As-prepared Solution Research Articles

Fluorescence and fluorescence resonance energy transfer of N-(aminobutyl)-N-(ethylisoluminol) functionalized gold nanoparticles

Abstract The synthesis of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) functionalized gold nanoparticles (ABEI-AuNPs) and their chemiluminescence properties were described in our previous work. Since the ABEI molecules coated on the surface of ABEI-AuNPs have the fluorescence (FL) activity, the FL property of these ABEI-AuNPs was studied in the present work. It was observed that the FL intensity of a single gold nanoparticle was 634 times brighter than that of one free ABEI molecule, even though 86% of the FL emission of ABEI molecules on the surface of ABEI-AuNPs was inhibited by gold cores through intra- and inter-particle quenching effects. Moreover, the photostability of ABEI-AuNPs was studied and 96% FL intensity of as-prepared ABEI-AuNPs solution remained after 5 min continuous excitation, almost 70% FL intensity remained after 45 min. ABEI-AuNPs exhibited much better resistance to photobleaching property than luminol-AuNPs. Furthermore, ABEI-AuNPs and acriflavine were designed as energy donor and energy acceptor, respectively, to construct a novel fluorescence resonance energy transfer (FRET) system. The efficient energy transfer from ABEI-AuNPs to acriflavine was observed. Taking advantage of excellent labeling property of gold nanomaterials, the FRET behavior between ABEI-AuNPs and acriflavine may find future applications in bioassays based on the FL detection.

Synthesis of luminescent nanocrystals and solid solutions in the YNbO4–EuNbO4 system via hydrothermal route

Luminescent nanocrystals having distinctive ellipsoidal morphology and the complete solid solution of monoclinic phase in the YNbO4–EuNbO4 system were hydrothermally formed under weakly basic conditions at 180–240°C for 5h. The excitation spectra of the Y1−xEuxNbO4 nanocrystals, which consisted of the charge transfer (CT) band around 240–270nm due to [NbO4]3−–Eu3+ interaction and several sharp bands corresponding to the f–f transitions of Eu3+, e.g. the most intense absorption band at 395nm (7F0→5L6), showed that the compounds could be excited by both ultraviolet and visible light. A dominant red emission at 610nm and a weak orange emission at 590nm assigned to 5D0→7F2 and 5D0→7F1 transitions of Eu3+, respectively were observed in the as-prepared nanocrystals containing europium under excitation at 395nm. The heat treatment at temperatures more than 1000°C in air was effective for the improvement in the photoluminescence intensity of the as-prepared solid solutions. By the enhancement in the crystallinity and crystallite growth of the monoclinic phase through heat treatment at 1300°C in air, the luminescence intensity of the as-prepared solid solution, Y0.75Eu0.25NbO4 (x=0.25), which showed the most significant photoluminescence, became more than 5 times as strong as that before the heat treatment.

Soluble colloidal manganese dioxide: Formation, identification and prospects of application

Soluble colloidal MnO2 was prepared by the reduction of KMnO4 by three reducing agents as MnSO4, Na2S2O3 and HCOOH in neutral aqueous solutions at 25°C. Under suitable conditions, these solutions were dark brown in color and found to remain stable and transparent for several weeks. The obtained colloid was characterized by spectrophotometric and coagulation methods. The spectral behavior of soluble colloidal MnO2 was studied. The λmax was 390 nm when MnO2 was prepared by the reduction of KMnO4 by MnSO4. Both the λmax and the molar extinction coefficient depended on the method of preparation of colloidal MnO2. The formation of MnO2 was confirmed by the determination of the oxidation state of Mn-species in MnO2. The behavior of as-prepared colloidal solution obeys Beer Lambert law, if the concentrations of the colloidal particles are assumed to be equal to [MNO4−]0. Both spectral analysis and that using Rayleigh’s law confirmed the existence of colloidal MnO2. The observed coagulating efficiency depends not only on the concentration of electrolyte but also on the charge carried by the cation of the electrolyte. Stability of the colloidal particles in the aqueous solutions is determined by the negative charge on the surface of the colloidal particles.

