Synthèse d'hydroxides doubles lamellaires de type nikel/Aluminium modifiés par les organoanions: Appliction à la détection électrochimique du méthylparathion et du funuron

Abstract

The present work is focused on the synthesis of an unique layer double hydroxide (LDH) based on nickel and aluminum (Molar ratio Ni/Al: 3/1) with nitrate at the interfoliar space. Physical and chemical characterizations have shown that this material (Labelled as NiAl) with the chemical formula Ni6Al2(OH)16(NO3)2.6H2O has a basal spacing of 7.94 Å. Subsequently, this material was modified by intercalation of bis (2-ethylhexyl) hydrogen phosphate (BEHP) by an anion exchange process. The significant shift of d003 peak at 21.02 Å reveals that the pristine material has been successfully modified. In addition, the presence of residual peaks on XRD patterns of pristine NiAl on the resulting material (Labelled as NiAl-BEHP) reveals the presence of non-intercalated phases, indicating a partial replacement of nitrate. A second material was obtained by intercalating dioctylsulfosuccinate (DSS) by coprecipitation. The resulting material (labelled as NiAl-DSS) is a single phase of chemical structure Ni6Al2(OH)16(DSS)2,8.9,8H2O characterized by a d003 at 27.4 Å and the absence of nitrate ions in the interlamellar space. Exploiting the organophilicity inducted during both modifications, these hybrid materials (NiAl-BEHP and NiAl-DSS) were used to develop electrochemical sensorsfor de detection of methylparathion and fenuron. NiAl-DSS powder incorporated within a carbon paste electrode was used for the detection of fenuron. After optimization of the experimental parameters (pH of the electrolytic solution and percentage of modifier in the paste), a detection limit of 17.8 nM was obtained. A glassy carbon electrode modified with a NiAl-BEHP dispersion was used for the detection of methylparathion. It has been shown that the electrochemical reactivities of two functional groups of this pesticide can be exploited for analytical purpose. The first reactivity assigned to -NO2 group was more sensitive and less precise whereas the second reactivity assigned to -NO group was less sensitive and more precise. Limits of detection of 4 nM and 14 nM were respectively obtained using -NO2 and NO peaks. In addition, using -NO peak for the quantification of MP, the sensitivity has been improved and the sensor was less influenced by the main interference PNP. Adding to the good performance exhibited by both sensors to their respective targets, they have been used for the determination of those pesticides in a river water with detection limits lower than the limit values allowed by environmental standards.