Fig. 2

UV-Vis spectra of (a) RO-A and (b) RO-D at different pH values. The spectra at the lowest pH (3.51 for RO-A and 3.65 for RO-D) are represented by bold red curves, while the spectra at the highest pH (9.70 for RO-A and 9.91 for RO-D) are represented by bold blue curves. The largest changes are seen at 330, 260, and 230 nm. The fit of the model function (Eq. (1)) to the values at 260 nm is shown in the upper right corner of (a) and (b).