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 − , SO4 2− and PO4 3− , 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 PO4 3− . 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 PO4 3− . 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.