Improvement of the photocatalytic activity of CeO2 on the degradation of chlorophenolic compounds obtained by solution combustion synthesis (SCS). Effect of urea as fuel

This work presents a detailed study to determine the optimal urea content in the synthesis of CeO2 by the solution combustion method and thus obtain the highest photocatalytic activity in the degradation of phenolic compounds. Four CeO2 with different molar ratios urea:Ce(IV) = 0:1, 2:1, 4:1, and 7:1 were synthesized. The synthesized oxides were evaluated in the photocatalytic degradation of 3-chlorophenol, 4-chlorophenol, and 2,4dichlorophenol using UV light. The synthesized materials were characterized by XRD, Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, FTIR spectroscopy, N2 physisorption, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. Raman characterization showed that using urea as fuel favors the formation of oxygen vacancies, increasing up to the urea:Ce(IV) = 4:1 ratio. Photoluminescence studies indicated a decrease on the recombination of photogenerated charges when the oxides are synthesized with urea. The CeO2 synthesized without urea showed 26.6% degradation of 3-chlorophenol, which increased up to 73.6% when it was synthesized with urea. The photocatalytic activity improved mainly due to a higher content of oxygen vacancies and lower recombination of the photogenerated charges. The synthesis method used led to the formation of CeO2 with improved physicochemical properties, so its implementation in the synthesis of other metal oxides and the use of other fuel agents is of great interest for its investigation.