Fast degradation of atrazine by nZVI-Cu⁰/PMS: Re-evaluation and quantification of reactive species, generation pathways, and application feasibility

Additive metal to zero-valent iron (ZVI) could enhance the reduction ability and the additive Cu⁰ was incorporated to ZVI to accelerate PMS activation with atrazine (ATZ) as target compound. The efficiencies of ATZ degradation and PMS decomposition climbed up firstly and then declined as Cu⁰ loading increased from 0.01 to 1.00 wt% with the maximums at 0.10 wt%. SO₄^•−, HO^•, Fe(IV), O₂^•− and ¹O₂ were generated by nZVI-Cu⁰/PMS based on the results of electron paramagnetic resonance (EPR) and simultaneous degradation of nitrobenzene, ATZ, and methyl phenyl sulfoxide (PMSO). The rate constant of Fe(IV) and ATZ was estimated as 7 × 10⁴ M⁻¹∙s⁻¹ via the variation of methyl phenyl sulfone (PMSO₂)formation at different ATZ concentrations. However, Fe(IV) contributed negligibly to ATZ degradation due to the strong scavenging of Fe(IV) by PMS. SO₄^•− and HO^• were the reactive species responsible for ATZ degradation and the yield ratio of SO₄^•− and HO^• was about 8.70 at initial stage. Preliminary thermodynamic calculation on the possible activation ways revealed that the dominant production of SO₄^•− might originate from the atomic H reduction of PMS in the surface layer of nZVI-Cu⁰. Ten products of ATZ degradation were identified by HPLC/ESI/QTOF and the possible degradation pathways were analyzed combined with theoretical calculation on ATZ structure. The decrease of temperature or increase of solution pH led to the decline of ATZ degradation, as well as the individual addition of common ions (HCO₃⁻, Cl⁻, SO₄²⁻, NH₄⁺, NO₃⁻ and F⁻) and natural organic matters (NOM). In real water, ATZ was still efficiently degraded with the decontamination efficiency decreasing in the sequence of tap water > surface water > simulated wastewater > groundwater. For the treatment of ATZ-polluted continuous flow, nZVI-Cu⁰ in double-layer layout had a higher capacity than the single-layer mode. Meanwhile, the leaching TFe and TCu were limited. The results indicate nZVI-Cu⁰/PMS is applicable and the multiple-layer layout of nZVI-Cu⁰ is suggested for ATZ-polluted ground water and soil remediation.