Resumo:
Emerging contaminants are chemical compounds found in extremely low concentrations
(micropollutants) that are unregulated or newly regulated in different countries in different
environmental matrices and that are threatening human and animal health. Pesticides benefit
food production by controlling unwanted pests, but overexposure and inappropriate
application contaminate the environment. Among them, the insecticide Fipronil and its
derivatives have shown great toxicity for insects, mammals and humans. Conventional water
and sewage treatment techniques do not efficiently remove these contaminants, requiring
alternative removal methods such as Advanced Oxidative Processes. In this work, sulfite
auto-oxidation catalyzed by cobalt complexed with ammonia deposited on silica (CoNSi) was
used to generate sulfate radicals. The material was characterized by ATR–FTIR, suggesting
that the silica vibrational modes did not change, and MEV–EDS, indicating a uniform
dispersion of cobalt over the surface of the material. BET analysis provided information on a
mesoporous material (type IV isotherm) with regular morphology (H1 hysteresis). The DSC
analysis showed that CoNSi is thermally stable under the conditions studied. Quantitative
analyzes of Fipronil were performed by HPLC-DAD, where the applied method was linear.
The Box–Behnken experimental design was used to define the best condition for removing
the analyte in water, where in 60 min, 76% removal of 1.8 ppm of Fipronil was obtained by
adding 0.30 g of the material and 0.30 g of the sulfite in a solution with stirring, aeration, pH
8.0, room temperature and protected from visible radiation. This result demonstrates that the
technique is very promising to be used as a complementary treatment in water and effluent
treatment plants. However, analysis of cobalt leaching into the solution by FAAS showed a
small amount of the metal (0.44 ppm) informing that the synthesis of the material must be
improved.
