An aqueous solution of doped polyaniline (PAN) was made from a saturated solution of the emeraldine base form in
dimethylformamide. A 3 mL portion of this solution was slowly added with stirring to 26 mL of water, which had been acidified to pH 3.5 with aqueous HCl. The pH of the final PAN solution was then adjusted to 2.5 by addition of aqueous HCl. The aluminum Keggin ion Al13O4(OH)24 (H2O)127+was prepared trom Al13O4(OH)25(H2O)11(SO4)3âx(H2O), which was available from a previous study.5 Briefly, 0.102 g of the sulfate salt was added to a solution of 0.042 g of BaCl2 in 200 mL of water and stirred overnight. The resulting 0.3 mM solution of the chloride salt of the aluminum Keggin ion was filtered using a 0.2 ím filter.