Native Defects in ZnO: Effect on Dye Adsorption and Photocatalytic Degradation

We investigated the influence of native defects on the adsorption and photocatalytic degradation of anionic and cationic dyes for different ZnO nanoparticles. We found that there was no relationship between the dye adsorption onto ZnO nanoparticles and their photocatalytic activity. Fast photocatalytic degradation could be observed for samples having a low concentration of nonradiative defects (and thus low recombination losses of photogenerated carriers), regardless of the amount of dye adsorbed onto the surface. While the absorption of cationic dyes was not significantly affected by ZnO nanoparticle properties, dye adsorption of several anionic dyes was strongly affected by native defects in ZnO. The defects involved in the dye adsorption are likely shallow donor centers exhibiting an electron spin resonance peak at g approximate to 1.957, resulting in positively charged sites at the surface.