Effect of Operating Conditions on the Yield of 2-Hydroxyterephthalic Acid for Tracing •OH Radical in Electrochemical Process

The boron-doped diamond electrode has been widely applied in electrochemical process for wastewater treatment based on the generation of hydroxyl radicals (^•OH). This study investigated the formation efficiency of 2-HTA through the interaction between ^•OH radical and terephthalic acid (TA) to monitor the ^•OH formation. Results show that the 2-HTA formation efficiency did not depend on the initial concentration of scavenger (here, TA) in the investigated range of 0.1 to 1 mM TA. Meanwhile, other factors, such as current density, supporting electrolyte, sodium hydroxide have a significant influence. The optimal condition was established: concentration of electrolyte (0.05 M Na₂SO₄); initial concentration of TA (0.1 mM); concentration of NaOH (1 mM); current density (j = 20 mA cm^–2). The selectivity of TA was evaluated by Faradaic efficiency (η) and hydroxylation yield (\({{{{\gamma }}}_{{{\text{TAOH}}}}}\)), indicating that Faradaic efficiency (η) for 2-HTA formation was in the range of 10^–5–10^–7, while the hydroxylation yield of ^•OH (\({{{{\gamma }}}_{{{\text{TAOH}}}}}\)) into 2-HTA was 0.03–0.12.