Lanthanum orthoferrite as photocatalyst prepared using sol-gel method for oily wastewater treatment

Abstract

Lanthanum orthoferrite (LaFeO3) is the perovskite type of photocatalyst that has potential to treat oily wastewater. Compared to better-known titanium dioxide (TiO2), LaFeO3 has been found to have a smaller band gap. The key purpose of this study was therefore to manipulate the physicochemical properties of LaFeO3 in order to enhance the degradation of oily wastewater by calcination heat treatment. Synthesis of the photocatalyst via the sol-gel route produced positive result. The precursor and LaFeO3 were characterized using X-ray diffraction for crystallinity test, thermogravimetric analysis and differential thermal analysis for thermal decomposition, ultraviolet- visible spectroscopy for optical properties, Fouriertransform infrared spectroscopy and Brunauer-Emmett-Teller, BET for surface area and field emission scanning electron microscope (FESEM) for surface morphology analysis. LaFeO3 was calcined at different temperature ranging from 500-900°C in two hours. Using glucose as chelating agent, LaFeO3 calcined at 600°C started to have a complete crystal structure. Sharper and stronger peak indicated greater crystallization with increasing calcination temperature, where crystallite sizes of 7.29 nm, 11.55 nm, 12.60 nm and 15.43 nm were obtained for samples calcined at 600 to 900°C. FESEM images revealed that samples calcined at 600°C appeared to be in porous and regular shape, forming a large network system with smaller particles size and higher surface area compared to samples calcined at higher temperature. The BET surface areas for the samples were 3.89 m2/g, 15.68 m2/g, 6.43 m2/g, 4.63 m2/g, and 2.40 m /g at the aforementioned calcination temperature intervals. The perovskite photocatalyst calcined at 600°C was thus chosen as the finest photocatalyst to undergo photocatalytic study. This LaFeO3-600 had the most outstanding surface area (15.68 m /g) with the lowest band gap value (1.88 eV) and smallest crystal size (7.29nm) compared to the others. Photocatalytic activity was conducted for 180 minutes where the first 30 minutes were for adsorption and desorption. The effects of the initial concentrations under visible light irradiation have been studied for 150 minutes and the findings indicate that the degradation efficiency were 70 %, 80 % and 65 % for concentrations of 1000 ppm, 10000 ppm and 20000 ppm respectively. Less than 5% was removed under visible light irradiance (photolysis), showing the stability of the pollutant. In conclusion, the perovskite-based photocatalyst LaFeO3 was successfully prepared via the sol-gel method, where LaFeO3-600 demonstrated the highest efficiency in degrading synthetic oily wastewater by up to 80% in 180 minutes.