DETERMINATION OF OPTIMAL PARAMETERS FOR SYNTHESIS OF SILVER NANOPARTICLES STABILIZED WITH POLYETHYLENE GLYCOL

В рамках данной работы представлены результаты исследования влияния концентраций стабилизатора и прекурсора на процесс синтеза наночастиц серебра. В качестве прекурсора использован нитрат серебра, а в качестве стабилизатора -полиэтиленгликоль с молекулярной массой от 200 до 600 Да. Синтез осуществляли методом химического восстановления в водной среде. Полученные образцы исследовали фотонно-корреляционной спектроскопией и спектрофотометрией. Установлено наличие характеристической полосы поглощения на 400 нм в спектрах поглощения всех образцов наноразмерного серебра, стабилизированного полиэтиленгликолем, что обусловлено возникновением поверхностного плазмонного резонанса у металлических наночастиц серебра. Также установлено, что при наибольшей и наименьшей концентрации стабилизатора, равных, соответственно, 0. 005 и 0,1 мас. %, в реакционной системе наблюдается формирование крупных частиц серебра со средним гидродинамическим радиусом от 132 до 1900 нм. В результате определены оптимальные параметры синтеза агрегативно устойчивых наночастиц серебра: концентрация нитрата серебра С (AgNO) = 0,05 M и концентрация полиэтиленгликоля, равная 0,01 - 0,05 %. Проведено компьютерное квантовохимическое моделирование. Установлено, что энергетически выгодным является взаимодействие атома серебра с концевой гидроксогруппой в молекуле полиэтиленгликоля в элементарном акте взаимодействия при стабилизации наночастиц серебра данным полимером. Данный тип взаимодействия характеризуется абсолютной химической жесткостью, равной ƞ = 0,146 эВ, и внутренней энергией E = -2048,34 ккал / моль. Within the framework of this work, the results are presented of a study of the effect of the concentrations of the stabilizer and precursor on the synthesis of silver nanoparticles. Silver nitrate was used as a precursor, and polyethylene glycol with a molecular weight from 200 to 600 Da was used as a stabilizer. The synthesis was carried out by the method of chemical reduction in an aqueous medium. The obtained samples were investigated by photon correlation spectroscopy and spectrophotometry. The presence of a characteristic absorption band at 400 nm in the absorption spectra of all samples of nanosized silver stabilized with polyethylene glycol was established, which is due to the appearance of surface plasmon resonance in metallic silver nanoparticles. It was also found that at the highest and lowest concentration of the stabilizer, equal, respectively, 0,005 and 0,1 mass. %, the formation of large silver particles with an average hydrodynamic radius from 132 to 1900 nm is observed in the reaction system. As a result, the optimal parameters for the synthesis of aggregatively stable silver nanoparticles were determined: the concentration of silver nitrate C(AgNO) = 0,05 M and the concentration of polyethylene glycol equal to 0,01 - 0,05 %. Computer quantum-chemical modeling is carried out. It is found that the interaction of the silver atom with the terminal hydroxogroup in the polyethylene glycol molecule in the elementary act of interaction during the stabilization of silver nanoparticles by this polymer is energetically advantageous. This type of interaction is characterized by an absolute chemical hardness equal to ƞ = 0,146, and an internal energy of E = -2048,34 kcal / mol.

ISOLATION OF CELLULOSE DERIVED FROM ORANGE PEEL AND ITS APPLICATION IN BIODEGRADABLE FILMS

"In this study, cellulose was extracted and isolated from orange peel (OP) via alkaline treatment, followed by a bleaching process. The orange peel derived cellulose (OPDC) was characterized and compared with microcrystalline cellulose (MCC). FTIR characterization confirmed the absorption peaks of cellulose for both OPDC and MCC. From the DSC analysis, it was found that MCC possessed higher thermal stability than OPDC. In addition, the results of FESEM and particle size analysis revealed the micro-size dimension of OPDC after the pretreatments. The crystallinity index (CrI) of OPDC (80.14%) was found to be significantly higher than that of untreated OP (23.54%). After that, biodegradable blended films with different weight ratio were prepared using OPDC and MCC with polyvinyl alcohol (PVA) by the solution casting method. According to the FTIR spectra, the shift of the characteristic absorption band and the change of the band intensity observed in the spectra of the PVA/OPDC blended films were similar to those of the PVA/MCC blended films. This confirmed the development of new inter- and intramolecular hydrogen bonds and changes in the conformation between PVA and cellulose. The tensile strength and elongation at break of both PVA/OPDC and PVA/MCC blended films decreased when the cellulose content increased in the PVA matrix. However, the elastic modulus of both films was enhanced when the amount of cellulose increased. By comparison, the PVA/OPDC blended film presented higher tensile strength and elastic modulus than the PVA/MCC blended film. Based on the natural weathering tests, the degradability of blended films increased with a rising amount of cellulose after exposure to degradation tests. The biodegradability of blended films was confirmed by the tiny black spots observed on their surface, which reflected the growth of microorganisms. It was further proven by the morphology studies performed on the surface of the films using FESEM."

