Uso potencial de arcillas modificadas con metales para la obtención de formulaciones de liberación lenta de herbicidas.

9 páginas., 5 gráficos, 2 tablas y 9 referencias. Versión extendida de la comunicación presentada en la "XIX Reunión Científica de la Sociedad Española de Arcillas - SEA05", celebrada en Salamanca del 26 al 28 de Septiembre de 2005. Enlace a la web de la Sociedad Española de Arcillas http://www.sea-arcillas.es/publicacionesSEA.htm[EN]Abstract A slow release system of the herbicide imazapyr was designed by adsorption on pillared clays. Pillared clays based on aluminum and mixed aluminum-copper solutions were synthesized. The aim was to check whether the introduction into the pillars of a metal complexing the herbicide molecules enhanced the sorption and release properties of the clay for the herbicide. A commercial aluminum pillared clay was also examined as a potential sorbent. The chemical analysis data as well as those of X-ray diffraction show that copper from pillaring solutions was partially introduced, and the basal spacing were increased about 9 Å in good agreement with the size of the Keggin ion. The textural properties indicate a reduction in the micro- and mesoporosity of the pillared clays after pillaring with copper solutions. The largest the copper content in the mixed Al-Cu pillared clays the largest the decrease in the surface area. However, imazapyr adsorption increased up to three-fold compared to the commercial pillared clay, and desorption percentages from the Cu-Al pillared clays were three-fold lower than the commercial one, whose desorption was completely reversible. These preliminary results show the potential use of Cu-Al pillared clays for the development of slow release formulations of the herbicide imzapyr, unlike those whose pillars are only made of aluminum.[ES]Resumen En el presente trabajo se ha intentado desarrollar un sistema de liberación lenta del herbicida imazayr mediante su adsorción en arcillas pilareadas. Se han sintetizado arcillas pilareadas con aluminio y con soluciones mixtas Cu-Al, a fin de comprobar si la formación de pilares mixtos de aluminio con un metal complejante del herbicida mejoraba las propiedades de adsorción y liberación del mismo. También se ha estudiado el empleo potencial de una arcilla pilareada comercial formada con pilares exclusivos de aluminio. Los resultados de análisis químico así como de difracción de rayos X muestran que parte del cobre de las soluciones pilareantes se ha introducido en las arcillas finales, cuyos espaciados basales presentan un incremento de aproximadamente 9 Å, que se corresponde con el tamaño del ión Keggin. Las propiedades texturales indican una disminución tanto de la microporosidad como de la mesoporosidad en las arcillas tras su pilarización con soluciones de Cu-Al, que es tanto mayor cuanto mayor es el contenido de Cu. A pesar de la reducción en la superficie de estas arcillas sintetizadas con Cu, la adsorción de imazapyr incrementaba hasta 3 veces con respecto a la arcilla pilareada comercial. A su vez los porcentajes de desorción en la arcillas pilareadas con Cu-Al eran hasta tres veces inferiores a los correspondientes a la arcilla pilareada comercial, cuya desorción era prácticamente reversible. Estos resultados preliminares avalan el uso potencial de arcillas pilareadas con Cu-Al para el desarrollo de formulaciones de liberación lenta del herbicida imazapyr, a diferencia de aquellas en las que los pilares se encuentran formados únicamente por aluminio.Peer Reviewe

