Surface-modified imogolite: Coupling reactions and sodium-montmorillonite intercalation products

The tubular aluminosilicate, imogolite, having a diameter of 23 A, a length of 2000 to 3000 A and an internal channel diameter of {dollar}approx{dollar}8.7 A was the material of interest in this study. Imogolite intercalates as a regular monolayer between the layers of Na-montmorillonite clay. The intercalated tubes align in van der Waals contact with one another and the clay layer. Therefore, the microporosity of this tubular silicate layered silicate, TSLS complex was restricted to the internal tube channels.; The focus of this work was concerted catalyst design. Modification of the external surfaces of imogolite was investigated as a possible route for enhancement of the microporosity of the TSLS complex. Surface modification was envisioned to promote lateral separation between the Na-montmorillonite intercalated surface-modified tubes. Removal of the surface-modifying agent by calcination might yield highly microporous products.; The internal and external surfaces of imogolite were silylated by allowing gamma-aminopropyltriethoxysilane (APS) to react with imogolite suspensions in acidic solution. The hydrolytic lability of the APS-modified imogolite was examined by monitoring the depletion of siloxane polymer from the tubular surfaces by dialysis against water at ambient pH. Bimodal depletion behavior was observed for APS-modified imogolite. This behavior was attributed to differences in the hydrolytic lability for siloxane polymer bound at the internal SiOH surfaces and the external AlOH surfaces. Covalent bonding between APS and imogolite SiOH sites was detected in the {dollar}sp1{dollar}H decoupled {dollar}sp{lcub}29{rcub}{dollar}Si MAS NMR spectrum of the APS-modified material. Polymer hydrolysis prevented the formation of ordered APS-modified imogolite intercalated products.; Gamma-aminopropylphosphonic acid (APP) was found both to chemisorb to the external Al(H{dollar}sb2{dollar}O){dollar}sp+{dollar} imogolite surface and to intercalate within the tube channel. Highly ordered washed products were obtained from APP-modified imogolite intercalated Na-montmorillonite at neutral pH. {dollar}sp{lcub}29{rcub}{dollar}Si and {dollar}sp1{dollar}H decoupled {dollar}sp{lcub}31{rcub}{dollar}P MAS NMR, FTIR, x-ray diffraction, elemental analysis and adsorption measurements were used to characterize the material. The products were identified as a quadruple layer of close-packed imogolite tubes intercalated between the layers of Na-montmorillonite. Reactions of APP with Na-montmorillonite yielded ordered intersalate compounds of APP or APP/APP{dollar}sp-{dollar} depending upon the reaction pH.