Degradation of 4-chlorophenol through activating oxidants byzero-valent Al/Fe-saturated attapulgite composites

Abstract

<p indent="0mm">Zero-valent aluminum (ZVAl) is a promising heterogeneous catalyst in advanced oxidation technologies. However, the natural dense oxide layer of ZVAl impedes electron transfer from the core metal. Herein, a commercial clay, that is, attapulgite (ATP), with the advantages of abundant yield and low cost, was treated with FeCl₃ through saturated ion-exchange to enhance its Fe content, and was further mixed with micro-sized ZVAl (mZVAl) to obtain a mZVAl/Fe-saturated ATP composite (mZVAl-FeATP). It was explored to activate three oxidants, namely, H₂O₂, persulfate (PS), and peroxymonosulfate (PMS), for 4-chlorophenol (4-CP) degradation. The mZVAl-FeATP presented better activation ability to PMS than to PS and H₂O₂. The synergistic oxidative degradation performance and mechanisms of the mZVAl-FeATP/PMS system were systematically explored. The results showed that the mZVAl-FeATP/PMS system can quickly degrade 4-CP at pH ranging from 3.00 to 9.00. The main reactive species were <inline-formula id="INLINE37"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup other="0"><mml:mrow other="0"><mml:mtext other="0">SO</mml:mtext></mml:mrow><mml:mn other="1">4</mml:mn><mml:mrow other="1"><mml:mo other="1">•</mml:mo><mml:mo other="1">−</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math></inline-formula>, •OH and ¹O₂. During the reaction process, mZVAl, acted as an electron donor, could not only reduce the adsorbed Fe(III) to Fe(II) on the surface of mZVAl-FeATP for PMS activation, but also promote Fe(III)/Fe(II) cycle. mZVAl-FeATP/PMS system with a good general applicability could effectively degrade various organic contaminants in different water sources, in addition to 4-CP. Moreover, the catalytic reactivity of mZVAl-FeATP can be restored by a second ball milling process. In short, this work provided a simple and environmentally-friendly modification strategy, which can overcome the obstacle of electron transferring caused by ZVAl’s oxide film and make full use of interlayer structure of clay minerals, thereby broadening the applications of zero-valent aluminum and clay minerals in the field of water environmental remediation.