We present the transformation of organic-inorganic hybrid titanicone films formed by TiCl(4) as metal precursor and ethylene glycol (EG) using solvent-free MLD to highly active photocatalytic films. The photocatalytic activities of the films were investigated using hydroxyl-functionalized porphyrin as a spectroscopic marker. TEM imaging and electron diffraction, XPS, UV-vis spectroscopy, and spectroscsopic ellipsometry were employed for structural and composition analyses of the films. The photocatalytic activity of Ti-EG films was investigated for different anneal temperatures and compared to TiO(2) films prepared by ALD using TiCl(4) as metal precursor and H(2)O (TiO(2) films). Overall, our results indicate that the photocatalytic activity of the thermally annealed Ti-EG film is about 5-fold increased compared to that of the TiO(2) film prepared by ALD for optimal process conditions. The combined results indicate that the structural and photocatalytic properties can be assigned to three states: (I) amorphous state, intermediate dye loading, low photocatalytic activity, (II) intermediate film state with both crystalline and amorphous regions, high dye loading, high catalytic activity, and (III) highly crystalline film with low dye loading and low photocatalytic activity. The formation of photocatalytic nanotubes (NTs) is demonstrated using sacrificial Ge nanowires (NWs) scaffolds to yield Ti-EG NT structures with controllable wall thickness structures and enhanced dye loading capacity. Our results demonstrate the feasibility and high potential of MLD to form metal oxides with high photocatalytic activity.

Molecular layer deposition (MLD) of TiCl 4 and ethylene-glycol (Ti-EG) was recently demonstrated as a vapor phase synthetic route for preparation of photocatalytic thin films via hybrid organic−inorganic thin films. The organic moieties of the hybrid material function as sacrificial components that undergo controlled decomposition during thermal annealing. Anneal temperature was shown to be an important factor determining the overall photocatalytic performances of the treated films with 650 °C optimal for photodegradation of dye molecules and anneal at 520 °C showing optimal performance for the direct photocatalytic production of H 2 O 2 . Both systems exhibit activities that are not typically attainable by titania, yet a fundamental understanding of the underlying details leading to these improved reactivities for the specific cases is still lacking. Here we demonstrate that thermal anneal of hybrid organic−inorganic thin films prepared by MLD yield oxygen-deficient titania with controllable levels of oxygen vacancies (OVs) and defect states that are adjusted by the temperature of the anneal process, performed under air. The anneal process result in nonstoichiometric oxide films with unique electronic properties including the tuning of band positions, accessibility to significantly deeper valence band position and controlled formation of electronic defect states that assist in charge separation for Au-titania catalyst. We correlate the oxygen deficiency and electronic structure of the annealed film with the photocatalytic activity for shedding light on the details that lead to the improved reactivity. These results extend the scope of using MLD in the context of photocatalysis with new routes for obtaining nonstoichiometric oxides which are key for enhancing and tailoring the reactivity of metal oxide (photo)catalysis.

Tailor-made metal oxide (MO) thin films with controlled compositions, electronic structures, and architectures are obtained via molecular layer deposition (MLD) and solution treatment. Step-wise formation of permeable hybrid films by MLD followed by chemical modification in solution benefits from the versatility of gas phase reactivity on surfaces while maintaining flexibility which is more common at the liquid phase.