Bottom-up and top-down approaches to the synthesis of 2D gadolinium-doped cerium oxide (CGO) at low temperature

Reference Presenter Authors
06-239 Leticia Poras Reis de Moraes Moraes, L.P.(Instituto de Pesquisas Energéticas e Nucleares); Marani, D.(Universidade Federal do ABC); Machado, M.F.(Instituto de Pesquisas Energéticas e Nucleares); Rodrigues, L.N.(Instituto de Pesquisas Energéticas e Nucleares); Fonseca, F.C.(IPEN-CNEN/SP); Esposito, V.(Technical University of Denmark); Sun, Z.(Queensland University of Technology);

In the last decades, 2D nanosheets have been studied for their physicochemical properties, which are different from the bulk of the original material or any other nanostructure, therefore a challenging and exciting area of nanomaterial synthesis. Nanosheets can be used in the production of low cost electro-optics, stable high-performance batteries, high performance catalysts, etc. In general, there are two main approaches in the synthesis of nanomaterials: top-down and bottom-up. A top-down approach starts from a macroscopic material, which undergoes exfoliation or grinding to reduce its size to a nanometric scale. However, this type of process induces defects, compromising its properties. In the bottom-up method the nanostructures are built molecule by molecule, resulting in a more homogenous and controlled material.

In this work, 2D nanostructures of gadolinium-doped cerium oxide (CGO) were synthesized by two simple and reproducible routes; both by aqueous precipitation induced by the hydrolysis of hexamethylenetetramine. The CGO materials synthesized were characterized by their composition, morphology and crystallographic characteristics. The combined experimental results indicated that different morphologies of 2D CGO can be obtained by controlling the synthesis parameters. The temperature of the reaction medium was decisive in the formation of a more homogeneous structure, establishing the optimum temperature to 10 ºC for the synthesis of nanosheets. The method of liquid exfoliation, with a solution of ethanol:water in an ultrasonic bath, was also established to obtain a suspension of nanosheets. Comparing the microscopic images of the materials synthesized by the top-down and bottom-up methods, it can be observed that the latter favours the formation of a more homogeneous nanostructure, leading to the obtention of exfoliated nanosheets with a shorter reaction and ultrasonic exfoliation time.