Synergistic Degradation of 4-Chlorophenol and 3-Chlorobenzoic acid via Organic Ligand–Assisted Fe(II)/Persulfate Activation: Molecular Pathways and Environmental Impacts

Chlorinated aromatic chemicals are highly hazardous, transmissible, and bioaccumulative. Developing an economically feasible catalytic method to facilitate the effective removal of chlorinated aromatic pollutants is critical for contamination prevention. The current study extensively investigated the utilization of organic ligands such as citrate (CA) and ethylenediaminetetraacetic acid (EDTA) to increase Fe(II)-activated persulfate (PS) for 4-chlorophenol (4-CP) and 3-chlorobenzoic acid (3-CB) degradation in water. The decomposition and consumption ability of persulfate in PS alone and Fe(II)/PS systems for 4-CP and 3-CB was very low because of the rapid utilization as well as discontinuous availability of Fe(II), which indicates the decline of Fe(III) to Fe(II). But, when using the citrate/Fe(II)/PS and EDTA/Fe(II)/PS combinations, the degradation of 4-CP and 3-CB was 78.86%, 75.01% and 84.84%, 80.99% within 30 min, respectively. The significant enhancement is due to both ligand-to-metal transfer of charges process, and this increased the process of rate determination through carrying electrons into the citrate and EDTA ligands to Fe(III), generating Fe(II). In addition, the 4-CP and 3-CB degradation facilitated with citrate/Fe(II)/PS and EDTA/Fe(II)/PS systems was efficiently degraded at acidic pH (2.0–6.0) conditions. The pseudo-first-order kinetics model accurately predicted 4-CP and 3-CB degradation in the organic ligand/Fe(II)/PS systems. The degradation percentage of 4-CP and 3-CB increased with increasing PS and Fe(II) concentrations. Moreover, both sulfate and hydroxyl radicals formed by citrate/Fe(II)/PS and EDTA/Fe(II)/PS systems were identified as major reactive oxygen species for 4-CP and 3-CB decomposition. The present investigation recommends an alternate strategy to enhance the Fe(II)-activated persulfate mechanisms.