Influence of the solid titanium source on the activity of La1_xTixFeO3 photo-CWPO catalysts under UV-A light

In the search for more efficient low-temperature catalysts able to oxidise biorecalcitrant pollutants in water, the selective substitution of La3+ by Ti3+ cations was reported to boost the UV-A light driven activity of LaFeO3 orthoferrites as H2O2-mediated photo-CWPO catalysts. La1_xTixFeO3 catalysts with 0 < x < 0.11 were obtained by a modified Pechini sol-gel route via the addition of a solid source of titanium during the synthesis. By using a span of crystallized and amorphous TiO2, the influence of the titanium source on the substitution rate in the orthoferrite network and on the performances of the catalysts under UV-A light was demonstrated using the degradation of 4-chlorophenol as test reaction. The amorphous content of the TiO2 precursor is proposed to be the key factor driving the substitution of La3+, the largest substitution of 11 % being obtained using a dried sol-gel TiO2 precursor. We suggest that the substitution proceeds during the thermal treatment via a solid-solid diffusion between TiO2 and the amorphous LaFeO3 before it crystallises. The catalyst robustness was influ-enced by the TiO2 nature. Small size Ti-LaFeO3 crystallites strongly lowered or blocked the Fe release, while no improvement was observed for large size crystallites vs. the pristine material, what was associated to a poor homogenization of the titanium in the network. We showed that the mineralization activity was proportional to the substitution rate of La1_xTixFeO3 catalysts, while a similar relationship could be drawn for the degradation activity only in the case of highly robust catalysts with pure heterogeneous surface reactions.

Automated summary

In the search for more efficient low-temperature catalysts, the substitution of La3+ by Ti3+ cations in LaFeO3 orthoferrites was found to enhance the UV-A light driven activity. La1_xTixFeO3 catalysts were synthesized using a modified Pechini sol-gel route with a solid source of titanium. The amorphous content of the TiO2 precursor played a crucial role in the substitution process. The substitution was proposed to occur via solid-solid diffusion between TiO2 and amorphous LaFeO3 during thermal treatment.