Thermal treatment of organoclays: Effect on the aqueous sorption of nitrobenzene on n-hexadecyltrimethyl ammonium montmorillonite

The aim of this work was to examine the effect of thermal treatment on organoclay sorptive properties. Aqueous sorption of nitrobenzene used as a probe compound was studied on Na-montmorillonite and two types of HDTMA-montmorillonite (where HDTMA is n-hexadecyltrimethyl ammonium exchanged by 41 and 90% of the clay cation exchange capacity) heated in air at 150, 250, 360 and 420 °C. Mild heating of sorbents (at 150 °C) results in a distinct increase of their sorptive efficacy. Treatment of organoclays at higher temperatures (250 and 360 °C) results in the significant sorbent changes as revealed by a C loss, decrease of a basal spacing and disappearance of symmetric and asymmetric stretching vibrations of CH2 but has a little impact on the sorptive efficacy (as compared with organoclays treated at 150 °C). Hence, even a significant carbon loss in thermally treated organoclays should not be necessarily linked to the loss of their sorptive potential. Further increase of the treatment temperature results in a decrease of a sorptive efficacy of all sorbents. Mild heating of organoclays in air could be useful for improving their sorptive potential. This improvement is assumed to result from the weakening of water–sorbate competition for sorption sites on a mildly heated sorbent.