Zeolite 4A activates peroxymonosulfate toward the production of singlet oxygen for the selective degradation of organic pollutants

Abstract

Zeolite 4A (Z4A), synthesized from natural kaolin by an easy and low-cost method, was used to activate inorganic peroxides for degrading organic pollutants in water. Z4A had a high catalytic capability for the activation of peroxymonosulfate (PMS) but a low effect on peroxydisulfate (PDS) or hydrogen peroxide (H2O2). The non-radical pathway dominated the degradation of the pollutants, due to acid-base interactions of PMS with Z4A, as indicated by the characterization of the fresh and used zeolite. Additionally, in the Z4A/PMS system, synergistic effects in the elimination of two representative contaminants (ciprofloxacin “CIP” and methyl orange “MO”) were observed. The Z4A/PMS system induced the opening of the piperazyl ring of CIP, and the cleavage of the azo-benzene bond of MO. These primary transformations occurred in electron-rich groups, as supported by theoretical analyses on atomic charge developed herein. Interestingly, Z4A showed high activating/degrading capability even after three reuse cycles without the involvement of the typical recycling steps (filtration, washing, and drying) for a solid recovery. Furthermore, when compared with a sonochemical process, the Z4A/PMS system was highly efficient and more selective for the degradation of both CIP in synthetic fresh urine and MO in simulated textile wastewater. This study offers relevant findings on the PMS activation toward the non-radical pathway using the zeolite 4A, which represents an interesting alternative to those materials composed of transition metals or carbonaceous structures, to treat organic pollutants in aqueous samples in a selective way.