Smectite clay pillared with copper complexed polyhedral oligosilsesquioxane for adsorption of chloridazon and its metabolites

Abstract

Chloridazon has been a widely used herbicide during the past decades, especially in sugar-beet cultivation. UV-induced degradation of chloridazon leads to the formation of desphenyl counterparts, i.e. desphenyl-chloridazon and methyl-desphenyl-chloridazon. Even if accumulation of these residues in natural waters is far from alarming, a low-cost effective and environmentally friendly adsorbent, capable of binding chloridazon and its degradation products is desirable to reduce their concentration in water even further below legal limits. Here we show that pillared smectite clay, prepared by cation exchange of sodium with copper complexed, cage-shaped polyhedral oligomeric silsesquioxane (Cu²⁺@POSS) could be a promising candidate for this purpose. X-ray diffraction and high resolution transmission electron microscopy evidenced a homogeneous layered structure where the interlayer spacing is enlarged by 7.1 ± 0.2 Å (the diameter of Cu²⁺@POSS) with respect to the pristine clay. Exposure of this pillared smectite clay to chloridazon and its metabolites in water showed that Cu²⁺@POSS intercalation significantly improved its adsorption capacity. In addition, after several thermal regeneration cycles, Cu²⁺@POSS_SWy-2 still exhibited excellent adsorption properties. These findings demonstrate that smectite clay pillared with copper complexed polyhedral oligosilsesquioxane is a promising environmentally friendly and relatively low cost material for herbicide waste remediation.