Photoresponse of Hematite Materials

Recently, it was shown that transient absorption decay for hematite nanoparticles was very fast, 70% of the transient absorption disappeared within 8 ps and no measurable transient absorption remained beyond 100 ps [43]. This represented a much faster decay than many other semiconductors, which is consistent with the observed poor charge transfer properties in hematite. It should be mentioned that this decay was independent of the excitation power, which suggests alternative relaxation mechanisms compared to those observed for Ti02 and ZnO for instance [43]. Since the relaxation was independent of pump power, probe wavelength, pH and surface treatment the fast decay was interpreted to be due to intrinsic mid-bandgap states and trap states rather than surface defects. This is in agreement with earlier investigations [44]. 

Semiconductor photocatalysis has been successfully applied in degradation of pollutants e.g. S02 and phenolic waste [69], It is mainly Ti02, which have been used and studied for this purpose, but there are reports where hematite has been used for photodegradation [52-54, 56, 57, 110, 111]. Hematite has also been studied as a gas sensing material [40]. 

In this section a more detailed description of the photoresponse for the various hematite materials, which have been studied for the aim of photooxidation. Due to the different ways of presenting the efficiency, a direct comparison of the photoelectrochemical properties of the materials when used for water oxidation is somewhat difficult. 

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