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1.
Environ Sci Pollut Res Int ; 25(7): 6762-6771, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29264851

RESUMO

In this work, iron oxide in the red mud (RM) waste was restructured to produce mesopores with surface [FeO x (OH) y ] sites for the efficient complexation/adsorption of ß-lactam antibiotics. Red mud composed mainly by hematite was restructured by an acid/base process followed by a thermal treatment at 150-450 °C (MRM150, MRM200, MRM300, and MRM450) and fully characterized by Mössbauer, XRD, FTIR, BET, SEM, CHN, and thermogravimetric analyses. The characterization data showed a highly dispersed Fe3+ oxyhydroxy phase, which was thermally dehydrated to a mesoporous α-Fe2O3 with surface areas in the range of 141-206 m2 g-1. These materials showed high efficiencies (21-29 mg g-1) for the adsorption of ß-lactam antibiotics, amoxicillin, cephalexin, and ceftriaxone, and the data was better fitted by the Langmuir model isotherm (R 2 = 0.9993) with monolayer adsorption capacity of ca. 39 mg g-1 for amoxicillin. Experiments such as competitive adsorption in the presence of phosphate and H2O2 decomposition suggested that the ß-lactamic antibiotics might be interacting with surface [FeO x (OH) y ] species by a complexation process. Moreover, the OH/Fe ratio, BET surface area and porosity indicated that this complexation is occurring especially on [FeO x (OH) y ]surf sites contained in the mesopore space.


Assuntos
Amoxicilina/química , Antibacterianos/química , Ceftriaxona/química , Cefalexina/química , Compostos Ferrosos/química , Adsorção , Óxido de Alumínio , Resíduos Industriais , Metalurgia
2.
J Environ Manage ; 195(Pt 2): 110-116, 2017 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-27157699

RESUMO

In this study, a multistage treatment system was proposed to treat real pharmaceutical wastewater containing the antibiotic amoxicillin. Ozonation (O3), and ozonation combined with aerobic biodegradation, were performed. The real pharmaceutical wastewater presented a high concentration of organic matter (TOC: 803 mg C·L-1 and COD: 2775 mg O2·L-1), significant amoxicillin content (50 mg L-1) and acute ecotoxicity (Aliivibrio fischeri aTU: 48.22). Ozonation proved to be effective for amoxicillin degradation (up to 99%) and the results also indicated the removal of the original colour of the wastewater, with average consumption of 1 g of ozone. However, the ozonation system alone could not achieve complete mineralization. Therefore, a combination of ozonation and biodegradation in a multistage system was proposed in order to improve cost and treatment efficiency. The multistage treatment system presented promising results, achieving degradation of more than 99% of the amoxicillin, more than 98% of the original chemical oxygen demand (COD), and 90% of initial toxicity, with the consumption of approximately 500 mg of ozone. This indicates that this system could prevent dangerous and biorecalcitrant antibiotics from entering water resources.


Assuntos
Ozônio/química , Águas Residuárias/química , Antibacterianos/química , Biodegradação Ambiental , Eliminação de Resíduos Líquidos , Poluentes Químicos da Água/química , Purificação da Água
3.
Water Sci Technol ; 74(3): 663-71, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27508371

RESUMO

Hydrophobic cavities produced by cetyltrimethylammonium cation (CTA(+)) exchanged and trapped in the interlayer space of montmorillonite were used to remove the harmful hormone contaminant ethinyl estradiol (EE2) from water. X-ray diffraction, thermogravimetry/derivative thermogravimetry, elemental analysis (carbon, hydrogen, nitrogen), Fourier transform infrared, scanning electron microscopy/energy dispersive spectroscopy, Brunauer-Emmett-Teller and contact angle analyses showed that the intercalation of 9, 16 and 34 wt% CTA(+) in the montmorillonite resulted in the d001 expansion from 1.37 to 1.58, 2.09 and 2.18 nm, respectively. EE2 adsorption experiments showed that the original clay montmorillonite does not remove EE2 from water whereas the intercalated composites showed high efficiency with adsorption capacities of 4.3, 8.8 and 7.3 mg g(-1) for M9CTA(+), M16CTA(+) and M34CTA(+), respectively. Moreover, experiments with montmorillonite simply impregnated with cetyltrimethylammonium bromide showed that the intercalation of CTA(+) to form the hydrophobic cavity is very important for the adsorption properties. Simple solvent extraction can be used to remove the adsorbed EE2 without significant loss of CTA(+), which allows the recovery and reuse of the adsorbent for at least five times.


