Photochemical synthesis of copper nanoparticles incorporated in poly(vinyl pyrrolidone)

The effect of the presence of poly(vinyl pyrrolidone) (PVP) on the copper nanoparticle formation, obtained by UV irradiation of ethanol solution of Cu(acac)₂ (acac = 2,4-pentanedionato), was investigated. At 254 nm, in conditions of light completely absorbed by complex, the PVP exhibited protective and stabilizing effects, as shown by the formation of a colloidal copper solution and by a block of the heterogeneous process, which leads to thin film formation on the quartz walls. The colloidal solution was tested for several months by plasmon position and it was found that it remained unaltered in inert atmosphere, but returned to the starting complex on contact with air. The PVP ability to control the particle size was investigated by carrying out photoreduction sensitized by Hacac at 254 and 300 nm, in the presence of PVP concentration varying from 0 to 0.2 M. In this range it was possible to obtain copper nanoparticles of dimensions decreasing from 30 to 4 nm. Besides this, the PVP (0.005–0.05 M) role as sensitizer was investigated by irradiating solutions of Cu(acac)₂ at 300 nm which is an inactive wavelength for copper reduction by direct light absorption. It was found that the PVP was an efficient sensitizer of the copper photoreduction. The nanoparticles were characterized by plasmon band, Trasmission Electron Microscope (TEM) as well as Dynamic Light Scattering (DSL) analysis. The overall results evidence the advantages of the PVP use in the nanoparticle copper formation through the photochemical technique such as the exclusive formation of colloidal copper, their size control, stable colloidal solution and complete return to the starting complex.     

Silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone)

This article describes a method for silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone) (PVP) as a stabilizer. The Co–Pt nanoparticles were prepared in an aqueous solution at 25–80 °C from CoCl₂ (3.0 × 10⁻⁴ M), H₂PtCl₆ (3.0 × 10⁻⁴ M), PVP (0–10 g/L), and NaBH₄ (4.8 × 10⁻³–2.4 × 10⁻² M). The silica coating was performed for the Co–Pt nanoparticle colloid containing the PVP ([Co] = [Pt] = 3.0 × 10⁻⁵ M) at 25 °C in (1/4) (v/v) water/ethanol solution with tetraethoxyorthosilicate (TEOS) (7.2 × 10⁻⁵–7.2 × 10⁻³ M) and ammonia (0.1–1.0 M). Silica particles, which had an average size of 43 nm and contained multiple cores of Co–Pt nanoparticles with a size of ca. 8 nm, were produced at 1.4 × 10⁻³ M TEOS and 0.5 M ammonia after the preparation of Co–Pt nanoparticles at 80 °C, 5 g/L PVP, and 2.4 × 10⁻² M NaBH₄. Their core particles were fcc Co–Pt alloy crystallites. Their saturation magnetization was 2.0-emu/g sample, and their coercive field was 12 Oe.     

Cytotoxicity and drug release behavior of PNIPAM grafted on silica-coated iron oxide nanoparticles

The nanoparticles containing thermosensitive and magnetic properties were investigated for their potential use as a novel drug carrier for targeted and controlled release drug delivery system. These thermosensitive and magnetic nanoparticles were prepared by grafting thermosensitive poly (N-isopropylacrylamide) (PNIPAM) on the surface of silica (SiO₂)-coated Fe₃O₄ nanoparticles with the particle size of 18.8 ± 1.6 nm. Adsorption and desorption behavior of bovine serum albumin (BSA) on the surface of PNIPAM-grafted SiO₂/Fe₃O₄ nanoparticles was studied, and the results indicated that these nanoparticles were able to absorb protein at temperature above the lower critical solution temperature (LCST) and to be desorbed below the LCST. Cytotoxicity studies conducted on Chinese hamster ovary (CHO-K1) cells using methyl tetrazolium (MTT) assays revealed that cell viability of 1 mg/mL PNIPAM-grafted nanoparticles was slightly decreased after 24 h of incubation as compared to the lower concentration of nanoparticles. Furthermore, the concentration of 0.5 mg/mL PNIPAM-grafted nanoparticles was totally biocompatible for 48 h, but had low cytotoxicity after 72 h of incubation. These PNIPAM-grafted nanoparticles did not induce morphological change in their cellularity after exposure for 24 and 108 h. These results demonstrate that PNIPAM-grafted nanoparticles are biocompatible and have potential use as drug carriers.     

