Study on optical interference effect of graphene oxide films on SiO2 and Si3N4 dielectric films

The optical interference effect has enabled the visualization of thin layers, even monolayers, of graphene by simple optical microscopy. In this study, we have controlled the optical interference effect by changing the thickness and types of dielectric films, i.e. SiO₂ and Si₃N₄. By investigating differences in RGB parameters between the graphene oxide layer and the dielectric layer, conditions for the highest visibility of the graphene oxide layer were determined. We also studied colors as a function of graphene oxide layer thickness and dielectric layer thickness. These color patterns can be effectively presented as two-dimensional color charts. When comparing SiO₂ and Si₃N₄ as dielectric layers, each layer was found to exhibit different interference fringe patterns, which is due to a mismatch of optical properties between the material layer and dielectric layer. The effects of optical properties (n, k) of the material layer on interference colors were also investigated.     

PMMA films refractive index modulation via TiO2 nanoparticle inclusions and corona poling

The present study is focused on the characterization of optical properties of poly (methyl methacrylate) (PMMA) films and the possibilities of modulation and fine tuning of their refractive index by the inclusion of different concentrations of nano-sized titanium dioxide (TiO₂) particles (less than 33 nm) and corona poling. The samples are prepared by the “spin coating” method and they are charged in a conventional point-to-plain corona system. The transparent PMMA/TiO₂ films exhibit good optical properties in the visible range. An investigation of the film’s surface refractive index by two wavelengths laser refractometry utilizing the disappearing diffraction pattern method is carried out. The refractive index increases with increasing the TiO₂ content in the nanocomposite films. The corona poling increases the refractive index values for all samples regardless of the polarity and concentration of TiO₂ nanoparticles. The results show that the prepared nanocomposite films have a potential application for optical devices.     

An experimental and theoretical study on the structure and photoactivity of XFe2O4 (X = Mn,Fe, Ni,Co, and Zn) structures

XFe₂O₄ magnetic nanoparticles (X = Mn, Fe, Co, Ni, and Zn) were prepared by using two methods: coprecipitation and hydrothermal. The synthesized nanoparticles were compared according to the separation in an external magnetic field and finally, the hydrothermal method was specified as a better synthesis method. The magnetic nanoparticles were characterized by physico-chemical analysis methods such as Vibrating Sample Magnetometer (VSM), X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), nitrogen adsorption-adsorption isotherm and Transmission Electron Microscopy (TEM). Magnetic properties of synthesized nanoparticles were studied by ab-initio theoretical methods to confirm and compare with the experimental results. According to the VSM analysis, all of magnetic nanoparticles had good magnetization while CoFe₂O₄ nanoparticles showed the ferromagnetic behavior. The magnetic properties of XFe₂O₄ configurations were studied using Density Functional Theory ab-initio method. The theoretical results were consistent with experimental magnetizations in the absence of external field. Finally, the photocatalytic behavior of prepared samples was investigated in the presence of oxone as an accelerated agent for degradation of an azo dye.     

Novel simple methods for the synthesis of single-phase valentinite Sb2O3

Several methods with solid and dissolved reactants were investigated as possible routes for synthesis of single-phase valentinite Sb₂O₃. The methods are based on simple chemical reaction between SbCl₃ and NaOH. The method with solid state reactants was established on self-propagating room temperature reaction (SPRT), while wet syntheses were based on the same chemical reaction, and performed in either distilled water or absolute ethanol. The prepared powders were characterized by X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction (SAED) and UV/vis diffuse reflectance spectroscopy. SPRT and aqueous solution syntheses resulted in single-phase valentinite Sb₂O₃, but with significantly different morphologies. In the case of SPRT method the obtained powder contains well crystallized prismatic shaped submicronic particles, with hexagonal or lozenge basis typical for valentinite crystal structure, while aqueous solution synthesis resulted in powder containing micronic agglomerates. The ethanolic solution synthesis product was Sb₂O₃ with cubic senarmontite as predominant phase and traces of orthorhombic valentinite. It was confirmed that not only the aggregate state, but also the choice of solvent has a great influence on the structural and optical characteristics of synthesized Sb₂O₃ powders.     

