Kleber G.B. Alves

Use of magnetic polyaniline/maghemite nanocomposite for DNA retrieval from aqueous solutions.

We demonstrated that the magnetic polyaniline/maghemite nanocomposite (Pani/γ-Fe2O3 MNC) is an efficient agent for retrieval of pure double stranded deoxyribonucleic acid (dsDNA) chains from aqueous solutions. The dsDNA chains used in the retrieval experiments were of sodium salt of Salmon Sperm DNA. Based on λ=260 nm absorption measurements, we have employed UV-Vis spectroscopy to estimate the concentration of DNA present in solutions, before and after the interaction with the MNC. The best results corresponded to a maximum amount of 75.2 mg of DNA absorbed per gram of MNC reached within only 10 min of joint exposure into the aqueous solution. After magnetic separation of the fully DNA-loaded Pani/γ-Fe2O3 MNC, we achieved essentially complete DNA desorption by appropriate changes in the pH of the solution. We have shown that it is possible to recycle the use of these MNC in several adsorption-desorption cycles. By comparing the present results to those of other DNA retrieval systems reported in the literature, we argued that the Pani/γ-Fe2O3 MNC here described represent a promising low-cost material for use as a fast, simple and efficient method of DNA separation and concentration.

Study of the Efficiency of Polypyrrole/ZnO Nanocomposites as Additives in Anticorrosion Coatings

We synthesized (ZnO nanoparticles)/polypyrrole (ZnO_NPs/PPy) hybrid nanocomposites and used them as additives in an epoxy paint to protect SAE 1020 carbon steel from corrosion. The nanocomposites were obtained by chemical polymerization of pyrrole in aqueous solution and sodium dodecyl sulfate solution containing dispersed ZnO nanoparticles. We characterized the nanoparticles by infrared absorption spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A large disparity in the distribution of ZnO particle sizes became evident from the TEM images, which also show the formation of hybrid nanocomposites consisting of polypyrrole coated ZnO nanoparticles. Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) tests, which were performed on SAE 1020 carbon steel plates coated with epoxy and ZnO_NPs/PPy, have shown that epoxy paints have their efficiency as anticorrosive coatings significantly improved when ZnO_NPs/PPy hybrid nanocomposites are added to them.

Solvent-fractionated sugar cane bagasse lignin: structural characteristics and electro-spinnability

Abstract Lignin is one of the most abundant macromolecules on Earth. Lignins are obtained as by-products from the paper industry and used mostly as fuel. Their diverse composition has limited the development of high added-value applications: however, because of their abundance and sustainable origin, there is a growing interest in using lignins as a raw material and as a replacement for oil derivatives. In order to use lignins in bio-refineries, several processes must be studied and standardized. Lignin fractionation using solvents is a promising process. In this study, lignin from sugar cane bagasse (L1) was fractionated with solvents, and the fractions were characterized to evaluate structural aspects relevant for the production of fibers. L1 was extracted into four fractions with toluene (E1), ethanol (E2), methanol (E3), and dimethyl sulfoxide (DMSO, E4). Fractions E2, E3, and E4, showed only slightly different molar masses and molar mass distribution, but have relevant differences in their structural characteristics and processability. The ethanol extract (E2) provided lignins with a more flexible structure, and electro-spinning resulted in the production of nanofibers with diameters between 60 and 120 nm; the methanol fraction (E3) produced nanospheres with diameters between 90 and 350 nm; the DMSO fraction (E4) covered only a surface with electro-spray. These results show the possibility of developing high added-value applications using fractions of lignin from distinct biomasses or from their combination.

Synthesis of ZnO Nanoparticles Doped with Cobalt: Influence of Doping on the Magnetic and Fluorescent Properties

We have investigated the influence of cobalt doping on the luminescent and magnetic properties of ZnO nanoparticles prepared by co-precipitation. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and by use of a vibrating sample magnetometer (VSM). XRD analyses revealed a standard ZnO wurtzite crystal structure and showed that the cobalt doped ZnO nanoparticles (ZnO:Co_NPs) were synthetized without impurities. The calculation based on the XRD shows the average crystallite sizes of ZnO to be in the 8-11 nm range. TEM images of ZnO and ZnO:Co indicated that these nanoparticles are nearly uniformly spherical with a diameter of about 10 - 15 nm. The PL spectra exhibited high [low] intensity in the UV [visible] region. While the PL shows a decreasing intensity with increasing doping doses, the peak at 544nm is not present in the cobalt-doped zinc oxide, and a the peak at 378 nm shifts to 390nm. The VSM measurement confirmed the presence of ferromagnetism and we observed an increase in the values of the saturation magnetization with increasing Co concentration.

Study of the Efficiency of Ag-SiO2 Nanoparticles as Additives in Anticorrosion Coatings

In this work, Ag-SiO2 nanoparticles were used as additives in an epoxy paint to evaluate their efficiency to protect SAE 1020 carbon steel from corrosion. Ag-SiO2 particles were characterized using X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). Samples of ABNT 1020 steel were coated with an industrial epoxy based paint added with Ag-SiO2 nanoparticles. Electrochemical tests of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were conducted to evaluate the anticorrosive behavior of the investigated coatings when exposed to saline solution. DLS data show that Ag-SiO2 particles have average diameters of around 223.4 nm. TEM images highlight the presence of Ag-SiO2 particles agglomeration. EIS and OCP measurements show that addition of 0.5% w/w Ag-SiO2 to the epoxy paint could improve the efficiency of the anticorrosive coating, when compared to the epoxy paint without any corrosion inhibitor. Results also show the importance of developing efficient dispersion techniques to avoid the agglomeration of the particles that may increase the porosity of the coating and thus affect its corrosion protection efficiency.

Effect of Alumina Ceramic Powder Dispersion on Mechanical Properties of PolyPropylene Polymers

The objectives of this paper are study effect of dispersion of hard alumina (Al2O3) microparticles-filled polypropylene (PP) composites. Al2O3/PP composites containing 1.0 – 5.0 wt% of the Al2O3 were prepared through melt blending and specimens were produced through injection moulding technique. This study sets out to evaluate the influence of adding hard particles to the mechanical properties of the composite obtained while keeping the processing characteristics of the material. The material was characterized as thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM). The tensile tests performed showed an increase in the mechanical properties of the composite (modulus and elongation (%)) by increasing the Al2O3 content. The SEM images show a change in the fracture behavior between pure PP (brittle fracture) and Al2O3/PP composites containing 3.0 and 5.0 wt % (ductile fracture). The research aims to establish a new parameter for the development of products and advances in the application of this material.