A composite titania thin film consisted of quasi-aligned single-crystalline rutile nanorods embedded in sol−gel-derived anatase aggregates was fabricated and its photoelectrochemical behavior was studied in detail. A monolayer of nearly single-crystalline rutile nanorods was first deposited on metallic Ti substrates through a controlled reaction between Ti and hydrogen peroxide. The gaps among the rutile nanorods were then filled with titania nanoparticles through a sol−gel dip-coating approach, which achieved a composite thin film of single-crystalline rutile nanorods embedded in anatase aggregates, after a subsequent thermal treatment at 723 K. The X-ray diffraction measurement revealed that the composite film with thickness of 180 nm contained anatase and rutile in a nearly 50:50 ratio. The UV−visible diffusive reflectance spectra estimated a band gap of 2.99 eV for the rutile monolayer and a slightly increased value of 3.03 eV for the composite film due to the embedding of the anatase nanoparticles. Photocurrent versus potential diagrams, photocurrent transient curves, and open-circuit potential measurement supported the fact that the anatase nanoparticles possessed better inherent photoelectrochemical properties than rutile. However, electrochemical impedance spectra characterization, together with photocurrent transient curves and open-circuit potential measurement, suggests that the single-crystalline rutile nanorods exhibited a higher electron-transfer rate. The combination of the two components in such an appropriate way enhanced significantly the charge separation effect arising from the anatase/rutile couple, which hence combined efficiently the “mixed crystal effect” and the “mixed morphological effect”. A steady-state photocurrent more than double the simple sum of those generated by the two components alone was detected for the current composite film, which can be attributed to the single-crystalline rutile nanorods that provide channels for rapid electron transfer to the conductive Ti substrates under an applied bias potential. As a result, this study concludes that the present nanostructure magnified significantly the well-established mixed crystal effect, that is, an enhanced charge separation arising from a mixture of anatase and rutile.

Facile photocatalytic emulsion polymerization was developed to fabricate polystyrene (PS) microspheres using a transparent anatase titania hydrosol both as a photocatalyst and stabilizer. Under the appropriate conditions, PS microspheres with a well-defined particle size distribution can be easily produced from 100 to 830 nm. The effects of cross-linking agent ethylene glycol dimethacrylate (EGDMA) and coupling agent acrylic acid (AA) on the particle size and the size distribution of PS microspheres were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and other characterization means. It is proven that EGDMA and AA play importance roles in the morphology of microspheres. In addition, AA bonds a large number of titania nanoparticles on the surface of PS microspheres because its carboxyl group forms inorganic armored polymer microspheres. This interfacial interaction between titania nanoparticles and PS chains causes the elevated glass-transition temperature of microspheres.

Polystyrene (PS) nanocomposite particles with high titania content are prepared by Pickering emulsion polymerization. A self‐made titania hydrosol modified by an anionic monomer sodium styrene sulfonate (NaSS) is used as a stabilizer and photocatalyst. The stability of the emulsion system is greatly improved by the electrostatic interaction between negatively charged NaSS and positively charged titania nanoparticles. The nanocomposite spheres with the diameter of around 120 nm are highly charged, indicating titania‐rich surfaces of latex particles. It is also proven by the field‐emission transmission electron microscope and field‐emission scanning electron microscope images. The well‐defined core‐shell structure of the obtained PS/titania composite particles is confirmed by the formation of fragile hollow titania nanospheres after thermogravimetric analysis tests. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5728–5736, 2009

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