Organoclays of high-charge synthetic clays and alumina pillared natural clays: Perchlorate uptake

Abstract

Several organoclays were synthesized from different types of high charge synthetic clays using octadecyltrimethylammonium (ODTMA) chloride or polyethylenimine (PEI). Two alumina pillared clays were also prepared using two naturally occurring montmorillonites. These organic–clay and inorganic–clay nanocomposites were characterized by powder X-ray diffraction (XRD) and tested for perchlorate uptake. The results showed that the highest perchlorate uptake capacity of 0.436±0.001 was achieved with ODTMA Na-3-mica followed by 0.269±0.016meq/g with ODTMA Na-2-mica. The uptake of perchlorate by synthetic Na-n-micas is as follows: ODTMA Na-3-mica>ODTMA Na-2-mica>ODTMA Na-1-mica>ODTMA Na-4-mica. Perchlorate uptake isotherms were determined for both ODTMA Na-3-mica and ODTMA Na-2-mica as a function of perchlorate concentration but apparently equilibrium was not achieved in both cases. The uptake of perchlorate by the ODTMA Na-n-micas could be attributed to exchange with chloride ions of the neutral surfactant occluded in between cationic chains during the cation exchange process. Organoclays prepared with PEI and hydroxy Al polymer pillared clays and their calcined counterparts showed little or no uptake because excess positive charge was not created in the interlayers in these nanocomposites unlike in the organoclays with Na-n-micas.