Preparation of ceria by combined sol–gel and hydrothermal method: insights from the effects of different bases on the particle size distribution

Cerium dioxide (CeO 2 ) nanoparticles were synthesized by sol–gel-based hydrothermal method. During synthesis, cerium(III) chloride heptahydrate (CeCl 3 ⋅7H 2 O) was used as cerium source; ammonia (NH 3 ), tetraethylammonium hydroxide (C 8 H 21 NO), tetra - n -butyl ammonium hydroxide (C 16 H 37 NO), benzyl trimethyl ammonium hydroxide (C 10 H 17 NO) and benzyl triethyl ammonium hydroxide (C 13 H 23 NO) ionic liquids were used as catalyst, deionized water (H 2 O) was used as hydrolysis agent and solvent, and 2-aminopropanoic acid (C 3 H 6 NO 2 ) was used as stabilizing agent. The nano-CeO 2 particles were characterized by several techniques X-ray diffractometer (XRD), particle size analyzer, Branauer–Emmett–Teller analyzer (BET), ultraviolet–visible spectrophotometer (UV–Vis), transmission electron microscope (TEM). XRD characterization confirms that CeO 2 crystals were analyzed as cubic fluorite structure. The full width at half maximum (FWHM) values referring to [111] lattice planes of CeO 2 indicate a decrease in crystallinity associated with different bases used during synthesis of particles. Small sized crystals were formed in weak ionization degree and branched structures. As the crystallite size decreases, both agglomeration and the hydrodynamic diameter increases as expected. The size distribution of nano-CeO 2 particles obtained by precipitation using different bases with a pH of 10 decreases from 25.92 to 20.57 nm. The size of nanoparticles prepared using ammonia at pH 9 and 8 are 15.60 and 9.50 nm, respectively. The most significant surface area change occurred in particles obtained using benzyl trimethyl ammonium hydroxide (BTMAH) and benzyl triethyl ammonium hydroxide (BTEAH). Such a significant reduction in surface area is believed to be due to the agglomeration or aggregation of particles with small crystallite size, resulting in smaller sized crystals as the alkyl group chain length and branching increase. These irregularities may result from the agglomeration and formation of large clusters observed by the TEM. The obtained CeO 2 nanoparticles are crystalline and can readily be dispersed in water without any additional processing or surfactant agent. Well-defined strong absorbance peak located at 200–800 nm was observed for all samples. The bandgap increases with the decrease in particle size, meaning that smaller particles exhibit better UV absorption. The fact that the particles obtained in the presence of BTMAH and BTEAH cut off longer wavelength proved that it is due to lower bandgap energies. Graphical abstract