Degradation of carbamazepine by singlet oxygen from sulfidized nanoscale zero-valent iron – citric acid system

Sulfidized nanoscale zero-valent iron (S-nZVI) is a notable system used for environmental decontamination. However, it is not much effective for the oxidative degradation of certain types of pollutants. Herein, we report that a combination of S-nZVI with citric acid (CA), as a ligand can efficiently degrade a recalcitrant organic pollutant, carbamazepine (CBZ) by an oxidative mechanism. The major reactive species produced in the S-nZVI-CA system was singlet oxygen (1O2, established by means of electron spin resonance (ESR) experiment), which was derived from an initially-formed O2− which in turn was obtained by reduction of O2 by Fe2+-citrate complex. Density functional theory (DFT) calculations and LC-MS product analyses revealed that the oxidative degradation of CBZ occurred by the electrophilic attack of 1O2. S-nZVI-CA system can also be used to degrade CBZ in real environmental matrices such as river and groundwater without interference from the sample matrices. Thus, this study demonstrates the utility of the S-nZVI-CA system as a suitable precursor of 1O2 in environmental remediation processes.