S��ntese e caracteriza����o de nanopart��culas de ��xido de ferro suportadas em matriz carbon��cea: remo����o do corante org��nico azul de metileno em ��gua

In this work were prepared composites of iron oxide and carbonaceous materials in two different weight proportions (Carbon/Fe 1/1 and 1/2). The physico-chemical properties of the composites were determined by temperature programmed reduction (TPR), adsorption/dessorption of N2, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and pulse titration H2. The XRD and XPS analysis showed a cubic iron oxide phase, identified as maghemite, formed over the carbon surface. The particle size of maghemite showed to be within 10-30 nm. Carbon/Fe 1/2 was the most active in MB removal kinetics and ESI-MS studies showed that MB removal by both composites leads to oxidized intermediates.

Emiss��o de ��xido nitroso de esta����o de tratamento de esgoto de lodos ativados por aera����o prolongada - estudo preliminar

Nitrous oxide emissions from an activated sludge plant which serves a research institute in Rio de Janeiro city were estimated from six unit processes (grit tank, sand trap, aeration tank, secondary settling tank, sludge recirculation line and aerobic digester sludge tank) and also from the plant effluent. Total estimated annual flux was 3.2 x 10(4) g N2O yr-1 of which about 90% was from the aeration tank. Emission factors estimated from population served, wastewater flow and nitrogen load (conversion ratio) were 13 g N2O person-1 yr-1, 9.0 x 10-5 g N2O Lwastewater-1 and 0.14%.

Influ��ncia da quantidade de am��nio na s��ntese de nanopart��culas de ��xido de ferro por microemuls��o

Iron oxide nanoparticles were synthesized in microemulsion systems composed by Triton X-100/hexyl alcohol/cyclohexane/aqueous solution. The nanoparticles were synthesized in microemulsions containing different amounts of ammonium, in order to evaluate the influence of this parameter on the size of the nanoparticles and on the phase transformation after heat treatment. Powder materials were obtained after centrifugation, washing and drying, and they were analyzed as synthesized and after heating at 350, 500 and 1000 ��C. It was observed that the higher amount of ammonium induced smaller particles and minor phase transformation, possibly due to a preferential nucleation process.

Adsor����o de chumbo, c��dmio e prata em ��xido de ni��bio (V) hidratado preparado pelo m��todo da precipita����o em solu����o homog��nea

This paper describes the adsorption of heavy metals ions from aqueous solution by hydrous niobium oxide. Three heavy metals were selected for this study: cadmium, lead and silver. Adsorption isotherms were well fitted by Langmuir model. Maximum adsorption capacity (Q0) for Pb2 +, Ag+ and Cd2 + was found to be 452.5, 188.68 and 8.85 mg g-1, respectively.

Adsor����o de ars��nio(V) pelo comp��sito magn��tico hidrotalcita: ��xido de ferro

In this work, hydrotalcite, a layered double hydroxide, had its adsorption and ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe. The removal of As(V) by a HT-Fe adsorbent was evaluated under various conditions. The Kinetic process was well described by a pseudo-second order rate model. The maximum adsorption capacity, calculated with the Langmuir model showed to be dependent on pH, reaching values of 24.09, 10.19 and 7.44 mg g-1, respectively, for pH values of 4.0, 7.0 and 9.0. The inhibition by competition of anions is dependent on the type of ionic species.

Co2 na desidrogena����o oxidativa do etilbenzeno utilizando catalisadores compostos de ��xido de ferro e ��xido de alum��nio

Materials containing aluminum and iron oxide were synthesized through the preparation of hybrid spheres and tested in the dehydrogenation of ethylbenzene in the presence of CO2. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites. These results also point to a competitive process between CO2 adsorption and the oxidative dehydrogenation of ethylbenzene for the basic sites (lattice oxygen). In spite of the coke deposition is originating from ethylbenzene and CO2, the amount of carbonaceous deposits was smaller with the presence of CO2, if compared with the dehydrogenation in the absence of CO2.

Remo����o de ��ons Pb2+ de solu����o de bateria automotiva por caulinita modificada com ��xido de mangan��s

Nine absorbents were prepared using a mixture of Amazonian kaolinite and MnO2 at three temperatures (600, 700 and 900 ��C) in order to retain Pb2+ ions contained in the battery solutions. The batch experiments carried out with the batteries used water for 3 h and the kinetic isotherm was fitted with the pseudo-second order Lagergren equation. Findings show that synthesized adsorbents AD4, AD5 and AD7 performed well in reducing the Pb2+ ion content from 0.36 to 0.00 mg g-1. The better performance for removing the Pb2+ ions occurred for adsorbents synthesized in the temperature range from 600 to 700 ��C.

Fluxos de ��xido nitroso em solos com cobertura de Floresta Ombr��fila Densa Montana na Serra dos ��rg��os, Rio de Janeiro

Soil fluxes of N2O were determined over one year in montane tropical rainforest of southeastern Brazil with average annual rainfall of 2.8 m. Annual mean (�� standard deviation) and median N2O fluxes were 3.0 �� 1.4 and 2.7 ��g N m-2 h-1, respectively, is 5-10 times lower than mean values reported in literature for tropical rainforest soils in the Amazon basin. N2O fluxes varied spatially and seasonally, were about twice as high during summer as in winter, and significantly influenced by both monthly precipitation and soil temperature.

