Maria José A. Sales

Thermal and electrical properties of starch–graphene oxide nanocomposites improved by photochemical treatment

Bionanocomposite films have been prepared by casting an aqueous suspension of acetylated starch (ST) and poly(vinyl alcohol) (PVA) loaded with graphene oxide (GO). A photochemical and reagentless method has been successfully performed to convert the GO phase into reduced graphene oxide (RGO). The nanocomposites have displayed improved thermal and electrical properties when the amount of the GO phase is increased and properly converted to RGO. The molecular-level interactions between components are mainly hydrogen-bonding type according to attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and Raman spectroscopies, as well as thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has confirmed the effective mixing between the GO and the ST-PVA matrix. The thermal diffusivity and electrical resistivity of ST-GO nanocomposites have increased one order and decreased two orders of magnitude, respectively, after the photochemical treatment. These findings have confirmed the effectiveness of the proposed approach to produce starch-based nanocomposites with improved thermal and electrical properties.

Comparative study of the oxidative and thermal stability of vegetable oils to be used as lubricant bases

Demand for lubricating oils is increasing in the growing Brazilian economy. The use of vegetable bases in exchange of minerals can bring socio-economic and environmental benefits for Brazil. The purpose of this study is to compare the thermal and oxidative stability of vegetable oils related to the bases commonly used as lubricants. In this study, thermogravimetric analysis of castor oil, cotton oil, macauba’s almond oil, passion oil, paraffinic mineral oil, naphthenic oil (NH-140) and synthetic oil (Etro) was performed in inert and oxidative atmosphere to study the thermal and oxidative degradation of the vegetable oils related to the most common lubricants’ oils base. These oils’ oxidation stability were determined by standard procedures (ISO 6886). The use of mineral oil’s additives in these vegetable oils was tested to verify the viability of these additives to improve the oxidative stability of the vegetable oils. The castor oil and the cotton oil presented results of thermal analysis similar to the mineral and synthetic bases values. The castor oil was the only vegetable oil that showed a great oxidative stability. All other vegetable oils had their oxidative stability significantly increased by the additives.

Synthesis of polyols and polyurethanes from vegetable oils–kinetic and characterization

The demand of vegetable oils by several sectors of the chemical industry is growing at a fast pace fueled by the fossil oil scarcity, its unpredictable price fluctuations and the ever increasing environmental concerns. The present work reports for the first time the synthesis of polyols and polyurethanes (PUs) from linseed seed (Linum usitatissimun L.) and passion fruit (Passiflora edulis Sims f. flavicarpa Degener) oils. The in situ epoxidation and hydroxylation of vegetable oils in a single step was successfully accomplished using a mixture of hydrogen peroxide (H2O2) and formic acid. Kinetic studies were performed on this system. The oils and the corresponding polyols were characterized by Fourier transform infrared (FT-IR), gel permeation chromatography (GPC) and thermogravimetry (TG)/derivative termogravimetry (DTG). The PUs were characterized by FT-IR, TG/DTG, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The study revealed a marked deviation on the properties between the starting materials and the end products. The PUs produced showed similar dynamic mechanical properties.

Photochemically-assisted synthesis of non-toxic and biocompatible gold nanoparticles.

This contribution describes the photochemically-assisted synthesis of aqueous colloidal suspensions of non-toxic and biocompatible spherical gold nanoparticles stabilized by branched polyethylenimine, or else Au-np-PEI. The method consists on 30min of photoexcitation (254nm, 16W) at room temperature of an aqueous diluted solution of chloroauric acid (HAuCl4) containing PEI. While the UV irradiation forms the [Au(3+)Cl4-]* excited species that succesively transforms into zero valent Au, PEI controls the nucleation step of nanoparticles formation. Varying the PEI to Au molar ratio permits one to tune the size of nanoparticles between 100nm to 8nm. The obtained colloidal suspensions display an intense plasmonic absorption band at 520-530nm and positive zeta potentials greater than +20mV. The cells viability for in vitro tests performed with human connective tissues and human breast adenocarcinoma (MCF-7) cell lines is over 80% and 90%, respectively, when they are incubated with Au-np-PEI formulations (25μgmL-1). The present photochemically-assisted synthesis is advantageous because it is fast and does not require for either hazardous or cytotoxic reductant agents and additional purification procedures.

Facile approach to suppress γ-Fe2O3 to α-Fe2O3 phase transition beyond 600 °C in Fe3O4 nanoparticles

Magnetic iron oxide nanoparticles on a zeolite template have been synthesized using wet chemical approach. The average particle size initially decreases from 8.5 to 6 nm (increasing zeolite concentration from 0 to 75 mg) but increases to 11 nm for higher zeolite concentration (100 mg). Room temperature magnetization curves show an initial decrease in saturation magnetization from 62 to 42 emu per gram due to decrease in particle size as well as increase in contribution from nonmagnetic zeolite template. Further increase in zeolite concentration to 100 mg results in a significant increase in saturation magnetization from 42 to 51 emu per gram. Calorimetric studies show a continuous enhancement in γ-Fe2O3 to α-Fe2O3 phase transition temperature from 590 to 715 °C by increasing the zeolite concentration from 0 to 75 gm. The exothermic peak corresponding to the γ-Fe2O3 to α-Fe2O3 phase transition has been completely suppressed for nanoparticles prepared in presence of 100 mg of zeolite. Mossbauer spectra of as-synthesized nanoparticles show an increase of superparamagnetic components from 7 to 36% corresponding to increase in zeolite concentration from 0 to 100 mg. Mossbauer spectra of pure Fe3O4 nanoparticles annealed at 500 °C shows formation of pure α-Fe2O3 phase and Mossbauer spectra of particles prepared in presence of 25 mg shows only 18% of α-Fe2O3 phase after annealing at 550 °C. Further increase in zeolite concentration to 50 and 75 mg (annealed at 550 °C) leads to pure γ-Fe2O3. Annealing of Fe3O4 nanoparticles prepared in the presence of 100 mg of zeolite at 650 °C shows formation of only 8% α-Fe2O3 phase. Our results show an easy and effective method to enhance the thermal stability of magnetic iron oxide nanoparticles making it suitable for high temperature applications.