TiO2 nanofibre-assisted photodecomposition of Rhodamine B from aqueous solution

Using liquid phase deposition method on cellulose substrate, TiO2 nanofibres were prepared with TiCl4 as a precursor. TiO2 nanofibres were obtained after heat treatment of the cellulose template. The remaining product was composed of micron-size TiO2 fibres with a nanofiber microstructure. It is shown that nanofibres are formed through the aggregation of TiO2 nanoparticles. X-ray diffraction analysis of the as-prepared solution indicates the formation of crystalline TiO2 anatase phase. EDX analysis was employed to measure the adsorbed mass of TiO2 on cellulose substrate. The effect of deposition time on the growth and morphology was investigated by scanning electron microscopy. Transmission electron microscopy studies demonstrate fine microstructures composed of 10–15 nm nanoparticles. Surface area of the TiO2 fibres, measured by Brunauer, Emmett and Teller analysis, was about 104 m2 g−1. Photodegradation of Rhodamine B as a standard dye shows that the prepared samples have a high photocatalytic activity due to large surface area.

Energy harvester using PZT nanotubes fabricated by template-assisted method

Lead zirconate titanate (PZT) nanotubes fabricated by template-assisted method using sol–gel solution infiltration are applied for energy harvester. To fabricate PZT nanotubes, an anodic aluminum oxide is used for the template, and as-prepared PZT solution dropped on the surface of the AAO is infiltrated by vacuum pump into the pores in the AAO. The template including PZT solution is dried at 80 °C for 1 min and dried again at 300 °C for 10 min, and then it treated at 650 °C for 30 min to anneal PZT and form the expected perovskite phase. The fabricated nanotubes were mixed with PDMS polymer composite and polyimide films coated Pt/Ti were used for electrodes. Finally, it demonstrated that the energy harvester could generate the output power of 37 nW/cm2.

Investigation on Temperature-Sensitive Poly (N-Vinylcaprolactam) Modified Calcium Alginate Microspheres

Temperature-sensitive calcium alginate-based microspheres were prepared in two steps. Firstly, free-radical polymerization of temperature-sensitive N-vinylcaprolactam monomer was performed in aqueous solution of sodium alginate, yielding a mixed aqueous solution bearing temperature-sensitivity composed of poly(N-vinylcaprolactam), sodium alginate-graft- poly(N-vinylcaprolactam) and sodium alginate. Then temperature-sensitive composite microspheres were prepared by inverse emulsification-crosslinking using the as-prepared solution as water phase, n-hexane as oil phase, Span-85 and Tween-85 as emulsifiers and calcium chloride as crosslinker respectively. The morphology and temperature-sensitivity of the composite microspheres were investigated by scanning electron microscope and turbidity method respectively. The controlled release behavior of the microspheres towards temperature was investigated preliminarily using berberine as a model drug.

Band energy levels and compositions of CdS-based solid solution and their relation with photocatalytic activities

CdS-based solid solution (AgIn)xCd2(1−x)S2 (x = 0, 0.02, 0.05, 0.1, 0.2, 1.0) was prepared through hydrothermal reaction. The physicochemical and optical properties of the as-prepared solid solution samples were characterized by X-ray diffraction (XRD), diffuse reflectance UV-visible absorption spectroscopy (DRS) and N2 adsorption–desorption isotherms. Through controlling the composition of CdS solid solution, its band-gap energy (Eg) can be easily tuned from ca. 2.4 to 1.8 eV. The band edge energy levels of all samples were determined through the measurement of the open circuit potential (OCP) and onset potential of photocurrent (Eonset) for their respective electrodes. The decrease in Eg of the solid solutions is attributed to the downward and upward shift of conduction and valence band potentials, respectively. It was found that In 5s5p and Cd 5s5p states mainly contribute to the bottom of conduction band, and Ag 4d and S 3p states mainly contribute to the top of valence band as confirmed by theoretical density of states (DOS) calculation. To test the photocatalytic activity of the prepared solid solution materials, the evolution of H2 and the reduction of polyoxometalate (POM: PMo12O403−) under visible light irradiation were used as probe reactions. The photocatalysis test results were well correlated with the band structures determined from the photoelectrochemical measurements and DOS calculation. The relative positioning between the band-edge levels and the substrate conversion potentials was the most critical and this can be controlled with the solid solution-based photocatalysts.

