Degradation of tris(1-chloro-2-propanyl) phosphate by the synergistic effect of persulfate and zero-valent iron during a mechanochemical process

Abstract

This study revealed a dual pathway for the degradation of tris(1-chloro-2-propanyl) phosphate (TCPP) by zero-valent iron (ZVI) and persulfate as co-milling agents in a mechanochemical (MC) process. Persulfate was activated with ZVI to degrade TCPP in a planetary ball mill. After milling for 2 h, 96.5% of the TCPP was degraded with the release of 63.16, 50.39, and 42.01% of the Cl⁻, SO₄²⁻, and PO₄³⁻, respectively. In the first degradation pathway, persulfate was activated with ZVI to produce hydroxyl (·OH) radicals, and ZVI is oxidized to Fe(II) and Fe(III). A substitution reaction occurred as a result of the attack of ·OH on the P–O–C bonds, leading to the successive breakage of the three P–O–C bonds in TCPP to produce PO₄³⁻. In the second pathway, a C–Cl bond in part of the TCPP molecule was oxidized by SO₄·⁻ to carbonyl and carboxyl groups. The P–O–C bonds continued to react with ·OH to produce PO₄³⁻. Finally, the intermediate organochloride products were further reductively dechlorinated by ZVI. However, the synergistic effect of the oxidation (·OH and SO₄·⁻) and the reduction reaction (ZVI) did not completely degrade TCPP to CO₂, resulting in a low mineralization rate (35.87%). Moreover, the intermediate products still showed the toxicities in LD₅₀ and developmental toxicant. In addition, the method was applied for the degradation of TCPP in soil, and high degradations (> 83.83%) were achieved in different types of soils.