Kinetics of the electrochemical mineralization of perfluorooctanoic acid on ultrananocrystalline boron doped conductive diamond electrodes

Abstract

This work deals with the electrochemical degradation and mineralization of perfluorooctanoic acid (PFOA). Model aqueous solutions of PFOA (100mg/L) were electro-oxidized under galvanostatic conditions in a flow-by undivided cell provided with a tungsten cathode and an anode formed by a commercial ultrananocrystalline boron doped diamond (BDD) coating on a niobium substrate. A systematic experimental study was conducted in order to analyze the influence of the following operation variables: (i) the supporting electrolyte, NaClO4 (1.4 and 8.4g/L) and Na2SO4 (5g/L); (ii) the applied current density, japp, in the range 50-200 A/m(2) and (iii) the hydrodynamic conditions, in terms of flowrate in the range 0.4×10(-4)-1.7×10(-4)m(3)/s and temperature in the range 293-313K. After 6h of treatment and at japp 200A/m(2), PFOA removal was higher than 93% and the mineralization ratio, obtained from the decrease of the total organic carbon (TOC) was 95%. The electrochemical generation of hydroxyl radicals in the supporting electrolyte was experimentally measured based on their reaction with dimethyl sulfoxide. The enhanced formation of hydroxyl radicals at higher japp was related to the faster kinetics of PFOA removal. The fitting of experimental data to the proposed kinetic model provided the first order rate constants of PFOA degradation, kc(1) that moved from 2.06×10(-4) to 15.58×10(-4)s(-1), when japp varied from 50 to 200A/m(2).

Efficient electrochemical degradation of poly- and perfluoroalkyl substances (PFASs) from the effluents of an industrial wastewater treatment plant

“…The removal of both 6:2 FTAB and 6:2 FTSA followed first-order kinetic trends, typically observed in BDD electro-oxidation processes that are governed by mass transfer limitations. In a previous work, BDD electrodes were recognized as strong generators of HO· at the anode surface during the electrooxidation of PFOA [51], a process that was enhanced at higher values of the applied current density. The concentration data shown in Figure 3 were fitted to a first-order kinetic model, ‫ܥ‬ = ‫ܥ‬ ݁ ି௧ , where C is the concentration of the compound at a given time t, C 0 is the initial concentration and k is the apparent kinetic constant.…”

Water Treatment Technologies for PFAS: The Next Generation

“…Electrochemical treatment refers to direct electron transfer from an anode to a molecule within an electrochemical cell designed with an anode, cathode, and electrolyte. Electrochemical cells can be divided or undivided, have demonstrated effectiveness for PFOA/PFOS at current densities of 1 to 50 mA/cm 2 , and use various custom‐synthesized mixed metal oxide anodes (Schaefer et al ; Urtiaga et al ; Gomez‐Ruiz et al ; Schaefer et al ). The materials of construction of an anode can have a meaningful influence on electrochemical treatment performance because the PFAS interaction at the surface of the anode constitutes the destructive mechanism.…”

“…Tin, iron, and lead‐based anodes have been found to be less effective for PFAS treatment, and, due to expected acidic conditions around the anode, are suspected of leaching heavy metals and facilitating PFAS adsorption—particularly for PFOS (Schaefer et al ). Boron‐doped diamond (BDD) anodes appear to be emerging as the most effective from an operational standpoint (Urtiaga et al ), though R&D continues to identify new options such as the titanium suboxide anode (Huang ). Consistent with other literature on destruction of PFOS, PFOS is comparatively more challenging to destroy than PFOA under similar conditions.…”

Electrochemical Advanced Oxidation Processes (EAOP) to degrade per- and polyfluoroalkyl substances (PFASs)

“…As stated previously, to boost the productivity of radicals and inhibit the emission of O 2 , the electrode materials reported in literatures include platinum (Pt) [43], carbon or graphite (C) [44,45], iridium dioxide (IrO 2 ) [46], ruthenium dioxide (RuO 2 ) [47], tin dioxide (SnO 2 ) [48], boron-doped diamond (BDD) [49], lead dioxide (PbO 2 ) [32], Ti 4 O 7 (Ebonex) [39], TiO 2 nanotube array [34] as well [24,36]. Among them, BDD has been reported to be the best for water treatment [49].…”

“…To improve the electrode's shelf life, the anode materials can be modified, such as by doping and nanofabricating [31,32,36,45]. For example, PbO 2 doped with F -was found to inhibit O 2 emission, accelerate oxidation and enhance degradation efficiency [32].…”