A high-efficient electrochemical degradation of diclofenac in water on planar and microstructured 2D, and macroporous 3D boron-doped diamond electrodes: Identification of degradation and transformation products

The highly efficient degradation of persistent organic substances by electrochemical advanced oxidation processes (EAOPs), which don't result in the formation of potentially harmful by-products, is crucial for the future of water management.

In this study, boron-doped diamond electrodes (BDDE) with three morphologies (planar 2D, microstructured 2D, and macroporous 3D) were employed for the anodic oxidation of diclofenac (DCF) in two working electrolytes (NaCl and Na₂SO₄). In total, 11 by-products formed during the electrochemical oxidation of DCF were identified via HPLC-HRMS. The identification of degradation products revealed the formation of various active chlorinated species. The utilization of a chlorine-free Na₂SO₄ electrolyte resulted in the formation of greater number of chlorinated species, while their elimination required a longer period compared to the use of NaCl electrolyte. The formation of by-products was also influenced by the specific type of BDD electrode, which was associated with variations in applied current density. This led to an uneven distribution of dichloro (2D BDDE) and trichloro (3D BDDE) patterns. However, none of the products showed signs of a high level of persistence.

The results revealed that the type of electrolyte is the most significant factor affecting the removal efficiency of DCF, while the different electrode morphologies do not lead to differences in the removal rates. The electrode type exerted a notable influence on the removal rates, which was associated with varying applied current densities, exclusively in the case of the Na₂SO₄ electrolyte. Over 99 % removal efficiency for DCF in NaCl, with power consumption of 1.8 kWh m⁻³ was achieved.