Nonpolar Solvothermal Fabrication and Electromagnetic Properties of Magnetic Fe3O4 Encapsulated Semimetal Bi Nanocomposites

Magnetic Fe3O4 nanoparticles (NPs) encapsulated semimetal Bi nanocomposites were fabricated by a solvothermal method based on the nonpolar 1-octadecene. Bi and Fe ions were introduced into the oil phase by the complex with sodium oleate in the as-prepared solution. The nanocomposites were oil soluble and dispersed well in any nonpolar solution with the surface modification of oleic acid. It is argued that hydroxyl groups as the reductant induce the formation of Bi microspheres and prevent Fe3O4 NPs from oxidation. The frequency dependence of complex permittivity and permeability indicates that Bi and interface polarization of Bi/Fe3O4 nanocomposites are responsible for the dielectric resonances, and superparamagnetic Fe3O4 NPs weaken the natural resonance.

Fluorine Based Superhydrophobic Coatings

Superhydrophobic coatings, inspired by nature, are an emerging technology. These water repellent coatings can be used as solutions for corrosion, biofouling and even water and air drag reduction applications. In this work, synthesis of monodispersive silica nanoparticles of ~120 nm diameter has been realized via Stöber process and further functionalized using fluoroalkylsilane (FAS-17) molecules to incorporate the fluorinated groups with the silica nanoparticles in an ethanolic solution. The synthesized fluorinated silica nanoparticles have been spin coated on flat aluminum alloy, silicon and glass substrates. Functionalization of silica nanoparticles with fluorinated groups has been confirmed by Fourier Transform Infrared spectroscopy (FTIR) by showing the presence of C-F and Si-O-Si bonds. The water contact angles and surface roughness increase with the number of spin-coated thin films layers. The critical size of ~119 nm renders aluminum surface superhydrophobic with three layers of coating using as-prepared nanoparticle suspended solution. On the other hand, seven layers are required for a 50 vol.% diluted solution to achieve superhydrophobicity. In both the cases, water contact angles were more than 150°, contact angle hysteresis was less than 2° having a critical roughness value of ~0.700 µm. The fluorinated silica nanoparticle coated surfaces are also transparent and can be used as paint additives to obtain transparent coatings.

Aqueous Phase Synthesized CdSe Magic-Sized Clusters: Solution Composition Dependence of Adsorption Layer Structure

We report dispersion solution composition dependence of the adsorption layer structure and the physical and optical properties of aqueous phase-synthesized semiconductor nanoparticles (NPs). We synthesized cysteine (Cys)-capped CdSe NPs with well-defined core structures, dispersed them in a series of aqueous solutions with different compositions, and then investigated their adsorption layer structure and physical and optical properties. Each CdSe NP consisted of a (CdSe)33 or (CdSe)34 magic-sized cluster (d - 1.45 nm) core, a ligand-Cys shell, and an adsorption layer. The dispersion solution composition strongly affected the adsorption layer structure of the CdSe NPs. The solution with a composition close to that of the as-prepared solution stabilized the physical and optical properties of the NPs. The solution with a composition different from that of the as-prepared solution, however, resulted in large changes in their adsorption layer structure and thus their physical and optical properties. The solution composed of neutral or weakly charged Cys and Cd-Cys complexes led to the adsorption layer with low charge density and that destabilized the NPs. The solution containing only neutral or weakly charged forms of Cys, without Cd-Cys complexes, was favorable to the formation of a thick adsorption layer with low charge density and that destabilized the NPs. The amount of adsorbed Cys in the adsorption layer depended on the dispersion solution composition. However, the amount of adsorbed Cd-Cys complexes in the adsorption layer was almost constant regardless of the dispersion solution composition.

