Shape- and size-controlled synthesis of ligand free CeO2 nanoparticles and their catalytic performances: From nanospheres to nanostars

Among the rare earth compounds CeO2 has become a technologically important material widely used in industrial applications and manufacturing processes[1]. Colloidal synthesis of nanoparticles (NPs) has attracted great interest... [ view full abstract ]

Among the rare earth compounds CeO2 has become a technologically important material widely used in industrial applications and manufacturing processes[1]. Colloidal synthesis of nanoparticles (NPs) has attracted great interest due to possibility of a precise control over size and shape which would allow controlling the exposed crystallographic facets and hence the catalytic performance. Here we report on the synthesis of ceria NPs with control over size and shape resulting from a branching process. This process results from a kinetically controlled overgrowth due to the presence of surfactants that display preferential adsorption on particular crystallographic facets thus tuning the length and width of branches.
CeO2 NPs were obtained through the thermal decomposition of cerium precursor in the presence of oleic acid, oleylamine, alkanediol and octadecene. Adjusting the experimental conditions allows us synthesizing NPs with different level of branching and shape evolving from spheres, flowers, cubes, kites and stars (Figure 1) all of them within the 7 to 45 nm size range. Some synthetic parameters allow tuning the final anisotropic degree of the NPs structure by controlling the branching events and growth. Tuning the amount of alkanediol molecules results on a shape evolution from irregular rombohedral NPs to branched structures. For the first time on ceria, organic ligands were replaced by shorter ones (Amino acids) or by inorganic ligands (Oxo- or polyoxometalates) which offer the advantage to stabilize NPs in polar solvents and decrease the steric hindrance of the organic once towards molecule absorbance[2,3]. The nanocryctals’ surface was functionalized through the solution phase ligand exchange in acidic media with further exposing them to amino acids or oxometalates. This mild exchange process allows to keep constant the NPs’ structure compare to other more aggressive treatments as for instance calcination. Finally, CO-CO2 conversion experiments were performed in order to test ceria branched structures as novel catalyst.
Figure 1. (a)HRTEM micrograph of CeO2 octapod. (b)Reconstruction of the lattice by inverse Fourier transformation. (c)FFT obtained from the selected area.
[1]C.Sun, et al, Energy & Environmental Science 2012, 5, 8475.
[2]J.D.Roo, et al, Langmuir, 2016, 32 (8), pp 1962.
[3]J.Huang, et al, ACS Nano 2014, 8(9), 9388.