The effect of pressure on the adsorption of crystal violet on oriented ZnO crystals

The effects of pressure up to 10 kbar on the shift of the peak locations and equilibrium characteristics of the monomeric isomers and the dimer of crystal violet (CV) dye have been established by comparing, at corresponding pressures, the photocurrent spectra of CV adsorbed to the surface of an oriented ZnO(0001) single crystal electrode with the optical absorption spectra of CV in solution. Dye concentrations range from 2×10−6 to 1.5×10−5 M in the electrolyte. The peaks of the monomeric isomers and the dimer of CV both in solution and adsorbed to the surface exhibit similar red shifts with increasing pressure, as is characteristic of π-π* excitations. In addition, the volume change of the system on isomerization and dimerization of the monomer in solution and the volume change of the system on adsorption of each species of CV to the ZnO surface are calculated. The results are interpreted to indicate the mode of adsorption on the surface.