the particle size and shape are two most important players in the field of photo catalytic activity. The photocatalytic phenomenon is dependent on the electron-hole separation process within the semiconductor. The photo -Fenton reaction demands the available electrons in the conduction band. If we decrease the particle size there will be size effect on band gap after a certain size limit and there will be a less available  free electrons.

This limit varies from material to material ... But crudely it should be higher than its quantum dot   size (roughly 10-14 nm is a good range).

Now the shape; we need enough surface to volume ratio, so any shape where surface to volume ratio is high that will give better performance.

2nd surface defects also plays an important role because those surface defects facilitates charge transfer phenomenon (by creating trap states in the band diagram)  

More our system can transfer charge to the dye more will be the yield. So Porous structures also have good potential. Any shape with porous surface and good surface to volume ratio will be a good contender to the photo catalytic processes

You have to take care of the charge transfer phenomenon within the S.C structure

(UV absorption, pl and raman study )

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