Enhanced hydroxyl radical generation by zero-valent iron/ethylenediamine tetramethylene phosphonic acid for Cr(VI) reduction and 2,4-dichlorophenol degradation

Zero-valent iron (ZVI) has emerged as a promising material for water remediation in recent years. However, the formation of a passivation layer on the surface of ZVI significantly reduces its reactivity. Ethylenediamine tetramethylene phosphonic acid (EDTMPA), a chelating agent, aids in the prevention and passivation of ZVI. This chelating agent has been used in combination with ZVI to remove 2,4-dichlorophenol (2,4-DCP) and hexavalent chromium Cr(VI) simultaneously. In this study, the addition of EDTMPA significantly enhanced the removal efficiencies of Cr(VI) and 2,4-DCP by 7.7 to 10 times compared to ZVI reaching complete removal of Cr(VI) and 80% removal of 2,4-DCP within 120 min. Quenching and probing experiments have shown that hydroxyl radicals (•OH) serve as the predominant reactive species responsible for the degradation of 2,4-DCP. Meanwhile, pristine ZVI effectively reduced Cr(VI) to the less hazardous Cr(III) and reacted with oxygen in water to generate Fe(II) and hydrogen peroxide (H2O2), both critical for initiating the subsequent Fenton reaction. The addition of EDTMPA effectively mitigated the formation of the passivation layer on the surface of the ZVI, maintaining its reactivity. The ZVI/EDTMPA system offers an effective method for simultaneous remediation of Cr(VI) and 2,4-DCP by optimizing the application of ZVI.