UV Raman spectroscopic study of hydrogen bonding in gibbsite and bayerite between 93 and 453 K

Abstract

Raman spectra of bayerite and gibbsite (hydrargillite) were measured at 453, 295 and 93 K and after H-D exchange at 423 K with gaseous D 2 O. Spectra in the O-H stretching vibration region were recorded with the use of ultraviolet laser excitation, which avoided the fluorescence problem typical for these materials. Lowering the temperature led to a spectral resolution improvement with additional bands resolved in the n(OH) spectrum of bayerite. It was established that the positions of the Raman bands are sensitive to the temperature of the sample. A spectral criterion based on different shifts of band positions with temperature was proposed as a method to distinguish between structural OH groups forming H-bonds between hydroxide layers or in the same plane of the layer. It was found that the highest wavenumber band at 3655 cm −1 in the spectrum of bayerite does not participate in H-bonding. A one-to-one correspondence between Raman spectra recorded in the n(OH) and n(OD) regions upon partial H-D exchange with D 2 O is evidence that the multiplicity of spectral bands is caused by different O-H· · ·O distances in the hydroxide lattice rather than by vibrational coupling of H-bonded hydroxyls.

Structure of Hydrated Gibbsite and Brucite Edge Surfaces: DFT Results and Further Development of the ClayFF Classical Force Field with Metal–O–H Angle Bending Terms

“…This also explains the cohesion of the gibbsite layers. 55,56,84 The C-MD simulations with the ClayFF-MOH model result in the ∠AlOH angular distributions with FWHM much closer to the DFT results, with FWHM ≈19.3°for the OH ip groups and FWHM ≈14.0°for the OH op groups. The maxima are different for the ClayFF-MOH-110°and ClayFF-MOH-116°sets of parameters, since the ∠AlOH op max values differ from the DFT results by 3.2°and 6.0°, respectively, while the ∠AlOH op max values differ from their respective DFT results by 0.5°and 2.3°, respectively (Figure 3d).…”

“…The initial bulk model of gibbsite was based on experimental neutron diffraction data, which provides unit cell parameters of 8.68 × 5.08 × 9.74 Å 3 , α = γ = 90°, β = 94.54° monoclinic symmetry . As proven experimentally , and confirmed theoretically, gibbsite hydroxyl groups adopt two different orientations in the bulk: in the (001) plane (OH ip ) and along the [001] direction (OH op ). Among the possible edge surfaces, the (100) gibbsite surface, which is the one observed experimentally, was studied here in addition to the bulk crystal and basal surfaces.…”

Dissolution kinetics of nanodispersed γ-alumina in aqueous solution at different pH: Unusual kinetic size effect and formation of a new phase

“…The small letters b and g indicate the bands that are assigned for bayerite and gibbsite by Refs. [66,67]. of the new phase-bayerite-complicates the investigations of the surface morphology owing to the phase transitions occurring during the evacuation of the sample material up to 350 • C. On this account we performed the adsorption measurements in two steps-first evacuating the sample at 100 • C, and second doing it with the preheated sample at 350 • C. So it is possible to decide between surface alteration due to the dissolution process on the one hand and the phase transition inside the solid material during the evacuation process otherwise.…”

“…Both IR [57,[60][61][62][63] and UV-Raman spectroscopy [60,[64][65][66][67] are able to identify the aluminum hydroxide phases due to differences in the hydroxyl stretching region. The results of our own measurements are shown in Fig.…”

Substrate Signal Inhibition in Raman Analysis of Microplastic Particles

“…Raman spectroscopy is a key analytical tool that is used to determine the chemical nature of a sample, thanks to light–matter interaction with specific spectral signatures, which facilitates the remote identification of a wide variety of materials. It is reliable, nondestructive, fast, and suitable for a wide scale of dimensions. − However, the weak Raman signal can be a disadvantage, requiring optimized and expensive instrumentation that can limit the scope of applications. ,, This is most evident in applications where the analysis of individual small-sized particles (in the micro-/nanoscale) is required, such as microplastic identification, − cell analysis, , and airborne-particle analysis. , This is further impaired by the presence of other parasitic signals that can mask the target signal of the analyte, such as the Raman scattering peaks of the substrate on which the analyte particles reside. For instance, analyzing microplastic particles on a silicon (Si) substrate can be affected by the strong Si Raman peaks, including the main peak at nearly 520.6 cm –1 and the broader (but less intense) second-order peak at around 940 cm –1 . , This is especially evident when analyzing smaller plastic particles (<10 μm) of a much weaker Raman signal, such as PMMA compared to Si .…”