Effects of the agglomeration state on the Raman properties of Co₃O₄ nanoparticles

Abstract

The features of the Raman spectra of Co 3 O 4 30-nm nanoparticles depend strongly on their agglomeration state. When measured at low incident laser power, the spectrum of isolated nanoparticles corresponds to that found in bulk materials, whereas the agglomerated nanoparticles present a clear red-shift and broadening of the Raman bands. On the other hand, when measured at even lower power, both agglomerated and isolated nanoparticles show the same spectrum of microscopic particles. These effects have been studied by variations of the 532-nm laser power and the environmental temperature. The thermal dependence of Raman spectra of agglomerated nanoparticles is different to that of isolated nanoparticles but is comparable to the one of bulk material. The different behaviour of the nanoparticles at different agglomeration state is associated to the transmission of phonons among the particles. On the other hand, an increase of the laser power causes a larger number of acoustic phonons, producing a variation of the vibration anharmonicity of the nanoparticles. This increase is more pronounced in the agglomerated nanoparticles, due to the transmission of phonons, causing a much intense modification of the Raman spectrum produced by the laser power. These results clearly indicate that the agglomeration state of the nanoparticles affects their Raman properties. Figure 2. MicroRaman spectroscopy of Co 3 O 4 microparticles, Co 3 O 4 nanoparticles, Co 3 O 4 dispersed nanoparticles, AlCo1 at a power laser excitation of a) 0.3 mW and b) minimun power laser to acquire the Raman spectra. Al 2 O 3 used as substrate is marked by squares.

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

“…It is clear that under shorter treatment time (≤12 h), an increase of treatment time produces a blueshift of the A 1g mode. For a 24‐h heat treatment, the Raman shift of A 1g mode decreases to 685.2 cm –1 , which is comparable to 686 cm –1 of Co 3 O 4 powders with an average size of 2 μm . With longer reaction time to 48h, A 1g mode increases again to higher wave number, but still lower than that of the bulk Co 3 O 4 crystal .…”

Solvothermal Systhesis of Size‐Controlled Porous Co3O4 Nanostructure Catalyst and Their Catalytic Properties for VOCs Removal

“…Raman spectroscopy was a powerful tool to rapidly and non‐destructively verify the intrinsic physical properties . The Raman spectra of Pd/Co 3 O 4 powder was showed in Figure , and a clear variation in the Raman shift and full width half maximum (FWHM) between the different samples were observed .…”

Enhanced Oxygen Reduction Stability and Activity by Co and N (or O) Interaction in CoO on N‐Doped Carbon Prepared through Spray Pyrolysis

“…In particular, the peaks exhibit a negative shift to ca. 13 cm −1 for CoO/NCs (see the inset), which is attributed to change in the electronic structure derived from higher insertions of nitrogen atoms in the carbon structure or lattice contraction of CoO caused by strong chemical interaction between cobalt oxide and NC at the surface of the catalysts ,…”

“…13 cm À1 for CoO/NCs (see the inset), which is attributed to change in the electronic structure derived from higher insertions of nitrogen atoms in the carbon structure [16] or lattice contraction of CoO caused by strong chemical interaction between cobalt oxide and NC at the surface of the catalysts. [37,38] X-ray photoelectron spectroscopy (XPS) spectra for the CoO/NC2 catalysts were obtained to determine their elemental composition and chemical state on the surface of the catalysts. As depicted in Figure 5a, the binding energy in the Co 2p band spectrum shows two main peaks, attributed to Co 2p 1/2 and Co 2p 3/2 at 797.0 eV and 780.9 eV, which is designated as Co 2 + (2p 1/ 2 , 780.5 eV and 2p 3/2 , 797.7 eV), CoÀO (796.6 eV) and strong CoÀN (782.8 eV) characteristics, while the second doublet pair at 802.6 eV and 786.2 eV are attributed to the shake-up satellite that represents CoO in the CoO/NC2 composite.…”