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With increasing environmental pollution, sustainable alternatives for packaging materials are important. This study aimed to evaluate the phytotoxicity and biodegradation of corn starch films reinforced with cellulose extracted from pineapple crowns. The films were produced by casting mixtures of corn starch, glycerol and cellulose at different concentrations (5%, 10% and 15%), along with a pure starch control film. The phytotoxicity assay showed that the addition of films to the soil does not negatively influence the germination and growth of lettuce seeds (Lactuca sativa). In the biodegradation assay, the films were completely degraded after 60 days, especially the film containing 15% cellulose, which experienced rapid biodegradation, with a high rate of initial mass loss. Analysis of the Fourier transform infrared (FTIR) spectra after degradation of the films showed no structural changes. These materials have no harmful effects on the environment and have great potential for application as rapid-use packaging.

Improvement of the performance of renewable electronic devices is a crucial point for the consolidation of this emerging technology. Herein, we develop a supercapacitor based on cellulose, carbon nanotubes, and ionic liquids. A conductive paper prepared by simple acid hydrolysis of cellulose and carboxylated carbon nanotubes was used as an electrode. A cellulose sponge impregnated with 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide was used as a separator/electrolyte. Electrochemical tests were performed in a two-electrode cell that presented a specific capacitance of 34.37 F/g when considered the active mass and 97.9% of capacitance retention after 5000 charge/discharge cycles.

The development of new materials and systems capable of storing energy efficiently with a fast power delivering has been the subject of several studies. Many techniques and instruments are used for the characterization of these systems. Some involve the use of electrochemical techniques, such as cyclic voltammetry and electrochemical impedance spectroscopy, while others use instruments specially developed for this purpose. In this study, we provide a simple and functional supercapacitor characterization system using a programmable sourcemeter with an embedded scripting language. For the validation of the system, commercial capacitors and supercapacitors devices based on activated carbon and manganese dioxide were used. In a few steps, the system is capable of efficiently determine the main parameters used in the characterization of supercapacitors, for instance, specific capacitance, specific energy density, specific power density and equivalent series resistance. From the data collected, the system can also determine the stability and performance of supercapacitors, which are fundamental parameters used in the development of new electrodes for energy storage devices. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1374

A simple and low-cost method is proposed to synthesize graphene oxide incorporated with silver nanoparticles. The inter-sheet distance was controlled by introducing hexylamine into the graphene oxide sheets. The materials were investigated by Raman, UV-vis and Fourier transform infrared spectroscopy, X-ray diffraction and field-emission scanning electron microscopy. The increase in inter-sheet distance, due to the presence of hexylamine, favored the growth of the silver nanoparticles within the sheets. We demonstrate that silver nanoparticles increased the electrical conductivity and capacitive properties of the graphene oxide based electrode. The high concentration of well dispersed silver nanoparticles on the surface of the graphene sheets resulted in ca. 90 times higher specific capacitance than bare graphene oxide, in addition to improved electrochemical activity. The proposed method is promising for the development of hybrid materials with enhanced properties for applications mainly in electrochemical energy storage devices.

This study aimed to develop a flexible carbon fiber/oxide layer coating composite with improved electrical properties for use in electronic devices. For this, lead titanate zirconate, cerium-doped lead titanate zirconate, and yttrium-doped lead titanate zirconate were grown on carbon fibers via microwaves-assisted hydrothermal synthesis. The performed synthesis presented advantages when compared to conventional routes used in nanoparticles obtention since it allows the morphological control even at low temperatures. Carbon fiber was selected as substrates due to their thermal stability, excellent mechanical properties, chemical characteristics that allow the creation of functional groups on their surface, and good microwave radiation absorption. The composites were investigated by X-ray diffraction, spectroscopy Raman, and field emission scanning electron microscopy. The electrochemical evaluations were made by four-point probe method, cyclic voltammetry, and electrochemical impedance spectroscopy. The syntheses were successful and the carbon fiber coated with lead zirconate titanate had promissory results, with a boost in the electrical conductivity and better capacitance behavior when compared to the undoped carbon fiber, showing to be a good alternative for applications in electrical devices.

Composite of PZT (lead zirconate titanate) and PLZT (lead lanthanum zirconate titanate) along an organic, renewable, conductive, and flexible matrix have been developed. The conductive paper was obtained through the reaction between the cellulose extracted from banana stem and functionalized MWCNT. This reaction was made in the presence of hydrogen (from H2SO4), which reduced the size of the cellulose by acid hydrolysis and promotes the interaction between its hydroxyls and the carboxyl groups of nanotubes. Afterward, the PZT particles were synthesized and grown up on the conductive paper by microwaves-assisted hydrothermal synthesis (MHS). The composite material was characterized by structure and morphology. Moreover, gas-sensing in the presence of methanol and electrical resistance as a function of temperature were also investigated. In this way, a simple, low-cost and successful synthesis was reported. Also, a promising flexible was obtained using a chemical transformation process from banana residue as source of cellulose.