Photo-induced inter-conversion reactions between atoms and small aggregates of chromium trapped in argon matrices

This paper presents the reactions of conversion which are induced by selective photo-irradiation. Three optical spectroscopies have been used: UV-Visible absorption, Raman scattering, and luminescence (emission and excitation profiles). Extensive use of Factor Analysis methods have been made. The UV-Visible absorption spectra of several deposits at various concentrations have been recorded, as well as their evolution after increasing times of photo-irradiation with wavelengths corresponding to each absorption band. Seven species are detected and five of them are identified: Cr atoms in three sites, a metastable entity which yields a Cr atom after 2 hours, and the Cr₂ dimer. The two remaining species have been identified by using Raman results: they correspond to the trimer Cr₃ and to a species described as a precursor for Cr₃ and noted Cr₂·Cr. Luminescence properties have been studied (emission spectra and excitation profiles). The whole data allow the identification of several reactions between the present species. Furthermore some possible chemical paths for these reactions are suggested through the comparison of absorption and luminescence data.     

Effect of surface treatment on the photovoltaic properties of titania nanorods and MEHPPV nanocomposites

In this work, anatase titanium dioxide (TiO₂) nanorods (NRs) were synthesized by low-temperature hydrolysis of titanium tetraisopropoxide (TTIP) and using oleic acid (OA) as capping agent. The OA-capped titania NRs were then processed using surface ligand exchange by pyridine (Py). The two types of NRs, with different capping agents hence obtained, were blended with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-l,4-phenylene vinylene] (MEHPPV) to prepare hybrid organic–inorganic nanocomposites. In order to elucidate the changes caused by the surface modifications, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction were used to study the morphology. The Fourier transform infrared spectroscopy (FTIR) analysis confirms that the ligands coordinated with the Ti center of TiO₂ NRs. The optical properties of the modified TiO₂ NRs are characterized by UV–Vis absorption spectra and photoluminescence (PL) spectra. Photoluminescence lifetime studies were conducted to predict the capping agent more suitable for photovoltaic applications.     

Co3O4/SiO2 nanocomposites for supercapacitor application

In this study, Co₃O₄/SiO₂ nanocomposites have been successfully synthesized by citrate–gel method by utilizing SiO₂ matrix for Co₃O₄ embedment. Spectroscopy analyses confirm the formation of high crystalline Co₃O₄ nanoparticles; meanwhile, microscopy findings reveal that the Co₃O₄ nanoparticles are embedded in SiO₂ matrix. Electrochemical properties of the Co₃O₄/SiO₂ nanocomposites were carried out using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) in 5 M KOH electrolyte. The findings show that the charge storage of Co₃O₄/SiO₂ nanocomposites is mainly due to the reversible redox reaction (pseudocapacitance). The highest specific capacitance of 1,143 F g ^?1 could be achieved at a scan rate of 2.5 mV s^?1 in the potential region between 0 and 0.6 V. Furthermore, high-capacitance retention (>92 %) after 900 continuous charge–discharge tests reveals the excellent stability of the nanocomposites. It is worth noting from the EIS measurements that the nanocomposites have low ESR value of 0.33 Ω. The results manifest that Co₃O₄/SiO₂ nanocomposites are the promising electrode material for supercapacitor application.     

Manganese(II), nickel(II), and cadmium(II) coordination polymers with tetrafluoroterephthalate: syntheses,crystal structures,and luminescence properties

Three new coordination polymers, [Mn(BDC-F₄)(DMF)₂(H₂O)₂] _n (1), [Ni(BDC-F₄)(DMF)(EtOH)] _n (2), and [Cd(BDC-F₄)(DMF)(EtOH)] _n (3), have been synthesized by assembling transition metal salts with the rigid ligand tetrafluoroterephthalic acid (H₂BDC-F₄) in mixed EtOH/DMF solvent at pH ca. 2. For complex 1, the octahedral coordination geometry of the Mn^II center is provided by two oxygen atoms from two dianionic BDC-F₄ ligands, two DMF ligands and two aqua ligands, giving a 1-D linear chain array. For complex 2, the Ni^II center is coordinated by two dianionic BDC-F₄ ligands, two EtOH ligands and two DMF ligands, resulting in a 1-D chain structure. For complex 3, the Cd^II center is coordinated by four dianionic BDC-F₄ ligands, one EtOH ligand and one DMF ligand, generating a 2-D layered structure. The results suggest that both the metal and the solution pH play an important role in the formation of the complexes. The spectroscopic, thermal, and luminescence properties of the complexes have been investigated.     

