Investigation of the physicochemical properties of amine-modified organoclays influenced by system pH and their potential to adsorb anionic herbicide

Abstract

Organically modified montmorillonites have already attracted the attention of researchers due to their eco-friendly characteristics and versatile application in our daily lives. Their application is now being widely explored as a potential carrier for preparing solid-laden controlled release formulations (CRFs) of herbicides. The suitability of a new formulation mainly depends on herbicide releasing behaviour under various conditions, which is governed by the interaction mechanisms between carrier materials and target herbicide. The physicochemical properties of carriers and herbicides are the key components for establishing the probable interaction mechanisms between them. The physicochemical properties of amine-modified organoclays are mostly pH dependent and this experiment investigated the effect of pH on surface chemistry and how it changes when system pH is varied. Results revealed that the organoclays converted from protonated to deprotonated conditions as well as from hydrophobic to hydrophilic states with increasing system pH, from acidic to alkaline conditions. The release of surfactants from the organoclays was higher in acidic and alkaline pH conditions than in neutral pH. The release of major structural elements was highest in acidic conditions, but gradually abated with increasing system pH until neutral conditions were achieved. After that they increased slightly to an alkaline state, except for iron (Fe). Zeta values of both organoclays gradually diminished as system pH increased. The surface area of organoclays was highest at neutral pH, and gradually waned towards acidic and alkaline pH. This ultimately affects adsorption of anionic herbicide onto the various pH-adjusted organoclays. The adsorption was highest at around the pKa value of the herbicide and gradually declined with increasing system pH to a neutral state, and then slightly increased towards a higher pH. Based on this, it can be concluded that system pH exerts a significant influence on the physicochemical properties of amine-modified organoclays. This may affect firstly, adsorption of pesticides onto the interlayer gallery of the organoclays for CRFs of pesticides; and secondly, the formulation’s releasing behaviour and ultimate efficacy of the synthesised formulation.