Assuntos
Bentonita/química , Compostos de Cetrimônio/química , Etinilestradiol/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Microscopia Eletrônica de Varredura , Espectrometria por Raios X , Termogravimetria , Purificação da Água/instrumentação , Difração de Raios X
4.
J Hazard Mater ; 317: 327-334, 2016 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-27318729

RESUMO

In this work, [FeOx(OH)y]/Al2O3 composites with different Fe oxyhydroxy contents, i.e. 10, 20 and 50wt% treated at 150, 200, 300 and 450°C were investigated as adsorbents of ß-lactamic antibiotics, i.e. cephalexin, ceftriaxone and especially amoxicillin, from aqueous solutions. The obtained results showed that the nature of the surface Fe(3+) species play a fundamental role on the adsorption process. The most efficient adsorption was obtained for the sample 150Fe50A (50% [FeOx(OH)y] supported in Al2O3 treated at 150°C) whereas the thermal treatment at higher temperatures caused a strong decrease on the adsorption capacity. Mössbauer, XRD, FTIR, Raman, TG-MS, SEM, CHN and BET of the composite 150Fe50A suggested an approximate composition of FeO0.65(OH)1.7 whereas at 450°C strong dehydroxylation process takes place to form FeO1.4(OH)0.21. These results combined with competitive adsorption using amoxicillin mixed with phosphate or H2O2 suggest that the antibiotic molecules adsorb by complexation on surface sites likely based on FeOx(OH)y by the replacement of the labile OH ligands.


Assuntos
Óxido de Alumínio/química , Antibacterianos/análise , Compostos Férricos/química , Águas Residuárias/química , Purificação da Água , beta-Lactamas/análise , Adsorção , Propriedades de Superfície
5.
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
6.
Nanoscale ; 7(1): 294-300, 2015 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-25408246

RESUMO

In this work, unique amphiphilic magnetic hybrid carbon nanotubes (CNTs) are synthesized and used as tensioactive nanostructures in different applications. These CNTs interact very well with aqueous media due to the hydrophilic N-doped section, whereas the undoped hydrophobic one has strong affinity for organic molecules. The amphiphilic character combined with the magnetic properties of these CNTs opens the door to completely new and exciting applications in adsorption science and catalysis. These amphiphilic N-doped CNTs can also be used as powerful tensioactive emulsification structures. They can emulsify water/organic mixtures and by a simple magnetic separation the emulsion can be easily broken. We demonstrate the application of these CNTs in the efficient adsorption of various molecules, in addition to promoting biphasic processes in three different reactions, i.e. transesterification of soybean oil, quinoline extractive oxidation with H2O2 and a metal-catalyzed aqueous oxidation of heptanol with molecular oxygen.

7.
Chemosphere ; 109: 143-9, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-24559933

RESUMO

In this work, a new approach is presented for the modification of the hazardous steel industry waste BFD (Blast Furnace Dust) into a versatile material for application in environmental remediation processes. Tar pitch, another waste, was used to agglomerate the very fine (submicrometric) dust particles to produce a compact and robust pelletized material that under simple thermal treatment produces notably reactive reduced Fe phases. SEM, TG/DTA, Mössbauer, XRD, Raman, BET and elemental analyses indicated that the tar/BFD composite (1:1wt ratio) pellets treated at 400, 600 and 800°C lead to tar decomposition to form a carbon binding coat concomitant with the reduction of the Fe oxides to produce primarily Fe3O4 (magnetite), FeO (wüstite) and Fe(0). Preliminary reactivity studies indicated that these treated composites, especially at 800°C, are active for the reduction of Cr(VI)aq and for the elimination of textile dye via reduction and the Fenton reaction.


