of course you can do that , but you need a complex/material that absorbs in the vis. Region, cheap , stable , robust and you should know the kinetics of this compound before applying it in your system

Also you need to know what kind of redox mediator you are going to use, i.e the oxidation and reduction potentials

Bayu:

Yep, you’ve hit on a couple of the critical questions involved in applying TiO2 to this problem of photo catalysis. This topic is currently “all the rage”, and you can find, literally, thousands of papers in the literature involved with, or describing applications of TiO2. Increasing the photo-efficiency of the many systems that show promise is (if you’ll pardon the expression) the “holy Grail” of this field.

It turns out that we study a TiO2 nanoparticle system in our lab here at Tufts University. And, we focus on increasing the photo / quantum efficiency of the system. (Personally, I study ice in that lab.) In my view, we’ve made significant progress and have cleared up many ambiguities and seemingly contradictory results found in the literature through careful research. At the risk of ‘self promotion’, let me recommend you read the following papers written by co-researchers and my academic advisor:

Shultz, M. J.; Groenzin, H.; Wang, C. Y.; Asong, N. COLL 145-Photo oxidation on TiO2: Competition with water. Abs. Pap. Am. Chem. Soc. 2006, 232.

Asong, N.; Dukes, F.; Wang, C. Y.; Shultz, M. J. The effect of iron doping on the adsorption of methanol on TiO2 probed by sum frequency generation. Chem. Phys. 2007, 339, 86-93.

Dukes, F. M.; Iuppa, E.; Meyer, B.; Shultz, M. J. Differing Photo-Oxidation Mechanisms: Electron Transfer in TiO2 versus Iron-Doped TiO2. Langmuir 2012, 28, 16933-16940.

These papers seem to be directly relevant to your question. In particular, the latest one by Dukes would seem to be most relevant.

The main criteria for efficacy is widely linked to quantum yield of the dye molecule and the injection rate of the charge from the dye to the semiconductor/catalyst. The efficiency for photovoltaics based on dye sensitised titanium dioxide seems to have become stuck at around 11 % so research in that field is in part at least looking to increase the number of electrons produced in the absorber per absorbed photons. (see Binks Physical Chemistry Chemical Physics 13, 12693 (2011)., M. B. Smith and J. Michl, Chemical Reviews 110, 6891 (2010) for examples of this.)

As for other catalysts/semiccnductors ZnO is also being studied and certainly for water splitting applications (to produce H2) people are looking to other transition metal oxides including iron oxides. This is a nice review from a few years ago about artificial photosynthesis vs solar fuels D. Gust, T. A. Moore, and A. L. Moore, Accounts of Chemical Research 42, 1890 (2009). I hope that has helped