X-ray imaging of newly-developed gadolinium compound/silica core–shell particles

A preparation method for gadolinium compound (Gd) nanoparticles coated with silica (Gd/SiO2) is proposed. Gd nanoparticles were prepared with a homogeneous precipitation method at 80 °C using 1.0 × 10−3 M Gd(NO3)3 and 0.5 M urea in the presence of 1.0 g/L stabilizer. Among stabilizers examined. Sodium n-dodecyl sulfate (SDS) was suitable as the stabilizer for preparing small Gd nanoparticles, and consequently Gd nanoparticles with a size of 46.2 ± 12.4 nm were prepared using the SDS. Silica-coating of the Gd nanoparticles was performed by a Stober method at room temperature using 0.013 M TEOS and 2.0 × 10−3 M NaOH in water/1-propanol solution in the presence of 1.0 × 10−3 M Gd nanoparticles, which resulted in production of Gd/SiO2 particles with an average size of 64.2 ± 14.4 nm. The Gd/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by measurement of electrophretic light scattering that amino group or carboxyl group was introduced onto the Gd/SiO2 particles. The gadolinium concentration of 1.0 × 10−3 M in the as-prepared colloid solution was increased up to a gadolinium concentration of 0.4 M by centrifugation. The core–shell structure of Gd/SiO2 particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The concentrated Gd/SiO2 colloid solution showed an X-ray image with contrast as high as a commercial Gd complex contrast agent. Internal organs in a mouse could be imaged injecting the concentrated colloid solution into it.

Control of shell thickness in silica-coating of Au nanoparticles and their X-ray imaging properties

This paper describes a performance of precise control of shell thickness in silica-coating of Au nanoparticles based on a sol–gel process, and an investigation into X-ray imaging properties for the silica-coated Au (Au/SiO 2) particles. The Au nanoparticles with a size of 16.9 ± 1.2 nm prepared through a conventional citrate reduction method were used as core particles. The Au nanoparticles were silica-coated with a sol–gel reaction using tetraethylorthosilicate (TEOS) as a silica source, sodium hydroxide (NaOH) as a catalyst, and (3-aminopropyl) trimethoxysilane (APMS) as a silane coupling agent. An increase in TEOS concentration resulted in an increase in shell thickness. Under certain concentrations of Au, H 2O, NaOH, and APMS, the Au/SiO 2 particles with silica shell thickness of 6.0–61.0 nm were produced with varying TEOS concentration. Absorption peak wavelength of surface plasmon resonance of the Au/SiO 2 colloid solution depended on silica shell thickness, which agreed approximately with the predictions by Mie theory. The as-prepared colloid solution could be concentrated up to an Au concentration of 0.19 M with salting-out and centrifugation. The concentrated colloid solution showed an X-ray image with high contrast, and a computed tomography value for the colloid solution with an Au concentration of 0.129 M was achieved 1329.7 ± 52.7 HU.

Preparation of silica-coated AgI nanoparticles by an amine-free process and their X-ray imaging properties

