A new approach about the intercalation of hexadecyltrimethylammonium into halloysite: preparation, characterization, and mechanism

Three organoclays were prepared by mixing an Algerian halloysite with a solution of hexadecyltrimethylammonium bromide (HDTMA-Br) equivalent to six times the cation-exchange capacity of our clay. Unlike a majority of studies which were focused on the initial concentration of the intercalating agent, this paper investigates the influence of the reaction time for a given initial concentration. Three intercalation times were examined: 2, 7, and 14 days. The resulting organoclays were analyzed by XRD, FTIR, TG–DTA, TEM, and N2 adsorption–desorption. The intercalation of HDTMA+ cations begins by a latency period up to 2 days, during which these cations interact with the external surface of halloysite. From 2 to 7 days, they migrate into the interlayer spaces, leading to an expansion of the basal distance from 7.3 to 26.0 A. Between 7 and 14 days, the expansion remains unchanged for an intercalation rate around 42%. FTIR analysis proved that the surfactant interacts with the inner surface hydroxyl groups. From 200 °C, thermal analysis highlighted a succession of stages linked to the removal of HDTMA+. The TEM images showed a decrease in the outer diameter of the intercalated nanotubes with an enlargement of lumen diameter up to 20 nm. The arrangement of HDTMA+ species into interlayer spaces reflected a paraffin-type monolayer configuration. Knowing that the intercalation of organic compounds into the clay minerals changes their behavior from hydrophilic to hydrophobic, a nanotubular organohalloysite with a basal expansion of 26.0 A could be a highly effective adsorbent for wastewater decontamination.