Degradation pathways of atrazine by electrochemical oxidation at different current densities: Identifications from...

Current density was the key factor that impacted pollutant degradation by electrochemical oxidation, and reaction contributions at various current densities were non-negligible for the cost-effective treatments of organic pollutants. This research introduced compound specific isotope analysis (CSIA) into atrazine (ATZ) degradation by boron doped diamond (BDD) with current density of 2.5-20 mA/cm², in order to provide "in-situ" and "fingerprint" analysis of reaction contributions with changed current densities. As results, the increased current density displayed a positive impact on ATZ removal. The Ʌ_C/H values (correlations of Δδ¹³C and Δδ²H) were 24.58, 9.18 and 8.74 when current densities were 20, 4, and 2.5 mA/cm², with ·OH contribution of 93.5%, 77.2% and 80.35%, respectively. While DET process favored lower current density with contribution rates up to ∼20%. What's more interesting, though the carbon and hydrogen isotope enrichment factors (ε_C and ε_H) were fluctuate, the Ʌ_C/H linearly increased accompanied with applied current densities. Therefore, increasing current density was effective due to the larger ·OH contribution even though side reactions may occur. DFT calculations proved the increase of C-Cl bond length and the delocalization of Cl atom, confirming dechlorination reaction mainly occurred in the direct electron transfer process. While ·OH radical mainly attack the C-N bond on the side chain, which was more benefit to the fast decomposition of ATZ molecule and intermediates. It was forceful to discuss pollutant degradation mechanism by combining CSIA and DFT calculations. Target bond cleavage (i.e., dehalogenation reaction) can be conducted by changing reaction conditions like current density due to the significantly different isotope fractionation and bond cleavage.