Highly robust La1-xTixFeO3 dual catalyst with combined photocatalytic and photo-CWPO activity under visible light for 4-chlorophenol removal in water

Abstract

A highly robust Ti-substituted LaFeO3 dual catalyst was synthesized via a facile Pechini sol-gel route using a dried amorphous sol-gel titania as titanium source and a final calcination at 800 °C that enabled solid-solid diffusion of titanium atoms within the perovskite network. Using an amorphous precursor instead of crystallized titania nanocrystals increased the Ti → La atomic substitution degree in the crystalline network from 5 at% to 11 at%, together with a strong increase in the catalytic activity. The partially substituted La1-xTixFeO3 catalyst with a 11 at% substitution degree allowed pure heterogeneous surface reactions to take place under pure visible light (λ > 420 nm), with an increase in the catalyst robustness by more than two orders of magnitude compared to the unmodified LaFeO3 counterpart, evidenced by the absence of any Fe release, the structural stability of the substituted catalyst and the absence of any loss of catalytic activity with test cycles. Further, the strategy of combining both photocatalysis and H2O2-mediated heterogeneous photo-Fenton advanced oxidation processes within one single heterogeneous catalyst allowed the dual La1-xTixFeO3 catalyst to simultaneously take advantage from the higher reaction rate of photo-Fenton and from the higher mineralization yield of photocatalysis in water treatment. As a result, the dual 11 at% Ti-substituted La1-xTixFeO3 catalyst clearly outperformed its unmodified LaFeO3 counterpart and led to a complete mineralization of the 4-chlorophenol substrate under pure visible light, with strongly enhanced H2O2 decomposition, 4-chlorophenol and TOC conversion rates. Finally, the activity of the La1-xTixFeO3 catalyst under visible light contributed significantly to its overall activity obtained using the full solar spectra.