Table 1.

Assignments of the main silica bands in the 700- to 4,000 cm ⁻¹ region

Band maximum (KBr powder, cm −1 )	Assignment a	Reference
3,745	ν (isolated silanol groups) Si-OH	[38,40]
3,700 to 3,000	ν hydrogen-bonded silanols (overlapping of the stretching modes in hydrogen-bonded hydroxyl bands produced by O-H bonds in adsorbed water and Si-OH)	[38,40]
1,867 and 1,980	Si-O-Si stretching modes	[38,40]
Approximately 1,628 to 1,630	Proton-containing components σOH (silanol groups and the deformation vibrations of the O-H groups in physically adsorbed molecular water at the silica surface)	[37-39]
Approximately 1,083	Si-O-Si stretching	[38,40]
1,000 to 1,300	νas, anti-symmetric stretching of Si-O-Si bonds	[38]
932 to 939	Si-OH stretching	[38,40]
Approximately 809	Bending vibration of Si-O-Si bonds	[38,40]
Approximately 790	Bending modes in Si-OH bonds	[38,40]

^aν^as/s, asymmetric/symmetric stretching mode.