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Iron(III)oxide in the form of hematite is, in many respects, an attractive material for the photocatalytic production of molecular oxygen from water. Especially over the past six years, several developments have advanced the performance of water oxidation cells based on this material. Nevertheless, the best versions of these photoelectrodes produce only about a fifth of the maximum photocurrent (and dioxygen) theoretically obtainable, while operating at photovoltages also well short of the theoretical maximum. Here we describe the factors limiting the performance of hematite as a photo-catalyst and outline approaches that have been, or might be, tried to overcome them. These factors include low hole mobility, bulk charge recombination, surface charge recombination, slow water oxidation kinetics, and poor light absorption. Whether hematite will soon become a practical photo-catalyst for water oxidation is uncertain. But, the schemes developed and the lessons learned will likely prove transferrable to other candidate photocatalyst materials.

Heating a gel consisting of briefly hydrolyzed tetraethyl orthosilicate (TEOS), 2–5-nm sized anatase, H2SO4, NaOH, KF, and H2 Oi n the mole ratio of 5.5:1:2.2:8.4:1.43:350 at 200 C for 7 h leads to production of ETS-10 crystals in fairly uniform size (� 500 nm) and shape having well-developed smooth facets in the truncated tetragonal bipyramidal structure. Characterization of the crystals revealed that the titanate ðTiO 2� 3 Þ quantum wires are well-preserved within the produced crystals. The required reaction period under our reaction condition (7 h) is much shorter than under the previously reported conditions which use Degussa P25 (a mixture of � 25 nm sized anatase and rutile) as the Ti source (>42 h at 200 C). The marked increase in crystallization rate and uniformity of size and shape is attributed to the use of very small anatase nanoparticles and briefly hydrolyzed tetraethyl orthosilicate (TEOS) as the Ti and Si sources, respectively. This report also demonstrates for the first time that TEOS can be used as the Si source. 2008 Elsevier Inc. All rights reserved.