Estudo e desenvolvimento de estratégias de remoção de organofosforados de soluções aquosas utilizando sílicas porosas e policloreto de vinila

Abstract

This work addresses the use of silicates and plastics in the removal of organophosphates from aqueous solutions. The studies were divided into three parts: 1. kinetic study of the hydrolysis of organophosphates by non-functionalized porous silica materials; 2. application of an amino-functionalized SBA-15 coordinated with lanthanide ions to catalyze the hydrolysis of bis(2,4-dinitrophenyl)phosphate; and, 3. kinetic study of ethyl paraoxon (POx) adsorption onto a flexible PVC tube. In the first part, the capacity of the porous silicas MCM-41, SBA-15, and SiO2 to catalyze the hydrolysis of di- and mono- phosphate esters was evaluated. Catalytic effects greater than 7000 times were observed for the hydrolysis of bis(4-nitrophenyl)phosphate in the presence of the materials. Such effects were supplemented by a sudden increase in speed, which was consequence of the hydration and hydroxylation of the silica surface. Hydrolysis reactions occur via an SN2(P) mechanism, in which silanol groups are acid-general catalysts stabilizing the leaving group whereas siloxide groups act as general-base catalysts in the activation of the nucleophilic water molecule. In the second part, SBA-15 type mesoporous silicas, functionalized with organic amino/ammonium groups and coordinated with La(III) and Ce(III) ions, were used to catalyze BDNPP hydrolysis. The materials were characterized by different techniques, showing a degree of functionalization of 13% (w/w) and coordination of 0.5 to 1.5% (w/w) of the lanthanides. Catalytic factors between 7 and 14-fold for BDNPP hydrolysis were observed with these materials and the hydration of the materials increased these factors from 66 to 95-fold in relation to the spontaneous hydrolysis. The addition of 0.1 M hydrogen peroxide supplemented the slow reaction stage and a catalytic factor of 63-fold was determined. These studies showed that these materials have potential for future development and applications. Finally, in the third part of this work, the capacity and kinetics for the adsorption of ethyl paraoxon (POx) by flexible PVC tubes were evaluated. The adsorption kinetics was analyzed using phenomenological models and the Langmuir adsorption-desorption (LAD) analysis. The adsorption kinetics followed a diffusion regime, in which the adsorption of the substrate from the external surface of the plastic to its interior was limited in all POx concentrations. The adsorption progress depended of several stages, the adsorption rate showed a descending hyperbolic dependence in relation to the increase of the initial POx concentration, being proportional to the diffusion coefficients estimated numerically using the LAD analysis. In addition, the adsorption exhibited a temporal dependence according to the Vermeulen's fractal-type model. The observations were consistent with an adsorption process hindered by the adsorbate itself. Despite of different structural framework, the silica materials were exceptionally efficient in catalysis after hydration and hydroxylation. Moreover, the adsorption of POx onto PVC tubes allowed to understand the consequences of the sorption process and the application of these materials, highly important in agriculture and other human activities.