Microesferas de quitosana reticuladas com tripolifosfato utilizadas para remoção da acidez, ferro(III) e manganês(II) de águas contaminadas pela mineração de carvão

Considerable attention has been paid to chitosan and derivatives as efficient adsorbents of pollutants such as metal ions and dyes in aqueous medium. Nevertheless, no report can be found on the remedial actions of chitosan microspheres crosslinked with tripolyphosphate to control acidity, iron (III) and manganese (II) contents in wastewaters from coal mining. In this work, chitosan microspheres crosslinked with tripolyphosphate were used for the neutralization of acidity and removal of Fe (III) and Mn (II) from coal mining wastewaters. The study involved static and dinamic methods. The neutralization capacity of the surface of the static system was 395 mmol of H3O+ per kilogram of microspheres, higher than that of the dynamic one (223 mmol kg-1). The removal of Fe(III) in wastewater was of 100% and that of Mn(II) was 90%.

Espectroscopia de impedância eletroquímica aplicada ao estudo das reações heterogêneas em ânodos dimensionalmente estáveis

This paper discusses different aspects related to the application of electrochemical impedance spectroscopy (EIS) in the study of heterogeneous electrochemical reactions occurring on Dimensionally Stable anodes (DSA®). The most relevant aspects of the semiconductor/electrolyte interface, the application of the EIS classical equivalent circuit approach and the ac porous model in DSA are presented. The paper shows that DSA type electrodes can be consistently investigated by using the ac porous model and an analysis is presented showing the advantage of applying this kind of approach to study heterogeneous reactions on DSA electrodes. Furthermore, some preliminary results on Ti/Ru0,3Ti(0,7-x)Sn x O2 based electrodes are presented to exemplify the use of the ac porous model analysis.

Desempenho de biomassas na adsorção de hidrocarbonetos leves em efluentes aquosos

Removal of hydrocarbons from aqueous effluents using biosorbents was investigated. The effluent was simulated by a dispersion of gasoline (simple hydrocarbons) in water. Corn-cob, wood powder, coconut mesocarp and sugar-cane bagasse were used as adsorbents and their performance verified by means of batch experiments performed in an agitated vessel. The influence of input variables such as hydrocarbon concentration, mass of biomass and agitation level on the adsorbents' capacity was studied by means of factorial design. The results indicated that, among the materials studied, coconut mesocarp and sugar-cane bagasse can be considered promising biomasses for treating aqueous effluents contaminated by hydrocarbons.

Obtenção de titânio metálico com porosidade controlada por metalurgia do pó

Titanium is an attractive material for structural and biomedical applications because of its excellent corrosion resistance, biocompatibility and high strength-to-weight ratio. The high reactivity of titanium in the liquid phase makes it difficult to produce it by fusion. Powder metallurgy has been shown to be an adequate technique to obtain titanium samples at low temperatures and solid-phase consolidation. The production of compacts with different porosities obtained by uniaxial pressing and vacuum sintering is briefly reviewed. Powder particle size control has been shown to be very important for porosity control. Sample characterization was made using scanning electron microscopy (SEM) images.

Ecomateriais: desenvolvimento e aplicação de materiais porosos funcionais para proteção ambiental

Fundamental aspects of the conception and applications of ecomaterials, in particular porous materials in the perspective of green chemistry are discussed in this paper. General recommendations for description and classification of porous materials are reviewed briefly. By way of illustration, some case studies of materials design and applications in pollution detection and remediation are described. It is shown here how different materials developed by our groups, such as porous glasses, ecomaterials from biomass and anionic clays were programmed to perform specific functions. A discussion of the present and future of ecomaterials in green chemistry is presented along with important key goals.

Seeing smells: development of an optoelectronic nose

The development of an array of chemically-responsive dyes on a porous membrane and in its use as a general sensor for odors and volatile organic compounds (VOCs) is reviewed. These colorimetric sensor arrays (CSA) act as an "optoelectronic nose" by using an array of multiple dyes whose color changes are based on the full range of intermolecular interactions. The CSA is digitally imaged before and after exposure and the resulting difference map provides a digital fingerprint for any VOC or mixture of odorants. The result is an enormous increase in discriminatory power among odorants compared to prior electronic nose technologies. For the detection of biologically important analytes, including amines, carboxylic acids, and thiols, high sensitivities (ppbv) have been demonstrated. The array is essentially non-responsive to changes in humidity due to the hydrophobicity of the dyes and membrane.

Compósitos magnéticos baseados em hidrotalcitas para a remoção de contaminantes aniônicos em água

In this work the adsorption features of hydrotalcites (Al, Mg- CO3) and the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic hydrotalcites were characterized by XRD, magnetization measurements, N2 adsorption isotherms and Mössbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for anionic contaminants in water.

Utilização de zeólitas sintetizadas a partir de xisto retortado na remoção de arsênio em águas contaminadas

The solid by-product of the oil shale processing (PETROBRAS - Brazil) was used as raw material to synthesize zeolites A and faujasite. Alkaline fusion followed by hydrothermal treatment was the synthesis procedure used, and five different starting material compositions were obtained. The more crystalline zeolite-type materials synthesized, the pretreated oil shale ash and commercial zeolites were used as adsorbents in the purification of pollutant solutions with arsenic. The zeolite-type material composed of a mixture of zeolite A (42.6%) and faujasite (52.9%) presented an ion exchange capacity comparable to the pure zeolites A and faujasite, much better than the pretreated ash.

