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.

Estudo do equilíbrio e cinética da biossorção do pb2+ por saccharomyces cerevisiae

The biosorption, based on the use of biomass for removal of ions is distinguished as an innovative and promising technology when compared with the traditional methods. In this context, the aim of the present work is to use Saccharomyces cerevisiae as biosorbent for the retention of Pb2+ metal ions. Factorial design was used for evaluation of the process. The observed equilibrium data were well described by Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity was 1486.88 mg/g. The results indicated that Saccharomyces cerevisiae is suitable for biosorption of Pb2+ metal ions.

Dessorção iônica e degradação de filmes de polipirrol dopado com dodecilsulfato induzidas por elétrons de alta energia

Electron stimulated ion desorption (ESID) and degradation studies of polypyrrole doped with dodecylsulfate (PPy/DS) deposited on FTO were performed using time-of-flight mass spectrometry (TOF-MS) for ion analysis. The results suggest a strong contribution from fragments of the dodecylsulfate hydrocarbon chain to the mass spectra. In the 650-1500 eV energy range the ion yield curves show maxima at about 600, 1200 and 1400 eV, which can be related to carbon, nitrogen and oxygen-containing fragments, respectively, and interpreted in terms of the Auger Stimulated Ion Desorption (ASID) mechanism. Degradation studies indicate rapid loss of heavier hydrocarbons and an increase of bulk and substrate fragments. Some degradation profiles suggest formation of new species.

Aplicação de Zr/Ti-PILC no processo de adsorção de Cu(II), Co(II) e Ni(II) utilizando modelos físico-químicos de adsorção e termodinâmica do processo

The aim of this investigation is to study how Zr/Ti-PILC adsorbs metals. The physico-chemical proprieties of Zr/Ti-PILC have been optimized with pillarization processes and Cu(II), Ni(II) and Co(II) adsorption from aqueous solution has been carried out, with maximum adsorption values of 8.85, 8.30 and 7.78 x10-1 mmol g-1, respectively. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data with a linear regression process. The energetic effect caused by metal interaction was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

Efeito de microondas na estrutura cristalina e na atividade catalítica de argilas

The effect of microwave (MW) irradiation on the crystalline structure of two natural clays and one commercial clay, Montmorillonite K10, was analyzed comparing the X-ray diffraction, N2 isotherms, NMR-MAS of 27Al and 29Si spectra of the clays before and after MW irradiation. The preparation of dioxolane ketals of isatin was used to analyze the MW effect on the catalyst activation. The yields achieved using catalysts activated by MW irradiation were lower (2 to 5%) than the yields achieved using catalysts activated by heat in a conventional oven.

Nanocompósitos cerâmicos a partir do processo de moagem mecânica de alta energia

Pb/Ti, Sn and Mg-based nanocomposite materials were prepared by the high-energy mechanical milling of commercial powders. The surface of these ceramic compounds was strongly influenced by the doping, diameter of the milling spheres and time of the mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. The mechanical processing parameters of these compounds were investigated through Brunauer, Emmett and Teller isotherms, wide angle X-ray diffraction, transmission electron microscopy and CO2 adsorption.

Preparação e caracterização de carvão ativado produzido a partir de resíduos do beneficiamento do café

Coffee fruit processing is one of the most polluting activities in agriculture due to the large amount of waste generated in the process. In this work, coffee parchment was employed as precursor for the production of carbons activated with ZnCl2 (CAP). The material was characterized using N2 adsorption/desorption at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The material showed a surface area of 521.6 m²g-1 and microporous structure. CAP was applied as adsorbent for the removal of methylene blue dye in aqueous medium. The adsorption capacity was found to be about 188.7 mg g-1.

