoparticles was synthesized via sonochemical method and then coated with silica (SiO₂) shells through a microemulsion process, resulting in the formation of core/shell structured LaCeF₃:Tb/SiO₂ nanoparticles. The obtained core/shell LaCeF₃:Tb/SiO₂ nanoparticles are spherical and uniform in size (average size about 60 nm), strongly fluorescent, and long fluorescence lifetime (1.87 ms). This kind of nanoparticles was water-soluble, which could be applied in biological labeling and other fields.     

Preparation and photocatalytic properties of magnetically reusable Fe3O4@ZnO core/shell nanoparticles

Fe₃O₄@ZnO binary nanoparticles were synthesized by a simple two-step chemical method and characterized using various analytical instruments. TEM result proved the binary nanoparticles have core/shell structures and average particle size is 60 nm. Photocatalytic investigation of Fe₃O₄@ZnO core/shell nanoparticles was carried out using rhodamine B (RhB) solution under UV light. Fe₃O₄@ZnO core/shell nanoparticles showed enhanced photocatalytic performance in comparison with the as prepared ZnO nanoparticles. The enhanced photocatalytic activity for Fe₃O₄@ZnO might be resulting from the higher concentration of surface oxygen vacancies and the suppressing effect of the Fe³⁺ ions on the recombination of photoinduced electron–hole pairs. Magnetization saturation value (5.96 emu/g) of Fe₃O₄@ZnO core/shell nanoparticles is high enough to be magnetically removed by applying a magnetic field. The core/shell photocatalyst can be easily separated by using a commercial magnet and almost no decrease in photocatalytic efficiency was observed even after recycling six times.     

Light-induced antifungal activity of TiO2 nanoparticles/ZnO nanowires

Antifungal activity of TiO₂/ZnO nanostructures under visible light irradiation was investigated. A simple chemical method was used to synthesize ZnO nanowires. Zinc acetate dihydrate, Polyvinyl Pyrrolidone and deionized water were used as precursor, capping and solvent, respectively. TiO₂ nanoparticles were deposited on ZnO nanowires using an atmospheric pressure chemical vapor deposition system. X-ray diffraction pattern of TiO₂/ZnO nano-composite has represented the diffraction peaks relating to the crystal planes of the TiO₂ (anatase and rutile) and ZnO. TiO₂/ZnO nanostructure antifungal effect on Candida albicans biofilms was studied and compared with the activity of TiO₂ nanoparticles and ZnO nanowires. The high efficiency photocatalytic activity of TiO₂ nanoparticles leads to increased antifungal activity of ZnO nanowires. Scanning electron microscope was utilized to study the morphology of the as prepared nanostructures and the degradation of the yeast.     

液相激光烧蚀合成ZnO及Zn/ZnO纳米颗粒及其光致发光性能

利用532 nm脉冲激光对沉浸在去离子水及十二烷基硫酸钠(SDS)水溶液中的金属锌靶进行液相激光烧蚀,合成了ZnO纳米颗粒和Zn/ZnO核壳结构的纳米粒子. 应用X射线衍射仪,透射电子显微镜,紫外可见光分光光度计和荧光光度计表征产物的微观结构和光学性能,并探讨其形成机理. 结果表明:在去离子水中分别烧蚀2 h和4 h生成的ZnO纳米粒子的平均粒径分别为43 nm和19 nm. 激光的长时间作用可以使纳米粒子粒径减小. 在0.005 mol/L的SDS水溶液中合成了Zn/ZnO核壳结构的纳米粒子,这是由于S 关键词： 脉冲激光烧蚀 ZnO纳米粒子 核壳结构 光致发光     

A facile synthesis of monodisperse CoFe2O4/SiO2 nanoparticles

Aminated-CoFe₂O₄/SiO₂ magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe₂O₄/SiO₂ NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe₂O₄/SiO₂ NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe₂O₄/SiO₂ NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe₂O₄/SiO₂ NPs can be used as an effective carrier for the enzyme immobilization.     

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.     

ZnO–ZnS heterostructures with enhanced optical and photocatalytic properties

ZnO–ZnS heterostructures were fabricated via using ZnO rods as template in different Na₂S aqueous solutions. These heterostructures are 5–6 μm in length and formed by coating ZnO rod with a layer of porous ZnS shell comprising primary crystals about 10 nm in diameter. Subsequently, intact ZnS polycrystalline tubes were obtained by removing the ZnO cores with 25% (wt) ammonia. The as-prepared products were characterized by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR), and electrochemical impedance spectroscopy (EIS). It was found that the electron transfer between ZnS shell and ZnO core strongly affect the photoluminescence and photocatalytic performances of these heterostructures. The rapid transfer of photo-induced electrons from the ZnS shell to the ZnO core leads to enhanced ultraviolet emission. However, if this correlation was destroyed, then the corresponding heterostructure exhibits improved photocatalytic efficiency due to the reduced volume recombination of the charge carries and the multiple reflection effect. Finally, a model based on band-gap alignment was proposed to elucidate the underlying mechanism of the enhanced UV emission and photocatalytic activity of these unique heterostructures.     

