Hi Nasir,

as widely reported in the literature there are a lot of method to dope TiO2 (for example using noble metal particles, other oxides, N, W, S, ecc.) The choice depends to your reaction. For example for photocatalytic water splitting usually an alcohol it is used as hole scavenger and Pt as co-catalyst.

If you simply need to disable possible hole reactions in photocatalysis, you could try iodide or simpler alcohols, like methanol or ethanol.