In this study, composites based on carbon fiber and a modified epoxy resin were obtained. The modification on the polymeric matrix was performed by adding functionalized multi-walled carbon nanotubes coated with zinc sulphide particles (MWCNT-ZnS), synthetized by hydrothermal synthesis assisted by microwave. For comparison, samples containing only functionalized multi-walled carbon nanotubes (MWCNTf) were also tested. The influences on chemical, structural, mechanical, and thermal properties of the composites were evaluated. For the filler characterization, X-ray diffraction, transmission electronic microscopy, and Raman spectroscopy were used. The modified polymeric matrix was evaluated by thermogravimetric analysis and the mechanical evaluation of the carbon fiber laminated composites was made by tensile and impact tests. The results showed that the tensile strength and Young’s modulus of the composites increased with the presence of carbon nanofillers. The absorbed energy on impact had higher values for the composites modified with MWCNTf. It was verified that the samples containing MWCNTf-ZnS were more thermally stable, mainly due to the ZnS particles coating the MWCNTf surface.

The production of biodiesel generates high amounts of glycerol as a byproduct. Thus, alternatives to reuse this byproduct need to be investigated. In this study, we evaluated the valorization of glycerol through a catalytic process with nickel/vanadium supported on γ-Al2O3 in different compounds, followed by the electrochemical characterization for energy storage of carbon-based materials (coke) produced during the catalytic reaction. The structural, morphological and compositional properties of the catalysts and carbon-based materials were investigated by X-ray diffraction, N2-physisorption, thermogravimetric analysis, Raman spectroscopy, inductively coupled plasma mass spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy. The glycerol reaction generated acrolein, dihydroxyacetone and methanol as main products. The addition of nickel to the catalyst increased the selectivity for methanol by ca. 44% for the catalytic cracking; while for the vapor reforming is observed a higher H2 production. The use of the coke residues for energy storage was investigated through cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 7.3 F g−1 at 3.75 mA g−1 was achieved, attributed to the high surface area, ease of access of the electrolyte ions to the entire surface of the electrode. This research reveals a zero-waste approach for the glycerol valorization reaction.

A capacitive, conductive and methanol sensor composite have been prepared by a simple process of acid hydrolysis, using potential cellulose source extracted from a residue of banana stem. The material was hydrolyzed with sulphuric acid in the presence of carboxylated multiwalled carbon nanotubes (MWCNTs) to promoted chemical interaction among cellulose and carbon surface. With these material was prepared a paper film used to design an electrode. The cellulose/MWCNT composite was investigated using x-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, transmission electron microscopy and size measurement. The electrical properties were evaluated by cyclic voltammetry, impedance spectroscopy, charge/discharge testing and simulation in an equivalent circuit. The gas sensor property was evaluated by an experimental apparatus, measuring the electric current front exposure the electrode to different concentrations of methanol in different temperatures. The cellulose/MWCNT electrode displays a strong dependence of a scan rate and potential range in capacitive properties. The chemical interaction archived between MWCNT and cellulose is relevant to develop a flexible cellulose composite, with specific capacitance of 3,08 mF/cm2 as functional nanotube integration. The flexible electrode developed in this study would be the ideal matrix to anchorage sensitive molecules and particles on specific applications like biosensor or electronic device.

The increase in global energy demand, with consequent environmental effects caused by the extensive use of fossil fuels, resulted in the intensification of studies concerning the development of new sustainable processes of energy storage. Aiming to solve issues like complex fabrication processes, high cost and side effects on the environment, the use of activated carbons derived from residual biomass as electrodes for energy storage devices has attracted much attention. In this study, activated carbons derived from citrus bergamia peels activated with phosphoric acid (AC - H3PO4) and manganese nitrate (AC – Mn3O4) were produced, and its chemical, structural, morphological and electrochemical properties were evaluated as electrodes for supercapacitor. The electrochemical properties were studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge, revealing the excellent performance of both AC – H3PO4 and AC – Mn3O4, materials. The maximum value of specific capacitance was achieved by AC – Mn3O4, reaching 289 F.g−1 at a current density of 0.1 A.g−1. Outstanding results regarding energy density in ionic liquid electrolyte were also obtained, with values of 50.8 Wh kg−1 at a power density of 240 W kg−1.

