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1.
Talanta ; 217: 121011, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32498917

RESUMO

This research describes a solid-phase microextraction device using carbon nanomaterials supported on steel threads. The device was used to pre-concentrate and extract 24 pesticides in water. The carbon nanomaterials were obtained by a chemical vapor deposition (CVD) process, using methane and acetonitrile as carbon source. The different pesticides were separated, detected, and quantified using gas chromatography coupled to mass spectrometry (GC-MS). The system, optimized and validated in the laboratory, presented good results. Linearity was between 0.0007 and 50.00 µg L-1, with determination coefficients greater than 0.9. The detection and quantification limits were in the range of 0.0002-1.1309 µg L-1 and 0.0007-3.7320 µg L-1, respectively. The studied pesticides presented recovery values in the range of 70 ± 8 to 123 ± 18%. Carbon nanomaterials exhibited high thermal and mechanical resistance, as the same fiber could be used for approximately 300 extractions. The device was applied to analyze environmental water samples collected from the São Francisco river basin in Brazil and in the Chinampas in Mexico City.

2.
J Environ Manage ; 242: 220-228, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-31048227

RESUMO

In this work, magnetic cobalt nanoparticles (CoNPs) were synthesized and applied to the removal of Remazol golden yellow RNL (RGY) from aqueous solutions and textile wastewater. The CoNPs were characterized and the Co content found in the CoNPs was 60.38% (m/m). The analysis of X-ray Diffraction (XRD) and Raman Spectroscopy indicated the presence of Co0 and CoO in the composition of the material, as confirmed by Thermogravimetric Analysis coupled to Mass Spectrometry (TG-MS). Images obtained by the Transmission Electron Microscope (TEM) showed that the CoNPs have sizes smaller than 10 nm, sphere morphology and high agglomeration capacity. The results obtained by nitrogen adsorption-desorption suggested that the nanomaterial presented a mesoporous characteristic, low specific surface area (15.70 m2 g-1) and a pore volume and pore diameter of 0.072 cm3 g-1 and 3.64 nm, respectively. CoNPs removed the RGY with high efficiency, reaching almost 100% removal in 30 min. The kinetic results showed that the reaction followed pseudo-second-order kinetics. Additionally, the removal process can be altered depending on the experimental condition. For instance, under acidic conditions, the reductive degradation prevailed, while in neutral or basic conditions, two simultaneous processes occur: reductive degradation and adsorption. Finally, CoNPs were applied to textile wastewater. The results showed high discoloration, reaching almost 88%. However, there was only a 32% decrease in chemical oxygen demand, showing that CoNPs are efficient at removing organic dyes from aqueous solutions.


Assuntos
Nanopartículas , Poluentes Químicos da Água , Adsorção , Cobalto , Têxteis
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.
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.

5.
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
6.
J Environ Sci Health B ; 48(3): 183-90, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23356339

RESUMO

This study evaluated the adsorption capacity of ethylenthiourea (ETU) and 1H-1,2,4-triazole (1,2,4-T) for two commercial activated carbons: charcoal-powdered activated carbon (CPAC) and bovine bone-powdered activated carbon (BPAC). The tests were conducted at a bench scale, with ETU and 1,2,4-T diluted in water, for isotherm and adsorption kinetic studies. The removal of the compounds was accompanied by a total organic carbon (TOC) analysis and ultraviolet (UV) reduction analysis. The coals were characterized by their surface area using nitrogen adsorption/desorption, by a scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) and by a zero charge point analysis (pHpcz). The results showed that adsorption kinetics followed a pseudo-second-order model for both coals, and the adsorption isotherms for CPAC and BPAC were adjusted to the Langmuir and Freundlich isotherms, respectively. The CPAC removed approximately 77% of the ETU and 76% of the 1,2,4-T. The BPAC was ineffective at removing the contaminants.


Assuntos
Carvão Vegetal/química , Recuperação e Remediação Ambiental/métodos , Praguicidas/química , Triazóis/química , Poluentes Químicos da Água/química , Adsorção , Animais , Bovinos , Recuperação e Remediação Ambiental/instrumentação , Cinética
7.
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.

8.
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
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