The effect of the sp³/sp² carbon ratio on the electrochemical oxidation of 2,4-D with p-Si BDD anodes

Highlights: • The efficiency of the electrolysis of 2,4-D depends on the sp³/sp² ratio of the diamond anode. • A higher sp³/sp² ratio lowers the energy required to mineralize the pesticide. • The sp³/sp² ratio influences the concentration but not the type of intermediates produced. • Chlorate and perchlorate production is favored at higher sp³/sp² ratios. - Abstract: Boron-doped diamond films on silicon substrates (p-Si BDD) with different sp³/sp² carbon ratios are systematically varied in electrodes used to oxidize 2,4-dichlorophenoxyacetic acid (2,4-D) in synthetic wastewater containing chlorides. 2,4-D is completely mineralized during the electrolysis. A higher sp³/sp² ratio in the anode results in a more rapid and efficient oxidative removal of 2,4-D. Chlorinated compounds such as 4-chlororesorcinol, 2-chlorophenol, and 2,4-dichlorophenol form as intermediates during the oxidative treatment. Although these compounds are completely depleted during the electrolysis, their maximum observed concentrations decrease as the sp³ content increases in the anode. On the contrary, higher maximum concentrations are observed for non-chlorinated intermediates, especially hydroquinone, and there is a greater formation of chlorates and perchlorates in chloride-containing solutions as the sp³ content increases in the anode.