Polymer–clay nanocomposites for the removal of trichlorophenol and trinitrophenol from water

Phenolic compounds pose health and environmental hazards. This study focused on two priority pollutants, trinitrophenol (picric acid—PA) and trichlorophenol (TCP), which were detected in rivers, lakes and water reservoirs. Polycation–clay mineral nanocomposites were characterized and designed for the removal of these pollutants from water. The adsorption kinetics of polydiallyl dimethylammonium chloride (PDADMAC) and poly-4-vinylpyridine-co-styrene (PVPcoS) on montmorillonite (MMT) was significantly faster (2–4 h) than on sepiolite (3–4 days), which was explained by the latterʹs porous structure. Consequently, polycation–MMT composites were chosen to test pollutant adsorption. Both PA (anionic) and TCP (non-ionic) showed higher affinity to the less charged polycation PVPcoS (40% of the monomers charged) than to the highly charged polycation PDADMAC. However, PA removal by the PVPcoS–MMT composite was nearly complete whereas TCP removal reached 40 to 60% of the added amounts. The adsorption isotherms of the pollutants suggested that the binding to PVPcoS–MMT was driven mainly by hydrophobic interactions, but also by electrostatic interactions in the case of PA. Differences were also seen in the binding kinetics of PA and TCP to dried and wet composites. The hydration properties of PA enhanced its binding to wet composites whereas the hydrophobic properties of TCP enhanced its binding to dehydrated composites. The results of this study emphasize the importance of better understanding pollutant–adsorbent interactions to enable more efficient tailoring of polymer–clay mineral composites for water treatment.