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the solar spectrum

consists of only 5% UV light, limiting the opportunity to obtain very good results for TiO2

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catalytic efficiency will change depending upon the matrix used for fixing TiO2. Not sure, about mechanism. Mechanism of degradation will be same as long as matrix does not interfere with the properties of TiO2.

Titanium Dioxide Photocatalysts for the degradation of Organic Dyes one of the pollutants . The typical photo-catalytic process involves the pollutants degradation bringing COD(Chemical oxygen demand) down.

Binary or ternary composite of TiO2 reduced the bandgap energy ( doping of nonmetal with TiO2 increase the energy of valence band or the doping with metal nanoparticle reduce the energy level of conduction band thus it allow to reduce the bandgap energy that falls under the visible region of the light spectrum this help to shows its photocatalytic activity under UV as well as the visible region of the light spectrum

Article Recent advances in graphene oxide and reduced graphene oxide...

I don't think if there is any difference in degradation mechanism. The role of TiO2 here is to form the reactive oxygen species (ROS), which can be used to degrade the pollutants.

Regards,

K