Ce₂O₃ and TiO₂ p-n heterojunction for enhanced degradation of p-nitrophenol under visible light.

Abstract

A sol–gel method is used to synthesize TiO2, using few organic products. In order to increase the photocatalytic activity in the near visible range (395 nm), cerium is used as a dopant at various concentrations ranging from 0.03 mol% to 4.40 mol%. The addition of cerium leads to the formation of p-n heterojunctions between Ce2O3 and TiO2, multiplying by 2 (under UV–visible light) or 2.6 (under visible light) the photocatalytic efficiency of the composite material with the best dopant amount, i.e. 0.06 mol% of cerium. X-ray diffraction showed the formation of TiO2 in its anatase form, while nitrogen adsorption/desorption isotherms showed changes in specific surface area as a function of the percentage of cerium added. The presence of cerium (III) in the sample is confirmed by XPS and the amount is determined quantitatively by ICP. DRUS analysis highlights the difference in bandgap caused by the Ce2O3 incorporated into the sample. In order to compare the different photocatalysts obtained, the degradation of p-nitrophenol is tested in their presence in water under UV light as well as a wavelength close to the visible range, i.e. 395 nm. Finally, based on the results obtained by electron paramagnetic resonance, a photoactivation mechanism of the mixed oxide is proposed