Adsorption of trichlorphon on phyllosilicate minerals: Effect of low molecular organic acids

ABSTRACT The effect of low molecular weight organic acids on the adsorption behaviour of trichlorphon on phyllosilicate minerals was investigated by the combination of adsorption measurements and molecular spectroscopic technique (Attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS)). The adsorption of trichlorphon on kaolinite (KAO) and montmorillonite (MON) was suppressed by increasing pH, indicating electrostatic interaction was the key role in the adsorption especially at low pH. In the presence of citric acid (CA), there was obvious promotion of the adsorption of trichlorphon on KAO and MON. In the presence of oxalic acid (OA), the adsorption on KAO was also promoted, while the adsorption on MON was inhibited especially at pH 4.0. The presence of CA and OA increased the adsorption by increasing the exposure of hydrophobic sites of KAO and MON. The ATR-FTIR and XPS results also indicated that the hydrophobic Si-O sites of phyllosilicate minerals were the preferred adsorption sites of trichlorphon in the presence of CA and OA and probably was driven by the hydrophobic effect. However, the weak effect of OA on MON caused the increasing of electrostatic repulsion between MON and trichlorphon molecule and thus inhibited the adsorption. This study has great significance for deeper understanding of the self-purification of soil and sediment systems in the presence of organic pollutants.