Zinc complex formation of organic ligands on zinc oxide and titanium dioxide

• ZnO and TiO2 films dispersing organic ligands were prepared by a sol–gel method.
• Layered zinc hydroxide was formed on the ZnO surface.
• Zinc complex was formed in the interlayer of the layered zinc hydroxide.
• Titanium complex was formed on the TiO2 particle surface.
• Zinc complex was formed in the presence of zinc ions on the TiO2 particle surface.

Thin films consisting of zinc oxide or titanium dioxide particles dispersing an organic ligand, i.e., 1,2-dihydroxynaphthalene (DHN) or 8-hydroxyquinoline (HQ), on the surface were prepared by the sol–gel method with steam treatment. The crystalline phases were identified by XRD analysis. The UV–vis absorption and photocurrent spectra of the films were analyzed for their photoelectrochemical characterization. The complex formation of the ligands was confirmed by FTIR spectroscopy. The ligand molecules formed zinc complexes in the interlayer of the layered zinc hydroxide which was formed on the zinc oxide surface. The zinc complex did not efficiently generate electricity because the electron injection from the DHN moiety or the zinc complex of HQ into the zinc oxide was blocked by the layered zinc hydroxide. The ligand molecules formed titanium complexes on the titanium dioxide surface, and also zinc complexes in the presence of zinc ions on the titanium dioxide surface. The zinc complex formation increased the photocurrent. It is suggested that electrons were directly injected from the DHN moiety into the titanium dioxide conduction band and indirectly injected from the excited states of the metal complex of HQ into the titanium dioxide conduction band.

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