AgI nanoparticles coated with silica shell (AgI/SiO2) were prepared with an amine-free process, i.e. a modified Stober method. A colloid solution of 3.9 × 10−4 M AgI nanoparticles was prepared mixing silver perchlorate at 3.9 × 10−4 M and potassium iodide at 7.8 × 10−4 M. A silica-coating was performed at 4.5 × 10−6 M 3-mercaptopropyltrimethoxysilane, 0.1 × 10−3–2.0 × 10−3 M NaOH, 11–25 M H2O, and 0.4 × 10−3–80 × 10−3 M tetraethylorthosilicate (TEOS) in the presence of 1.0 × 10−4 M AgI nanoparticles in ethanol. The AgI/SiO2 particles with a size of 53.2 ± 9.3 nm and an AgI core size of 13.5 ± 4.2 nm were prepared at 1.2 × 10−3 M NaOH, 15 M H2O, and 4.0 × 10−3 M TEOS. The AgI concentration of 1.0 × 10−4 M in the as-prepared colloid solution was increased up to an AgI concentration of 0.32 M by salting-out and centrifugation. The core–shell structure of AgI/SiO2 particles was undamaged, and the colloid solution was still colloidally stable, even after the condensation. The concentrated AgI/SiO2 colloid solution showed a high-contrast X-ray image, and its computed tomography value was 2908 ± 37 HU. Internal organs in a mouse could be imaged injecting the concentrated colloid solution into it.

Preparation and Properties of Novel Regenerated Cellulose Fibers via direct Dissolution of Cellulose in LiOH Complex Aqueous Solution

It is the first time that cellulose was dissolved in LiOH/thiourea/urea aqueous solution, in which cellulose can be dissolved directly and quickly. The process of cellulose dissolution was observed by polarized optical microscopy. It has found that cellulose could be dissolved completely in LiOH complex solvent within 2 minutes. The as-prepared cellulose solution exhibit better thermal stability than cellulose dissolved in NaOH complex solutions. The unique gel-sol transition has been noticed and studied when the cellulose solution was stored at 25 to 64 °C for tens of hours. In addition, cellulose in the novel solvent was extruded, and regenerated by H 2 SO 4 /Na 2 SO 4 aqueous solution. The structure of the resulting celluloses fibers was characterized by scanning electron microscope and Wide X-ray diffraction. The novel cellulose fibers possess circular cross-sections with few inconspicuous microvoids as well as relatively high molecular weight, and a typical family II cellulose structure with high degrees of crystallinity, which lead to good mechanical properties.

Atomic force microscopy study of nanocrystalline ceria thin films

This work reports on the structural and morphological characterization of ceria thin films grown by chemical solution deposition (CSD) techniques. The coating solution was prepared starting from cerium 2,4-pentadionate, Ce(CH3COCHCOCH3)3, and propionic acid, C2H5COOH, further concentrated by distillation. The as-prepared solution was spin coated on single crystalline (100) SrTiO3 (STO) substrates. The precursor films were heat treated in air at 900°C both by a rapid heating and quenching to room temperature (A) and annealing (B). The X-ray structural analysis and the SEM and AFM morphological analysis for the CeO2/STO thin film have revealed the influence of the thermal treatment on the growth mechanism. The as-obtained polycrystalline nanostructured ceria thin films present an average grain size of 40–50 nm and a roughness of 1.5–5.4 nm, depending on the thermal treatment. The annealing renders the ceria thin film a smoother surface with respect to the rapid heat treatment followed by quenching, performed both at the same temperature.

Isomerization and fluorescence characteristics of sterically hindered azobenzene derivatives

We report synthesis and isomerization behaviors of sterically hindered azobenzene derivatives ( 1 and 2) with decyloxy and hydroxy groups, respectively, and their fluorescence enhancement under UV light irradiation characterized by means of absorption and fluorescence spectroscopy measurements. Upon irradiation of as-prepared solution ( 1) with UV light (∼200 mJ/cm 2) a cis-rich photostationary state was reached. Obviously different from 2 showing very fast thermal cis-to- trans isomerization within 2 min, slow cis-to- trans thermal back isomerization of 1 with a long alkyl chain at ambient temperature was observed on the time scale of weeks. In contrast to no striking changes in absorption and fluorescence spectra of compound 2, the azobenzene 1 showed green fluorescence upon prolonged irradiation with UV light (about 3–8 J/cm 2 exposure doses), although both the initial trans-rich and cis-rich states of azobenzene molecules were not fluorescent in solution. The stability of fluorescence efficiency caused by drying and redissolving processes was examined.

