Adsorption and Polymerization of Aniline on Cu(II)-Montmorillonite: Vibrational Spectroscopy and ab Initio Calculation†

Batch adsorption experiments in the presence of oxygen were performed to study the interlayer reactions of aniline on Cu(II)-montmorillonite in aqueous solutions. At concentrations below a critical value of CC = 2.6 mmol dm-3 only a colored Cu(II)−aniline complex is formed, characterized by a stability constant of log(Kassoc/dm3 mol-1) = 1.5. At concentrations beyond Cc aniline polymerizes yielding a dark brown product, which is identified by two vibrational spectroscopy techniques, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and FT-Raman spectroscopy. Vibrational assignment of aniline, polyaniline, and the interlayer reaction products of aniline at Cu(II)-montmorillonite was achieved by a comparison of the band position and intensity observed in the ATR and FT-Raman spectra with wavenumbers and intensities (IR and Raman) from ab initio quantum-mechanical calculations. Density functional theory (DFT, B3LYP/6-31G*) has been used to calculate the geometry, frequencies, and...