Vibrational spectra and dissociation of aqueous Na2SiO3 solutions

Abstract

To facilitate molecular spectroscopic observation of the mysterious transition of dissolved sodium silicate molecules into nanoparticles of desired silica gel and zeolite structures, the IR and Raman spectra of Na 2 H 2 SiO 4 monomers are studied here in details. It is demonstrated that the 3-0.2 mol/L aqueous solutions of Na 2 SiO 3 and Na 2 SiO 3 Â 9H 2 O contain mostly Na 2 H 2 SiO 4 monomers dissociated about 30%-80%, respectively. In contrast to the common belief the Si-O vibrations of these monomers depend on their dissociation level generating FTIR and Raman bands which are frequently associated with polymer silica structures in the current literature. To stay consistent with the molweight and dissociation measurements, these vibrational assignments are revised in this paper. Some unique and unexpected effects of D 2 O used instead of H 2 O as solvent are also reported.

Concentration- and pH-dependence of highly alkaline sodium silicate solutions

“…In general the low frequency band can be assigned to the symmetric and the two high frequency bands to asymmetric [Si-O] stretches of the different silica species and structures in the sodium silicate solutions. The position and intensities of these bands have previously been shown to depend on both concentration and/or SiO 2 :Na 2 O ratio in the solutions, reflecting changes in structure and speciation [25][26][27].…”

A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy

“…Although there are a number of studies on the assignments of vibration bands of silica solids, glasses and gels [31,32], the assignments related to the distribution of anionic species in sodium silicate solution, especially very dilute solutions, are still unclear and some even incompatible [16][17][18]. To obtain the distribution of silicate species with pH and concentration, a silicate speciation model was set up using WinSGW program [33].…”

“…Halasz et al reported infrared spectra of sodium silicate solutions dissolved from Na 2 SiO 3 and Na 2 SiO 3 ·9H 2 O at pH >13 [18].…”

“…In alkaline and diluted solutions (SiO 2 :Na 2 O < 1.65, 0.4 mol L −1 ), monomer, dimer, and cyclic trimer silicate species are dominant. Quit recently, Halasz et al assigned the infrared and Raman bands for the silicate species existing in sodium metasilicate solutions and claimed that silicate monomers predominated in 0.2-3 mol L −1 aqueous metasilicate solutions [18].…”

Modern Spectroscopic Methods Applied to Nanoscale Porous Materials

“…Thus FTIR and Raman spectroscopic methods are very efficient for studying kinetic processes and precursor clusters as well as to identify small-sized crystalline particles in the final product. 10,13,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In addition, FTIR and Raman spectroscopy are very sensitive to atomic bonding and thus gives the opportunity to study active sides and interactions between embedded functional molecules and framework atoms in porous materials. 5,12,[33][34][35][36][37][38][39][40][41][42] Raman spectroscopy compares favourably to FTIR spectroscopy because of the better signal-to-noise ratio in the low-energy spectral range and the better spatial resolution when a microscope is used.…”