Sodium tetraborate simultaneously enhances the degradation of acetaminophen and reduces the formation potential of chlorinated by-products with heat-activated peroxymonosulfate oxidation

In this study, sodium tetraborate (Na 2 B 4 O 7 ) was introduced to enhance the degradation of acetaminophen (ACT) in heat-activated peroxymonosulfate (PMS) process. The elimination of ACT in Na 2 B 4 O 7 /heat/PMS process followed the pseudo -first order kinetics. The corresponding k obs value with 10 mM Na 2 B 4 O 7 was 33.1 times higher than that in heat/PMS process. 1 O 2 and HO· were identified as primary reactive species via quenching experiments and electron paramagnetic resonance technology. B(OH) 4 − , the hydrolysis product of Na 2 B 4 O 7 , reacted with PMS to generate HOOB(OH) 3 − . 1 O 2 was generated by the self-decomposition of PMS using B(OH) 4 − as catalyst, while HO· was produced via the breakage of peroxide bond of PMS and HOOB(OH) 3 − under high temperature. ACT was degraded by reactive species via the pathways of -NH- bond breakage, -OH replacement, -NH 2 oxidation and benzene ring cleavage. Nine transformation intermediates were detected by LC/Q-TOF/MS, and the toxicity of reaction solution decreased significantly with the elimination of ACT. Increasing Na 2 B 4 O 7 dosage, PMS concentration, initial pH and reaction temperature were conducive to ACT elimination. Humic acid, Cl − and CO 3 2− inhibited the degradation of ACT heavily, while SO 4 2− and NO 3 − had the negligible effects. Moreover, B(OH) 4 − could react with free chlorine to the inert B(OH) 3 OCl − and further significantly suppress the formation of chlorinated by-products for the treatment of Cl − -containing water in Na 2 B 4 O 7 /heat/PMS process. This study provided an effective way to enhance the oxidation capacity of heat/PMS process and suppress the formation of chlorinated by-products in chloride-containing water, and the findings had important implications for using borate buffer in the studies of PMS-based advanced oxidation processes.