Synthesis and optical properties of BaTiO3:Eu3+@SiO2 glass ceramic nano particles

BaTiO₃:(5 %)Eu³⁺ nanoparticles and BaTiO₃:(5 %)Eu³⁺@SiO₂ composites were synthesized by the solvothermal method. The effects on the structure, morphology and luminescent properties were studied using samples with different molar ratios of BaTiO₃:(5 %)Eu³⁺@SiO₂: 60:40, 50:50, 40:60, 30:70, 20:80, 10:90, 08:92, 6.5:93.5, 05:95, and 1.5:98.5. When the amount of silica in the composites was increased, the orange emission of Eu³⁺ increased, too; this was observed by exciting the charge transfer band centered at 283 nm. Furthermore, an increase in the intensity of the emission was obtained under excitation at 394 nm as a consequence of the improvement in the crystallinity of the samples. The presence of silica and the degree of crystallinity of the samples were determined through the Fourier transform infrared spectra and X-ray diffraction patterns. All of the results suggest that our ceramic material could be a good candidate for biomedical applications such as biolabeling, since the luminescence of BaTiO₃:(5 %)Eu³⁺@SiO₂ composites have an emission intensity higher than that of nanoparticles composed solely of BaTiO₃:Eu³⁺. This work demonstrates that BaTiO₃:Eu³⁺@SiO₂ composites have an emission intensity higher than that of nanoparticles composed solely of BaTiO₃:Eu³⁺.     

Catalytic synthesis of pyrazine,piperazine, and 1,4-diaza[2,2,2]-bicyclooctane

A study is made of the deamination of diethylenetriamine over acidalkali catalysts, i. e., kaolin and alumina with promoters. Promoters which raise the acidity of the catalyst, affect the formation of triethylene diamine favorably. Increasing the amount of additive increases the amount of triethylenediamine, and cuts the optimum temperature at which it is formed. On kaolin or Al₂O₃+15% B₂O₃, the yield of triethylenediamine amounts to 30% theory. Addition of MoO₃ facilitates dehydrodeamination and hydrogenolysis of the diethylenetriamine. The optimum promoter for preparing pyrazine is MoO₃ along with a small amount of acid oxides. On the Al₂O₃+5% MoO₃+1% P₂O₅, the pyrazine yield is 27.5% theory. Triethylenediamine can be separated from mixtures of it with piperazine by azeotropic distillation with mxylene or a mixture of mesitylene and α-memylnaphthalene.     

Influence of chemical nature of aerosilogel surface on proton conductivity of the Nafion-containing composites

Aerosilogel modified with hydroxylaluminum (=Al-OH) groups has been synthesized via the molecular layering procedure, and aerosilogel modified with aminopropylsilyl groups [≡Si(CH₂)₃NH₂] has been prepared via chemisorption of (3-aminopropyl)triethoxysilane. The modified aerosilogel have been further used to prepare composite Nafion-containing electrolytes Nafion. Electrical conductivity of the produced materials has been studied by impedance spectroscopy. Chemical modification of the gel surface strongly affects proton conductivity of Nafion-containing composites.     

Composition and properties of CeO2-SiO2 composite films prepared from film-forming solution

This study focuses on the preparation and properties of CeO₂-SiO₂ thin films with thickness ≤60 nm that can be used as protective coatings for solar cell panels and electrochromic counter electrodes. Thin-film CeO₂-SiO₂ systems on glass and quartz substrates, which are manufactured from film-forming solutions based on cerium(III) nitrate, salicylic acid, and tetraethoxysilane and thermally treated, are mixtures of cerium(IV) (cubic modification) and silicon(IV) (amorphous phase) oxides. The films synthesized are distinguished by a net structure and high visible transmittance (～90-100%). The morphology, phase composition, and optical properties of films were studied by X-ray diffraction, X-ray spectral microanalysis, scanning electron microscopy, spectrophotometry, and ellipsometry.     

