Aggregation kinetics of CeO<Subscript>2</Subscript> nanoparticles in KCl and CaCl<Subscript>2</Subscript> solutions: measurements and modeling

To characterize the environmental transport and health risks of CeO₂ nanoparticles (NPs), it is important to understand their aggregation behavior. This study investigates the aggregation kinetics of CeO₂ NPs in KCl and CaCl₂ solutions using time-resolved dynamic light scattering (TR-DLS). The initial hydrodynamic radius of CeO₂ NPs measured by DLS was approximately 95 nm. Attachment efficiencies were derived both from aggregation data and predictions based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The deviations of the DLVO predictions were corrected by employing the extended DLVO (EDLVO) theory. The critical coagulation concentration (CCC) of CeO₂ NPs at pH = 5.6 is approximately 34 mM for KCl and 9.5 mM for CaCl₂. Furthermore, based on the EDLVO theory and the von Smoluchowski’s population balance equation, a model accounting for diffusion-limited aggregation (DLA) kinetics was established. For the reaction-limited aggregation (RLA) kinetics, a model that takes fractal geometry into account was established. The models fitted the experimental data well and proved to be useful for predicting the aggregation kinetics of CeO₂ NPs.     

Photoluminescence of nanoparticles of (Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>(Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.05</Subscript> solid solution

We have ground bulk samples to obtain nanoparticles of (Ga₂S₃)_1–x (Eu₂O₃) _x solid solutions, the sizes of which were determined using an atomic force microscope. The photoluminescence spectra of the nanoparticles were studied in the temperature interval 77–300 K. We have established the mechanisms for emission and transfer of energy from the matrix to the rare-earth ion, and we determined the Stokes shift (ΔS = 0.7 eV), the Huang–Rhys parameter (S = 16), and the optical phonon energy (ħ−ω = 23 meV).     

China rose petal as biotemplate to produce two-dimensional ceria nanosheets

China rose petal was used as robust biotemplate for the facile fabrication of novel ceria nanosheet with a thickness of about 7 nm via a continuous infiltration process. The presence of well-resolved peaks ([111], [200], [220], and [311]) for the products revealed the formation of the fluorite-structured CeO₂. The detailed characterization by field-emission scanning electron microscope (FESEM), field-emission transmission electron microscope (FETEM), and atomic force microscopy (AFM) exhibited the biomorphic structure of polycrystalline ceria film with the nanoparticle size of ca. 6.98 nm. Based on the surface chemistry and biochemistry processes, a possible mechanism for the formation of CeO₂ nanosheets is proposed. Furthermore, nitrogen adsorption–desorption measurement and photoluminescence spectrum (PL) were employed to characterize the samples. The ceria nanosheet showed the existence of mesopores (pores 2–4 nm diameter) on its surface and a broad emission ranging from 350 to 500 nm in photoluminescence spectrum. X-ray photoelectron spectroscopy analysis (XPS) confirmed that the mesoporous nanosheets possessed more surface vacancies than the bulk CeO₂; hence these hierarchical CeO₂ layers appear to be potential candidates for catalytic applications.     

Antiferromagnetic interactions in Er-doped SnO<Subscript>2</Subscript> DMS nanoparticles

Diluted magnetic semiconductor (DMS) nanoparticles of Sn_1−x Er _x O₂ (x = 0.0, 0.02, 0.04, and 0.1) were prepared by sol–gel method. The X-ray diffraction patterns showed SnO₂ rutile structure for all samples with no impurity peaks. The decrease in crystallite size with Er concentration was confirmed from TEM measurements (from 12 to 4 nm). The UV–Visible absorption spectra of Er-doped SnO₂ nanoparticles showed blue shift in band gap compared to undoped SnO₂. The electron spin resonance analysis of Er-doped SnO₂ nanoparticles indicate Er³⁺ in a rutile lattice and also decrease in intensity with Er concentration above x = 0.02. Temperature-dependent magnetization studies and the inverse susceptibility curves indicated increased antiferromagnetic interaction with Er concentration.     

