Particle size distribution study by small-angle X-ray scattering technique and photoluminescence property of ZnO nanoparticles

ZnO nanoparticles have been synthesised by thermal decomposition of zinc acetate at ～800°C. The structural characteristics and size distribution of ZnO nanoparticles have been investigated by X-ray powder diffraction (XRD) and small-angle X-ray scattering (SAXS), respectively. SAXS study reveals nanoparticles are of different sizes: namely 23 wt% of 8 nm, 19 wt% of 21 nm and 58 wt% of 51 nm. These ZnO nanoparticles possess yellow visible emission at 552 nm. The polydispersity and single emission peak at 552 nm in ZnO nanoparticles suggest that the yellow emission might be a bulk property instead of having a surface origin in nanostructured ZnO. The surface impurities are characterised by Fourier-transform infrared spectroscopy. The quenching of band edge emission in ZnO nanoparticles seems due to the presence of surface impurities.     

Synthesis and characterization of SnS/ZnO nanocomposite by chemical method

SnS nanorods and SnS/ZnO nanocomposite have been synthesized by chemical method. Structure and phase purity of the samples were confirmed by powder X-ray diffraction. Transmission electron microscope image of SnS nanorods showed the average diameter of nanorods was about 85 nm and length was several micrometers. Transmission electron microscope image of SnS/ZnO nanocomposite showed the average particle size of ZnO nanoparticle was about 12 nm. The formation of SnS/ZnO nanocomposite was confirmed by elemental analysis using energy dispersive X-ray spectroscopy. From the microRaman spectrum of SnS/ZnO nanocomposite, it was observed that the intensity of B_2g mode of SnS nanorods decreased dramatically compared to that of pure SnS nanorods, since the surface of the SnS nanorods were coated with ZnO nanoparticles. Both direct and indirect band gap transitions were observed for SnS nanorods from the optical absorption spectrum and the optical absorption spectrum of SnS/ZnO nanocomposite showed absorption in the visible region.     

A facile synthesis of silver nanoparticle with SERS and antimicrobial activity using Bacillus subtilis exopolysaccharides

In this study, we report a facile synthesis of silver nanoparticle having SERS and antimicrobial activity using bacterial exopolysaccharide (EPS). Bacillus subtilis (MTCC 2422) was grown in nutrient broth and the extracellular EPS secreted by the organism was extracted and purified. The purified EPS was used for the synthesis of silver nanoparticles. The kinetics of silver nanoparticle synthesis was deduced by varying the exposure time and the concentration of EPS. The rate constant (k) for the synthesis of silver nanoparticle was calculated from the slope of ln(A^∞ ? A^t) versus time plot. The k value was found to be 3.49 × 10^?3, 5.81 × 10^?3 and 5.03 × 10^?3 per min for particle synthesis using 2, 5 and 10 mg/mL EPS, respectively. The nanoparticles synthesised had an average particle size of 5.18 ± 1.49 nm, 1.96 ± 0.77 nm and 2.08 ± 0.88 nm for 2, 5 and 10 mg/mL EPS, respectively. The synthesised particles were characterised using UV-Vis absorbance spectroscopy, high-resolution transmission electron microscopy (HRTEM) attached to EDS (energy dispersive spectroscopy), Fourier transform infrared spectroscopy (FTIR), surface enhanced Raman spectroscopy (SERS) and zeta potential analyser. To our knowledge, this is the first study to report SERS activity of microbial Bacillus subtilis EPS-based synthesis of silver nanoparticle. HRTEM images showed silver nanoparticle entrapped in polysaccharide nanocages. Silver nanoparticle showed higher adherence towards the bacterial surface, with good bactericidal activity against Pseudomonas aeroginosa and Staphylococcus aureus.     

Room temperature ferromagnetism in Tb-doped ZnO dilute magnetic semiconducting nanoparticles

Pure and Tb-doped ZnO nanoparticles have been synthesized by chemical co-precipitation method. The transmission electron microscopy study reveals the spherical morphology of synthesized nanoparticles with average particle size 14–18 nm. The effect of Tb-doping on structural, optical and magnetic properties has been studied. X-ray diffraction shows that pure and Tb-ZnO nanoparticles exhibit wurtzite structure having hexagonal phase with primitive unit cell. It further reveals that there is no effect of Tb-doping on the X-ray diffraction pattern up to 2 % doping, however, higher doping concentration result in accumulation of Tb on ZnO surface. Photoluminescence spectra reveal that the doping Tb in ZnO changes crystallographic structure generating non-radiative oxygen vacancies. Three emission peaks located around 423, 485 and 515 nm has been observed. Pure ZnO nanoparticles show diamagnetic character, however, Tb-doped ZnO nanoparticles exhibit room temperature ferromagnetism. The correlation between defects generated upon Tb-doping to the observed ferromagnetism, in the synthesized nanoparticles, has been reported.     

