Transition of chromium oxyhydroxide nanomaterials to chromium oxide: a hot‐stage Raman spectroscopic study

Abstract

The transition of disc-like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot-stage Raman spectroscopy. The structure and morphology of α-CrO(OH) synthesised using hydrothermal treatment were confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The Raman spectrum of α-CrO(OH) is characterised by two intense bands at 823 and 630 cm −1 attributed to ν 1 Cr III -O symmetric stretching mode and the band at 1179 cm −1 attributed to Cr III -OH δ deformation modes. No bands are observed above 3000 cm −1 . The absence of characteristic OH stretching vibrations may be due to short hydrogen bonds in the α-CrO(OH) structure. Upon thermal treatment of α-CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm −1 , which are attributed to Cr 2 O 3 . This hot-stage Raman study shows that the transition of α-CrO(OH) to Cr 2 O 3 occurs before 350 • C.

Electrochemical Investigation of the Hydrogen Evolution Reaction on Electrodeposited Films of Cr(OH)3 and Cr2O3 in Mild Alkaline Solutions

“…3. For increasing laser power, the peaks characteristic of Cr 2 O 3 [34][35][36][37][38] gain intensity, as already observed for nanoparticles of Cr 2 O 3 [33]. However, differently from the case of nanoparticles [33] the Raman spectrum of Cr 2 O 3 @Ti recorded with a laser power of 0.7 mW looks featureless, which could be attributed to the film here investigated being amorphous (see x-ray diffractogram in Supporting Information, Fig.…”

A micro‐Raman spectroscopic study of Cr(OH)3 and Cr2O3 nanoparticles obtained by the hydrothermal method

“…It is interesting to note that at these experimental conditions, the spectrum of as‐prepared nanoparticles shows only two broad signatures, peaked at approximately 850 and 530 cm −1 , while the spectrum of Cr 2 O 3 displays several intense signatures, the most prominent ones being at 305, 350, 551, 609 and ∼700 cm −1 . The first four of these have previously been attributed to the crystalline form of Cr 2 O 3 ,[] while the feature at ∼700 cm −1 has been assigned to the B 2 g ( ν a ) mode of a highly disordered CrO 2 surface. [] The broader signature observed at about 1390 cm −1 has been assigned to combinations and overtones and has previously also been reported by Li et al [] and Yang et al [] The signatures theoretically expected at 266 and 235 cm −1 have previously been observed at low temperatures only[] and were not detected in this work either.…”

“…The first four of these have previously been attributed to the crystalline form of Cr 2 O 3 ,[] while the feature at ∼700 cm −1 has been assigned to the B 2 g ( ν a ) mode of a highly disordered CrO 2 surface. [] The broader signature observed at about 1390 cm −1 has been assigned to combinations and overtones and has previously also been reported by Li et al [] and Yang et al [] The signatures theoretically expected at 266 and 235 cm −1 have previously been observed at low temperatures only[] and were not detected in this work either. It is an important note that the presence of seven Raman active modes, two A 1 g and five E g , is consistent with the corundum structure of Cr 2 O 3 that, as mentioned earlier, belongs to the D 3 d point group.…”

“…[] In line with our observations, these authors report phase transitions for the manganese oxide when using a laser power higher than 0.6 mW and could measure local temperature increases of at least 400 °C. In this context, it is interesting to recall some other recent works that have reported the transformation of CrO 2 into Cr 2 O 3 [] and of CrO(OH) into Cr 2 O 3 [] due to laser radiation and thermal treatment, respectively. That metals and metallic oxides heat up significantly under radiation can be explained by their low heat capacity and their high capacity to absorb light that result in considerable temperature increases.…”

Photocatalysis with Chromium‐Doped TiO2: Bulk and Surface Doping

“…Bands in the 950-1000 cm À1 region are characteristic of symmetric and antisymmetric stretching vibrations of the CrO 2 moiety in the tri-or tetramer. [40] Low-intensity bands were also observed in the 985-889 cm À1 region, but this wavenumber range corresponded to a bond length that was too short and a bond order that was too large to be solely due to Cr III ÀO vibrational modes. [39] However, Yang et al recently studied the Raman spectrum of a-CrOOH and attributed two intense bands at 823 and 630 cm À1 to n s (Cr III ÀO) vibrations.…”