Synthesis of VO2 (B) nanorods for Li battery application

Vanadium dioxide nanorods were synthesized through a hydrothermal reaction from V₂O₅ xerogel, poly(vinyl pyrrolidone) (PVP) and lithium perchlorate (LiClO₄). The prepared samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical discharge–charge cycling in lithium battery. SEM images reveal the nanorods to have dimensions on the order of 1–3 μm in length and 10–50 nm in diameter. The measured initial discharge capacity of the lithium battery with a cathode made of VO₂ (B) nanorods was 152 mA h/g.     

Nanostructures and magnetic properties of cobalt ferrite (CoFe2O4) fabricated by electrospinning

This paper describes the fabrication of cobalt ferrite (CoFe₂O₄) nanostructures (in the form of nanofibers and nanoparticles) by the electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and cheap Co and Fe nitrates as metal sources. The as-spun and calcined CoFe₂O₄/PVP composite samples were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun CoFe₂O₄/PVP composite nanofibers (fiber size of 320±48 nm in diameter) at 500, 600, and 800°C in air for 3 h with different heating rates of 5 or 20°C/min, either NiFe₂O₄ nanofibers of ∼10−200 nm in diameter or nanoparticles with particle sizes of ∼50−400 nm having a well-developed spinel structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature and heating rate. A faster heating rate allowed for a rapid removal of the PVP matrix and resulted in a complete change from fibrous structure to particle in the calcined CoFe₂O₄/PVP composite nanofibers. Room temperature magnetization results showed a ferromagnetic behavior of the calcined CoFe₂O₄/PVP composite nanofibers, having their hysteresis loops in the field range of ± 4500 and 3000 Oe for the samples calcined respectively with heating rates of 5 and 20°C/min. The values of the specific magnetization (M _s) at 10 kOe, remnant magnetization (M _r), M _r/M _s ratio, and coercive forces (H _c) are obtained from hysteresis loops. It was found that the values of M _s, M _r, M _r/M _s, and H _c depended strongly on morphology of the CoFe₂O₄ nanostructures.     

The responses of Ht22 cells to oxidative stress induced by buthionine sulfoximine (BSO)

Background  

glutathione (GSH) is the most abundant thiol antioxidant in mammalian cells. It directly reacts with reactive oxygen species (ROS), functions as a cofactor of antioxidant enzymes, and maintains thiol redox potential in cells. GSH depletion has been implicated in the pathogenesis of neurological diseases, particularly to Parkinson's disease (PD). The purpose of this study was to investigate the change of cellular antioxidant status and basic cell functions in the relatively early stages of GSH depletion.     

Cu1.5[Cr(CN)6]⋅6.5H2O nanoparticles: synthesis, characterization, and magnetic properties

We have synthesized nanoparticles of Cu_1.5[Cr(CN)₆]⋅6.5H₂O of varying size by using poly(vinylpyrrolidone) (PVP) as a protecting polymer. The particle size variation has been achieved by varying the amount of the PVP surfactant with the reactants. The prepared nanoparticles have been investigated by using X-ray diffraction, transmission electron microscopy, and direct-current magnetization techniques. The nanoparticles crystallize in a face centred cubic structure (space group: Fm3m). The approximate particle sizes for the three samples are 18, 9, and 5 nm, respectively. Non-PVP nanoparticles (18 nm) show a magnetic ordering temperature of 65 K. A decrease in the magnetic ordering temperature was observed with decreasing particle size. These nanoparticles are magnetically very soft, showing negligibly small values of the coercivity and remanent magnetization. The maximum magnetization and spontaneous magnetization values at 5 K are found to decrease with decreasing particle size. The observed magnetization behaviour of the nanoparticles has been attributed to the increasing surface spin disorder with decreasing particle size.     