Chemical,morphological, structural,optical, and magnetic properties of Zn<Subscript>1−x</Subscript>Nd<Subscript>x</Subscript>O nanoparticles

In the present investigation, we made an endeavor to fabricate the ZnO nanoparticles and achieved the tunable properties with Nd doping. The Nd-doped ZnO nanoparticles were characterized via X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies that confirmed the successful doping of Nd ions in the ZnO crystal lattice without amending its hexagonal phase. The particle morphology revealed nearly spherical particles with uniform size distribution. The band gap of these samples was determined using diffuse-reflectance spectra (DRS) and was found to vary from 3.17 to 3.21 eV with increasing Nd concentration. A broad and intense emission band at 1083 nm for Nd doped ZnO nanoparticles is observed and is assigned to corresponding emission transition ⁴F_3/2?→?⁴I_11/2 of Nd³⁺ ions. Furthermore, the magnetic studies indicate that the Nd doping altered the magnetic behavior of nanocrystalline ZnO particles from diamagnetic to ferromagnetic at 300 K and that the magnetization of these samples decreased with increasing Nd concentration. The tunable optical band gap as well as room-temperature ferromagnetism of these samples may find applications in both optoelectronics and spintronics.     

Surface functionalization for subsequent receptor coupling on inorganic nanoparticles

A two-stages process for an effective coupling of inorganic nanoparticles with biological receptor molecules is reported. Initial particle surface functionalization applies an ethylene glycol-based phosphonic acid or a corresponding ester analog with an azide functional group for subsequent receptor coupling under mild click chemistry conditions. A simple carbohydrate was applied as model receptor, while a luminescent LaPO₄:Ce,Tb with dimensions of 5–7 nm was chosen for the nanoparticle. Analysis of the particle surface applied IR and TGA, while effects of the surface modification on the particle core were investigated by XRD, TEM, SAXS, and fluorescence spectroscopy. The receptor content was determined using a photometric assay, leading to a surface loading of ~40 receptors per particle. This translates to a surface area of ~6.5 nm² per receptor based on the inorganic particle core.     

Fast one-step synthesis of ZnO sub-microspheres in PEG200

ZnO sub-microspheres were synthesized via a new, simple, and one-step method by using zinc acetate dihydrate as a precursor and PEG200 as a solvent and modifier. The effect of temperature (160–210 °C) on the crystallization, surface morphology, and luminescence properties of ZnO spheres was investigated using different characterization techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, and room temperature photoluminescence. The results show that the ZnO crystal has a hexagonal wurtzite structure. The products have monodispersed spherical morphology with diameters in the range of 200–600 nm. They have intensive UV emission peaks at ~380 nm and relatively weak and broad green peaks at ~550 nm. The PEG200 molecules adsorb on the surface of ZnO spheres. On the basis of the experimental results, a mechanism was proposed to elucidate the formation of ZnO sub-micron spheres.     

Structural and optoelectronic characterization of prepared and Sb doped ZnO nanoparticles

This paper briefly reports the structural and optoelectronics properties of prepared pure and Sb doped ZnO nanoparticles. Doping with suitable elements offers an efficient method to control and enhance the optical properties of ZnO nanoparticles, which is essential for various optoelectronics applications. Sb doped ZnO nanoparticles have significant concern due to their unique and unusual electrical and optical properties. In the present work, we report the synthesis of Sb doped ZnO successfully with average particle size range from 26 to 29 nm via direct precipitation method. The phase purity and crystallite size of synthesized ZnO and Sb doped nano-sized particles were characterized and examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental analyses of undoped and doped ZnO nanoparticles were examined by using energy-dispersive X-ray spectroscopy (EDAX).We investigated and measured the optoelectronics properties of synthesized ZnO and Sb doped ZnO nanoparticles by employing photoluminescence and UV–Visible spectroscopy. The influence of Sb doping on photoluminescence (PL) spectra of ZnO nanoparticles, which consists of UV emission and broad visible emission band, is found to be strongly dependent upon the Sb concentration for all the Sb doped ZnO nanoparticles samples under investigation. The UV–Visible absorption study shows an increase in band gap energy as Sb is incorporated on the ZnO nanoparticles.     

