Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 5 de 5
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
2.
Nanomaterials (Basel) ; 10(5)2020 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-32455949

RESUMO

Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO2 (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO2-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO2-P25 lattice induces tensile strain in Cu-impregnated TiO2-P25, whereas compressive strain in Cr- and V-impregnated TiO2-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N2 adsorption-desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC-UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO2-P25, the reactivity order being Cu > V >> Cr > TiO2-P25 under 366 nm irradiation, while TiO2-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC-MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.

3.
J Agric Food Chem ; 55(24): 9936-43, 2007 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-17960882

RESUMO

Direct degradation of imazapic, an herbicide of the imidazoline family, has been investigated in aqueous solution at different concentrations, pH values, and temperatures. The efficiency of the photodegradation process has been evaluated through degradation rate constants that could be fitted best with pseudo-first-order kinetics ( Ct = C0 e(- kt )). Ultrahigh resolution mass spectrometry (FTICR/MS) was used in electrospray ionization mode as a tool to study the photolysis process on a molecular level, whereas UV-vis and high-performance liquid chromatography/mass spectrometry analysis were used to follow, by time, the evolution of the intermediates. Taking advantage of the high resolving power of FTICR/MS to perform precise formula assignments taking account of the natural abundance of isotopes, we herein propose and demonstrate an approach using 2D-derived van Krevelen visualization (O/C, H/C, m/z) to confirm the formation of imazapic intermediates. Such an approach allows a qualitative analysis of intermediates and elucidates the plausible reaction pathways of the photolysis process. More than eight photoproducts were separated and identified as a phototransformation of the imidazole ring. A mechanistical pathway was proposed.


Assuntos
Herbicidas/química , Imidazóis/química , Espectrometria de Massas/métodos , Ácidos Nicotínicos/química , Fotólise , Cromatografia Líquida de Alta Pressão , Relação Dose-Resposta a Droga , Análise de Fourier , Herbicidas/análise , Concentração de Íons de Hidrogênio , Imidazóis/análise , Cinética , Ácidos Nicotínicos/análise , Solubilidade , Espectrofotometria Ultravioleta , Temperatura
4.
Anal Bioanal Chem ; 389(5): 1459-67, 2007 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-17554530

RESUMO

The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox.


Assuntos
Imidazóis/química , Fotólise , Espectrometria de Massas por Ionização por Electrospray/métodos , Cromatografia Líquida de Alta Pressão , Ciclotrons , Análise de Fourier , Herbicidas/química
5.
Neurochirurgie ; 37(5): 348-52, 1991.
Artigo em Francês | MEDLINE | ID: mdl-1758567

RESUMO

The authors report the case of a 40 years old woman with a fronto parietal tumefaction and intracranial hypertension caused by a paraganglioma of the cranial vault. The clinical follow up is marked by rapid local recurrence of the tumor after complete excision. Usually paragangliomas arise in any area of the body where paraganglionar structures are situated (glomus jugulare, carotid glomus, vagus nerve). Other rare locations have been reported and remain difficult to be explained. The location at the cranial vault is exceptional. this tumor would probably arise from the paraganglionar cells which migrate from the neural crest following the trigeminal branches particularly the ophtalmic division.


Assuntos
Neoplasias Encefálicas/diagnóstico , Recidiva Local de Neoplasia , Paraganglioma/diagnóstico , Adulto , Neoplasias Encefálicas/complicações , Neoplasias Encefálicas/cirurgia , Feminino , Lobo Frontal , Cefaleia/etiologia , Humanos , Paraganglioma/complicações , Paraganglioma/cirurgia , Lobo Parietal , Tomografia Computadorizada por Raios X
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA