Radiation Chemistry Provides Nanoscopic Insights into the Role of Intermediate Phases in CeO₂ Mesocrystal Formation

Abstract

The role of intermediate phases in CeO 2 mesocrystal formation from aqueous Ce III solutions subjected to g-radiation was studied. Radiolytically formed hydroxyl radicals convert soluble Ce III into less soluble Ce IV .T ransmission electron microscopy( TEM) and X-rayd iffraction studies of samples from different stages of the process allowed the identification of several stages in CeO 2 mesocrystal evolution following the oxidation to Ce IV :(1) formation of hydrated Ce IV hydroxides,s erving as intermediates in the liquid-to-solid phase transformation;(2) CeO 2 primary particle growth inside the intermediate phase;( 3) alignment of the primary particles into "pre-mesocrystals" and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of "mineral bridges". Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.

Non-classical crystallization of CeO2 by means of in situ electron microscopy

“…3b). 12 Moreover, the primary particles are found to mutually align in highly ordered structures (see Fourier transformation in Fig. S2†).…”

“…3b in ref. 12). This is quite surprising given the fact that for radiation synthesis of metal nanoparticles, the particle size displays strong dose rate dependence.…”

“…A fairly recent example of radiation induced synthesis of a nanomaterial utilizing the oxidative route is the production of CeO 2 from CeCl 3 aqueous solution. 12 In this process, hydroxyl radicals formed upon radiolysis of water, oxidize highly soluble Ce 3+ to sparsely soluble Ce 4+ . The latter forms hydrated Ce( iv ) hydroxides, which serve as intermediates in the liquid-to-solid phase transformation.…”

“…In this work we explore a non-classical crystallization route using in situ LP-EM. We choose the formation of CeO 2 mesocrystals as a model process because of several reasons: (1) it allows us to use a water solution of a Ce 3+ salt without any organic surfactants/additives; (2) radiolytic oxidation has been relatively little studied both in a LP-EM and upon gamma-radiation, and the formation mechanism in LP-EM conditions is not clear; (3) we compare a radiolytic process in a LP-EM confined cell and in a large volume of a Gamma-Cell 12 thus enabling a unique study of the influence of the irradiation dose rate on nucleation and crystal growth by combining bulk and nanoscale approaches. Furthermore, we take advantage of the versatile irradiation conditions provided in LP-EM to study the influence of induced concentration gradients on the crystal growth during the radiolytic oxidation in solution.…”

Isolating Single Sn Atoms in CuO Mesocrystal to Form Ordered Atomic Interfaces: An Effective Strategy for Designing Highly Efficient Mesocrystal Catalysts

“…[2][3][4][5][6] Metal oxide mesocrystals (MOMs) have demonstrated outstanding performances, e.g., in lithium-ion batteries, [7] gas sensing, [4,8] photocatalysis, [9] and biomedicine, [10] much better than those of the conventional single crystal and polycrystal systems. However, most reported MOMs contain only a single component, such as TiO 2 , [7,11] CuO, [5,12] ZnO, [13,14] Fe 2 O 3 , [15] and CeO 2 , [16,17] and there are rare reports on the synthesis and application of metal oxide mesocrystal composites (MOMCs), especially in industrial catalysis. Several Tuning the electronic structures of mesocrystals at the atomic level is an effective approach to obtaining unprecedented properties.…”