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31.
María Luisa Ojeda Antonio Campero Jos Guadalupe Lpez-Corts María Carmen Ortega-Alfaro Celso Velsquez Cecilio Alvarez 《Microporous and mesoporous materials》2008,111(1-3):178-187
A metal Fischer carbene [(CO)5WC(φ)OCH2CH3] was covalently linked for the first time to the silanol groups of the mesoporous channels of SBA15 by following two different synthetic anchoring routes. The first one goes through the reaction of the SBA15 mesoporous silica walls functionalized by aminopropyltriethoxysilane (APTES) with a tungsten carbene Wφ, while in the second approach a precursor synthesized by reacting APTES with the carbene Wφ is then anchored via a direct bond to the silanol groups in the interior pore channels of SBA-15.
This tethering is helpful to prevent the decomposition of the metallic complex. XRD, N2 adsorption–desorption, and TEM analysis provide strong evidence that the mesoporous support structure retains its long-range ordering after the grafting process, despite a significant reduction of its specific surface area, pore-volume and pore-size. The chemical bonding of the tungsten carbene to the silanol groups of SBA-15 materials was studied with solid-state NMR spectroscopy. Both 13C MAS NMR and 29Si CP MAS NMR spectra confirm the covalent linking of the carbene to the silica-pore system. 相似文献
32.
CVD aluminide coatings deposited on a Directionally Solidified (DS) substrate were oxidized at 1,100 °C up to 240 h under
isothermal and cyclic oxidation conditions to study the growth mechanisms of the oxide scales and the possible degradation
of the coatings. The specimens were investigated using light and scanning electron (SEM) microscopy, energy-dispersive spectrometry
(EDS) and X-Ray Diffraction (XRD). The results indicate that the coatings provide a much greater beneficial effect under isothermal
conditions than upon cycling. The cycled specimens undergo oxide-scale spallation and increased roughening, which can derive
from growth and thermal stresses as well as from the NiAl → Ni3Al phase transformation associated with Al depletion. Under isothermal conditions, typical oxide scales formed with the appearance
of some rumples. However, the origin of rumpling is uncertain from these experimental results. 相似文献
33.
Guadalupe del C Pizarro Oscar G Marambio Manuel Jeria‐Orell Miguel C Avellán Bernabé L Rivas 《Polymer International》2008,57(7):897-904
BACKGROUND: Polymers supporting chemicals used in agriculture have recently been developed to overcome the serious environmental problems of conventional agrochemicals. The success of these formulations is based on a suitable choice of polymer support. Degradable polymeric hydrogels are of particular interest. The gradual release of the bioactive agent can be achieved by hydrolytic or enzymatic cleavage of the linking bond. RESULTS: In this context, poly[(1‐vinyl‐2‐pyrrolidone)‐co‐(2‐hydroxyethyl methacrylate)] [poly(NVP‐co‐HEMA)] has been used as a bioactive carrier reagent. Herein, we report a controlled‐release system with the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) using an ultrafiltration system. Hydrolysis was studied by testing the release at various pH values. A high release with poly(NVP‐co‐HEMA)–2,4‐D was observed at pH = 7 and 10 after two days (Z = 2). The release percentage of copolymer–herbicide increased at pH = 10. It showed release values between 79.0 and 94.5%. Poly(NVP‐co‐HEMA)–herbicide can release a bioactive compound in aqueous solution at pH = 3, 7 and 10. CONCLUSION: Based on the results of homogeneous hydrolysis, it is argued that the herbicide release rate depends on the pH of the reaction environment. This functional polymer could be employed as a biodegradable material for applications in agrichemical release. Copyright © 2008 Society of Chemical Industry 相似文献
34.
Ma. Guadalupe D. Gutiérrez-Padilla Angela Bielefeldt Mark Hernandez 《Cement and Concrete Research》2010,40(2):293-301
Laboratory experiments were conducted to compare the degradation of low and high quality concrete under conditions simulating sewer pipes with and without bacteria. Small concrete samples were exposed to hydrogen sulfide, multiple species of bacteria found in corroding sewer pipes and artificial wastewater. Experiments without bacteria were used as controls. The corrosion rates of the concrete samples exposed to bacteria over 227 days were 0.08 mm/yr (millimeters per year) for the concrete from a domestic manufacturer with moderate strength and a lower water-cement ratio (Low-w/c) versus 0.208 mm/yr for the concrete samples from a foreign country with low strength and a higher water-cement ratio (High-w/c). The (Low-w/c) concrete was more resistant to the biodegradation even though a lower pH was attained for its bioactive systems. Experiments showed the influence of biogenic sulfuric acid production on short term corrosion rates. 相似文献
35.
