Electrospun TiO2/carbon composite nanofibers as effective (photo)electrodes for removal and transformation of recalcitrant water contaminants

Electrochemical (EC) and photoelectrochemical (PEC) water treatment systems are gaining popularity, necessitating new electrode materials that offer reliable performance across diverse application platforms. For applications specifically targeting dilute chemical pollutants (i.e., parts-per-million concentrations or less), beneficial electrode properties include high surface area to overcome kinetic overpotential losses, low electrode areal electrical resistance, and high water permeability with sufficient mechanical strength for use in electroactive membrane-based treatment systems. Here, we used electrospinning to fabricate (photo)electrodes from carbon nanofibers (CNFs) containing titanium dioxide (TiO2) nanoparticles. Optimal CNF/TiO2 composites were electrochemically and photochemically active with a surface area of ∼50 m2 g−1 and electrode areal resistance of 2.66 Ω cm2, values comparable to commercial carbon-based electrode materials (e.g., Kynol Activated Carbon Cloth). Transformation experiments with carbamazepine (CBZ), a recalcitrant organic contaminant, suggest CNF/TiO2 electrodes function dually as sorbents, first binding CBZ prior to oxidation at positive applied potentials. Complete CBZ transformation was observed in both EC (dark) and PEC (UV light; 280 mW cm−2) systems over 90 minutes, with PEC systems exhibiting 1.5-fold higher transformation rates (kobs ∼ 0.18 min−1) at +1.00 V (vs. Ag/AgCl). Composite electrodes also exhibited stability across repeated use, yielding consistent current densities over five experimental cycles (120 min each) of CBZ transformation (0.25 ± 0.03 mA cm−2). Because of their high surface area, electrical conductivity, photoactivity, and electrochemical stability, these electrospun CNF/TiO2 composites represent promising (photo)electrode alternatives for diverse EC and PEC applications.