Spinning Carbon Nanotube-Gel Fibers Using Polyelectrolyte Complexation

Biopolymer-single walled carbon nanotube (SWNT)-biopolymer fibers were prepared using a continuous flow spinning approach. Polyelectrolyte complexation was facilitated by injecting a SWNT-biopolymer dispersion into a coagulation bath containing a biopolymer of opposite charge. We showed that the ability to spin fibers and their properties depend on processing conditions such as polyelectrolyte pH, sonolysis regime (conditions employed to disperse SWNT) and the order of adding the anionic and cationic biopolymer solutions. Maximizing the ionic nature through changes in the pH increased spin-ability, while combining a sonicated dispersion with an as-prepared (non-sonicated) polyelectrolyte solution allowed us to optimize sonolysis conditions while retaining spin-ability of fibers with smooth surface morphology. Addition of the cationic biopolymer-SWNT dispersion to the anionic biopolymer solution resulted in mechanical reinforcement with the increase in SWNT loading fraction. All fibers decreased their electrical resistance upon exposure to water vapor.

Large-Scale Fe3O4Nanoparticles Soluble in Water Synthesized by a Facile Method

Large-scale hydrophilic Fe 3O 4 nanoparticles (NPs) were prepared in the presence of citrate and sodium nitrate via a facile method. The Fe 3O 4 NPs are quite stable and can be freely dispersed in water. The as-prepared magnetic nanoparticle solution can be stable for more than 1 month. The mean diameter of the Fe 3O 4 NPs can be controlled in the range of ∼20 to ∼40 nm in mean diameter. The NPs show superparamagnetic properties with a relatively high saturation magnetization moment 58 emu/mg at room temperature. Furthermore, a possible formation mechanism is proposed to explain why the magnetic nanoparticles are very well soluble in water.

Morphology and Viscoelastic Properties of Poly(Vinyl Chloride)/ Poly(Vinyl Alcohol) Incompatible Blends

The effects of the pre-mixing method and degree of saponification poly(vinyl alcohol) (PVA) on the morphology of poly(vinyl chloride) (PVC)/PVA blends were investigated. Two pre-mixing methods were employed: a powder method and an aqueous solution method. In the powder method, both components were blended in powder form before melt kneading using a mixing roll. In the aqueous solution method, the PVC powder was added to an as-prepared PVA aqueous solution, followed by drying and then pounding before melt kneading. In the case of PVA with a degree of saponification of 98 mol%, PVA domains several hundred μm across were dispersed in the PVC matrix in the powder method system, whereas finer PVA domains with sizes ranging from sub μm to several μm were observed in the aqueous solution method. In the cases of PVA with saponification degrees of 88 and 78 mol%, domain sizes of several tens of μm were observed for both powder and solution methods. This indicates that there was no apparent influence of pre-mixing method on the domain size. When poly(methyl methacrylate) (PMMA) was added to the PVC/PVA blend, smaller PVA domains (with sizes ranging from 5 to 10 μm) were observed in both powder and solution method systems than without the PMMA. Viscoelastic properties showed specific interactions between PVC and PMMA, and between PMMA and PVA.

Stability of nanocrystalline silicon particles in solution

The luminescence and surface compositional properties of nanocrystalline silicon (nc-Si) particles dispersed in a solution using hydrofluoric (HF) acid and supersonic wave treatments have been studied by using photoluminescence (PL) and Fourier transform infrared (FT-IR) measurements. The as-prepared solution emitted a red light with a peak at 720 nm. When the nc-Si particles were immersed in the solution for 250 h, the PL peak wavelength blue-shifted from 720 to 650 nm because of size reduction due to the surface oxidation of nc-Si particles in the solution. At the same time, the PL intensity of this sample was also decreased with a subsequent formation of defects on the nc-Si particle surface. After leaving for over 250 h, the sample exhibited a stable red luminescence.