Rodrigo Máximo Sánchez-Román Marcos Vinicius Folegatti Alba María Guadalupe Orellana González 《Water Resources Management》2010,24(4):761-773
The Piracicaba, Capivari, and Jundiaí River Basins (RB-PCJ) are mainly located in the State of São Paulo, Brazil. Using a dynamics systems simulation model (WRM-PCJ) to assess water resources sustainability, five 50-year simulations were run. WRM-PCJ was developed as a tool to aid decision and policy makers on the RB-PCJ Watershed Committee. The model has 254 variables. The model was calibrated and validated using available information from the 80s. Falkenmark Water Stress Index went from 1,403 m3 person???1 year???1 in 2004 to 734 m3 P???1 year???1 in 2054, and Xu Sustainability Index from 0.44 to 0.20. In 2004, the Keller River Basin Development Phase was Conservation, and by 2054 was Augmentation. The three criteria used to evaluate water resources showed that the watershed is at crucial water resources management turning point. The WRM-PCJ performed well, and it proved to be an excellent tool for decision and policy makers at RB-PCJ. 相似文献
36.
Guadalupe Bustos Ana Beln Moldes Jos Manuel Cruz Jos Manuel Domínguez 《Journal of the science of food and agriculture》2005,85(3):466-472
An effective process for the chemical–biotechnological utilization of trimming wastes of vineshoots, an agricultural waste with little use, is reported. Initial treatment with sulfuric acid (prehydrolysis) allowed the solubilization of hemicelluloses to give xylose and glucose‐containing liquors (suitable to make fermentation media for lactic acid production with Lactobacillus pentosus) and a solid phase containing cellulose and lignin. The solid residues from prehydrolysis were treated with NaOH in order to increase their cellulase digestibility. In the alkaline treatments, the effects of temperature (in the range, 50–130 °C), reaction time (30–120 min) and NaOH concentration (4–12 wt% of solution) on the composition and susceptibility to enzymatic hydrolysis of solid residues were assessed by means of an experimental plan with factorial structure. The lignin content decreased, whereas the susceptibility towards the enzymatic hydrolysis increased with temperature, reaction time and NaOH concentration within the tested range. Using the cellulosic residues achieved under the harsher conditions, favorable fermentation kinetics during simultaneous saccharification and fermentation carried out by L rhamnosus for lactic acid production were observed. The nutrients employed were the complete MRS broth and a cheaper medium developed using viticulture lees coming from the white wine making technology. In all cases the final lactic acid concentration achieved was similar, although the volumetric productivity was lower when using lees due to inhibitory effects over the enzymatic hydrolysis. Copyright © 2004 Society of Chemical Industry 相似文献
37.
Good adhesion between copper film and AlN substrate is obtained when the surface of AlN is laser-irradiated prior to copper
film deposition and post deposition annealing is conducted. Surface chemistry of AlN substrates before and after laser irradiation
and the interfacial reactions of copper film/AlN couples were studied with Auger Electron Spectroscopy (AES) to understand
the adhesion mechanisms. The surface of as-received AlN substrates was covered with a thin sheath of Al2O3. Laser irradiation removed the surface Al2O3 layers, smoothened the surface, and decomposed AlN leaving metallic aluminum on the surface. The interfacial reactions in
the copper film/AlN couple are affected by the amounts of oxygen and metallic aluminum available at the interface. The adhesion
mechanism is the formation of a Cu-O-Al compound at the interface of copper film/AlN couple. Since copper does not react with
AlN, laser induced decomposition of AlN seems to be the driving force for the formation of the compound.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
38.
39.
C. Martín-Cordero M. A. Pedraza A. M. Gil M. J. Ayuso 《Journal of chemical ecology》1997,23(8):1913-1916
Fruits (berries) of Viscum cruciatum accumulate bipiperidyl (ammodendrine) and quinolizidine (retamine and lupanine) alkaloids. Viscum obtains the alkaloids by root parasitism on the host plant Retama sphaerocarpa. The presence of these alkaloids in the fruits of Viscum cruciatum may represent some competitive disadvantage to mistletoe itself because the seeds may not be so well dispersed by blackcaps (Sylvia atricapilla). 相似文献
40.
Cano-Reséndiz O de la Rosa G Cruz-Jiménez G Gardea-Torresdey JL Robinson BH 《Journal of hazardous materials》2011,189(1-2):472-478
We identified contaminants associated with the Cata mine tailing depot located in the outskirts of the city of Guanajuato, Mexico. We also investigated strategies for their phytomanagement. Silver and antimony were present at 39 and 31 mg kg(-1), respectively, some twofold higher than the Dutch Intervention Values. Total and extractable boron (B) occurred at concentrations of 301 and 6.3 mg L(-1), respectively. Concentrations of B in soil solution above 1.9 mg L(-1) have been shown to be toxic to plants. Plant growth may also be inhibited by the low concentrations of extractable plant nutrients. Analysis of the aerial portions of Aloe vera (L. Burm.f.) revealed that this plant accumulates negligible concentrations of the identified contaminants. Calculations using a whole system model (Phyto-DSS) showed that establishing a crop of A. vera would have little effect on the drainage or leaching from the site. However, this plant would reduce wind and water erosion and potentially produce valuable cosmetic products. In contrast, crops of poplar, a species that is tolerant to high soil B concentrations, would mitigate leaching from this site. Alternate rows of trees could be periodically harvested and be used for timber or bioenergy. 相似文献