Microstructure of HDTMA+-Modified Montmorillonite and its Influence on Sorption Characteristics

A series of organoclays with monolayer, bilayer, pseudotrilayer, paraffin monolayer and paraffin bilayer were prepared by ion exchange. The microstructural parameters, including BET-N2 surface area, pore volume, pore size, surfactant loading and distribution, were deter-mined by X-ray diffraction (XRD), N2 adsorption-desorption and high-resolution thermogra-vimetric analysis (HRTG). The results show that both BET-N2 surface area and pore volume decrease from low to high surfactant loading as the average pore size increases. After modify-ing montmorillonite with hexadecyltrimethylammonium bromide (HDTMAB), two basic or-ganoclay models were proposed on the basis of HRTG results: 1) the surfactant mainly occu-pied the clay interlayer and 2) both the clay interlayer space and external surface were modi-fied by surfactant. In the former case, the sorption mechanism of p-nitrophenol to the organo-clay at relative low concentration involves both surface adsorption and partition whereas the latter mainly involves partition. This study demonstrates that the distribution of adsorbed sur-factant and the arrangement of adsorbed HDTMA+ within the clay interlayer control the effi-ciency and mechanism of sorption by the organoclay rather than BET-N2 surface area, pore volume, and pore diameter