Synthesis of silver and lithium sub-micro- and nanoparticles coated with derivatives of <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butyl thiacalix[4]arenes

The effect of solvent nature and temperature on the formation of 3D-dimensional SAM (self-assembled monolayers on nanoparticles) based on synthetically available stereoisomers of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by pyrrolidide and octylamide groups (cone, partial cone, and 1,3-alternate) with lithium and silver nanoparticles were determined by dynamic light-scattering and transmission electron microscopy. It was found that the variation of the temperature of the system and the nature of the solvent leads to the formation discrete or extended particles (CH₂Cl₂) (98–110 nm), nanostructures (CH₃CN) (120–295 nm) or three-dimensional SAM (DMF) (1–13 nm; 46–622 nm).     

FMR and TEM Studies of Co and Ni Nanoparticles Implanted in the SiO<Subscript>2</Subscript> Matrix

Fused silica plates have been implanted with 40 keV Co⁺ or Ni⁺ ions to high doses in the range of (0.25–1.0) × 10¹⁷ ions/cm², and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO₂ matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and Ni nanoparticles implanted in the SiO₂ matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature are presented.     

Novel NdCo<Subscript>5</Subscript> nanoflakes and nanoparticles produced by surfactant-assisted high-energy ball milling

High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders. In this work, NdCo₅ nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo₅ flakes have a thickness below 150 nm and an aspect ratio as high as 10²–10³; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures, T _SR1 = 276 and T _SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk.     

The magnetic and hyperthermia studies of bare and silica-coated La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> nanoparticles

The magnetic nanoparticles of La_0.75Sr_0.25MnO₃ perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods and probed by DC magnetic measurements. The nanoparticles of the mean crystallite sizes 11–40 nm exhibit T _C in the range of ≈310–347 K and the sample possessing 20-nm crystallites was identified as the most suitable for hyperthermia experiments. In order to obtain a colloidally stable suspension and prevent toxic effects, the selected magnetic cores were further encapsulated into silica shell using tetraethoxysilane. The detailed magnetic studies were focused on the comparison of the raw product, the bare nanoparticles after mechanical processing and the silica-coated nanoparticles, dealing also with effects of size distribution and magnetic interactions. The heating experiments were carried out in an AC field of frequencies 100 kHz–1 MHz and amplitude 3.0–8.9 kA m⁻¹ on water dispersions of the samples, and the generated heat was deduced from their warming rate taking into account experimentally determined thermal losses into surroundings. The experiments demonstrate that the heating efficiency of the coated nanoparticles is generally higher than that of the bare magnetic cores. It is also shown that the aggregation of the bare nanoparticles increases heating efficiency at least in a certain concentration range.     

Young’s modulus of PS/CeO<Subscript>2</Subscript> composite with core/shell structure microspheres measured using atomic force microscopy

Organic–inorganic composite microspheres with PS as a core and CeO₂ as a shell were synthesized by in situ chemical precipitation method. The size of PS core was 117, 163, 206, and 241 nm, respectively, and the shell thickness was about 10 nm. The CeO₂ shell was composed of a large number of nanoparticles, of which the size was 4–6 nm. Atomic force microscopy was employed to probe the mechanical properties of core–shell structured ceria-coated polystyrene (PS/CeO₂) composite microspheres. On the basis of Hertz’s theory of contact mechanics, compressive moduli were measured by the analysis of force–displacement curves captured on the microsphere samples. For a fixed CeO₂ shell thickness, the Young’s modulus of composite microspheres increased with an increase of PS core size. The calculated Young’s moduli (E) values of composites for 136, 185, 242, and 261 nm in diameter were 5.78 ± 0.9, 7.23 ± 1.3, 11.46 ± 1.7, and 14.54 ± 1.4 GPa, respectively. The results revealed the effect of the CeO₂ shell on the elastic deformation of the PS core. This approach will provide fundamental insights into the actual role of organic/inorganic core/shell composite abrasives in chemical mechanical polishing.     

