Artigos publicados

Polyphosphates can stabilize but also aggregate colloids

2020

Physical Chemistry Chemical Physics - Royal Society of Chemistry (RSC)

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​Rayssa Jossanea Brasileiro Motta and Ana Zélia Falcão Almeida and Bruna Luiza Batista de Lima and Ricardo Schneider and Rosangela de Carvalho Balaban and Jeroen Sebastiaan van Duijneveldt and Rodrigo José de Oliveira

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Phosphates are well known as dispersants for a variety of colloidal particles. Here however we use rheological measurements to show that high molecular weight polyphosphates (PP) can instead act as a flocculant for LAPONITE® clay platelets. The proposed mechanism is bridging of PP between clay particle edges, leading to highly charged clusters forming a Wigner glass. Dynamic light scattering shows a bimodal cluster size distribution, independent of PP molecular weight, but the highest molecular weight gave the highest viscous and loss moduli for the PP–clay solid. These unique all-inorganic solids may have application in solid-state ionic conducting materials, controlled release fertilizers and biomedical applications.

Use of sweet ‘Pêra’ peel as an adsorbent in the treatment of textile effluents

2019

Revista Brasileira de Engenharia Agrícola e Ambiental - FapUNIFESP (SciELO)

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Ketyla K. R. do Nascimento and Fernando F. Vieira and Marcello M. de Almeida and Josué da S. Buriti and Aldre J. M. Barros and Rodrigo J. de Oliveira

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The disposal of industrial wastewater into aquatic bodies without proper treatment can cause severe damage to the environment and human health. The objective of this study was to perform the drying of the sweet orange (Citrus sinensis L. Osbeck) peel cultivar Pêra and evaluate the viability of its use as biosorbent in the removal of a direct dye. Drying was carried out in an oven with air circulation at temperatures of 60 and 80 ºC. The mathematical models of Page, Henderson and Pabis, Logarithmic, Midilli and Two-term exponential were fitted to the moisture data as a function of time. The material was characterized by scanning electron microscopy, point of zero charge, and infrared spectroscopy. In the adsorption study, a complete 24 factorial design was used to analyze the influence of mass, initial concentration, solution pH and contact time on adsorbed quantity (qt) and removal percentage of the dye (R%). In the drying, the two-term exponential model fitted best to the experimental data. The characterization of the material indicated that the adsorbent has zero charge point of 3.5 and porous structure, and the infrared analysis indicated the presence of carboxylic and hydroxyl groups. In the adsorption, the adsorbed quantity of the dye increased under conditions of lower pH and biosorbent mass and higher initial concentration and contact time. The removal percentage of dye increases with higher biosorbent mass. The biosorbent used is a promising waste for the adsorption of the burgundy-16 dye.

Thermal, chemical, biological and mechanical properties of chitosan films with powder of eggshell membrane for biomedical applications

2019

Journal of Thermal Analysis and Calorimetry - Springer

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Santos, Kleilton Oliveira and Barbosa, Rossemberg Cardoso and da Silva Buriti, Josué and Bezerra Junior, André Gonçalves and de Sousa, Wladymyr Jefferson Bacalhau and de Barros, Sandra Maria Carvalho and de Oliveira, Rodrigo José and Fook, Marcus Vińicius Lia

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​The objective of this work was to develop chitosan films incorporated with the eggshell membrane powder (MCO) by the solvent evaporation method with application perspective as curatives. Chitosan was obtained from the deacetylation of chitin extracted from shrimp shells of Litopenaeus vannamei Boone, and the membranes were manually extracted from chicken eggshells, dehydrated in an oven at 60 °C for 2 days, crushed and passed through a 325 mesh to obtain the powder. Then, the solution of 1% (w v−1) chitosan in 0.1 mol L−1 lactic acid was prepared, in which the membrane powder was dissolved, obtaining films with percentages of 10, 20 and 30% of MCO (w w−1). For this, the mixture was stirred under mechanical stirring at 600 rpm for 24 h, poured into Petri dishes and oven-dried at 40 °C for 24 h. The chitosan powder was characterized as to the degree of deacetylation and viscosimetric molar mass and the MCO was characterized as to its constituents. In turn, the films were characterized by TG, DSC, DRX, FTIR, surface tension, water vapor permeability, tensile test and cytotoxicity. Based on the results, it can be concluded that, due to the thermal, physical, chemical and mechanical stability of the films, the addition of chitosan matrix loading caused instability of the material; however, the composition with 10% presented higher properties, showing better stability. The materials presented potentiality, due to being biocompatible, biodegradable, low cost, and also contributing to reduce environmental pollution.

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Fast self-healing and rebuildable polyphosphate-based metallo-gels with mixed ionic-electronic conductivity

2019

Journal of Colloid and Interface Science - Elsevier

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Skovroinski, Euzébio and de Oliveira, Rodrigo J. and Galembeck, André

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The development of self-healing materials opens perspectives to fabricate devices with unprecedented lifetimes and recyclability that can be integrated with flexible electronics. However, the timescale at which these materials operate remains an important challenge to overcome. This article describes the fast self-healing behavior of aluminum/iron polyphosphate metallo-gels and their hybrids with polyaniline and gives a detailed investigation of their electrical behaviors. The samples can be cut, molded and healed by manual handling. The rebuilding process is mediated by water uptake and was directly observed by environmental scanning electron microscopy. Metallo-gels with and without polyaniline can be mixed to give homogeneous samples, where the conducting polymer is uniformly distributed within the inorganic matrix. Cyclic voltammetry experiments showed that polyaniline behaves within the metallo-gel in the same manner as it does in aqueous electrolytes. Furthermore, polyaniline adds electronic conductivity to the originally ion-conducting polyphosphate metallo-gel, as demonstrated by impedance spectroscopy. The ionic and electronic conductivities are 1.3–1.7 × 10−2 S·cm−1 and 5.2 × 10−4 S·cm−1, respectively. Such properties result from the “free” and “bound” water within the hydrogel network and the dynamic nature of the aluminum-phosphate interactions within the supramolecular network. The features presented here make these materials good candidates to be used as moldable electroactive binders in carbon-based electrodes and in all-solid-state flexible separators for repairable electrochemical capacitors and batteries.

