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1.
Environ Sci Pollut Res Int ; 25(26): 26482-26492, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-29987469

RESUMO

The removal of emergent contaminants via adsorption on granular activated carbon, prepared from Macauba palm, has been studied, contributing to the recovery of the residual biomass, endocarp, obtained in the Macauba palm oil extraction process. The material was characterized by different techniques, such as Raman spectroscopy, thermal analysis, adsorption/desorption of N2, zeta potential, and scanning electron microscopy. The N2 adsorption studies showed that the material presents wide micropores and narrow mesopores, and has a surface area of 907.0 m2 g-1. Its maximum adsorption capacity towards the three main emerging contaminants (bisphenol A, ethinylestradiol, and amoxicillin) is much higher than that obtained with benchmark adsorbents (0.148, 0.104, and 0.072 mmol g-1, respectively). The influence of temperature and pH on the adsorption was also analyzed, allowing an improved description of the adsorption mechanism and showing very promising results.


Assuntos
Arecaceae/química , Carvão Vegetal/química , Resíduos Industriais/análise , Poluentes Químicos da Água/análise , Adsorção , Arecaceae/crescimento & desenvolvimento , Compostos Benzidrílicos/análise , Biomassa , Preparações Farmacêuticas/análise , Fenóis/análise , Propriedades de Superfície
2.
Environ Sci Pollut Res Int ; 24(7): 5991-6001, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-27106074

RESUMO

In this work, mesoporous silica mobil composition of matter no. 41 (MCM-41) was synthesized by the sol-gel method. Two different surface modifications were made to transform this material into a very active adsorbent and catalyst support: (i) impregnation of iron nanoparticles and (ii) hydrophobization via chemical vapor deposition (CVD) with ethanol. The materials prepared with different iron contents, i.e., 2.5, 5, and 10 %, after hydrophobization, were characterized by several techniques. CHN analysis and Raman spectroscopy proved that approximately 15 % of carbon is deposited during CVD process mainly as organized carbonaceous structures. The specific surface area was determined by the BET method as up to 1080 m2 g-1, which explains the excellent results of the materials in the adsorption of model dyes methylene blue and indigo carmine. Mössbauer spectroscopy, thermogravimetric (TG)/DTG analysis, and transmission electron microscopy (TEM) images showed that the iron supported may be partially reduced during the CVD process to Fe2+ species, which are stabilized by the carbon coating. This iron species plays an important role in the oxidation of different contaminants, such as quinoline and methylene blue. The results obtained in the catalytic tests showed to be very promising.


Assuntos
Dióxido de Silício/química , Purificação da Água/métodos , Interações Hidrofóbicas e Hidrofílicas , Ferro/química , Nanopartículas Metálicas , Nanotecnologia , Porosidade
3.
Chemosphere ; 159: 602-609, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27343867

RESUMO

Amphiphilic magnetic composites were produced based on chrysotile mineral and carbon structures by chemical vapor deposition at different temperatures (600-900 °C) and cobalt as catalyst. The materials were characterized by elemental analysis, X-ray diffraction, vibrating sample magnetometry, adsorption and desorption of N2, Raman spectroscopy, scanning electronic microscopy, and thermal analysis showed an effective growth of carbon structures in all temperatures. It was observed that at 800 and 900 °C, a large amount of carbon structures are formed with fewer defects than at 600 and 700 °C, what contributes to their stability. In addition, the materials present magnetic phases that are important for their application as catalysts and adsorbents. The materials have shown to be very active to remove the oil dispersed in a real sample of emulsified wastewater from biodiesel production and to remove methylene blue by adsorption and oxidation via heterogeneous Fenton mechanism.


Assuntos
Asbestos Serpentinas/química , Carbono/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Poluentes Químicos da Água/análise , Adsorção , Catálise , Azul de Metileno/química , Oxirredução , Análise Espectral Raman , Propriedades de Superfície , Difração de Raios X
4.
J Hazard Mater ; 241-242: 73-81, 2012 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-23036701

RESUMO

New magnetic composites based on metallic nickel and molybdenum carbide, Ni/Mo(2)C, have been produced via catalytic chemical vapor deposition from ethanol. Scanning electron microscopy, thermal analysis, Raman spectroscopy and X-ray diffraction studies suggest that the CVD process occurs in a single step. This process involves the reduction of NiMo oxides at different temperatures (700, 800 and 900°C) with catalytic deposition of carbon from ethanol producing molybdenum carbide on Ni surface. In the absence of molybdenum the formation of Ni/C was observed. The magnetic molybdenum carbide was successfully used as pollutants removal by adsorption of sulfur and nitrogen compounds from liquid fuels and model dyes such as methylene blue and indigo carmine. The dibenzothiofene adsorption process over Ni/Mo(2)C reached approximately 20 mg g(-1), notably higher than other materials described in the literature and also removed almost all methylene blue dye. The great advantage of these carbide composites is that they may be easily recovered magnetically and reused.