Preparation of cerium hydroxycarbonate by a surfactant-assisted route

Cerium hydroxycarbonate (CeOHCO₃) with shuttle-like morphology has been conveniently synthesized at 90 °C from aqueous solution in the presence of polyvinylpyrrolidone (PVP). The products were characterized by X-ray diffraction, transmission electron microscopy and photoluminescent (PL) techniques. The as-prepared CeOHCO₃ was found to have a PL emission at about 347 nm. Experimental conditions as well as the role of PVP played in the reaction were also explored.     

Toxicity of amorphous silica nanoparticles in mouse keratinocytes

The present study was designed to examine the uptake, localization, and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24 h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118, and 535 nm SiO₂) and then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 μg/mL) compared to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO₂ toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100, and 200 μg/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size of the particles is critical to produce biological effects.     

Preparation of phase pure and well-crystallized Li4Ti5O12 nanoparticles by precision control of starting mixture and calcining at lowest possible temperatures

In an attempt to obtain spinel Li₄Ti₅O₁₂ with smallest possible grain size and highest possible phase purity via a solid state route, we tried to elevate reactivity of the reactant mixture by mechanical activation and appropriate choice of the starting materials. From the stoichiometric mixture comprising Li₂CO₃ and 150 nm anatase, we needed to heat at 950 °C for 1 h to obtain 81–88% phase purity (PhP) of Li₄Ti₅O₁₂ with its average grain size ca 600 nm. After mechanical activation with a multi-ring mill for 30 min, 850 °C was enough to obtain 85–87% pure 500 nm spinel. From a combination of LiNO₃ and 50 nm anatase, 90–91% phase pure product with its grain size 240 nm was obtained at 750 °C due to fusion of the nitrate and shorter diffusion path. By using CH₃COOLi.2H₂O and 50 nm anatase we obtained 130 nm Li₄Ti₅O₁₂ with its PhP ca 90% by milling the mixture preliminarily calcined at 500 °C for 1 h and heating subsequently at 700 for 1 h.     

Design optimization of tunneling field-effect transistor based on silicon nanowire PNPN structure and its radio frequency characteristics

Recently, a number of semiconductor devices have been widely researched in order to make breakthroughs from the short-channel effects (SCEs) and high standby power dissipation of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). In this paper, a design optimization for the silicon nanowire tunneling field-effect transistor (SNW TFET) based on PNPN multi-junction structure and its radio frequency (RF) performances are presented by using technology computer-aided design (TCAD) simulations. The design optimization was carried out in terms of primary direct-current (DC) parameters such as on-current (I_on), off-current (I_off), current ratio (I_on/I_off), and subthreshold swing (SS). Based on the parameters from optimized DC characteristics, basic radio frequency (RF) performances such as cut-off frequency (f_T) and maximum oscillation frequency (f_max) were analyzed. The simulated device had a channel length of 60 nm and a SNW radius of 10 nm. The design variable was width of the n-doped layer. For an optimally designed PNPN SNW TFET, SS of 34 mV/dec and I_on of 35 μA/μm were obtained. For this device, f_T and f_max were 80 GHz and 800 GHz, respectively.     

Investigation of microwave absorbing properties for magnetic nanofiber of polystyrene–polyvinylpyrrolidone

Aligned magnetic blend of polystyrene–polyvinylpyrrolidone (PS–PVP) nanofibers were prepared by this method. First, polystyrene–polyvinylpyrrolidone (PS–PVP) blend solution in THF was synthesized. Then magnetic of PS–PVP–Fe₃O₄–polyethylene glycol (PEG) was prepared by masking method. Finally, magnetic nanofiber of PS–PVP–Fe₃O₄–PEG was prepared by electrospinning method, too. An electric potential difference of 25 kV was applied between the collector and a syringe tip, and the distance between the collector and the tip was 13 cm. Fe₃O₄ is exhibit various magnetic properties of which the complex permeability and the permittivity, in particular, are important in determining their high frequency characteristics. The magnetic oxide particles and nanofiber of nanometer size were characterized by TEM and SEM respectively. The thermal properties of nanofibers were determined by TGA and DSC. The magnetic characterization of the fibers was also performed by VSM and AFM techniques. On the other hand, nanofiber with diameters ranging from 30 to 40 nm, showing at room temperature, coercive field values of around 25 kV and saturation magnetization was 1.1 emu/g. Microwave reflection loss of the sample was tested at 8–12 GHz microwave frequencies and the results showed that magnetic nanofiber possessed the microwave absorbing properties.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

