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391.
Batista AC Villanueva ER Amorim RV Tavares MT Campos-Takaki GM 《Molecules (Basel, Switzerland)》2011,16(5):3569-3579
This research evaluated the importance of the adsorption properties of chitosan a chitosan/zeolite conjugate film for the removal of Cr(VI) ions from solutions in the 5-260 mg/L concentration range, when the pH was adjusted to 4.0 and 6.0. The uptake capacities of the films formed by chitosan and by the chitosan/zeolite conjugate were calculated by mass balance. The equilibrium isotherms were fitted to the Langmuir, Freundlich and Redlich-Peterson models. The chitosan film seems to be a good sorbent for Cr(VI) at pH 4, but its physical instability suggests the need for a more resilient support. Due to this fact zeolite was added to the chitosan matrix in solution and a chitosan/zeolite (CS/Zeo) film was thus formed. The solubility of the film and the characterization of the different matrices by FTIR, TGA and X-Ray showed that a cross-linked structure was formed between the chitosan and zeolite and the solubility of the film increased. In this study, the low manufacturing cost of the CS/Zeo matrix, the good uptake of Cr(VI) at acidic pH (17.28 mg/g) and the non desorption of Cr(VI) from the film in water suggests this combination should be tested in industrial environment. 相似文献
392.
Luciana M. Brito Fabián Vaca Chávez Maria Inês Bruno Tavares Pedro J.O. Sebastião 《Polymer Testing》2013
Starch and PLA were used alone and in blends to prepare nanostructured materials using both hydrophilic and organophilic clays, and PVA. All nanostructured materials were obtained by the solution intercalation method using water and chloroform as solvents. These systems were characterized by using conventional X-ray diffraction (XRD), conventional NMR and the non-conventional fast field cycling (FFC) NMR technique. The spin-lattice relaxation times were measured as a function of the Larmor frequency. The FFC results showed that the starch has only one relaxation time related to the amorphous region. PLA hybrids presented two distinct spin-lattice relaxation times. The blends of the two polymers also showed two relaxation times. The renormalized Rouse formalism was applied to describe the polymer molecular dynamics behavior in the studied systems containing starch. By adding clay or PVA, differences could be observed in relaxation time corresponding to the more amorphous region, indicating that, when adding clay and PVA, the effect that each has on the dynamics of the mixture is cancelled out. 相似文献
393.
E. Almeida G. A. Tavares J. A. Bendassolli V. F. Nascimento Filho 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):351-355
A method for simultaneous determination of Cr, Fe, Co, Ni, Cu, Zn, As e Pb in liquid chemical waste using Energy Dispersive
X-Ray Fluorescence (EDXRF) technique was evaluated. A small sample amount (200 μL) was dried on a 6.35 μm thickness Mylar
film at 60 °C and the analyses were carried out using an EDXRF spectrometer operated with an X-ray Mo tube (Zr filter) at
30 kV/20 mA. The acquisition time was 300 s and the Ga element was utilized as internal standard at 25 mg/L for quantitative
analysis. The method trueness was assessed by spiking and the detection limit for those elements ranged from 0.39 to 1.7 mg/L.
This method is notable because it assists the choice of the more appropriated waste treatment procedure, in which inter elemental
interference is a matter of importance. In addition, this inexpensive method allows a non-destructive determination of the
elements from 19K to 92U simultaneously. 相似文献
394.
395.
We establish necessary optimality conditions for variational problems with a Lagrangian depending on a combined Caputo derivative of variable fractional order. The endpoint of the integral is free, and thus transversality conditions are proved. Several particular cases are considered illustrating the new results. 相似文献
396.
Optimization of the extraction conditions of the volatile compounds from chili peppers by headspace solid phase micro-extraction 总被引:2,自引:0,他引:2
Junior SB de Marchi Tavares de Melo A Zini CA Godoy HT 《Journal of chromatography. A》2011,1218(21):3345-3350
A method involving headspace-solid phase micro-extraction (HS-SPME), gas chromatography with flame ionization detection (GC-FID) and gas chromatography with mass spectrometry (GC-MS) was developed and optimized to investigate the volatile composition of Capsicum chili peppers. Five SPME fibers were tested for extraction: carboxen/polydimethylsiloxane (CAR/PDMS-75μm), polydimethylsiloxane (PDMS-100μm), divinylbenzene/polydimethylsiloxane (DVB/PDMS-65μm), carbowax/divinylbenzene (CW/DVB-70μm), and divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS-50/30μm), the last of which was shown to be the most efficient fiber to trap the volatile compounds. Optimization of the extraction conditions was carried out using multivariate strategies such as factorial design and response surface methodology. Eighty three compounds were identified by GC-MS when using the optimized extraction conditions, the majority of which were esters. 相似文献