Role of Near-Electrode Solution Chemistry on Bacteria Attachment and Poration at Low Applied Potentials

Abstract

This research investigated mechanisms for biofouling control at boron-doped diamond (BDD) electrode surfaces polarized at low applied potentials (e.g., −0.2 to 1.0 V vs Ag/AgCl), using Pseudomonas aeruginosa as a model organism. Results indicated that electrostatic interactions between bacteria and ionic electrode functional groups facilitated bacteria attachment at the open-circuit potential (OCP). However, under polarization, the applied potential governed these electrostatic interactions and electrochemical reactions resulted in surface bubble formation and near-surface pH modulation that decreased surface attachment under anodic conditions. The poration of the attached bacteria occurred at OCP conditions and increased with the applied potential. Scanning electrochemical microscopy (SECM) provided near-surface pH and oxidant formation measurements under anodic and cathodic polarizations. The near-surface pH was 3.1 at 1.0 V vs Ag/AgCl and 8.0 at −0.2 V vs Ag/AgCl and was possibly a contributor to bacteria poration. Interpretation of SECM data using a reactive transport model allowed for a better understanding of the near-electrode chemistry. Under cathodic conditions, the primary oxidant formed was H2O2, and under anodic conditions, a combination of H2O2, Cl•, HO2 •, Cl2 •–, and Cl2 formations likely contributed to bacteria poration at potentials as low as 0.5 V vs Ag/AgCl.

Facing the Challenge of Poly- and Perfluoroalkyl Substances in Water: Is Electrochemical Oxidation the Answer?

“…88 By contrast, Lin et al 14 when high anode potentials/currents are applied, the surface of an anode is highly acidic regardless of the bulk pH. 67 In the case of porous Ti 4 O 7 electrodes, the measured-pH inside the pores using a Pt/IrO x ultramicroelectrode was 2.6, significantly lower than the bulk electrolyte (pH 6.1), due to diffusional restrictions of protons formed by water electrolysis in the pores. 85 The speciation of PFASs in the anode surface vicinity, as well as their partitioning and susceptibility to electrolysis, will be highly dependent on the initial concentration of the PFAS, ionic strength, and presence of methanol in the supporting electrolyte and is likely to lead to experimental artifacts when using highly conductive electrolytes and high initial PFAS concentrations, particularly in the mM range.…”

“…reported the highest PFOA removal rate constant at pH 5 (6.94 × 10 –6 m s –1 ), whereas lower values were determined at pH values of 3, 7, 9, and 11. In addition, when high anode potentials/currents are applied, the surface of an anode is highly acidic regardless of the bulk pH . In the case of porous Ti 4 O 7 electrodes, the measured-pH inside the pores using a Pt/IrO x ultramicroelectrode was 2.6, significantly lower than the bulk electrolyte (pH 6.1), due to diffusional restrictions of protons formed by water electrolysis in the pores .…”

“…The pH in the vicinity of the anode surface is highly acidic at typically applied high current densities/potentials needed for PFAS degradation, which may lead to the protonation of PFASs present at the anode surface. It is worth noting that the impact of pH on PFAS electrooxidation and adsorption onto the electrode will depend on PFAS concentration, as the apparent p K a of PFAS is an aggregation-dependent value .…”

Ultrathin Diamond Nanofilms—Development, Challenges, and Applications

“…[236] Other applications include the simultaneous detection of cells via optical microscopy and impedance measurement in a microfluidic setup (see Figure 12), [237] and cell attachment study on modified (transparent) BDD electrodes by fluorescence microscopy (number of cells, life/dead) under applied anodic potentials. [238] It should be noted that during the synthesis of OTEs, especially for application in spectroelectrochemistry: a balance between film thickness, a thinner film which has a higher transparency, conductivity of the doped diamond coating, a higher boron content which leads to loss of transparency, while with a low dopant concentration which leads to the low conductivity of the synthesized film, has to be established; these optimized parameters for synthesis are still under scientific discussion.…”

Disparities between experimental and environmental conditions: Research steps toward making electrochemical water treatment a reality

“…Because electrocatalytic processes are driven by reactions on electrode surfaces, the accessibility and long-term stability of the electrode surface is essential to ensuring continuous, sustained operation. As such, it is surprising that there is limited research evaluating electrode scaling and fouling [63][64][65][66]. For example, Figure 3a depicts an electrochemical reactor whose performance was inhibited after a couple of days under continuous flow operation of real groundwater with high hardness (~350 mg L -1 as CaCO3).…”