Adsorption of sulfometuron and other anions on pillared clay

The adsorption of several anions of agronomic and ecological importance, sulfometuron 2-[3-(4,6-dimethylpyrimidin'2-yl)ureidosulfonylbenzoic acid, sulfate, acetater and chloride on pillared clay was studied. Pillared clay (PC) is a very effective adsorbent of anions from aqueous solutions. The fractions ofsulfometuron adsorbed from aqueous solutions were more than 90% of added, but low solubility limited the added amounts. The maximal adsorbed amount of sulfate was 0.72 mol kg-1 and of acetate was 0.41 mol kg-1. Addition of 100 and 500 mM of NaCl as the background electrolyte did not affect the adsorption of sulfometuron, but drastically reduced the adsorption of sulfate and acetate. Acetate at 1000-fold larger excess competes with sulfometuron for the surface sites, but sulfate does not. Acetate decreased dramaticatly the adsorption of sulfate when both anions were added simultaneously but acetate did not adsorb on the clay with pre-adsorbed sulfate. The sequence of adsorption affinity of anions to the PC surface is: sulfometuron >> sulfate > acetate >> chloride. The binding coefficient was 12 000 M-1 for sulfometuron, 650 M-1 for sulfate, 350 M-1 for acetate, and 15 M-1 for chloride. The dominant mode of sulfometuron adsorption on PC is via strong electrostatic interactions. The proposed interactions of sulfate with PC are outer- and inner-sphere complexation. The pH is reduced with sulfate adsorption and Al is released. The proposed mode of acetate interactions with PC is mainly via inner-sphere complexation. In this case the pH increases with acetate adsorption, indicating exchange of acetate with surface hydroxyls, and Al is not released.This research was supported by Grant 8803-1-96 of the Ministry of Science and Arts, Israel, for French-Israeli collaboration, and partially supported by a Grant G-0405-95 from G.I.F., the German-Israeli Foundation for Scientific Research and Development. Dr. T. Undabeytia acknowledges the Spanish Government (ref. PF9633975424) and the European Community (Contract N. FAIR-BM-970892) for a postdoctoral fellowship at the Seagram Center.Peer Reviewe

Photo-oxidation of water mediated by a clay-anchored Os catalyst

The oxidation of water to oxygen by one-electron oxidants such as Ce4+, M( bpy)33” camp lexes (M = Fe, Ru, OS; bpy = 2,2’-bipyridine) or IrC16- is a mechanistically difficult reaction which, to occur at an appreciable rate, requires very active catalysts. Supported and unsupported noble metal oxides (PtOZ, IrO,, RuOz and their mixed oxides) have been used exten- sively for this purpose [ 1 - 71. Homogeneous catalysts, such as simple Co(I1) salts [ 4,8] or amine complexes [ 91, diaq~obis(bpy)Ru~II) [lo] or a diaquo- ~-0x0 dimer of Ru(III) [ll], have also been used with variable success. We wish to report here an OS-based molecular catalyst, covalently linked to a mineral surface. This type of catalyst is clearly of interest for the photo- chemical cleavage of water or for any energy-storing photoreaction which requires the transformation of oxidizing equivalents into oxygen

Fe-pillared clay mineral-based formulations of imazaquin for reduced leaching in soil

8 pages, 7 figures, 6 tables, 64 references.Slow release formulations of the herbicide imazaquin (2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydro-1H-imidazol-2-yl)quinoline-3-carboxylic acid) were prepared by its adsorption on Fe-pillared clay minerals (Fe PILCs). Fe PILCs were synthesized by the reaction of Na+-montmorillonite (SWy-2) with base-hydrolyzed solutions of Fe and Al. The Fe/(Fe+Al) ratios used were 0, 0.05, 0.15 and 0.50. Fe PILCs showed basal spacing values of 5.2 and 1.8nm which were due to iron clusters between delaminated clay layers, and intercalated aluminum polyoxocations, respectively. As iron content increased, the pillaring process yielded PILC with lower microporosity and larger mesoporosity. The affinity of imazaquin on Fe PILCs was very high relative to Al PILC, as revealed in its higher herbicide adsorption values and lower desorption percents. Competitive adsorption of anions such as sulfate, phosphate and chloride provided evidence of formation of inner sphere complexes of imazaquin on Fe PILCs. Slow release formulations were prepared by enhanced adsorption of the herbicide from imazaquin-cyclodextrin (CD) complexes in solution. CDs were able to enhance up to 8.5-fold the solubility of imazaquin, by the formation of inclusion complexes where the quinolinic moiety of the herbicide was partially trapped within the CD cavity. Release of the herbicide in sandy soil was about 1/2-fold lower from Fe PILC formulations relative to the commercial formulation.This research was supported by the MEC Project CTM2009-07425 and the Junta de Andalucía Project P09-RNM4581. Both projects received funding by the European Social Fund.Peer Reviewe