Electrocatalytic degradation of sulfadimethylpyrimidine by Bi/nZVI in citric acid buffer solution

With the rapid development of medicine and animal husbandry, a significant amount of sulfonamide residues are being introduced into water systems, leading to a range of environmental and health issues. Modified nano zero-valent iron (nZVI) has garnered considerable attention for its ability to activate molecular oxygen and efficiently degrade SAs through Fenton-like reactions. In this study, sulfonamide dimethylpyrimidine (SMZ) was successfully degraded via electrocatalytic oxidation using bismuth-modified zero-valent iron (Bi/nZVI) in a citric acid (CA)-sodium citrate (NaCA) buffer solution. The findings demonstrated that Bi doping facilitated the reduction of activation energy required for molecular oxygen activation into H2O2. Additionally, the formation of ferrous citrate complexes through iron-citrate complexation enabled Fenton-like reactions with spontaneously generated H2O2 within the system. The reduction of Fe2+/Fe3+ potential was beneficial to the iron cycle process, thus enhancing the degradation effect of SMZ. Three reactive oxygen species (ROS), namely ·OH, ·O2−, and 1O2, existed in this system with their contributions ranked as follows: ·OH >·O2−>1O2. Mass spectrometry analysis reveals four possible degradation pathways for SMZ in this system: hydroxylation addition, SO2 removal, S—N bond breaking, and C—N/C=N bond breaking within nitrogen-containing heterocyclic rings. The development of this novel system not only offers a new technical approach for removing sulfonamides from water but also provides theoretical support for treating other organic pollutants.