Síntese e caracterização de catalisadores suportados em óxido de grafite para redução fotocatalítica de nitrato e nitrito em água

Abstract

Contamination by nitrate and nitrite is common in surface and groundwater due to the application of nitrogen fertilizers and animal manure to the soil, use of septic systems and atmospheric deposition. High concentrations of these contaminants can cause damage to human health and the environment such as baby blue syndrome, carcinogens and eutrophication of lakes and rivers. Heterogeneous photocatalysis has shown to be a promising technology in the decontamination of water by these species. Studies have shown that the performance of the photocatalytic process can be improved with the addition of graphite oxide, as it is able to be activated at wavelengths closer to the region of the visible spectrum and thus delay electron / gap recombination. Due to the need to treat these chemical species, the removal of nitrate and nitrite by photocatalytic treatment in water was evaluated by developing and testing monometallic and bimetallic catalysts supported on graphite oxide in order to obtain conversion. The supports were synthesized using Hammers methodology with modifications in the amount of reagents and used as raw material, powdered graphite and polymeric activated carbon. The catalysts were synthesized by the technique of successively impregnating the metal onto the support. The photocatalytic tests were conducted in a bench scale system, with UV-C radiation source. The metals were deposited on the surface of the supports by the impregnation method. Palladium (Pd) was used to produce monometallic catalysts, while bimetallic ones were obtained by depositing tin (Sn) and copper (Cu) to the former. Photocatalytic tests were performed with a solution of potassium nitrate, sodium nitrite and formic acid (electron donor) prepared in the laboratory, under nitrogen flow. Monometallic catalysts 5% Pd / CAPGGO_1, 5% Pd / GPGO and bimetallic 5% Pd-1% Sn / CAPGGO_1, 5% Pd-1% Sn / GPGO, 5% Pd-1% Cu / CAPGGO_1, 5% Pd -1% Cu / GPGO showed conversion of 90 to 100% of nitrite in all tests. The nitrate conversion was around 9.1 to 14.6% for monometallic catalysts 5% Pd / CAPGGO_1 and 5% Pd / GPGO, from 11.1 to 33.2% for bimetallic catalysts with tin deposition 5 % Pd-1% Sn / CAPGGO_1, 5% Pd-1% Sn / GPGO and from 33.4 to 50.9% for catalysts with copper deposition 5% Pd-1% Cu / GPGO and 5% Pd-1 % Cu / CAPGGO_1, respectively. The characterization of the materials was carried out through the techniques of absorption spectrometry in the infra red region with Fourier transformation (FTIR), X-ray diffraction, by atomic absorption spectrometry and Determination of the surface area. The method showed no difference in N2 (g) conversion, however the supports showed differences in activity and selectivity. The results are promising for the continuation of research with modification in the synthesis of Graphite Oxide to obtain Graphene Oxide.