Thermally stimulated discharge current (TSDC) characteristics in β-phase PVDF–BaTiO3 nanocomposites

β-phase polyvinylidene fluoride (PVDF)–BaTiO₃ nanocomposite samples have been prepared by solution mixing method. XRD data represent that the crystallinity of PVDF decreases with increase in loading level of BaTiO₃ nanoparticles. DSC curve represents that the melting point of PVDF is lightly affected by loading concentration of BaTiO₃. The morphology and microstructure of PVDF and PVDF embedded by BaTiO₃ nanofillers were investigated by using inverted contrast microscopy (ICM) and scanning electron microscopy (SEM). FTIR interferrometry is proven that PVDF and BaTiO₃ are not chemically interacting; therefore, interaction of BaTiO₃ is van der Waals type of interaction. The thermally stimulated discharge current (TSDC) of PVDF and PVDF–BaTiO₃ nanocomposites sample was characterized by single peak. The observed TSDC peak is discussed on the basis of dipolar and interfacial polarization.     

Method of radioisotope isolation from cyclotron targets

The extraction of titanium and rhenium by oxygen-containing solvents (alcohols, ketones) has been investigated. The investigations on the titanium extraction have been carried out from hydrochloric acid solutions, on the rhenium extraction from alkaline solutions. The adsorption of cobalt and zinc on a strongly basic anion exchanger has been determined from the MCl₂?HCl?LiCl (M=Ni, Cu) and GaCl₃?HCl solutions. On the basis of the results obtained methods for the isolation of radioactive isotopes⁴⁴Ti,^56,58Co,^65,69mZn, and^183,184Re from irradiated mixtures have been elaborated. Technical characteristics of the isolated cyclotron-produced isotopes are presented.     

Comparative study on the synthesis, photoluminescence and application in InGaN-based light-emitting diodes of TAG:Ce phosphors

Cerium-doped terbium aluminum garnet phosphors, Tb₃Al₅O₁₂:Ce³⁺ (TAG:Ce³⁺), were prepared with different methods: co-precipitation (CP), half dry-half wet (HDHW), sol-combustion (SC) and Pechini method plus conventional solid state reaction (SS) method. Comparative study on the phase-formation, particle size, morphologies and luminescent characteristics of the phosphors synthesized with different methods was carried out by means of XRD, FE-SEM and photoluminescence (PL) analysis and SC method was confirmed by the comparison of the results to be an easy and an effective process for preparing efficient and nano-sized Tb₃Al₅O₁₂:Ce³⁺ phosphors. Various factors influencing particle size, morphology and PL of the phosphors, such as precursor preparation, reaction temperature and heating time, were also investigated. Light-emitting diodes (LEDs) were fabricated with each phosphor and a ∼460 nm emitting InGaN chip. The LEDs from SS, HDHW and CP exhibit strong white emission while those from SC and Pechini emit yellow, revealing that the emission characteristics of LEDs are influenced not only by the morphology and the particle size of the phosphors, but also by the preparing process of the phosphors.     

Some improvements in the estimation of137Cs in urine by the AMP-chlorostannate method

An accurate and reliable method has been developed for the estimation of radiocesium in urine. Initially cesium is adsorbed on ammonium phosphomolybdaste (AMP) precipitate and separated by ion exchange from other contaminants. Cesium thus separated is estimated as cesium chlorostannate, Cs₂SnCl₆, from a 50 (v/v)% solution of concentrated HCl in ethyl alcohol. While the results are in good agreement with the values obtained by γ-spectrometry using a Marinelli beaker in its range of applicability, the present method has a much lower detection limit. It is observed that the method has significant advantages over the methods available with respect to analysis time, accuracy and detection limits.     