Biomateriais: deposição de hidroxiapatita sobre superfície de Ti-cp modificada por aspersão térmica

The osseointegrated titanium implants are reliable and safe alternatives to treatments for long periods of time. For surface modification, thermal aspersion of TiO2 was used. The samples with and without TiO2 were treated with NaOH and SBF in order to obtain a layer of HA. Characterization was done by SEM and FTIR. The images of HA obtained by SEM show a uniform morphology and a porous structure with spherical particles. The IR spectra show that the surface of Ticp/ TiO2 is more favorable for the HA deposit, as can be seen by the increase of the crystalline structure and the very intense and defined bands of the OH group of HA that is verified about 3571 and 630 cm-1. Thus the Ticp/ TiO2 surface presents a satisfactory nucleation of HA when compared to Ticp.

Um sistema simples para preparação de microesferas de quitosana

This article describes the construction and optimization of an inexpensive apparatus for the production of uniform and porous chitosan microspheres. It also describes the control of the main operational parameters and strategies for the production of uniform chitosan microspheres.

Sílica quimicamente modificada com os grupos p-anisidina, p-fenitidina e p-fenilenodiamina usada como adsorvente para Pb2+, Cu2+, Cd2+ e Ni2+ em soluções aquosa e etanólica

Silica gel was chemically modified with the aromatic amines p-anisidine, p-phenytidine and p-phenylenediamine, using grafting reactions. The resulting modified silicas were characterized by infrared spectroscopy and N2 adsorption/desorption isotherms. The organic groups were covalently immobilized in a monolayer form. These modified silicas were investigated as adsorbents for Pb2+, Cu2+, Cd2+ and Ni2+ in aqueous and ethanol solutions. In a general way, the adsorption capacity values for all adsorbents presented the following sequence: Pb2+ >> Cu2+ @Cd2+ @ Ni2+. Adsorption studies for all adsorbents, in competitive medium, showed better selectivity for Cu2+ and Pb2+ in aqueous medium and for Pb2+ in ethanol solution. Desorption studies were carried out using HCl and HNO3 as eluents.

Imobilização de ferro (II) em matriz de alginato e sua utilização na degradação de corantes têxteis por processos Fenton

In this work Fenton and photo-Fenton processes for textile dye degradation were investigated using iron (II) immobilized in alginate spheres. Photomicrographs obtained by scanning electron microscopy showed an irregular and porous surface with a homogeneous distribution of iron. The Fenton process was used to evaluate the degradation efficiency of reactive dyes and this procedure showed a low degradation effect. The association of artificial visible light or solar radiation in the Fenton process (foto-Fenton process) showed degradation ratios of 70 and 80% respectively in 45 min. It was also observed that the iron-alginate matrix can be reused.

Estudo de adsorção de compostos sulfurados utilizando um diesel comercial dopado com benzotiofeno e dibenzotiofeno

Desulphurization process by adsorption was studied employing a commercial diesel dooped with 1000 mg/L of benzothiophene and dibenzothiophene. The adsorbents materials employed were three types of activated alumina (acid, basic and neutral). For comparison, adsorption process was made also using oxidized diesel sample. The results showed that the adsorbents were selective for sulphur compounds removal from fuels. The contact time have influence in adsorption process achieving 80% of removal for not oxidized dibenzothiophene. The three studied alumina types showed similar behavior and a greater selective in dibenzothiophene adsorption than benzothiophene. Dibenzothiophene removal is more effective in samples not oxidized, whereas the benzothiophene was almost totally removed in oxidized sample.

Efeito de substâncias empregadas para remoção de cobre sobre o teor de compostos secundários da cachaça

High copper content is of great concern among producers of sugar-cane spirits who frequently use filters instead of cleaning the stills. This study compared the efficiency of activated carbon, ion-exchange-polymeric resin, and activated-carbon/iron-oxide magnetic composite for copper reduction without removing excessive organic compounds that are important for the beverage's quality. Resin was the most efficient copper adsorbent, removing fewer organic compounds. The composite also removed copper; however, it also removed large amounts of organic compounds. Activated carbon didn't remove sufficient copper to reduce its concentration to less than 5 g L-1, and it removed large amounts of higher alcohols and esters.

Remoção de azul de metileno de solução aquosa usando zeólitas sintetizadas com amostras de cinzas de carvão diferentes

Batch sorption experiments were carried out to remove methylene blue from its aqueous solutions using zeolites synthesized from fly ashes as an adsorbent. The adsorbents were characterized by XFR, XRD and SEM. Nearly 90 min of contact time are found to be sufficient for the adsorption of dye to reach equilibrium. Equilibrium data have been analyzed using Langmuir and Freundlich isotherms and the results were found to be well represented by the Freundlich isotherm equation. Adsorption data were fitted to both Lagergren first-order and pseudo-second-order kinetic models and the data were found to follow pseudo-second-order kinetics.