TiO<Subscript>2</Subscript> nanotube height effect on the efficiency of dye-sensitized solar cells

Performance of dye-sensitized solar cells (DSSCs) based on TiO₂ nanotubes (NTs) filled with TiO₂ nanoparticles (NPs) was studied as a function of NT height (h). The NT height was varied in the range of 1.5–7.0 μm, while the NT diameter was kept constant at ~80 nm. The studies showed that DSSC efficiency, current density, and fill factor linearly increased with h and ranged in 1.76–6.5%, 3.62–13.2 mA/cm², and 0.66–0.76, respectively, within the h range studied. The electrochemical impedance spectroscopy was also performed to study DSSC electron transport properties. Based on both photovoltaic and electrochemical impedance spectroscopy data, the results were explained as being due to the increased dye loading that led to higher light-harvesting efficiency.     

Optical properties of pyridine funtionalized TbF<Subscript>3</Subscript> nanoparticles

The preparation of pyridine functionalized TbF₃ nanoparticles are described in this report. Synthesized nanoparticles were characterized using the TEM, UV/Vis, FTIR and photoluminescence spectroscopy. TEM micrograph reveals the nanorod shaped, uniform in size with a particles size in the range of 20–30 nm. FTIR spectrum shown characteristic absorption bands of pyridine and a small intensity band at 411 cm⁻¹ corresponding metal nitrogen ν(Tb–N) bonding. Uv-vis spectrum shown the characteristic absorption transitions of Tb³⁺ ion. A strong emission transition at 540 nm (⁵D₄ → ⁷F₅) was observed on excite by visible light at 414 nm.     

Synthesis of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel nanoparticles using a mixture of bayerite and magnesium sulfate

This article reports a novel method to prepare MgAl₂O₄ spinel nanoparticles. By calcining a powder mixture of bayerite and magnesium sulfate at 800 °C and washing with water, single-phase MgAl₂O₄ spinel nanoparticles were prepared. The powder mixture and the calcined products were characterized by differential thermal and thermogravimetric analysis (DSC-TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) nitrogen-gas adsorption method. The obtained MgAl₂O₄ spinel nanoparticles have an average particle size of 12 nm, a narrow size distribution, and weak agglomeration. The specific surface area of the MgAl₂O₄ spinel powder is 110 m²/g. The formation of MgAl₂O₄ spinel is attributed to a solid-state reaction between γ-Al₂O₃ and MgSO₄.     

Characterization of channel waveguides in Pr:YLiF<Subscript>4</Subscript> crystals fabricated by direct femtosecond laser writing

Single tracks and pairs of tracks are written in the volume of Pr-doped LiYF₄-crystals using tightly focused femtosecond laser radiation (λ=1045 nm, τ _p=400–500 fs, f=0.1–1 MHz). Waveguiding between the tracks is demonstrated and optimized by varying the distance between the tracks and the laser writing conditions. The stress-induced guiding mechanism is explained based on TEM, interference microscopy, near-field and far-field measurements. It is shown that the single-crystalline material is getting poly-crystalline under femtosecond laser irradiation. By measuring the lifetime of the ³P₁→³H₅ transition and the emission spectrum at excitation with λ=444 nm, no influence on these properties of the guided light is observed. This possibly enables the realization of a channel waveguide laser in the visible spectral range.     

Fabrication of magnetic gold nanorod particles for immunomagnetic separation and SERS application

The preparation and application of rod-shaped core–shell structured Fe₃O₄–Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe₃O₄ core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 ± 2 nm and an average length of about 50 ± 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Pt nanoparticles supported over Ce–Ti–O: the solvothermal and photochemical approaches for the preparation of catalytic materials

