we can see the obvious differences in photo-degradation efficiency and adsorption of water pollutant by changing the dopant in catalysts, especially the adsorption. I always think about what processes and reactions can be happened to this change?
The reason of differences in photocatalytic performance is the changes of electronic structure. Each atom has different electron configuration, electron negativity and atomic/ionic radius. Therefore, each dopant state will be located depending on the atom. Various electronic structure = differences in light absorption and recombination rate, so these effects will cause differences in photocatalytic activity.
Moreover, the presence of new atoms may influence on the morphology of the final photocatalyst and active sites, which is also a important factor, because it affects water adsorption properties and the photocatalytic activity.
I hope this answer is sufficient for you. The subject is extensive, so I am not sure if this is an answer you are looking for.