Cyanobacteria as Nanogold Factories II: Chemical Reactivity and anti-Myocardial Infraction Properties of Customized Gold Nanoparticles Biosynthesized by Cyanothece sp.

Cyanothece sp., a coccoid, unicellular, nitrogen-fixing and hydrogen-producing cyanobacterium, has been used in this study to biosynthesize customized gold nanoparticles under certain chemical conditions. The produced gold nanoparticles had a characteristic absorption band at 525–535 nm. Two types of gold nanoparticle, the purple and blue, were formed according to the chemical environment in which the cyanobacterium was grown. Dynamic light scattering was implemented to estimate the size of the purple and blue nanoparticles, which ranged from 80 ± 30 nm and 129 ± 40 nm in diameter, respectively. The highest scattering of laser light was recorded for the blue gold nanoparticles, which was possibly due to their larger size and higher concentration. The appearance of anodic and cathodic peaks in cyclic voltammetric scans of the blue gold nanoparticles reflected the oxidation into gold oxide, followed by the subsequent reduction into the nano metal state. The two produced forms of gold nanoparticles were used to treat isoproterenol-induced myocardial infarction in experimental rats. Both forms of nanoparticles ameliorated myocardial infarction injury, with a slight difference in their curative activity with the purple being more effective. Mechanisms that might explain the curative effect of these nanoparticles on the myocardial infarction were proposed. The morphological, physiological, and biochemical attributes of the Cyanothece sp. cyanobacterium were fundamental for the successful production of “tailored” nanoparticles, and complemented the chemical conditions for the differential biosynthesis process. The present research represents a novel approach to manipulate cyanobacterial cells towards the production of different-sized gold nanoparticles whose curative impacts vary accordingly. This is the first report on that type of manipulated gold nanoparticles biosynthesis which will hopefully open doors for further investigations and biotechnological applications.

Green bio-inspired synthesis, characterization and activity of silver nanoparticle forms of Centaurea virgata Lam. and the isolated flavonoid eupatorin

A green synthesis method of silver nanoparticles (AgNPs) usingCentaurea virgataLam. extract and the isolated compound eupatorin was investigated in this study. Ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) spectroscopy, thermal gravimetric analysis, X-ray diffraction analysis and zeta potential were used for characterization of AgNPs. The UV-Vis spectrum exhibited a characteristic absorption band at 420 nm for monodisperse nanoparticles. FTIR measurements also proved the formation. X-ray diffraction patterns showed peaks at (110) and (112), which are characteristic for hexagonal crystals and also showed peaks at (111), (200) and (240), which are characteristic for orthorhombic crystals. The TEM images of AgNPs show that the morphology of AgNPs was predominantly spherical. Obtained AgNPs were highly stable according to the zeta potential values. The nitric oxide scavenging activity, which is also related to anticancer activity, of AgNPs was evaluated. It can be concluded thatC. virgataLam. extract and eupatorin can be used as a reducing agent for potential antioxidant AgNP formation.

Use of Nanostructured Layered Double Hydroxides as Nanofilters in the Removal of Fe2+and Ca2+Ions from Oil Wells

Four new metal-aluminum layered double hydroxides (LDHs), Mg-Al(OH)2PO4(1), Mg-Al(OH)2PO4PF6(2), Ca-Al(OH)2SO4(3), and Ca-Al(OH)2PO4PF6(4), were prepared by the coprecipitation method followed by mild hydrothermal processing at 60°C. Mg2+and Ca2+in solution with Al3+were titrated with NaOH over 3–5 h to yield Mg-Al and Ca-Al layered double hydroxides, respectively, incorporating PO43−, PO43−PF6−, and SO42−anions in the interlamellar spaces. The isolated compounds were characterized with the help of XRD, IR, and SEM/EDAX, and their ability to remove scale-forming ions from the aqueous system was studied with the help of atomic absorption spectroscopy (AAS). The SEM micrographs of Mg-O-Al-OH and Ca-O-Al-OH layers intercalated with PO43−and/or [PO4PF6]4−anions are similar consisting of uniform nanospheres with an average size of 100 nm, while the M-O-Al-OH layer of compound3, intercalated with SO42−anions, consists of hexagonal nanoplate crystals. In the infrared spectra, the characteristic absorption band for water molecules was observed in all the compounds. The XRD pattern showed thatd012andd104peaks of M-Al-PO4LDHs corresponding to interplanar spacing of 3.4804 and 2.5504 Å, respectively, shifted to higher 2θvalues for the M-Al-PO4PF6system, which indicates a decrease in the interlamellar spacing as PF6−was incorporated along with PO43−anion. The XRD pattern for Ca-Al-SO4LDHs was quite different, showing the presence of low-angle peaks at 2θ = 11.68 and 14.72°. The results of the column adsorption studies showed that there was a significant removal of Ca2+by all the compounds under investigation with an efficiency of 84–99%. However, compounds1and2remove Fe2+effectively with the efficiency of 98.73 and 99.77%, respectively; compounds3and4were shown to have little or no effect.

