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1.
Sci Rep ; 6: 31406, 2016 08 09.
Artigo em Inglês | MEDLINE | ID: mdl-27503274

RESUMO

The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.


Assuntos
Bismuto/química , Compostos de Cálcio/química , Hidrogênio/química , Óxidos/química , Titânio/química , Vanadatos/química , Técnicas Eletroquímicas , Processos Fotoquímicos , Semicondutores , Energia Solar , Água
2.
Nanotechnology ; 27(8): 085105, 2016 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-26820520

RESUMO

The combination of magnetic hyperthermia therapy with the controlled release of chemotherapeutic agents in tumors may be an efficient therapeutic with few side effects because the bioavailability, tolerance and amount of the drug can be optimized. Here, we prepared magnetoliposomes consisting of magnetite nanoparticle cores and the anticancer drug gemcitabine encapsulated by a phospholipid bilayer. The potential of these magnetoliposomes for controlled drug release and cancer treatment via hyperthermic behavior was investigated. The magnetic nanoparticle encapsulation efficiency was dependent on the initial amount of magnetite nanoparticles present at the encapsulation stage; the best formulation was 66%. We chose this formulation to characterize the physicochemical properties of the magnetoliposomes and to encapsulate gemcitabine. The mean particle size and distribution were determined by dynamic light scattering (DLS), and the zeta potential was measured. The magnetoliposome formulations all had acceptable characteristics for systemic administration, with a mean size of approximately 150 nm and a polydispersity index <0.2. The magnetoliposomes were stable in aqueous suspension for at least one week, as determined by DLS. Temperature increases due to the dissipation energy of magnetoliposome suspensions subjected to an applied alternating magnetic field (AMF) were measured at different magnetic field intensities, and the values were appropriated for cancer treatments. The drug release profile at 37 °C showed that 17% of the gemcitabine was released after 72 h. Drug release from magnetoliposomes exposed to an AMF for 5 min reached 70%.


Assuntos
Antimetabólitos Antineoplásicos/farmacologia , Preparações de Ação Retardada/química , Desoxicitidina/análogos & derivados , Lipossomos/química , Nanopartículas de Magnetita/química , Animais , Antimetabólitos Antineoplásicos/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Preparações de Ação Retardada/farmacologia , Desoxicitidina/metabolismo , Desoxicitidina/farmacologia , Composição de Medicamentos , Liberação Controlada de Fármacos , Estabilidade de Medicamentos , Óxido Ferroso-Férrico/química , Hipertermia Induzida/métodos , Luz , Lipossomos/farmacologia , Campos Magnéticos , Nanopartículas de Magnetita/ultraestrutura , Células-Tronco Mesenquimais/citologia , Células-Tronco Mesenquimais/efeitos dos fármacos , Tamanho da Partícula , Fotoquimioterapia/métodos , Cultura Primária de Células , Ratos , Ratos Endogâmicos Lew
3.
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
4.
J Nanosci Nanotechnol ; 9(3): 2081-7, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19435085

RESUMO

It is well known that nano-sized materials often present chemical, electronic, magnetic, and mechanical properties that are potentially interesting for many technological applications comparatively to their corresponding bulk properties. This paper describes the main differences in magnetic properties among nanomagnetite powders prepared by three methods: (I) reduction-precipitation of ferric chloride by reaction with Na2SO3; (II) reduction of hematite with coal, and (III) reduction of hematite with hydrogen gas. The obtained materials were characterized by powder X-ray diffraction (XRD), saturation magnetization measurements, and Mössbauer spectroscopy. Saturation magnetization values varied from 60 to 86 J T(-1)kg(-1). XRD and Mössbauer spectroscopy results at 298 K showed the clear effect of the preparation routes on the crystallographic structure and crystallite size of the magnetic species. Magnetite was formed in varying proportions in all samples, with crystallite sizes estimated by Scherrer formula of about 10, 26, and 33 nm for samples prepared by methods (I), (II), and (III), respectively. The Mössbauer spectrum of the sample prepared by method (I) consisted of broad lines and hyperfine field for magnetite lower than that typically reported for the bulk material.

5.
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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