One-Pot Scalable Fabrication of Chitosan-Capped Antibacterial Sulfur Nanoparticles from Elemental Sulfur

Sulfur nanoparticles (SNPs) have shown good potential in numerous fields due to their unique composition and properties. However, the direct utilization of abundant and inexpensive elemental sulfur for the large-scale fabrication of high-quality SNPs is still in its infancy. Herein, a simple one-pot approach for the preparation of SNPs is presented, and gram-scale SNPs can be readily prepared in one batch in the laboratory. By adding elemental sulfur-ethylenediamine precursor to the acidic chitosan (CS) solution, chitosan-capped sulfur nanoparticles (CS-SNPs) can be formed immediately. Benefiting from the capping of CS, CS-SNPs simultaneously possess small and uniform size with an average diameter of 19 nm, good aqueous dispersibility and stability, and favorable antioxidant capability against 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) free radicals. Moreover, CS-SNPs also exhibit fine antibacterial activity against Staphylococcus aureus, and the minimum and optimal inhibitory concentrations are 256 and 512 µg mL⁻¹, respectively. Considering the easy fabrication process and attractive attributes of CS-SNPs, this investigation not only offers an effective method for the scalable fabrication of robust SNPs but also provides a feasible way for the value-added utilization of elemental sulfur.     

Mechanosynthesis of nanocrystalline MgFe2O4—neutron diffraction and Mössbauer spectroscopy

The evolution of nanocrystalline n-MgFe₂O₄ by high-energy milling a mixture of MgO and α-Fe₂O₃ for periods of between 0 h and 12 h has been investigated by neutron diffraction in addition to previous Mössbauer, XRD and HRTEM measurements. Complete transformation of the milled products to n-MgFe₂O₄ only occurs on milling to ～8 h even though the average particle size decreases to <?～10 nm after milling for 2 h. The applied field Mössbauer spectra of n-MgFe2O4 can be well described by two subspectra representing core and shell regions with different cation distributions and spin canting angles. The neutron pattern of nanocrystalline MgFe₂O₄ is described well by two components comprising nanoparticles of core and shell dimensions ～7(1) nm and ～0.7(1) nm, respectively, in support of the Mössbauer core-shell model.     

Optical properties of chalcogen-loaded zeolite (ZSM-5)

Sulfur, selenium, and tellurium were loaded into sub-millimeter size ZSM-5 single crystals, and the optical properties have been comparatively studied. S and Te show similar features, while Se is unique. S and Te have optical absorption edges at wavelengths of ～400 nm with transmission dips at ～450 nm, while Se has the edge at ～550 nm. The three materials provide photoluminescence at visible wavelengths, with the intensities of S and Te being stronger than that of Se by two orders. These optical properties imply that S and Te in the zeolite form small atomic units such as S₃ and Te₂, while Se condenses into single-chain structures.     

Effect of intrinsic ZnO thickness on the performance of SnS/CdS-based thin-film solar cells

Tin monosulfide (SnS) has promising properties as an absorber material for thin-film solar cells (TFSCs). SnS/CdS-based TFSCs have the following device structure: SLG/Mo/SnS/CdS/i-ZnO/AZO/Al. The optimization of thickness of intrinsic zinc oxide (i-ZnO) for SnS-absorber layers and its impact on SnS/CdS heterojunction TFSCs has been investigated at different thicknesses ranging from 39 nm to 73 nm. With the increase in thickness of i-ZnO from 39 nm to 45 nm, the overall performance improved. The highest PCE of 3.50% (with V_OC of 0.334 V, J_SC of 18.9 mA cm⁻², and FF of 55.5%) was observed for 45 nm-thick i-ZnO layers. Upon a further increase in the i-ZnO thickness to 73 nm, the device performance deteriorated, indicating that the optimum thickness of the i-ZnO is 45 nm. The device performances were analyzed comprehensively for different i-ZnO thicknesses.     

