Fast Synthesis of CeO₂ Nanoparticles in a Continuous Microreactor Using Deep Eutectic Reline As Solvent

Abstract

Hydrothermal methods have conventionally enabled the synthesis of a wide range of nanomaterials. However, these simple, single-step syntheses lack scalability due to the need of high temperatures and autogenous pressures to enable the dissolution of reagents and crystallization of the product. In this work, we demonstrate for the first time fast continuous synthesis of ceria nanoparticles at moderate conditions through the combination of the deep eutectic solvent reline (an eutectic mixture of choline chloride and urea) as reaction medium and the high heat and mass transfer rate offered by microreactors. Almost 100% yields are obtained within 100 s of residence time at 160 °C, with some conversion achieved even at temperatures as low as 120 °C. Such rapid synthesis takes place thanks to the molecular structure of the solvent which facilitates the fast nucleation of cerium oxycarbonate as an intermediate product. As expected in a kinetically controlled system, pressure and initial cerium concentration have negligible effects on the yield obtained. The rapid reaction, the cheap, benign, and environmentally friendly solvent, and the lack of additional additives in this work opens the door to sustainable large-scale continuous synthesis of ceria nanoparticles as well as other nanostructured materials.

Ionic liquids and deep eutectics as a transformative platform for the synthesis of nanomaterials

“…218 More recently, this approach has been adapted by Exposito et al to take advantage of the high heat-and masstransfer conditions offered by continuous flow reactors. 308 This yielded quantitative yields of nanostructured CeO 2 with short residence times and relatively mild synthesis conditions, even under conventional heating. Please do not adjust margins Please do not adjust margins crystalline (high-temperature, high water fraction) iron oxide nanoparticles.…”

“…217 More recently, this approach has been adapted by Exposito et al to take advantage of the high heat- and mass-transfer conditions offered by continuous flow reactors. 308 This approach allowed quantitative yields of nanostructured CeO 2 , even with short residence times and conventional heating, overall forming a relatively mild set of synthesis conditions.…”

Recent Advances in the Synthesis of Inorganic Materials Using Environmentally Friendly Media

“…Among all the literature, although reline still plays an important role (since it features in approximately one out of four studies (80/343) on both traditional liquid-phase syntheses and electrodeposition), the interest in new methods has grown significantly and NADESs are becoming more and more important every day. Among the newest and most interesting investigations using “traditional” ChCl:urea, the latter DES was used: in the field of metal oxides synthesis, to prepare nontoxic photoluminescent SnO nanoparticles for cell imaging [ 87 ], in the solvothermal synthesis of iron oxide from iron monitored in operando by SANS and EXAFS [ 88 ], in the synthesis of ceria nanoparticles in a continuous microreactor [ 89 ], to conjugate Fe 3 O 4 nanoparticles on graphene oxide [ 90 ], to obtain NixCo 2 -x(OH) 3 Cl nanoparticles with an optimal Ni/Co ratio suitable for use as cathodic materials [ 91 ], as a solvent and nitrogen source for preparing fluorescent carbon dots [ 92 ], and for the synthesis of titanomagnetite NPs with enzyme-like activity [ 93 ]. Finally, reline was also used very recently as a template to prepare polyacrylates/nanohydroxyapatite scaffolds and polycrystalline sub-nanometrical chalcogen nanoparticles (SeTe) with high activity towards tumor cell lines [ 94 ].…”

Deep Eutectic Solvent-Mediated Synthesis of Bullet-Shaped Cerium Zinc Oxide and Sheet-Like Cerium Zinc Hydroxide Nitrate: Colorimetric and Fluorometric Detection of Pyrophosphate Ions

“…Unlike other solvents, deep eutectic solvents (DESs) as an emerging novel type of ionic liquids possess many useful characteristics such as significant ionic conductivity, insignificant volatility, excellent polarity and appreciable thermal stability, biodegradability, non-toxicity, and harmless features to the environment. − Therefore, DESs have been increasingly utilized as another alternative to hazardous solvents. In addition, several works have suggested that DES can play a pivotal role in initiating the formation and the growth of nanomaterials, directing to the target morphology and crystallography . DESs were also found to serve as templates, reagents, or shape-directing agents for the preparation of nanomaterials. ,, …”

“…In addition, several works have suggested that DES can play a pivotal role in initiating the formation and the growth of nanomaterials, directing to the target morphology and crystallography. 43 DESs were also found to serve as templates, reagents, or shape-directing agents for the preparation of nanomaterials. 8,44,45 In our previous works, we demonstrated that basic DES could serve as a green solvent for manufacturing different materials with more improved properties.…”