Abstract
Understanding the action mechanism of sodium ions in sodium silicate solutions is necessary for the synthesis of nanosilica. The microstructure of sodium silicate solutions with SiO2:Na2O ratios ranging from 2 to 4 was characterized by 29Si nuclear magnetic resonance spectroscopy, and the magnetic shielding tensor of the nuclear magnetic field was calculated using the density functional theory. Sodium ions contribute significantly to the magnetic shielding tensor, thereby playing a key role in the structural evolution of sodium silicate solution species. Wave function analysis was used to further study the mechanism of action of sodium ions. Theoretical calculation results show that Na not only affects the magnetic shielding and regulates the splitting and change of NMR peaks but also regulates the aggregation-free energy and growth morphology of silica nanoparticles. Thus, the structural regulation of sodium ions on nanosilica growth and aggregation was proposed. Magnetic shielding caused by partial symmetry disappears with the reduction of sodium ions in the system, resulting in uniform magnetic shielding. Meanwhile, the anisotropic aggregation free energy of microscopic particles tends to be isotropically distributed, resulting in the spherical growth tendency of the nanosilica particles. Small-angle X-ray scattering and transmission electron microscopy were used to verify these conclusions. In this work, we adopted the leading quantum chemical computational methods with advanced computer technology and quantum chemical methods to research the microscopic effect of sodium ions during nanosilica growth, thereby overcoming the limitations of the analytical experience and paradigm established with traditional organic chemistry and providing important theoretical reference value for the field of spectral systems and characterization measurement methods. At the same time, the reasonable mechanism of action is proposed, which greatly expands the product application field of nanosilica.
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