Assuntos
Alcatrão/química , Poeira/análise , Eliminação de Resíduos/métodos , Cromo/química , Recuperação e Remediação Ambiental , Compostos Ferrosos/química , Peróxido de Hidrogênio/química , Ferro/química , Oxirredução , Temperatura
8.
Chem Commun (Camb) ; 49(92): 10778-80, 2013 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-24052000

RESUMO

A unique bistable copper-metallacyclic complex is used as an elegant molecular switch for the reversible formation of emulsions by simple pH variation. This switch may have several exciting applications in biphasic processes such as catalysis and separation science technologies.

9.
J Hazard Mater ; 248-249: 295-302, 2013 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-23399907

RESUMO

In this work, chrysotile was used as support to grow carbon nanotubes and nanofibers to produce fibrous amphiphilic magnetic nanostructured composites. Iron impregnated on the chrysotile surface at 1, 5 and 15 wt% was used as catalyst to grow carbon nanostructures by CVD (chemical vapor deposition) with ethanol at 800°C. Raman, TG/DTA, Mössbauer, XRD, BET, SEM, TEM, elemental analyses and contact angle measurements suggested the formation of a complex amphiphilic material containing up to 21% of nanostructured hydrophobic carbon supported on hydrophilic Mg silicate fibers with magnetic Fe cores protected by carbon coating. Adsorption tests for the hormone ethynilestradiol (EE), a hazardous water contaminant, showed remarkable adsorption capacities even compared to high surface area activated carbon and multiwall carbon nanotubes. These results are discussed in terms of the hydrophobic surface of the carbon nanotubes and nanofibers completely exposed and accessible for the adsorption of the EE molecules combined with the hydrophilic Mg silicate surface which allows good dispersion in water. The composites are magnetic and after adsorption the dispersed particles can be removed by a simple magnetic process. Moreover, the fibrous composites can be conformed as threads, screens and pellets to produce different filtering media.


Assuntos
Asbestos Serpentinas/química , Carbono/química , Etinilestradiol/química , Nanofibras/química , Nanotubos/química , Poluentes Químicos da Água/química , Adsorção , Estrogênios/química , Ferro/química , Silicatos de Magnésio/química , Fenômenos Magnéticos , Eliminação de Resíduos Líquidos/métodos
10.
J Nanosci Nanotechnol ; 12(3): 2661-7, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22755105

RESUMO

In this work, it is demonstrated how a novel technique based on temperature-programmed chemical vapor deposition (TPCVD) can be used to investigate the synthesis of carbon nanotubes (CNTs) from methane on a classic catalyst FeMo(x)/MgO (x = 0.07, 0.35 and 1.00). TPCVD monitors carbon deposition by measuring H2 formed during CH4 decomposition and affords information on the different catalytic species, deactivation process, reaction kinetics and carbon yields. The obtained results showed for FeMgO catalyst a simple TPCVD peak related to the production of carbon beginning at 760 degrees C with maximum at 800 degrees C followed by a rapid deactivation resulting in a low carbon yield. The addition of Mo to Fe/MgO catalyst completely changes the TPCVD profile with the formation of a new catalytic species active at temperatures higher than 900 degrees C, which is stable and continuously decomposes CH4 to produce high carbon yields. Raman, TG/DTG, Mössbauer, SEM, TEM, XRD and TPR analyses suggested that this active catalytic phase is likely related to Fe-Mo and Fe-Mo-C phases active to produce single wall and mainly multiwall carbon nanotubes.

