Surfactant effects on the synthesis of porous cerium oxide from a type IV deep eutectic solvent

Abstract

In this work we present a novel, low temperature and green method for atom-efficient solvothermal synthesis of crystalline, micelle templated cerium IV oxide (ceria) from a type IV deep eutectic solvent (DES) comprising a hydrated cerium containing metal salt, cerium(III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O), and a hydrogen bond donor, urea, in a molar ratio of 1 : 3.5. Self-assembled nanostructures of ionic and non-ionic surfactants have been recently reported in a cerium nitrate hexahydrate : urea DES [Manasi et al., J. Chem. Phys., 2021, 155, 084902], which can be exploited to produce nano-templated ceria from these solution. In this work, we have used high concentration (20% w/w) solutions of C-12 and C-16 alkyl chain length cationic surfactants (C_nTAB and C_nTANO₃) and C-16 alkyl chain length non-ionic surfactant BrijC₁₀ in the DES to alter the porosity of the cerium oxide produced. The characterisation of the cerium oxide has been carried out using SEM/TEM, N₂ sorption, SAXS and TPR to understand and quantify the nature of the crystallinity, morphology and porosity along with CO oxidation for the catalytic activity of the material. The cerium oxide produced by this method has porosity on the 2–5 nm scale and a BET surface area between 40 and 150 m² g⁻¹ depending on the amount and type of surfactant. Materials prepared using halide-free cationic surfactants show superior catalytic activity and low activation energies along with high porosity and present potential for improved ceria performance in many industrial applications.