The detection function of a sensing material is dependant of a high surface to volume ratio, but also to the exposed crystallographic facets. It should then be possible to tailor the reactivity and sensitivity of the sensing materials by controlling their shape and size, for a given composition [1]. We already showed that the composition of the cobalt ferrite CoxFe3-xO4 influences their catalytic properties [2]. In order to understand and control the gas sensing properties as well as the catalytic properties, we synthesized cobalt ferrites as nanoparticles with various shapes and sizes. Nanoparticles with specific shapes allow to study the influence of the cristallographic facets, hence the cation distribution at the surface, in the gas interaction with the particles.
By solvothermal methods, we synthesised CoFe2O4 nanooctahedra (Fig. 1) and nanocubes (Fig. 2). Conventional TEM coupled with EDS, high resolution TEM, environmental TEM, were carried out in order to understand the mechanisms involved in the growth of the grains and their reaction under gas. Octahedron-like nanoparticles of CoFe2O4 were submitted to H2 -O2 cycles, at ambient temperature, under 1mbar gas pressure in an TEM 300 kV. The {100} facets extended which led to truncated octahedra and the {111} facets became more rounded under oxygen. The phenomenon was reversible and rounded particles under O2 became facetted under H2 (Figure 3). These CoFe2O4 nanooctahedra exhibit a high sensibility to oxidative gases like NO2 at low gas concentration, and the shape effect on sensibility was clearly demonstrated.The study of nanocubes under oxydo reduction cycles is under progress.
[1] C. Wang, L. Yin , L. Zhang, D. Xiang and R. Gao, Sensors 2010, 10, 2088-2106
[2] L. Ajroudi,S. Villain,V. Madigou,N. Mliki,Ch. Leroux, J. Cryst. Growth 312 (2010) 2465–2471.
[3] A. L. Lopes-Moriyama, V. Madigou, C. Pereira de Souza, Ch. Leroux Powder Tech., 256,482-489 , 2014
Acknowledgments :
This work was done in the general framework of the CAPES COFECUB Ph-C 777-13 french – brazilian cooperation project.
Figures:

Figure 1 : Cobalt ferrite nanooctahedron

Figure 2 : Cobalt ferrite nanocube

Figure 3 : Shape changes of a cobalt ferrite ferrite nanoparticle during a oxydo-reduction cycle
To cite this abstract:
Andre-Luis Lopes-Moriyama, Indira Aritana Fernandes de Medeiros, Veronique Madigou, Madjid Arab, Carlson Pereira de Souza, Suzanne Giorgio, Christine Leroux; Gas sensing properties of cobalt ferrite nanooctahedra and nanocubes. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/gas-sensing-properties-of-cobalt-ferrite-nanooctahedra-and-nanocubes/. Accessed: December 4, 2023« Back to The 16th European Microscopy Congress 2016
EMC Abstracts - https://emc-proceedings.com/abstract/gas-sensing-properties-of-cobalt-ferrite-nanooctahedra-and-nanocubes/