Removal of polyethylene terephthalate microplastics from water with reactive oxygen species generated by electrochemical and photoelectrochemical processes

This work explores electrochemical (EO) and photoelectrochemical (PEC) oxidation of polyethylene terephthalate (PET) microplastics (MPs) focusing on the electrogeneration of reactive oxygen species (ROS). The degradation processes of 100 and 1000 mg dm-3 dispersion of MPs were studied by assessing the concentration of generated ROS, the weight loss, the presence of intermediates in the solution through total organic carbon (TOC) and high-performance liquid chromatography (HPLC) measurements, and the chemical modifications of MPs using FT-IR spectroscopy. Moreover, the results were discussed in terms of normalised specific surface degradation rate kd and electric energy per mass EEM. EO, performed using a boron-doped diamond (BDD) electrode at 2.5 mA cm- 2, led to 13.25 and 10.19% weight loss for 100 and 1000 mg dm-3 MPs dispersions, respectively. PEC process, employing a TiO2 nanotubular photoanode at 0.1 mA cm-2, removed 16 and 6.98% of the initial mass for the same concentrations. Although the experimental conditions differed, the similar weight loss obtained with both methods emphasises the crucial role of ROS in the degradation process. Notably, the synergistic effect of light and electrochemistry in the PEC process, make this approach extremely promising for efficient microplastic degradation. This is further supported by the energy consumption: EO required approximately 104 and 103 kWh kg-1 for 100 and 1000 mg dm-3 MPs, respectively, while PEC consumed about 102 kWh kg-1 at both the concentrations.