Chlorine-free electrochemical disinfection using graphene sponge electrodes

Electrochemical degradation of per- and polyfluoroalkyl substances (PFAS) using low-cost graphene sponge electrodes

“…Besides the high chemical, thermal and structural stability of the mineral wool template, graphene sponge electrodes produced using this method present high electrochemical stability during both anodic and cathodic polarization, due to the formation of C-Si and C-O covalent bonds between the silicate present in the mineral wool and graphene, and thus strong interfacial adhesion between the RGO nanosheets and SiO2 (Hintze et al, 2016;Ramezanzadeh et al, 2016;Shemella & Nayak, 2009). The characterization of the graphene sponges used in this study was reported in our recent work Norra et al, 2021), and is summarized in Text S1.…”

“…Yet, the hydrophobic fluorinated tail of PFASs did not interact with the unpolarized graphene sponge. This may be a consequence of the negative surface charge of the BRGO sponge at pH 7, as the determined zeta potential at this pH value is -36.2 mV (Norra et al, 2021). Thus, electrostatic repulsion with the PFASs anions (pKa= -3.94 -2.9, Table S1) plays a dominant role.…”

“…Graphene-based sponges were synthesized according to the previously reported procedure (Norra et al, 2021). In brief, to synthesize a boron-doped reduced graphene oxide anode (BRGO), 6 g of boric acid was dissolved in 2 g L -1 GO.…”

“…Furthermore, graphene sponge anodes may enable efficient C-F bond cleavage without compromising the quality of the treated water, as there is no formation of chlorate and perchlorate even in the presence of high chloride concentrations, and the current efficiency for chlorine formation was only 0.04% in the presence of 20 mM NaCl Norra et al, 2021). This makes it a unique anode material.…”

“…In our recent studies Norra et al, 2021), we presented a new, graphene-based sponge electrode, which exhibited high electrocatalytic activity for electrochemical degradation of persistent organic and microbial contaminants, and remarkably low electrocatalytic activity for chloride oxidation; the current efficiency for chlorine production in the presence of 20 mM NaCl was only 0.04% at the 173 A m -2 of anodic current density, and there was no chlorate and perchlorate formation . The graphene-based sponges entailed other advantages such as their synthesis using a simple, low cost and easily scalable hydrothermal self-assembly method using mineral wool as supporting template, structural stability and flexibility, as well as the possibility to functionalize the graphene-based coating and tailor their electrocatalytic activity for the removal of persistent organic and microbial contaminants (e.g., iodinated contrast agents, triclosan, diclofenac, Escherichia coli) by a simple introduction of dopants (e.g., atomic dopants, two-dimensional materials, MXenes) Norra et al, 2021). Moreover, the material demonstrated exceptional stability to anodic polarization, likely due to the strong interfacial adhesion and covalent bonding between the graphene nanosheets and SiO2 (Hintze et al, 2016), a major component of the mineral wool supporting template.…”