Vibrational spectra and dissociation of aqueous Na2SiO3 solutions

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 Na₂H₂SiO₄ monomers are studied here in details. It is demonstrated that the 3–0.2 mol/L aqueous solutions of Na₂SiO₃ and Na₂SiO₃ × 9H₂O contain mostly Na₂H₂SiO₄ 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 D₂O used instead of H₂O as solvent are also reported.