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.