Fabrication of Cu@Ag core–shell nanoparticles for nonlinear optical applications

We report the preparation of the core–shell structured Cu@Ag nanoparticles by a simple wet chemical route at room temperature. The surface plasmon resonance band at 405 nm is indicative of the formation of Cu@Ag nanoparticles. The powder X-ray diffraction and energy dispersive X-ray analyses were carried out to elucidate the structure and chemical composition respectively. The morphological investigations made by electron microscopes revealed that the particles are spherical in shape with core–shell structures having size of about 50 nm. The X-ray photoelectron spectroscopy was performed to elucidate surface state composition of the core–shell structured nanoparticles based on the binding energies and confirmed the formation of Cu@Ag core–shell nanoparticles. The enhanced non-linear optical response of the Cu@Ag core–shell nanoparticles was demonstrated by z-scan experiment using He–Ne laser. This report provides a simple, economical and practical technology to fabricate Cu@Ag core–shell nanoparticles with enhanced nonlinear optical properties.     

Structural verification and optical characterization of SiO2–Au–Cu2O nanoparticles

In this paper, SiO₂–Au–Cu₂O core/shell/shell nanoparticles were synthesized by reducing gold chloride on 3-amino-propyl-triethoxysilane molecules attached silica nanoparticle cores for several stages. Cu₂O nanoparticles were synthesized readily with the size of 4–5 nm using a simple route of sol–gel method Then, they were clung to the surface of Au seeds. The morphology of the resultant particles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy images demonstrate growth of monodispersed gold seeds and Cu₂O nanoparticles in narrow size up to 10 nm and 5 nm, respectively. The presence of gold and Cu₂O coating was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Absorption spectroscopy shows considerably 40 nm blue shift in absorption edge for SiO₂–Au–Cu₂O nanostructure rather than SiO₂–Au core/shell nanoparticles.     

Magnetic losses in metal nanoparticle-insulator nanocomposites

Metal nanoparticle-insulator nanocomposites were synthesized and characterized for their magnetic loss and frequency-stability to understand the role of metal particle size and oxide passivation. Cobalt nanocomposites were synthesized with different matrices such as lead-borosilicate glass, silica and polymers, and fabricated into toroids for characterizing their microstructure and magnetic properties. X-ray Diffraction and Transmission Electron Miscroscopy were used to characterize the microstructure while Vibration Sample Magnetometry and impedance spectroscopy were used to obtain saturation magnetization, coercivity, permeability and magnetic loss. Nanocomposites with particles in the size range of 40–90 nm showed poor frequency stability and high loss beyond 200 MHz while finer particles (25–40 nm) resulted in stable properties beyond 500 MHz. The high coercivity and FMR broadening with oxide-passivated nanoparticle composites, however, degraded the magnetic losses at 500 MHz even with finer particles. The role of particle size and surface effects in suppressing the permeability and enhancing the frequency-stability is discussed.     

Effect of Sn doping on microstructural and optical properties of ZnO nanoparticles synthesized by microwave irradiation method

Pure and Sn-doped ZnO nanostructures have been synthesized by the microwave irradiation method. The influence of Sn loading on the morphology and microstructure was evaluated by using field emission scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrum analysis techniques, X-ray diffraction, and Fourier transform infrared spectroscopy. A change in the growth pattern, from needle-like particles for pure ZnO to agglomerated spherical crystallites for Sn-doped ZnO, has been observed. TEM observations indicated that the average particle size of the pure ZnO nano needles is in the range of 40–60 nm, whereas on addition of Sn spherical nanoassemblies size lies in the range of 10–21 nm. The pure ZnO and Sn-doped ZnO nanostructures were further characterized for their optical properties by UV–Vis reflectance spectra (DRS) and photoluminescence (PL) spectroscopy.     

Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo

The potential of cationic SiO2 nanoparticles was investigated for in vivo gene transfer in this study. Cationic SiO2 nanoparticles with surface modification were generated using amino-hexyl-amino-propyltri-methoxysilane (AHAPS). The zeta potential of the nanoparticles at pH = 7.4 varied from -31.4 mV (unmodified particles; 10 nm) to +9.6 mV (modified by AHAPS). Complete immobilization of DNA at the nanoparticle surface was achieved at a particle ratio of 80 (w/w nanoparticle/DNA ratio). The surface modified nanoparticle had a size of 42 nm with a distribution from 10-100 nm. The ability of these particles to transfect pCMVbeta reporter gene was tested in Cos-1 cells, and optimum results were obtained in the presence of FCS and chloroquine at a particle ratio of 80. These nanoparticles were tested for their ability to transfer genes in vivo in the mouse lung, and a two-times increase in the expression levels was found with silica particles in comparison to EGFP alone. Very low or no cell toxicity was observed, suggesting silica nanoparticles as potential alternatives for gene transfection.     

