Removal of bisphenol A from acidic sulfate medium and urban wastewater using persulfate activated with electroregenerated Fe2.

Model solutions of bisphenol A (BPA) in 0.050 M Na2SO4 at pH 3.0 have been treated by the electro/Fe2+/persulfate process. The activation of 5.0 mM persulfate with 0.20 mM Fe2+ yielded a mixture of sulfate radical anion (SO4-) and OH, although quenching tests revealed the prevalence of the former species as the main oxidizing agent. In trials run in an IrO2/carbon-felt cell, 98.4% degradation was achieved alongside 61.8% mineralization. The energy consumption was 253.9 kWh (kg TOC)-1, becoming more cost-effective as compared to cells with boron-doped diamond and Pt anodes. Carbon felt outperformed stainless steel as cathode because of the faster Fe2+ regeneration. All BPA concentration decays agreed with a pseudo-fist-order kinetics. The effect of persulfate, Fe2+ and BPA concentrations as well as of the applied current on the degradation process was assessed. Two dehydroxylated and three hydroxylated monobenzenic by-products appeared upon SO4- and OH attack, respectively. The analogous treatment of BPA spiked into urban wastewater yielded a faster degradation and mineralization due to the co-generation of HClO and the larger OH production as SO4- reacted with Cl-.

Electrochemical measurements and theoretical studies for understanding the behavior of catechol, resorcinol and hydroquinone on the boron doped diamond surface.

Using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)) with a boron-doped diamond (BDD) electrode it was possible to study the behavior of hydroquinone (HQ), catechol (CT) and resorcinol (RS), in aqueous solutions as well as to associate the electrochemical profiles with computational simulations. It led to understanding the factors that influence the direct electrooxidation of HQ, CT and RS on the BDD surface. Theoretical calculations demonstrated that the compounds with lower HOMO energy and high ionization potential (IP) are more stable, showing a higher E pa, denoting that HOMO energies and IP are related to the difficulty of oxidizing (losing an electron) a specific compound. Analyzing the electro-oxidation reactions of HQ, CT and RS by using computational calculations, it was possible to verify the reversibility behavior, direct oxidation pathway and the possible intermediates formed during electron-transfer. The results clearly demonstrated that the reversibility was attained for HQ and CT, while this behavior is not feasible, thermodynamically speaking, for RS and this was confirmed by DFT calculations. For direct oxidation mechanisms, HQ and CT are quickly oxidized, but RS produces stable intermediates. These experimental and theoretical results also explain the behavior when the compounds were analyzed by electroanalytical techniques, suggesting that the interactions by direct electron-transfer determine the stability of response (sensitivity) as well as the limit of detection. The results are described and discussed in light of the existing literature.