A utiliza����o de etanol em c��lula a combust��vel de ��xido s��lido

This work reports a review on the status and technical feasibility of the application of ethanol as fuel for Solid Oxide Fuel Cells (SOFC), presenting both external reform and cell with direct utilization of ethanol. Based on this survey, both experimental results and mathematical modeling indicated the technical feasibility of power generation by ethanol SOFC, with cell units producing 450 mW/cm��, sufficient for scale up to large stationary plants. The quantitative assessments in the literature show this field to be promising for researchers and private sector investment as well being a strategic technology for government policy in the short and long term.

Aumento del contenido de ��cidos h��micos en un carb��n de bajo rango a trav��s de la oxidaci��n con aire y con per��xido de hidrogeno o ��cido nítrico

Low-rank coals are an important source of humic acids, which are important in retention processes of water and nutrients in plants. In this study coal samples of Montelibano, Colombia, were oxidized with air at different temperatures and subsequently with H2O2 and HNO3. The materials were characterized by FTIR, proximate and elemental analysis, and quantification of humic acids. The oxidation process led to an increased content of oxygenated groups and humic acids in the carbonaceous structure. The solid oxidized with air at 200 ��C for 12 h and re-oxidized with HNO3 for 12 h showed the highest percentage of humic acids (85.3%).

Remo����o de cromo (VI) de solu����es aquosas utilizando o comp��sito magn��tico calcinado hidrotalcita-��xido de ferro: estudo cin��tico e de equil��brio termodin��mico

In this work, hydrotalcite, a layered double hydroxide, had its ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe 500. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. Removal of chromium (VI) from aqueous solutions using HT-Fe 500 was achieved using batch adsorption experiments. The adsorption capacity, calculated with the Langmuir-Freundlich model showed to be dependent on temperature, reaching values of 25.93 and 48.31 mg g-1, respectively, for temperatures of 25 and 30 ��C.

Emiss��es de ��xido nitroso do tanque de aera����o de uma esta����o de tratamento de esgotos com sistema de lodos ativados convencional

Nitrous oxide (N2O) emissions were measured monthly from January to June 2010 in the aeration tank of a wastewater treatment plant (WWTP) in Southeast Brazil. Emissions were lower in summer than winter and were positively related with influent ammonium (NH4+) concentration. The average N2O emission was 1.11 kg N day-1 corresponding to 0.02% of the influent total nitrogen load. The average emission factor calculated for the population served was 2.5 lower than that proposed by the Intergovernmental Panel on Climate Change (IPCC) for inventories of N2O emissions from WWTPs with controlled nitrification and denitrification processes.

EMISS��ES DE ÓXIDO NITROSO E METANO DO SOLO EM ��REAS DE RECUPERA����O DE PASTAGENS NA AMAZ��NIA MATOGROSSENSE

AbstractThis study evaluates the chemical processes responsible for the nitrous oxide (N2O) and methane (CH4) fluxes in the managed pasture (PM) and unmanaged pasture (PNM). In addition, the impact of nitrogen fertilization on the N2O and CH4 fluxes was assessed. The experiments were conducted on three farms in Alta Floresta city in the state of Mato Grosso. Both regular and intensive samples were collected from PM, PNM, and forest areas for each of the properties. The gases were sampled using static chambers in the morning. Higher N2O fluxes were recorded in the PMs, whereas the CH4 fluxes showed no influence of nitrogen fertilization in both regular and intensive samples. Low fertilizer levels resulted in low N2O emissions.

Óxido de zinco dopado com g��lio preparado pelo m��todo Pechini

Óxido de zinco dopado com g��lio (ZnO:Ga) foi preparado pelo m��todo Pechini a partir de citrato de zinco e hidr��xido de g��lio. Utilizsando este m��todo, foi poss��vel obter ZnO:Ga cristalino pela calcina����o do precursor polim��rico em ar a 900��C por 4 horas. A resina homog��nea contendo 2% de dopante s�� p��de ser obtida com a adi����o de ��cido etilenodiaminotetrac��tico (edta). A adi����o do edta, tamb��m, ocasionou a diminui����o de tamanho de part��cula do ��xido.

Sistema TS-FF-AAS com chama acetileno-ar como alternativa em rela����o �� chama acetileno-��xido nitroso em FAAS na determina����o de estanho

Este trabalho prop��e o desenvolvimento de um procedimento anal��tico para a determina����o em linha de estanho em solu����es anal��ticas empregando a t��cnica de espectrometria de absor����o at��mica com nebuliza����o t��rmica em tubo met��lico aquecido na chama (TS-FF-AAS) como alternativa ao uso da chama de ��xido nitroso-acetileno em espectrometria de absor����o at��mica, cujo comburente apresenta um custo elevado frente ao ar comprimido. Foram avaliados par��metros para a otimiza����o do sistema, tais como: vaz��o do carregador (ar), volume de amostra injetada e concentra����o do ��cido (HCl). Foi constru��da curva anal��tica linear [A= -0,00163 + 0,00319 [Sn], (r= 0,9998)] no intervalo de 10 a 80 mg Sn L-1. O limite de detec����o, o desvio padr��o relativo (n=12) e a freq����ncia anal��tica foram: 1,7 mg L-1 Sn, £ 2,7% and 120 h-1 respectivamente. O sistema TS-FF-AAS �� uma alternativa para a determina����o de Sn.