Light scattering calculations from Au and Au/SiO2 core/shell nanoparticles

Given the importance of the optical properties of Au and Au/SiO₂ core/shell nanoparticles, in this article we focus our attention on the light scattering properties of such systems and on a relative comparison. In particular, we report theoretical results of angle-dependent light scattering intensity and scattering efficiency for Au and Au/SiO₂ core/shell nanoparticles increasing the Au particle radius from 30 to 130 nm, and for Au/SiO₂ core/shell particles changing the core-to-shell sizes ratio. Finally, a comparison between the scattering efficiency of the Au and Au/SiO₂ core/shell nanoparticles is drawn. The results of this work can be used in the design of tunable efficiency light scattering devices (biological and molecular sensors, solar cells).     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

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).     

Y2Si2O7:Eu/SiO2 core shell phosphor particles prepared by flame spray pyrolysis

This paper reports the synthesis of core shell phosphor particles (Y₂Si₂O₇:Eu/SiO₂) produced by flame spray pyrolysis with yttrium and europium nitrates and colloidal silica dispersed precursor solutions. Particles of various structures were produced, including heterogeneous, core shell and non-spherical core shell particles, depending on the synthesis conditions; the ideal core shell structure was obtained under the highest flame temperature and high silicon concentration in the precursor solution. Based on the phase diagram, the formation of the core shell structure was caused by the separation of each component at the liquid phase in the synthesis route. In the energy-dispersive X-ray spectroscopy, yttrium could be detected only at the core part of the particle, while silicon and oxygen could be detected at both the shell and core parts. Under ultraviolet excitation, the ideal core shell particles of Y₂Si₂O₇:Eu showed photoluminescent characteristics. Consequently, it could be concluded that Y₂Si₂O₇:Eu/SiO₂ core shell phosphor particles were successfully synthesized by flame spray pyrolysis.     

Ag-deposited silica-coated Fe3O4 magnetic nanoparticles catalyzed reduction of p-nitrophenol

In this paper, a novel approach was successfully developed for advanced catalyst Ag-deposited silica-coated Fe₃O₄ magnetic nanoparticles, which possess a silica coated magnetic core and growth active silver nanoparticles on the outer shell using n-butylamine as the reductant of AgNO₃ in ethanol. The as-synthesized nanoparticles have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectra (FT-IR), vibration sample magnetometer (VSM), and have been exploited as a solid phase catalyst for the reduction of p-nitrophenol in the presence of NaBH₄ by UV-vis spectrophotometry. The obtained products exhibited monodisperse and bifunctional with high magnetization and excellent catalytic activity towards p-nitrophenol reduction. As a result, the as-obtained nanoparticles showed high performance in catalytic reduction of p-nitrophenol to p-aminophenol with conversion of 95% within 14 min in the presence of an excess amount of NaBH₄, convenient magnetic separability, as well as remained activity after recycled more than 6 times. The Fe₃O₄@SiO₂-Ag functional nanostructure could hold great promise for various catalytic reactions.     

Influence of Surface Coating on Structural and Photoluminescent Properties of CaMoO4:Pr Nanoparticles

CaMoO₄:Pr(core), CaMoO₄:Pr@CaMoO₄ (core/shell) and CaMoO₄:Pr@CaMoO₄@SiO₂ (core/shell/shell) nanoparticles were synthesized using polyol method. X-ray diffraction (XRD), thermogravimatric analysis (TGA), UV–vis absorption, optical band gap energy analysis, Fourier transform infrared (FTIR), FT-Raman and photoluminescence (PL) spectroscopy were employed to investigate the structural and optical properties of the synthesized core and core/shell nanoparticles. The results of the XRD indicate that the obtained core, core/shell and core/shell/shell nanoparticles crystallized well at ~150 °C in ethylene glycol (EG) under urea hydrolysis. The growth of the CaMoO₄ and SiO₂ shell (~12 nm) around the CaMoO₄:Pr core nanoparticles resulted in an increase of the average size of the nanopaticles as well as in a broadening of their size distribution. These nanoparticles can be well-dispersed in distilled water to form clear colloidal solutions. The photoluminescence spectra of core, core/shell and core/shell/shell nanoparticles show the characteristic charge transfer emission band of MoO₄ ^2? (533 nm) and Pr³⁺ 4f²?→?4f², with multiple strong ³H₄?→?³P₂, ¹D₂?→?³H₄ and ³P₀?→?³?F₂ transitions located at ~490, 605 and 652 nm, respectively. The emission intensity of the CaMoO₄:Pr@CaMoO₄ core/shell and CaMoO₄:Pr@CaMoO₄@SiO₂ core/shell/shell nanoparticles increased ~4.5 and 1.7 times,respectively, with respect to those of CaMoO₄:Pr core nanoparticles. This indicates that a significant amount of nonradiative centers existing on the surface of CaMoO₄:Pr@CaMoO₄ core/shell nanoparticles can be eliminated by the shielding effect of CaMoO₄ shells.     

