Supplementary data
Synthesis, characterization and magnetic properties of ultrafine
Co3O4 octahedra
Y.H. Chen,1) J.F. Zhou,1) D. Mullarkey,1) R. O’Connell,1) W. Schmitt,2) M.
Venkatesan,1) M. Coey, 1), H.Z. Zhang1,1)
1School
of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, Dublin
2, Ireland 2School of Chemistry, Trinity College, Dublin 2, Ireland
The crystal structures of typical products were characterized by XRD, as shown in Fig. S1.
The recorded diffraction peaks of the starting material (precursors or after reaction of 0 min)
contain two phases. The trigonal β-Co(OH)2 phase (JCPDS 30-0443) was the predominant
phase, plus a small amount of rhombohedral CoOOH phase (JCPDS 73-1213), as shown in
Fig. S1a using blue triangular symbols. After reaction for 30 minutes (Fig. S1b), the dominant
phase is rhombohedral CoOOH phase with some residual Co(OH)2 phase (black square
symbols indexed). After a reaction for 6 hours (Fig. S1c) in ammonia solution, all products
were found to be transformed to the spinel Co3O4 phase (JCPDS 42-1467). XRD results
indicate that the oxidation follows a process from Co(OH)2 to CoOOH then to Co3O4 at
temperature of 120 oC.
1
Electronic mail: hongzhou.zhang@tcd.ie
Co3O4
533
511
422
440
CoOOH
2
400
222
220
Co(OH)
20
30
40
50
60
103
201
(a)
111
110
100
102
101
110
015
102
(b)
101
012
100
001
003
(c)
001
Intensity (a.u.)
111
311
Supplementary data
70
80
2(degree)
Fig. S1. XRD patterns of (a) starting material, (b) reaction after 30 min and (c) reaction after
6 h.
Figure S2a-S2c shows typical SEM images of products with varied reaction time in the
second hydrothermal oxidation stage. The starting materials are nanoplates with diameters of
80-120 nm and thicknesses of 20-40 nm, as shown in Fig. S2a. After a reaction of 30 min with
ammonia, approximately 5-8 % of the products were 10-20 nm particles, though most of the
products remained as hexagonal plates with a rough border (Fig. S2b). After reaction for 6
hours, most of the products appear as octahedral shapes with diameters between 20-40 nm.
These products were further analysed using TEM. A typical TEM image of the starting
Co(OH)2 nanoplate is displayed in Fig. S2d. The largest facet of the plate-like particle is its
close-packed plane of trigonal β-Co(OH)2 as shown in the electron diffraction pattern (EDP)
in Fig.S2g. After undergoing a reaction in dilute ammonia solution at 120 oC for 30 minutes,
the products had become a mixture of plate-like and rhombohedral particles as shown in Fig.
S2e. The corresponding EDP shows a rhombohedral CoOOH structure as indexed in Fig. S2h.
Supplementary data
Weak and diffuse diffraction spots/rings of the EDP indicate a large amount of amorphous
material. After reacting in the autoclave for six hours, particles with octahedral structures were
formed completely as shown in Fig. S2f. The corresponding EDP in Fig. S2i shows sharp
rings with dots and suggests polycrystalline particles with spinel Co3O4 structure. Contrast
from high angle annular dark field (HAADF) images of the octahedral particles a solid
octahedral structure. It is also noted that all octahedral particles in our experiments (about 810 particles randomly selected) are defect-free, according to HRTEM measurements.
Fig. S2. Typical SEM, TEM images and EDP patterns from products after reaction in dilute
ammonia solution (2.5 wt %) at 120 oC for (a, d, g) 0 min (starting materials), (b, e, h) 30 min,
and (c, f, i) 6 h.