Self-assembly of aluminium-pillared clay on a gold support

Abstract

Multilayer films of self-assembled aluminium Keggin ion pillared laponite and saponite have been grown layer-by-layer on a gold support. 4-Aminothiophenol (4-ATP) was used for anchoring the first clay layer on the gold surface. Subsequently layers of clay and Al pillar were adsorbed by dipping the substrate into the appropriate solutions. Characterization of the films was performed by X-ray photoelectron spectroscopy (XPS), IR spectroscopy (FTIR–ERS), ellipsometric thickness measurements and X-ray diffraction (XRD). XPS elemental analysis showed that both clay and pillar were present on the gold substrate. From the atomic film compositions, the charges on the Keggin ions were determined to be +3 and +5 for laponite and saponite, respectively. Ellipsometry and IR spectroscopy indicated gradual and regular growth for both films. Structural order in the synthesized films was demonstrated by X-ray diffraction. The interlayer free spacing (IFS) was found to be 6 Å by XRD, which corresponds to the increase in ellipsometric film thickness after each aluminium layer adsorption. Aluminium-pillared laponite films have been used as chemically sensitive films on surface acoustic wave (SAW) devices to measure the adsorption capacity of six volatile organic compounds (VOCs). The influences of the different terminal film layers and calcination-induced chemical changes on the extent of adsorption of the VOCs were investigated.