Conversion of “Waste Plastic” into Photocatalytic Nanofoams for Environmental Remediation

2018

ACS Applied Materials & Interfaces - American Chemical Society (ACS)

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Geovania C. de Assis and Euzébio Skovroinski and Valderi D. Leite and Marcelo O. Rodrigues and André Galembeck and Mary C.F. Alves and Julian Eastoe and Rodrigo J. de Oliveira

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Plastic debris is a major environmental concern, and to find effective ways to reuse polystyrene (PS) presents major challenges. Here, it is demonstrated that polystyrene foams impregnated with SnO2 are easily generated from plastic debris and can be applied to photocatalytic degradation of dyes. SnO2 nanoparticles were synthesized by a polymeric precursor method, yielding specific surface areas of 15 m2/g after heat treatment to 700 °C. Crystallinity, size, and shape of the SnO2 particles were assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), demonstrating the preparation of crystalline spherical nanoparticles with sizes around 20 nm. When incorporated into PS foams, which were generated using a thermally induced phase separation (TIPS) process, the specific surface area increased to 48 m2/g. These PS/SnO2 nanofoams showed very good efficiency for photodegradation of rhodamine B, under UV irradiation, achieving up to 98.2% removal. In addition the PS/SnO2 nanofoams are shown to retain photocatalytic activity for up to five reuse cycles.

Self-supported copper (Cu) and Cu-based nanoparticle growth by bottom-up process onto borophosphate glasses

2017

Journal of Materials Science - Springer

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Lenz, Guilherme F. and Bini, Rafael A. and Bueno, Thiago P. and de Oliveira, Rodrigo J. and Felix, Jorlandio F. and Schneider, Ricardo

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In this study, we present a new method for obtaining an effective catalytic system composed of glass, with Cu or CuO nanoparticle growth on a glass matrix through bottom-up process. The system is based on active borophosphate glass material doped with \(\hbox {Cu}^{+}\) ions, which was obtained by a classical melt-quenching glass production technique. The thermal annealing of doped glasses under reductive/oxidative atmosphere enables the glassy material to act successfully as host material of both copper and copper oxide nanoparticles. We have investigated the structural and optical properties of the \(\hbox {Cu}^{0}\) and CuO nanostructures by using X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance and Raman spectroscopy. Supported nanostructures with triangular and acicular shape were made without the necessity of chelating agents. The catalytic activity of these systems was efficiently tested for the reduction of p-nitrophenol in the presence of \(\hbox {NaBH}_{4}\), achieving a good rate constant around \(2.8 \times 10^{-3}\) and 7.3 \(\times 10^{-3}\,\hbox {s}^{-1}\) for \(\hbox {Cu}^{0}\) and CuO nanostructures, respectively. The catalyst was reused for three times without losing its activity significantly, simply taking and washing the pellet in fresh water, making these materials promising candidates for applications in the fields of catalysis.

Localized to long-range conductivity in polyaniline/magnetite nanocomposites followed by dielectric relaxation spectroscopy

2015

Colloid and Polymer Science - Springer

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de Araújo, A. C. Vaz and de Oliveira, R. José and Alves, S., Jr. and de Azevedo, W. Mendes

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Polyaniline (PAni) and magnetite (Fe3O4) are well-known semiconducting materials with quite different conduction mechanisms: localized conductivity for magnetite and long-range conductivity for PAni. Fe3O4 nanoparticles were used to polymerize aniline, forming a PAni/Fe3O4 hybrid nanocomposite. The microstructural evolution and the electrical behavior of this nanocomposite were studied by dielectric relaxation spectroscopy (DRS). Albeit being a powerful technique to probe the electrical properties of materials, DRS has not yet been used to characterize such system in reasonable detail. The dc conductivity for pure magnetite was approximately 10−6 S cm−1, while the values for the PAni/Fe3O4 nanocomposites were 1 order of magnitude higher. The Fe3O4 nanoparticles behave like a material composed of packed grains, with substantial grain volume and grain boundary effects, leading to different dielectric responses at high and low frequencies. The partial consumption of Fe3O4 during polymerization results in smaller magnetic crystals embedded within the PAni matrix, and the decreased number of crystallite interfaces leads to lower interfacial resistance. Hence, the formation of PAni causes a decrease in the material’s volume resistance and imparts long-range conduction pathways on the material. This work shows the feasibility of using DRS to follow the microstructural evolution of a nanocomposite and changes in its conduction mechanisms, which are essential for the proper development of novel materials and devices.

Dicationic Magnetic Ionic Liquids with Tunable Heteroanions

2013

Chemical Communications - Royal Society of Chemistry (RSC)

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Brown, Paul and Butts, Craig and Eastoe, Julian and Padron-Hernandez, Eduardo and Machado, Fernando Luis de Araujo and de Oliveira, Rodrigo J.

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Dicationic magnetic ionic liquids with heteroanionic anions allow for tunability of physicochemical properties while retaining magnetic susceptibility.

Third- and fifth-order susceptibilities of cobalt oxide nanoparticles dispersed in n-heptane