The role of ligand in the activation of peroxymonosulfate by Fe3O4 for the degradation of organic pollutants

Advanced oxidation processes based on peroxymonosulfate (PMS) hold remarkable promise for addressing emerging organic pollutants (EOPs) and are worthy of systematic investigation. However, the existing technology has not been widely applied due to bottlenecks such as reaction efficiency. Herein, we proposed a novel system incorporating nitrilotriacetic acid (NTA) as a functional ligand to enhance the activation of PMS by Fe3O4, thereby facilitating a better efficiency for the degradation of EOPs. Results indicated that the system can achieve an optimal removal rate of 99.6% for atrazine (ATZ) in the presence of NTA. Quenching experiments and electron paramagnetic resonance techniques were employed for mechanism exploration. The results revealed that the enhanced Fe(II)/Fe(III) cycling on the surface of Fe3O4, triggered by the addition of NTA, accelerates the reduction of trivalent iron and continuously activates PMS to generate radicals, particularly SO4−. The mechanistic analysis showed that in the first stage, the lower degradation efficiency was because the free radicals, in addition to reacting with the pollutants, could also self-quench with the uncomplexed Fe(II) and Fe(III) on the surface, the free NTA in the solution, or with the PMS. In the second stage, the ATZ achieved rapid degradation as the concentration of substances competing for free radicals decreased. Our work elucidates the key role of NTA functional ligand in the Fe3O4/PMS advanced oxidation processes, which may provide new for the efficient degradation of EOPs.