Assuntos
Poluentes Ambientais/isolamento & purificação , Gasolina/normas , Imãs/química , Molibdênio/química , Níquel/química , Petróleo/normas , Adsorção , Catálise , Gasolina/análise , Índigo Carmim/isolamento & purificação , Azul de Metileno/isolamento & purificação , Microscopia Eletrônica de Varredura , Estrutura Molecular , Petróleo/análise , Análise Espectral Raman , Propriedades de Superfície , Tiofenos/isolamento & purificação , Difração de Raios X
5.
Chemosphere ; 78(9): 1116-20, 2010 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-20060564

RESUMO

In this work, controlled reduction of red mud with H(2) was used to produce active systems for two different environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Mössbauer, powder X-ray diffraction, thermal analyses and scanning electron microscopy analyses showed that at different temperatures, i.e. 300, 400, 500 and 600 degrees C, H(2) reduces red mud to different phases, mainly Fe(3)O(4), Fe(0)/Fe(3)O(4) and Fe(0). These Fe phases are dispersed on Al, Si and Ti oxides present in the red mud and show high reactivity towards two environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Reduction with H(2) at 400 degrees C showed the best results for the oxidation of the model dye methylene blue with H(2)O(2) at neutral pH due to the presence of the composite Fe(0)/Fe(3)O(4). The reduced red mud at 500-600 degrees C produced Fe(0) highly active for the reduction of Cr(VI) in aqueous medium. Another feature of these red mud based system is that after deactivation due to extensive use they can be completely regenerated by simple treatment with H(2).


Assuntos
Cromo/química , Peróxido de Hidrogênio/química , Ferro/química , Corantes/química , Recuperação e Remediação Ambiental , Compostos Férricos/química , Temperatura Alta , Hidrogênio/química , Azul de Metileno/química , Oxirredução
6.
Chemosphere ; 71(1): 90-6, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-18061239

RESUMO

We describe the use of highly reactive Fe(0)/Fe3O4 composites for the reduction of Cr(VI) species in aqueous medium. The composites were prepared by simple mechanical alloying of metallic iron and magnetite in different proportions, i.e. Fe(0) 25, 50, 75 and 90wt%. While after 3h of reaction pure Fe(0) and pure Fe3O4 showed only a low reduction efficiency of 15% and 25% Cr(VI) conversion, respectively, the composites, in particular Fe(0)(25wt%)/Fe3O4, showed a remarkable activity with ca. 65% Cr(VI) conversion. Kinetic experiments showed a high reaction rate during the first 3h, which subsequently decreased strongly, probably due to a pH increase from 6 to 8. Experiments with composites based on Fe(0)/alpha-Fe2O3, Fe(0)/gamma-Fe2O3 and Fe(0)/FeOOH showed very low activities, suggesting that Fe(oct)2+ in the magnetite structure plays an important role in the reaction. Scanning and high resolution electron microscopies and Mössbauer spectra (transmission and conversion electron Mössbauer spectroscopy) indicated that the mechanical alloying process promotes a strong interaction and interface between the metallic and oxide phases, with the Fe(0) particles completely covered by Fe3O4 particles. The high efficiency of the composite Fe(0)/Fe3O4 for Cr(VI) reduction is discussed in terms of a special mechanism where an electron is transferred from Fe(0) to magnetite to reduce Fe(oct)3+ to Fe(oct)2+, which is active for Cr(VI) reduction.


Assuntos
Cromo/química , Poluentes Ambientais/química , Compostos Férricos/química , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Oxirredução
7.
Rapid Commun Mass Spectrom ; 20(12): 1859-63, 2006.
Artigo em Inglês | MEDLINE | ID: mdl-16715481

RESUMO

Electrospray ionization (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were used to monitor the oxidation of phenol by a novel heterogeneous Fenton system based on a Fe(0)/Fe(3)O(4) composite and H(2)O(2). On-line ESI-MS(/MS) shows that this heterogeneous system promotes prompt oxidation of phenol to hydroquinone, which is subsequently oxidized to quinone, other cyclic poly-hydroxylated intermediates and an acyclic carboxylic acid. A peroxide-type intermediate, probably formed via an electrophilic attack of HOO(.) on the phenol ring, was also intercepted and characterized. ESI-MS(/MS) monitoring of the oxidation of two other model aromatic compounds, benzene and chlorobenzene, indicates the participation of analogous intermediates. These results suggest that oxidation by the heterogeneous system is promoted by highly reactive HO(.) and HOO(.) radicals generated from H(2)O(2) on the surface of the Fe(0)/Fe(3)O(4) composite via a classical Fenton-like mechanism.

8.
Chemosphere ; 60(8): 1118-23, 2005 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-15993160

RESUMO

In this work a novel heterogeneous Fenton system based on Fe(0)/Fe3O4 composites is described. The composites with several Fe(0)/Fe3O4 ratios were prepared by two different methods, i.e. mechanical alloying of Fe(0) and Fe3O4 powders and controlled reduction of Fe3O4 with H2. Reaction studies and detailed Conversion Electron Mössbauer surface characterization of the composites Fe(0)/Fe3O4, Fe(0), Fe3O4, alpha-Fe2O3 and gamma-Fe2O3 suggested that Fe2+surf species are essential to produce an active Fenton system. Kinetic studies for the oxidation of the dye methylene blue, used as an organic model molecule, and for the peroxide decomposition suggest that the reactions proceed via HO* radicals generated from Fe2+surf species and H2O2 in a Fenton like mechanism. The increase in activity caused by the addition of Fe(0) is discussed in terms of a creation of Fe2+surf species during the preparation of the composite and by an electron transfer mechanism from Fe(0) to Fe3+surf during the Fenton reaction to regenerate the Fe2+surf active species.


Assuntos
Ferro/química , Corantes/química , Compostos Férricos/química , Peróxido de Hidrogênio/química , Azul de Metileno/química , Oxirredução , Eliminação de Resíduos Líquidos
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