Development of LaFeO3 photocatalyst synthesized from soluble bio-organic substances for abatement of wastewater pollutants

In recent years, scientific research has been directed towards environment protection, because of increasing pollu-tion problems. For this reason, it is necessary to find new eco-friendly synthesis methods for materials manufacture, optimize technologies for energy production from renewable sources, remedy the already polluted waters and soils and solve wastes accumulation problems by recycling. The present work concerns the production and characterization of LaFeO3, a perovskite-type oxide with photo-catalytic properties activated by visible light. The oxide was synthesized by an auto-combustion method [1] using soluble bio-organic substances (SBO) extract-ed from composted urban wastes [2]. In this synthesis SBO replaced the traditional citric acid, as fuel, templating and chelating agents, while metal nitrates represented metal sources and oxiders. The synthesis parameters (such as pH, fuel-to-metal cations ratio and reducers-to-oxidizers ratio) were optimized and SBO (as they are or treated in order to remove ashes) were employed to test how they can affect the synthesis products. Also the effect of inorganic residues present in SBO species and found in perovskite oxides was evaluated. The morphologic, structural and chemical characterization of the samples was carried out by means of X-Ray Diffraction combined with Rietveld refinement, Scanning and Transmission Electron Microscopies, gas-volumetric N2 uptake at 77 K and FTIR spectroscopy. All samples showed 5-10 m2/g of specific surface area and limited mesoporosity, but a sonication treatment allows to largely increase these values causing the opening of closed porosities formed during the auto-combustion process, as already evidenced in previous works [3,4]. LaFeO3 samples were used as photo-catalysts for the abatement of two model contaminants: Crystal Violet, a cationic dye, and 4-methylphenol, a representative phenolic compound that could be found in wastewaters. In the first case, pollutant abatement reached 100% of yield at suspension pH of 9.8, whereas the photo-degradation of 4-methylphenol was less efficient and greatly influenced by pH, with abatement yield from 10% at pH=8 up to 33% at pH=12. These data suggest a different action mechanism of the photo-catalyst towards the two substrates. In particular different interactions between catalyst and substrates can be considered: in the case of Crystal Violet, a direct interaction between photo-catalyst reactive oxygen anionic species and the cationic dye could occur, whereas in the case of 4-methylphenol the interaction of the substrate with the catalyst is favored at pH=12, i.e. when the phenate anionic form is preponderant: in this situation the anionic form of the pollutant can approach the catalyst surface, favoured by the interaction with the cationic Fen+ and La3+ species of perovskite material. References 1 F. Deganello, G. Marcì, G. Deganello, J. Eur Ceram. Soc., 29 (2009) 439–450. [2] E. Montoneri, D. Mainero, V. Boffa, D.G. Perrone, C. Montoneri, Int.J.Global Environmental Issues, 11 (2011) 170. [3] G. Magnacca, G. Spezzati, F.Deganello, M. L. Testa, 2013, RSC Adv. 3 (2013), 26352-26360. [4] S. Jabariyan, M. A. Zanjanchi, Ultrason. Sonochem. 19 (2012) 1087–1093.