The effect of topologically close-packed (TCP) phase formation on the electrochemical corrosion behavior of the UNS N26455 (Ni–16Cr–16Mo) superalloy was evaluated using different electrochemical techniques. We verified that this superalloy is resistant to highly corrosive environments but its corrosion potential decreases and the anodic current density increases as the TCP phase concentration increases in the microstructure. Its anodic behavior indicates that there is a selective dissolution process associated with this secondary phase, which is completely dissolved before repassivation occurs. Although the repassivation potential remains nearly unchanged, the degraded points configure defects that may negatively affect the material’s performance during service.

Carbon-based hybrid structures have attracted much attention due to their superior chemical, thermal, mechanical and electrical properties. A 3D sponge-like structure based on reduced graphene oxide/carbon nanotubes decorated with zinc sulfide synthetized by a hydrothermal micro-wave assisted synthesis (MHS) was produced and its chemical, structural, morphological and electrochemical properties evaluated as electrodes for supercapacitor devices. XRD confirmed the structure of the nanocomposite, XPS was performed to examine the chemical state of the compounds. The morphology analysis realized by FESEM confirmed the success of the proposed methodology to produce the rGO/MWCNTf-ZnS nanocomposites revealing good homogeneity. The electrochemical properties were studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge. It was observed that the increase of MWCNTf-ZnS content increased the specific capacitance and reduced the resistivity of the 3D hybrid structure, reaching 95 F g−1, thus, approaching the ideal electric double layer storage capacitor behavior in samples containing MWCNTf-ZnS.

The corrosion properties of three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels were studied based on X-ray photoelectron spectroscopy (XPS) analyses, immersion and polarization tests. The test results were compared with those of a type 304 austenitic stainless steel. The XPS analyses indicated substantial Si content in the anodic passive films formed on shape memory stainless steels in sulfuric acid solution and that the high protectiveness of these films results from a protective film consisting of a (iron, chromium)–mixed silicate. The corrosion rate of the shape memory stainless steels in boiling nitric acid solution was lower than that of austenitic stainless steel. The high silicon content was found to play an important role in the corrosion behavior of these shape memory alloys in highly oxidizing environments. Due to their high manganese content, the shape memory stainless steels showed poor corrosion behavior in 3.5% sodium chloride solution when compared with austenitic stainless steel.

Passive films formed on three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels (SMSSs) were studied based on polarization tests, EIS, XPS and Mott–Schottky analyses. The test results were compared with those of a type 304 austenitic stainless steel. The results indicated that silicon plays an important role in the passive film properties of Fe–Mn–Si–Cr–Ni–(Co) SMSSs. Anodic passive films formed on Fe–Mn–Si–Cr–Ni–(Co) SMSSs are highly protective and consist of a chromium oxyhydroxide with incorporation of silicon in the chemical form of a silicate. Mott–Schottky analyses suggested that passive films on Fe–Mn–Si–Cr–Ni–(Co) SMSSs are less defective and thicker than those on austenitic stainless steel.

The corrosion behavior of three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels (SMSS) in 0.5 M H2SO4 solution was studied through electrochemical and immersion tests. The test results were compared with that of a type 304 (SS 304) austenitic stainless steel. The three SMSSs exhibited a passive behavior in 0.5 M H2SO4 solution; however, their anodic behavior in the active dissolution region was markedly different. The passive current densities of the SMSSs were similar to that of SS 304, although the critical anodic current required for passivation was higher. The corrosion rate of the SMSSs was much higher than that of SS 304. It was observed that the amount of Cr and Mn plays an important role in the corrosion behavior of SMSSs. The best corrosion behavior in acid media was shown by the SMSS that contained the

O objetivo do presente trabalho baseia-se em avaliar uma matriz metálica de aço 316L com adição de 1,3, 5 e 10% de carbeto de nióbio em peso, a temperatura de 1150°C e tempo de sinterização de 60minem forno tubular resistivo com atmosfera controlada em nitrogênio, bem como verificar as propriedades mecânicas, morfológicas e químicas com diferentes proporções matriz/reforço, tais como dureza, análise de superfície em microscópio ótico para verificar a dispersão do carbeto na matriz, análise de difração de raios Xe ensaio de corrosão do material. Os resultados apresentaram boa sinterabilidade nestes parâmetros, comprovada pelas imagens de microscopia e difração de raios X, e o componente desenvolvido apresentou melhora na dureza quando comparado ao mesmo material sem reforço de carbeto de nióbio.