Study of α-Fe2O3 formation and its measurement in oxide films of wheel surface during ELID grinding process

This paper presents the study of forming mechanism of [Formula: see text]-Fe2O3 in oxide films on electrolytic in-process dressing (ELID) grinding wheel surface. To investigate the component content and the microtopography of oxide films, XRD, XPS, IR spectrum analysis, SEM, and TEM measurements are performed on ELID grinding wheels. In XRD test results, the characteristic absorption band of [Formula: see text]-Fe2O3 is found in the oxide film. XPS tests show that there is full of ferrous iron and oxygen element in the oxide film. Also, the characteristic spectral line of XPS is identical to the standard spectrum of [Formula: see text]-Fe2O3. Several vibration peaks (471, 1029, 1384, 1630, 3430) are observed by IR spectrum analysis. It can be easily seen by contrast with the standard photographs that the vibration peak of 1029 is of Fe-O vibration band in IR spectrum of [Formula: see text]-Fe2O3 powder. Therefore, these measurement results confirm the existence of [Formula: see text]-Fe2O3 in the oxide films, and explain the polishing effect of oxide films during ELID grinding. The fresh oxide film is porous and moisture rich. However, the oxide film after squeezing to dry is investigated by SEM imaging to present tortoiseshell cracks. Geometrically, [Formula: see text]-Fe2O3 appears to be nearly spherical with particle size around 5–50 nm. This indicates fine polishing improvement by oxide films, and is identified as the mechanism responsible for excellent surface quality by ELID grinding.

Sonochemical Synthesis of Nanostructured ZnO/Ag Composites in an Ionic Liquid

In the present paper we show that nanocrystalline ZnO/Ag composites can be obtained via an ultrasonic-assisted approach in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate. Different techniques including, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and ultraviolet-visible spectroscopy (UV-vis) were utilized to characterize the synthesized materials. The XRD results revealed the formation of ZnO wurtzite structure along with metallic Ag in the ZnO/Ag composite. The particle size was estimated from the XRD results to be about 35 nm. The UV spectrum of ZnO/Ag showed the characteristic absorption band of wurtzite crystal structure of ZnO, and the presence of Ag in the ZnO/Ag composite led to a slight red shift. The employed ionic liquid acts as a template leading to the formation of nanoparticles of ZnO and of ZnO/Ag.

Synthesis and Properties of Lead Free Ferroelectric Na0.5Bi0.5TiO3 Ceramic at Different Sintering Temperature

Lead Free Ferroelectric Na0.5Bi0.5TiO3 (NBT) Ceramic has been synthesized using sol gel method. The prepared NBT samples have been sintered at different temperatures 850°C, 950°C, 1050°C and 1150°C to achieve best sintering temperature. Structural analyses have been carried out using XRD and FTIR measurements. XRD patterns confirm perovskite structure having rhombohedral symmetry for all samples which is also supported by characteristic absorption band at ~627cm-1 in FTIR spectra. Dielectric properties of NBT samples with frequency and temperature have been studied. NBT sample sintered at 1050°C exhibit comparatively high value of dielectric constant (ε’) and phase transition temperature (Tm). Ferroelectric properties of NBT samples have been studied at room temperature. Comparatively, better ferroelectric properties are observed for NBT sample having remnant polarization (Pr)~ 14.7 μC/cm2and coercive field (Ec)~ 26.8 kV/cm sintered at 1050°C.

Copper Quantum Dots Formation in a Borosilicate Glass

This Borosilicate glass offers superior properties to the ordinary silicate glass. Metallic quantum dots embedded in glass are promising materials which can be used in modern optical devices. However, the introduction of metallic quantum dots into borosilicate glass has not been studied. We investigated the formation of copper quantum dots in Cu-doped borosilicate glass matrix using thermal annealing process. The reductant SnO included in borosilicate glass played an important role in the formation of the metallic quantum dots. Specifically, Cu quantum dots were formed only when SnO content reached at least 0.5 wt% after borosilicate glass was heated at 600 °C for 60min, which was evidenced by the detection of the characteristic absorption band at about 560nm originated from the surface plasmon resonance of Cu nanoparticles. The optimal concentration of SnO was found to be 1.5 wt% and the mean size for the heating-induced Cu quantum dots was calculated to be ~1.7 nm. Our data offer a simple approach to prepare the metallic quantum dots in borosilicate glass matrix and suggest a new type of metallic quantum dots for applications where superior durability, chemical and heat resistance are required.