Sorption and thermal polymerization of vinyl monomers in low density polyethylene-iron (III) oxide composite

The nature of the species produced after sorption and thermal polymerization of acrylic acid, methyl methacrylate and 4-vinylpyridine in low density polyethylene-iron (III) oxide composite was investigated by Mössbauer and IR spectroscopies. The values of the Mössbauer parameters indicate no change in the oxidation state of iron (III) in the LDPE-Fe2O3 composite before and after sorption and thermal polymerization of the monomers. Acrylic acid interacts with iron (III) oxide particles yielding acrylates, hydroacrylates, polyacrylates and polyhydroacrylates. The iron (III) oxide particles remained unchanged after sorption and thermal polymerization of methyl methacrylate although some thermal polymerization is observed in the presence of Fe2O3-doped LDPE. Iron (III) oxide acts as catalyst for the radical polymerization of methyl methacrylate on LDPE-Fe2O3. The interaction of iron (III) oxide and 4-vinylpyridine after its sorption and thermal polymerization in LDPE-Fe2O3 is mainly by coordination bonding of the pyridine ring of the polymer to the iron of Fe2O3.

Facile Method to Tune the Particle Size and Thermal Stability of Magnetite Nanoparticles

Nucleation and growth mechanism of iron oxide nanoparticles on zeolite template and their stability dependence are reported. Hyperfine field resulting from the variation of particle size indicates the effect of zeolite on particles growth; particle size decreases at lower concentration of zeolite. At higher concentration, a fraction of nano Fe3O4 experiences hyperfine field (45 and 49 T) similar to bulk particles. Effect of incubation and digestion time on the particles growth and the binding effect with zeolite are discussed. Annealing treatments show that the binding of nanoparticles with zeolite stabilizes the nanoparticles with regard to agglomeration and structural transformation. Thermogravimetry-differential thermal analysis (TG-DTA) shows that increase in dehydration temperature from 335.1 to 351.7 K results in zeolite content increasing from 0 to 1000 mg. Weight loss of the particles prepared in incubation time of 0.5 min is 9.46% and reaches 13.9% in 240 min. The weight loss remains practically constant at ca. 9% irrespective of the digestion method.

Effect of iron(III) oxide on the thermal polymerization of methyl methacrylate in low density polyethylene matrix

The effects of the temperature and fine particles of Fe2O3 upon methyl methacrylate (MMA) thermal polymerization in low density polyethylene (LDPE) matrix were investigated. The MMA mass increment in the composite matrix is a temperature dependent process. It reaches values 10 folds higher at 90°C compared to the mass increment at 60°C. The apparent polymerization rate is dependent of Fe2O3 concentration reaching a maximum at 0.17–0.26 % of Fe2O3 in the composite. The thermal process is catalysed by Fe2O3.

Pseudohalides of Main Group Metals: The Alcaline Earth Tricyanomethanides - The Crystal Structures of Calcium and Barium Tricyanomethanide.

The alcaline earth tricyanomethanides Mg(tcm)2-2H20, Ca(tcm)2, Sr ( tcm) 2 H 2 0 and Ba(tcm)2-2H20 were prepared from aqueous solutions of the respective chlorides and solid silver tricyanomethanide. Their infrared spectra and thermal behavior are described. The crystal structures of Ca(tcm)2 and Ba(tcm)2-2H20 were determined by single-crystal X-ray diffraction. The crystal structure of Ca(tcm)2 is identical with that found for several transition metal tricyanomethanides / l / , containing two independent interpenetrating networks. Ba(tcm)2-2H20 has a unique crystal structure corresponding to a co-ordination polymer with ninefold co-ordinated Ba atoms connected by water molecules and tricyanomethanide anions.

Facile green synthesis of nanomagnets for modulating magnetohyperthermia: tailoring size, shape and phase

This study reports the successful production of both isometric and anisometric iron oxide-based nanoparticles using, respectively, ammonia and urea for co-precipitating Fe2+/Fe3+ from aqueous solution. Spherical nanoparticles (SNPs) with 10–20 nm in diameter are obtained using ammonia under reflux from 1 h to 9 h, with their relative magnetite/maghemite content decreasing from 10 to 0.05. However, using a lower and higher concentration of urea under reflux from 1 h to 12 h results in rod-like nanoparticles (RNPs) with length/width varying from 40/16 to 80/20 nm and hexagonal nanoparticles (HNPs) with diagonal varying from 150 to 100 nm, respectively. For RNPs (HNPs) the relative magnetite/goethite content increases with refluxing time from 0.25 to 2 (1.25 to 3.75). Hysteresis cycles (300 K) show unblocked SNPs and blocked RNPs and HNPs with coercivity (remanence) increasing with refluxing time from 55 to 80 Oe (1 to 5 emu g−1) and 70 to 130 Oe (5 to 13 emu g−1), respectively. Saturation magnetization of SNPs, RNPs and HNPs spans from 50 to 65 emu g−1, 12 to 60 emu g−1 and 57 to 80 emu g−1, respectively. Under AC magnetic field (522 kHz), with amplitude ranging from 70 to 310 Oe, SNPs show a strong hyperthermia effect, following HNPs with mild and RNPs with weak effects.