Zinc oxide incorporating iron nanoparticles with improved conductance and capacitance properties

Iron nanoparticles were incorporated into zinc oxide powders by an in situ dispersion method. The products were fully characterized by X-ray diffractometry, diffuse reflectance, FTIR spectrophotometry and complex impedance spectroscopy. The XRD patterns agreed with that of the ZnO typical wurtzite structure, the sharp diffraction peaks indicating good crystallinity of ZnO and ZnO-Fe nanoparticles. The average particle size determined by the Scherrer equation showed an increase from 20 to 25 nm for ZnO and ZnO-Fe respectively. The UV peak positions of the modified samples shifted to a longer wavelength compared to pure ZnO, providing evidence of changes in the acceptor level induced by iron nanoparticles. The optical band gap of the samples was found to be 3.14 eV for ZnO and 3.04 eV for ZnO-Fe. The electrical properties were investigated between 273 and 413 K, at several frequencies. Besides, a detailed analysis of the impedance spectrum showed an appreciable improvement of the conductivity due to the addition of iron nanoparticles. The incorporation of Fe-NPs appears to be responsible for conductance variations, charge transfer and capacitance improvement. The above properties make these materials to be regarded as very promising electrode materials for high-efficiency energy storage.     

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.     

Effect of zinc oxide concentration in fluorescent ZnS:Mn/ZnO core–shell nanostructures

In the present work, we have prepared zinc sulphide (ZnS:Mn)/zinc oxide (ZnO) core–shell nanostructures by a chemical precipitation method and observed the effect of ZnO concentration on the fluorescent nanoparticles. Change in the morphological and optical properties of core–shell nanoparticles have been observed by changing the concentration of ZnO in a core–shell combination with optimum value of Mn to be 1 % in ZnS. The morphological studies have been carried out using X-ray diffraction (XRD) and transmission electron microscopy. It was found that diameter of ZnS:Mn nanoparticles was around 4–7 nm, each containing primary crystallites of size 2.4 nm which was estimated from the XRD patterns. The particle size increases with the increase in ZnO concentration leading to the well-known ZnO wurtzite phase which was coated on the FCC phase of ZnS:Mn. Band gap studies were performed by UV–visible spectroscopy and a red shift in absorption spectra have been observed with the addition of Mn as well as with the capping of ZnO on ZnS:Mn. The formation of core–shell nanostructures have been also confirmed by FTIR analysis. Photoluminescence studies show that emission wavelength is red shifted with the addition of ZnO layer on ZnS:Mn(1 %). These core–shell ZnS:Mn/ZnO nano-composites will be a very suitable material for specific kind of tunable optoelectronic devices.     

Graphene sheets decorated with ZnO nanoparticles as anode materials for lithium ion batteries

ZnO/graphene composites were synthesized using a facile solution-based method. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectra revealed that ZnO nanoparticles with a particle size of around 4 nm were densely and homogeneously deposited on graphene sheets. As the anode material for the lithium ion batteries, the ZnO/graphene composites delivered a stable capacity of 404 mAh/g after 100 cycles at a current rate of 0.5 C, which is much superior to bare ZnO nanoparticles. The battery performance result indicates the presence of graphene sheets in the composites effectively enhance the conductivity and accommodate the volume change.     

Pristine and cadmium-doped zinc oxide: chemical synthesis and characterizations

The chemical synthesis of pristine and cadmium-doped ZnO powders using a simple, cost-effective at 65 °C is reported and characterized for their structures, optical and morphological studies using X-ray diffraction, UV–visible–Near Infra-Red (UV–Vis–NIR) spectroscopy, scanning electron microscopy measurement techniques where XRD spectra confirm the formation of ZnO and Cd-doped ZnO with hexagonal crystal structure. The particle size of ZnO is reduced on Cd-doping from 16 to 14 nm. Plane-view surface morphology analysis supported for spherical-type crystallites and UV–Vis–NIR spectra reveal shift in the band edge of ZnO after Cd-doping. Photo-degradation study of Methylene Blue dye shows Pristine ZnO degrades dye faster than Cd-doped ZnO.     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Development of a Compact Electrostatic Nanoparticle Sampler for Offline Aerosol Characterization

A compact electrostatic nanoparticle sampler has been developed to support the offline analysis of nanoparticles via electron microscopy. The basic operational principle of the sampler is to electrically charge particles by mixing nanoparticles and unipolar ions produced by DC corona discharge, and electrostatically collecting charged particles. A parametric study was first performed to identify the optimal operating condition of the sampler: a total flow rate (i.e., the sum of the particle and ion carrier flow rates) of 1.0 lpm, an aerosol/ion carrier flow rate ratio of 1.0, and a collection voltage of 4.5 kV. Under the above condition, the sampler achieved a collection efficiency of more than 90 % for particles ranging from 50 to 500 nm. The effect of particle material on the sampler’s performance was also studied. The prototype had lower collection efficiencies for oleic acid particles than for sodium chloride particles in the size range from 50 to 150 nm, while achieving a comparable efficiency in the size range large than 150 nm. Effects of particle diameter, particle material, and total flow rate on the sampler’s collection efficiency are explained by the particle charging data, i.e., charging efficiencies and average charges per particle.