Ce–Ti–O supports with different Ce/Ti molar ratios were synthesized by the solvothermal method using hexadecyltrimethylammonium bromide. Pt nanoparticles were then supported by photochemical deposition. The shape, size, and structure of these materials were analyzed by high-resolution transmission electron microscopy. The single CeO₂ support was also prepared, consisting of agglomerated cubic particles ranging from ~3 to 8 nm. When titania was combined with ceria, a nanostructured architecture was produced, evidencing the strong influence of Ti in the support structure. Photodeposition of Pt nanoparticles is more efficient on Ce–Ti–O supports than in pristine CeO₂. Crystalline Pt nanoparticles (mainly of ~2 to 4 nm) were detected. The catalytic properties of the materials were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. It was observed that Pt supported on Ce–Ti–O is more active and selective than Pt on CeO₂ or TiO₂ separately. The catalyst with 40 mol% Ce leads to total conversion of cinnamaldehyde in a few minutes; however, higher selectivity toward the desired product (cinnamyl alcohol) was obtained with higher amounts of Ce (50 mol%).     

Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus <Emphasis Type="Italic">Penicillium</Emphasis> sp.

In this work, the fungus Penicillium was used for rapid extra-/intracellular biosynthesis of gold nanoparticles. AuCl₄ ⁻ ions reacted with the cell filtrate of Penicillium sp. resulting in extracellular biosynthesis of gold nanoparticles within 1 min. Intracellular biosynthesis of gold nanoparticles was obtained by incubating AuCl₄ ⁻ solution with fungal biomass for 8 h. The gold nanoparticles were characterized by means of visual observation, UV–Vis absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The extracellular nanoparticles exhibited maximum absorbance at 545 nm in UV–Vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanocrystals. TEM exhibited the formed spherical gold nanoparticles in the size range from 30 to 50 nm with an average size of 45 nm. SEM and TEM revealed that the intracellular gold nanoparticles were well dispersed on the cell wall and within the cell, and they are mostly spherical in shape with an average diameter of 50 nm. The presence of gold was confirmed by EDX analysis.     

Electromagnetic wave absorption properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> octahedral nanocrystallines in gigahertz range

Large-scale octahedral Fe₃O₄ nanocrystallines with crystalline size of 100−500 nm were synthesized by a facile solvent-thermal method for electromagnetic wave application. The Fe₃O₄ nanocrystallines showed a higher saturation magnetization (M _s ) value of 86.8 emu/g and larger coercivity (H _cj ) value of 255 Oe than that of magnetite polycrystallines because of their good crystallization and dispersion. The epoxy resin composites with 40 vol% Fe₃O₄ powders provided good electromagnetic wave absorption performance (RL < −20 dB) in the range of 2.0–4.3 GHz over the absorber thicknesses of 3.5–6.8 mm. A minimum RL value of −47 dB was observed at 3.1 GHz with a thickness of 4.8 mm.     

Single enzyme nanoparticle for biomimetic CO<Subscript>2</Subscript> sequestration

Nanoparticle technology is being increasingly used in environmental sciences. We prepared single enzyme nanoparticle (SEN) by modifying the surface of carbonic anhydrase (CA) with a thin layer of organic/inorganic hybrid polymer. SEN-CA appears to be improving the stability of free enzyme. CA, as ubiquitously found enzyme, is involved in gaseous CO₂ sequestration and is being looked as a promising candidate for combating global warming. We report here physical characterization of SEN-CA using transmission electron microscope (TEM), Fourier-transform infrared analysis (FTIR), X-ray diffraction analysis (XRD), and energy dispersive X-ray (EDX). Average size of SEN-CA particles appears to be in the range of 70–80 nm. We also report the effect of SEN formation on the kinetic parameters of free CA such as Michaelis–Menten constant (K _m), maximum reaction velocity (V _max), and storage stability of free CA and SEN-CA. The V _max of SEN-CA (0.02857 mmol/min/mg) and free enzyme (0.02029 mmol/min/mg) is almost similar. K _m has decreased from 6.143 mM for SEN-CA to 1.252 mM for free CA. The stabilization of CA by SEN formation results in improved the half-life period (up to 100 days). The formation of carbonate was substantiated by using gas chromatography (GC). The conversion of CO₂ to carbonate was 61 mg of CaCO₃/mg of CA and 20.8 mg of CaCO₃/mg of CA using SEN-CA and free CA, respectively.