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

Zerin Yeşil Acar, Meltem Asiltürk, and Ertuğrul Arpaç

Department of Dentistry Services, Vocational Schools, Burdur Mehmet Akif Ersoy University, Burdur, Turkey

Received: 11 October 2021 Accepted: 5 April 2022

Abstract:

Cerium dioxide (CeO₂) nanoparticles were synthesized by sol–gel-based hydrothermal method. During synthesis, cerium(III) chloride heptahydrate (CeCl₃⋅7H₂O) was used as cerium source; ammonia (NH₃), tetraethylammonium hydroxide (C₈H₂₁NO), tetra-n-butyl ammonium hydroxide (C₁₆H₃₇NO), benzyl trimethyl ammonium hydroxide (C₁₀H₁₇NO) and benzyl triethyl ammonium hydroxide (C₁₃H₂₃NO) ionic liquids were used as catalyst, deionized water (H₂O) was used as hydrolysis agent and solvent, and 2-aminopropanoic acid (C₃H₆NO₂) was used as stabilizing agent. The nano-CeO₂ 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 CeO₂ crystals were analyzed as cubic fluorite structure. The full width at half maximum (FWHM) values referring to [111] lattice planes of CeO₂ 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-CeO₂ 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 CeO₂ 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

Keywords: Ionic liquid; Quaternary ammonium hydroxide; Dispersible CeO2; Sol–gel; Hydrothermal; Nano-ceria

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02217-w

Chemical Papers 76 (8) 4927–4939 (2022)