Aplicação de adsorção para remover amônia de efluentes suinícolas pré-tratados

The aim of this work is to evaluate the use of natural zeolites to remove the NH4+ that remains in effluents from swine facilities which were submitted to physico-chemical and biological treatments. Experiments were made in batch made adding 5% (w/w) of adsorbent (0.6-1.3 and 3.0-8.0 mm) to synthetic and real swine facilities effluents. The results show that ammonium removal is influenced by adsorbent particle size and the presence of other ions in the effluent. The adsorption equilibrium was described by Langmuir as well as Freundlich isotherms and the kinetic data fitted well a pseudo-second order model.

Amostragem do material particulado e fração orgânica volátil das emissões em motor ciclo diesel sem a utilização de túnel de diluição

Using a sampling method of particulate matter (PM) without the use of a dilution tunnel allows for evaluations of the volatile hydrocarbons (HC) in the emissions of diesel cycle engines. The procedure in this work applied a heated filter with temperature controlled. The volatile compounds are condensed at low temperature, allowing for evaluation of the HC by thermal desorption of the PM and for analysis of the condensed compounds of the exhaust gases.

Sintesis de poliuretanos a partir de polioles obtenidos a partir del aceite de higuerilla modificado por transesterificación con pentaeritritol

Castor oil was reacted by transesterification with various percentages in mass of pentaerythritol to obtain different esters of pentaerythritol. Alternatively, glycerol was also used instead of pentaerythritol for the same reaction in order to establish comparative reference products. The products of the reactions were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy in order to detect and quantify (in terms of the molecular mass and structural information) the components of the products obtained. Analysis for hydroxyl value, acid value, viscosity and specific gravity were used to complete the characterization of the polyols obtained and also of the original castor oil. The polymer characterization was accomplished by tensile stress-strain tests, Shore A hardness, thermogravimetric analysis and chemical resistance to solvents.

Adsorção e dessorção aniônicas individuais por gibbsita pedogenética

Anion adsorption/desorption dynamics was studied as individual processes on surface of particles of a gibbsitic clay. The data suggest a remarkable gibbsite role as nitrate leaching retardant in soil. The opposite behavior of gibbsite towards adsorption/desorption of silicate and phosphate suggests the need of an adequate compromise solution regarding interval and rate applications of anions in cultivated gibbsitic soils. The high P adsorption verified in pH values lower than that reported for the point of zero charge of synthetic Al-hydroxides implies that this process takes place in pedogenic gibbsites through inner sphere complexation.

Caracterização de subproduto da indústria de alumínio e seu uso na retenção de cádmio e chumbo em sistemas monoelementares

The present work aimed to characterize an aluminum industry by-product in natura (L.A. nat) and after phosphate and thermal pretreatments; evaluate the adsorption/desorption capacity of Cd and Pb by this L.A. nat form and after the aforementioned pretreatments, comparing them with an in natura iron mining by-product (L.F. nat). The L.A. nat presented a high pH as well as a high Na concentration and also an oxide-rich mineralogy. Pretreatment of the by-product had no significant effect upon Cd and Pd adsorption/desorption. The L.A. nat performed better than the L.F. nat as an Cd and Pb adsorbent.

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.

Adsorção de íons fosfato em óxido de nióbio hidratado

The adsorption kinetics of phosphate on Nb2O5.nH2O was investigated at initial phosphate concentrations 0.25, 0.50 and 1.00 mg.L-1. The kinetic process was described by a pseudo-second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The effective desorption could be achieved using water at pH 12.

Nióbia sintética modificada como catalisador na oxidação de corante orgânico: utilização de H2O2 e O2 atmosférico como oxidantes

In this work synthetic niobia was used to promote the oxidation of methylene blue dye in aqueous medium. The niobia was characterized by N2 adsorption/desorption, XRD and TG measurements. The presence of reactive species on the niobia surface strongly increased the oxidation rate of the methylene blue dye. The reaction mechanism was studied by ESI-MS suggesting that the oxidation of the organic dye involve oxidizing species generated mainly after previous treatment with H2O2. It can be observed that the catalyst is a good material in the activation of gas (atmospheric oxygen) or liquid (hydrogen peroxide) oxidant agent with a total discoloration of the dye solution after only 1 h of reaction.