Photosensitization, photocatalysis and photo fenton reactions of hemin anchored SRTIO3 / sno2 composite for the degradation of rhodamine b: a comparative study with pristine SrTiO3 and SnO2

In the present study anchoring of hemin a protoporphyrin IX Fe (III) molecule on the surface of SrTiO3/SnO2 composite (H-(STO / SnO2)) is attempted. STO / SnO2 composite show activity under visible light due to the staggering band edge positions. However the activity under solar light is very poor. When hemin is anchored on the STO/SnO2 composite the activity increases by 22 folds. The activity can be further improved by the addition of H2O2 as an oxidant by 70 folds. This higher activity in presence of H2O2 can be due to the synergistic effect of photocatalysis, photosensitization and photo-Fenton process. The higher efficiency of H-(STO / SnO2) composite sample along with H2O2 can also be accounted to the efficiency of non-radiative electron-transfer through Inter System Crossing (ISC) from the excited singlet to triplet state which increases the life time of the charge carriers. Triplet state is more favorable than the excited singlet state for the transfer of electrons from the hemin molecule to the conduction band of H-(STO / SnO2) composite and in turn to the adsorbed oxygen molecule. The actual life time of singlet state is ̴ 10-9 s and the triplet state is ̴ 10-5 s. The process of electron trapping either by oxygen triplet or by Fe3+ ion in the hemin molecule (in the presence of H2O2) reduces the rate of recombination of photo generated charge carriers.