Intercalation of Organic Ammonium Ions into Layered Graphite Oxide

The intercalation of large organic ammonium ions (tetramethylammonium ions (TMA+), tetraethylammonium ions (TEA+), tetrapropylammonium ions (TPA+), and tetrabutylammonium ions (TBA+)) into layered graphite oxide (GO) was systematically investigated. The intercalation reactions were completed at 25 °C after 3 days, and stable colloidal suspensions were obtained at TAAl/Hs = 5 (molar ratio of tetraalkylammonium ions (TAA+) over exchangeable protons in GO). The sediments after centrifuging the colloidal suspensions showed amorphous phase X-ray diffraction patterns, indicating that exfoliation of the layered structure into nanosheets took place in the suspension. When the sediments were dried at 70 °C for 3 days, layered structures of TAA+-intercalated GO materials with basal spacings of 1.56, 1.67, 1.84, and 2.37 nm, respectively, appeared. The basal spacing of the layered compounds decreased with a decrease of relative humidity during drying. When the dried TAA+-intercalated GO compounds were exposed to a humid saturated atmosphere, the basal spacing increased gradually, finally becoming an amorphous structure. The maximum saturation of intercalated TAA+ ions into GO decreased with the increase in alkyl chain length. When the TAA+-intercalated materials were washed with distilled water and acid-treated, a process of deintercalation of TAA+ ions from the interlayer occurred. A schematic model for the deintercalation−intercalation involving a exfoliation process is proposed. The layered structure of TAA+-intercalated GO materials is discussed in terms of the dimension of the GO layer and the sizes of H2O molecules and TAA+ ions.