The Effect of O6+ and Si7+ ion beam irradiations on poly(lactide-co-glycolide) (50: 50) copolymer

Sterilization by ion beam radiations unfortunately also has a significant effect on the degradation of many polymers. The aim of present study is to examine the effect of heavy ion beam irradiation on poly(lactide-co-glycolide) (PLGA) (50: 50). The radiation effect is manifested through its degradation behavior and changes in the morphological, optical and structural properties. PLGA films are prepared by solvent casting method and subsequently irradiated with swift heavy ions O⁶⁺ and Si⁷⁺ ion with fluence in the range of 5 × 10¹⁰?1 × 10¹² ions/cm². The dominant effect on PLGA films is chain scission as evidenced by change in surface modification. Changes in optical and structural properties were analyzed by UV-Vis, XRD and FTIR spectrometric techniques. XRD technique is not responsive to degradation occurring in samples. Surface modifications caused by ion irradiations have been observed with SEM.     

Preparation and characterization of cellulose nanocrystals via ultrasonication-assisted FeCl3-catalyzed hydrolysis

Cellulose nanocrystals (CNC) was obtained from bamboo pulp via ultrasonication-assisted FeCl₃-catalyzed hydrolysis process, with parameters optimized by response surface methodology. The optimal parameters were reaction temperature: 107 °C, reaction time: 58 min, ultrasonication time: 186 min. The morphological, crystal structural, chemical structural and thermal features of the prepared cellulose nanocrystals were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Fourier transfer infrared (FTIR) and thermogravimetric analysis. The results showed that the cellulose nanocrystals formed an interconnected network structure and CNC was rod-like with the length of 100–200 nm and the width of 10–20 nm. XRD result revealed that, compared with cellulose pulp, the crystallinity index of CNC increased from 69.5 to 79.4 %, while the cellulose I crystal structure remained. FTIR analysis demonstrated that CNC had the similar chemical structures to that of cellulose pulp, which indicated that the chemical structures of CNC remained unchanged in the presence of FeCl₃-catalyzed hydrolysis process and ultrasonication treatment. Thermogravimetric analysis revealed that the resulting CNC exhibited relatively high thermal stability. The research shows that ultrasonication-assisted FeCl₃-catalyzed hydrolysis could be a highly efficient method for preparing CNC.     

Fabrication and sensing property for conducting polymer nanowire-based biosensor for detection of immunoglobulin G

Conducting polymers are excellent sensing materials in the design of bioanalytical sensors because of their electronic conductivity, low energy optical transitions, biocompatibility, and room temperature operation. Among them, Polypyrrole (Ppy) is one of the most extensively used conducting polymers because of a number of properties such as redox activity, rapid electron transfer, and ability to link a variety of biomolecules to pyrrole groups by chemical treatment. In this study, Ppy nanowires were synthesized by an electrospinning method. The nanowires were prepared from a solution mixture of Ppy and poly(ethylene oxide). The method of detection in such a device is based on the selective binding of antigen onto an antibody that is covalently attached to the nanowires. Thus, anti-IgG was immobilized on Ppy nanowires using an EDC {[N-(3-dimethyl aminopropyl)-N₂-ethylcarbodiimide hydrochloride]}-NHS(N-hydrosuccinimide) modified technique. Fluorescence images of BSA–FITC (fluorescein isothiocyanate labeling of bovine serum albumin) conjugation demonstrated that antibody was functionalized on the Ppy nanowires without non-specific binding and facilitated selective detection of antigen. Current–voltage (I–V) characterization was used to monitor the change in the conductivity of nanowires while the specific binding interaction occurred. These results of electrical properties enable Ppy nanowire-based biosensors to detect biomolecules in real-time.     

Application of solvation excess concept to solutions of 3 : 1 and 1 : 3 electrolytes

Data on water activity in solutions of a series of 3 : 1 and 1 : 3 electrolytes [AlCl₃, Al(NO₃)₃, LaCl₃, La(NO₃)₃, H₃PO₄, NaH₂PO₄] have been generalized in the frame of solvation excesses concept. Solvation excess reflects the distribution of the selected structural elements (ions or solvent particles) in the solution. The computed values have demonstrated the opposite contributions of ion association and hydration of ions and ion associates. Solvation excess concept allows determination of water molecules fraction constituting the excess at ions and their associates. The comparison of results obtained with different choice of model structural units has shown the electrolyte concentration ranges of validity of the respective models.