Facile synthesis and photocatalytic activity of hierarchical WO3 core–shell microspheres

In this work, we present a facile template-free precipitation method for the large-scale preparation of hierarchical WO₃ core–shell microspheres in which the core was composed of aggregated nanoparticles encapsulated by a hierarchical shell layer self-assembled by ultrafine nanoplates with a thickness of about 15 nm. The products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), differential scanning calorimetry and thermogravimetry (TG/DSC). The experimental parameters affecting the morphology were discussed in detail. We found that the concentration of citric acid and pH value of the reaction solution had profound effects on the morphology of the products. In addition, a formation mechanism was proposed for producing hierarchical WO₃ core–shell microspheres. Furthermore, the obtained hierarchical WO₃ core–shell microspheres showed superior photocatalytic activities for the degradation of rhodamine B (RhB) under visible light irradiation.     

Photoactive materials prepared by homogeneous hydrolysis with thioacetamide: Part 2—TiO2/ZnO nanocomposites

Photocatalytic active titanium dioxide (TiO₂)/zinc oxide (ZnO) composite was prepared by homogeneous hydrolysis of a mixture of titanium oxo-sulphate and zinc sulphate in aqueous solutions with thioacetamide and subsequent annealing at the temperature of 600 °C. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission microscopy (HRTEM). Nitrogen adsorption-desorption was used for surface area (Brunauer-Emmett-Teller—BET) and porosity determination. The photoactivity of the prepared TiO₂/ZnO samples was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry under irradiation of 254 and 365 nm wavelengths. Under the same conditions, the photocatalytic activity of a commercially available photocatalyst (Degussa P25), the pure anatase TiO₂ nanoparticles and cubic ZnO were examined.     

Preparation and characterization of bifunctional, Fe3O4/ZnO nanocomposites and their use as photocatalysts

Bifunctional magnetic-optical Fe₃O₄/ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe₃O₄ nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe₃O₄ with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1 h when the amount of catalyst was 0.51 g L⁻¹ and initial concentration of MO was 6 × 10⁻⁵ mol L⁻¹ in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe₃O₄/ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.     

Influence of Shell Formation on Morphological Structure,Optical and Emission Intensity on Aqueous Dispersible NaYF4:Ce/Tb Nanoparticles

A highly water-dispersible NaYF₄:Ce/Tb (core), NaYF₄:Ce/Tb@NaYF₄(core/shell) and NaYF₄:Ce/Tb@NaYF₄@SiO₂ (core/shell/SiO₂) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF₄ and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO₂ NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l’Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO₂ NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors.     

Structural characterization of ZnO/ Er2O3 core/shell nanowires

Zinc oxide/erbium oxide core/shell nanowires are of great potential value to optoelectronics because of the possible demonstration of laser emission in the 1.5 μm range. In this paper we present a convenient technique to obtain structures of this composition. ZnO core nanowires were first obtained by a vapor–liquid–solid (VLS) method using gold as a catalyst. ZnO nanowires ranging from 50 to 100 nm in width were grown on the substrates. Erbium was incorporated into these nanowires by their exposure to Er(tmhd)₃ at elevated temperatures. After annealing at 700 C in air, the nanowires presented 1.54 μm emission when excited by any of the lines of an Ar⁺ laser. An investigation of nanowire structure by HRTEM indicates that indeed the cores consist of hexagonal ZnO grown in the 001 direction while the surface contains randomly oriented Er₂O₃ nanoparticles. EXAFS analysis reveals that the Er atoms possess a sixfold oxygen coordination environment, almost identical to that of Er₂O₃. Taken collectively, these data suggest that the overall architectures of these nanowires are discrete layered ZnO/ Er₂O₃ core/shell structures whereby erbium atoms are not incorporated into the ZnO core geometry.     

Polishing behavior of PS/CeO2 hybrid microspheres with controlled shell thickness on silicon dioxide CMP

Organic-inorganic composite microspheres with PS as a core and CeO₂ nanoparticles as a shell were synthesized by in situ decomposition reaction of Ce(NO₃)₃ on the surfaces of PS microspheres prepared through soap-free emulsion polymerization. The shell thickness of the composite microspheres could be turned by varying the concentration of Ce(NO₃)₃ in the reaction solution. The whole process required neither surface treatment for PS microspheres nor additional surfactant or stabilizer. The as-synthesized PS/CeO₂ composite microsphere samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Oxide chemical mechanical polishing (CMP) performance of the PS/CeO₂ composite abrasives with different shell thickness was characterized by atomic force microscopy (AFM). The results indicated that the as-prepared core-shell structured composite microspheres (220-260 nm in diameter) possessed thin shell (10-30 nm) composed of CeO₂ nanoparticles (particle diameter of 5-10 nm), and the final CeO₂ contents of the composite microspheres ranged from 10 to 50 wt%. A possible mechanism for the formation of PS/CeO₂ composite microspheres was discussed also. The CMP test results confirmed that the novel core-shell structured composite abrasives are useful to improve oxide CMP performance. In addition, there is an obvious effect of shell thickness of the composite abrasives on oxide CMP performance.     

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.