Use of a silver ion selective electrode to assess mechanisms responsible for biological effects of silver nanoparticles

For a detailed analysis of the biological effects of silver nanoparticles, discrimination between effects related to the nano-scale size of the particles and effects of released silver ions is required. Silver ions are either present in the initial particle dispersion or released by the nanoparticles over time. The aim of this study is to monitor the free silver ion activity {Ag⁺} in the presence of silver nanoparticles using a silver ion selective electrode. Therefore, silver in the form of silver nanoparticles, 4.2 ± 1.4 nm and 2–30 nm in size, or silver nitrate was added to cell culture media in the absence or presence of A549 cells as a model for human type II alveolar epithelial cells. The free silver ion activity measured after the addition of silver nanoparticles was determined by the initial ionic silver content. The p {Ag⁺} values indicated that the cell culture media decrease the free silver ion activity due to binding of silver ions by constituents of the media. In the presence of A549 cells, the free silver ion activity was further reduced. The morphology of A549 cells, cultivated in DME medium containing 9.1% (v/v) FBS, was affected by adding AgNO₃ at concentrations of ≥30 μM after 24 h. In comparison, silver nanoparticles up to a concentration of 200 μM Ag did not affect cellular morphology. Our experiments indicate that the effect of silver nanoparticles is mainly mediated by silver ions. An effect of silver on cellular morphology was observed at p {Ag⁺} ≤ 9.2.     

Aggregate structure and crystallite size of platinum nanoparticles synthesized by ethanol reduction

Monodispersed platinum (Pt) nanoparticles were synthesized from reducing hydrated hydrogen hexachloroplatinic acid (H₂PtCl₆·nH₂O) with ethanol in the presence of polyvinylpyrrolidone (PVP) as a steric stabilizer. Concentration of both PVP and ethanol influenced the aggregate structure and crystallite size of the nanoparticles. When the molar ratio of monomeric unit of PVP to Pt, i.e., [PVP]/[Pt], was one, the synthesized Pt particles coagulated pronouncedly into an inter-connected particulate network or self-organized into spherical superstructures with an apparent diameter ranging from 60 to 80 nm, depending on the ethanol concentration. The geometry and structure of these complex aggregates were characterized by fractal analysis. Fractal dimensions of 2.13–2.23 in three dimensions were determined from the Richardson’s plot, which suggests that a reaction-limited cluster–cluster aggregation model (RCLA) was operative. The Pt colloids became apparently more stable when the [PVP]/[Pt] ratio was increased greater than 20. Crystallite size of the Pt nanoparticles was found to increase linearly with the ethanol concentration as the [PVP]/[Pt] was held at one. This suggests that the reduction rate of PtCl₆ ²⁻ ions in solution is critically important to the synthesized crystallite size.     

Photo-curable epoxy functionalized cyclotetrasiloxane as a gate dielectric for organic thin film transistors

We synthesized a new photo-curable organic/inorganic hybrid material, cyclotetrasiloxane (CTS) derivative containing cyclohexene-1,2-epoxide functional groups (CTS-EPOXY), and its characteristics are compared with a prototypical organic gate insulator of poly(4-vinylphenol) (PVP) in the organic thin film transistors (OTFTs) using pentacene as an active p-type organic semiconductor. Compared with PVP, CTS-EPOXY shows better insulating characteristics and surface smoothness. A metal/insulator/metal (MIM) device with the 300-nm-thick CTS-EPOXY film shows more than two orders of magnitude lower current (less than 40 nA/cm² over the voltage range up to 60 V) compared with PVP. In addition, the pentacene TFT with CTS-EPOXY as a gate dielectric layer shows slightly higher field-effect mobility of μ_FET = 0.20 cm²/V s compared to that with PVP.