抄録
The dynamics of rhodamine B (RB) in D_2O solutions was examined in the absence and presence of a smectite clay mineral, synthetic sodium-saponite (SSA), by ^1H nuclear magnetic resonance (NMR) spectroscopy. Hybridization of RB with the exfoliated SSA particles significantly decreased the intensity of NMR resonance signals of RB protons with the linewidth broadening, compared to RB alone. This indicated that the dynamics of RB molecules adsorbed onto the surface of SSA clay particles was very slower than in free state. The photodegradation profiles of RB in the presence of SSA clay particles were also monitored by ^1H NMR spectroscopy. After visible light irradiation, nine new resonance signals resulting from reaction products were detected in the ^1H NMR spectrum. The analysis of two-dimensional ^1H-^1H COSY and TOCSY spectra of the reaction mixture indicated that the ethyl group(s) of RB molecule adsorbed onto the surface of SSA particles was destroyed in the photodegradation process and that not only N-ethylamine (and/or N,N-diethylamine) as a major product but also other chemical species such as acetoaldehyde, acetic acid and formic acid were also produced. The detection of the minor products by NMR indicated the photodegradation of RB dye under the present experimental conditions involves oxidative reaction processes in which RB itself and/or the N-de-ethylation products react with the dissolved oxygen to produce the minor chemical species.
