Preparação, caracterização e aplicação de eletrodos tridimensionais de carbono vítreo reticulado recobertos com filmes de PbO2 para a degradação do corante reativo AR 19 e glifosato
Abstract
Electrodeposition of a PbO2 film was performed onto reticulated vitreous carbon (RVC)
substrates with porosities of 45, 60, and 80 ppi, at 65 ºC in a flow reactor, starting with a
solution containing Pb(NO3)2, surfactant, and HNO3. Investigation was made of the effects of
current density and electrodeposition time on the coverage and uniformity of the PbO2 film
formed. The electrodes were characterized using scanning electron microscopy, X-ray
diffractometry, and linear potential scanning. The use of high currents resulted in the formation
of thick films in regions close to the counter-electrode, which compromised film adhesion,
while the application of lower currents ensured a uniform and adherent PbO2 coating. In tests of
the decoloration of AR 19 dye using the best electrodes produced, better performance was
achieved using RVC/PbO2, compared to VC/PbO2, due to the greater specific surface area and
increased hydrodynamic turbulence caused by the tridimensional substrate, which increased the
mass transport coefficient and therefore enhanced the degradation process. The optimum
conditions for use of the RVC/PbO2 electrode were 3.5 mA cm-2 and 30 minutes of
electrosynthesis. Electrochemical degradation of the herbicide was performed using the 60 ppi
RVC/PbO2 electrode in a flow reactor. Box-Behnken design was used to study the effects of
current density, flow, and temperature on the kinetics of degradation (COD) and mineralization
(TOC), current efficiency (ε), and energy consumption (η). The best degradation and
mineralization kinetics values were obtained with the upper limits of the variables studied (30
mA cm-2, 150 mL min-1, and 50 oC). Increasing the flow rate from 150 to 1500 mL min-1
increased εG from 18% to 65%, and decreased ηG from 72 to 33 kWh kg-1, reflecting a higher
mass transport coefficient. In comparative tests, using degradation of the herbicide and phenol,
the performance of the RVC/PbO2 electrode was slightly lower than that of a boron-doped
diamond (BDD) electrode. Considering that the RVC/PbO2 device is less expensive than DDB
electrodes, it can be concluded that this tridimensional electrode is promising for use in the degradation of organic pollutants.