Mid- and Near-Infrared Study of Hydroxyl Groups at a Silica Surface: H-Bond Effect

Abstract

This paper studies the IR absorption of the OH stretching modes νOH and of their first overtones 2νOH for silanol groups at silica surfaces. Heat treatment of silica induces a condensation of silanol groups. The subsequent decrease in silanol concentration results in strong modification of the spectral profiles. The spectra are interpreted in terms of distributions of OH oscillators. The mechanical anharmonicity coefficient x OH and the ratio of the fundamental/overtone extinction coefficients ϵ(νOH)/ϵ(2νOH) both increase for decreasing νOH wavenumber decreases, i.e., as the strength of the H-bond increases. The decadic integrated intensities are plotted against silanol concentrations. The intensity of the νOH mode significantly increases with hydrogen bonding, whereas that of 2νOH slightly decreases. As a consequence, compared to the fundamental mode, the first overtone provides a better picture of the distribution of OH states. Analysis of the infrared spectra also demonstrates the presence of cooperative bonding between silanol groups at the silica surface.

Effect of Silica Surface Properties on the Formation of Multilayer or Submonolayer Protein Hard Corona: Albumin Adsorption on Pyrolytic and Colloidal SiO2 Nanoparticles

“…By considering that these particles exhibit a ζ-potential of −33 mV (see below), this behavior indicates that attractive hydrophobic forces and, as DLVO forces are concerned, attractive van der Waals forces prevailed in some extent on the electrostatic double layer repulsive force, actually entropic/osmotic in nature. 46 In this respect, a contact angle of 87.96 ± 0.24° was measured by P-SiO 2 , close to the conventional boundary for a classification of a surface as hydrophobic (>90°) or hydrophilic (<90°). 48 This value is in agreement with the enthalpy of adsorption of water on P-SiO 2 , found to be very close to the latent heat of water liquefaction, 30 considered as a reference threshold when measuring hydrophilicity/hydrophobicity by water adsorption calorimetry.…”

“…10 times higher for H-bonded ≡Si−OH characterized by νOH below 3600 cm -1 . 46 Based on these findings, it seems reasonable to propose that the amount of silanols (weakly interacting) responsible for the νOH pattern in the range of 3800-3600 cm -1 might be similar for P−SiO 2 and M−SiO 2 , or even slightly lower for the second one. Dh was measured both while keeping unadsorbed proteins in the suspension media and after removing them; i.e., leaving NPs with irreversibly adsorbed BSA molecules suspended in bare PBS buffer.…”

Near-infrared investigation of folding sepiolite

“…The combination mode at ~4570 cm -1 does not shift, but the stretching overtone at 7270 cm -1 nearly vanishes and gives its place to a strong band at ~7320 cm -1 (fundamental at 3742 cm -1 , anharmonicity X = 82 cm -1 , mid-infrared data not shown). The new bands are similar to those of hydrated silica (Morrow and McFarlan 1992;Carteret 2009) and constitute the signature of the SiOH groups in the Mg 2+ -depleted, silica-like portion of the leached sepiolite. Very similar spectra have been reported for smectites subjected to acid treatment (Madejová et al 2009).…”

Implications of silica on biorefineries – interactions with organic material and mineral elements in grasses

“…When the silica particles have grown to their final size, silanol groups (Si‐OH) are left on their surfaces. The surface density of these depend on especially high temperature which dehydroxylate silica surfaces . Surface silanol groups make silica hydrophilic, attracting water molecules for hydrogen bonding .…”