11.
J Colloid Interface Sci ; 379(1): 84-8, 2012 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-22608147

RESUMO

In this work, hybrid magnetic amphiphilic composites were prepared by the catalytic growth of carbon nanotubes (CNTs) and nanofibers CNF on layered silicates fragments. SEM, TEM, Raman, XRD, Mössbauer, TG/DTA showed that CVD with CH(4) at 800°C produced CNF and magnetic Fe cores fixed on the surface of microfragments of silicates layers. Due to the amphiphilic character, the composites can be easily dispersed in water and efficiently adsorb hydrophobic contaminant molecules. For example, the composites showed remarkable adsorption capacities for the hormone ethinylestradiol, e.g. 2-4 mg m(-2), compared to ca. 0.1 mg m(-2) obtained for high surface area activated carbon and multiwall CNT. These results are discussed in terms of a high hydrophobic exposed surface area of the CNT and CNF fixed on the layered silicates fragments surface. Moreover, the composites can be easily removed from water by a simple magnetic separation process.


Assuntos
Etinilestradiol/química , Magnetismo , Nanofibras/química , Nanotubos de Carbono/química , Silicatos/química , Tensoativos/química , Adsorção , Tamanho da Partícula , Propriedades de Superfície
12.
J Hazard Mater ; 194: 393-8, 2011 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-21890267

RESUMO

A magnetic fraction (15%) from a waste of foundry sand (WFS), composed of sand, carbon, bentonite clay and iron (10%) was modified by thermal treatment at 400, 600 and 800°C under inert atmosphere. Mössbauer analyses showed that the thermal treatment increased the amount of Fe(3)O(4) from 25 to 55% by reduction of Fe(2)O(3) and highly dispersed Fe(3+) by the carbon present in the waste. The Fe(3)O(4) caused a significant increase on the activity of two important reactions with application in environmental remediation: the Fenton oxidation of indigo carmine dye with H(2)O(2) and the reduction of Cr(VI) to Cr(III). The magnetic fraction of WFS was also mixed with hematite (Fe(2)O(3)) and thermally treated at 400, 600 and 800°C. This treatment produced large amounts of surface Fe(3)O(4) and increased substantially the rate of Fenton reaction as well as Cr(VI) reduction. This reactivity combined with the presence of carbon (an adsorbent for organic contaminants), bentonite clay (an adsorbent for metallic contaminants) and the granulometry/packing/hydrodynamic features make WFS a promising material for use in reactive permeable barriers.


Assuntos
Cromo/química , Ferro/química , Temperatura Alta , Magnetismo , Microscopia Eletrônica de Varredura , Oxirredução
13.
Chemosphere ; 81(1): 7-12, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20723968

RESUMO

Composites based on iron supported on high surface area activated carbon were prepared and characterized with (57)Fe Mössbauer spectroscopy, X-ray diffraction, saturation magnetization measurements and temperature-programmed reduction. Upon thermal treatment, the supported iron oxides react with carbon to yield reduced chemical species, i.e. Fe(3)O(4) and Fe(0). This so produced composite was found to be highly efficient in two environmental applications: (i) degradation of textile dye and (ii) reduction of Cr(VI) in aqueous medium. Sequential reuses evidenced a progressive chemical deactivation of the composites due to a corresponding oxidation of the reactive species. Even after being virtually deactivated, the initial chemical reducing ability of the composites can be regenerated by heating at 800 degrees C under N(2) atmosphere, and then reused for several consecutive times.


Assuntos
Carvão Vegetal/química , Recuperação e Remediação Ambiental/métodos , Ferro/química , Poluentes Químicos da Água/química , Cromo/análise , Cromo/química , Corantes/análise , Corantes/química , Peróxido de Hidrogênio/química , Poluentes Químicos da Água/análise
14.
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
15.
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
16.
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.

17.
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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