TiO/LaFeO Composites for the Efficient Degradation of Benzoic Acid and Hydrogen Production.

LaFeO/TiO composites were prepared in the range 0-12.2 wt% of LaFeO, characterized, and tested for both benzoic acid (BA) and 4-methoxycinnamic acid (MCA) degradation in aqueous solution, and hydrogen evolution. The preparation method was via ball-milling without thermal treatment. The composite materials presented agglomerates of LaFeO with an average size from 1 to 5 μm, and the TiO powder was well dispersed onto the surface of each sample. They showed varying activities for BA degradation depending on composition and light wavelength. The 6.2 wt% and 12.2 wt%-LaFeO/TiO composites exhibited the highest activity under 380-800 nm light and could degrade BA in 300 min at BA concentration 13.4 mg L and catalyst 0.12 g L. Using a 450 nm LED light source, all composites degraded less than 10% of BA, but in the presence of HO (1 mM) the photocatalytic activity was as high as 96% in <120 min, 6.2 wt%-LaFeO/TiO composite being the most efficient sample. It was found that in the presence of HO, BA degradation followed first order kinetic with a reaction rate constant of 4.8 × 10 s. The hydrogen production rate followed a classical volcano-like behavior, with the highest reactivity (1600 μmol hg at 60 °C) in the presence of 3.86%wt- LaFeO/TiO. It was also found that LaFeO/TiO exhibited high stability in four recycled tests without losing activity for hydrogen production. Furthermore, a discussion on photogenerated charge-carrier transfer mechanism is briefly provided, focusing on lacking significant photocatalytic activity under 450 nm light, so p-n heterojunction formation is unlikely.