Theoretical investigations into the nucleation of silica growth in basic solution part I – ab Initio studies of the formation of trimers and tetramers

Abstract

We have performed the first ab initio study that considers all possible oligomerization reactions available to silicic acid in basic solution (ignoring high-energy multiply charged species), up to and including tetramers. Energies have been computed at the MP2/6-31+G(d)//HF/6-31+G(d) level of theory, with a hybrid solvation model which includes explicit waters and CPCM continuum corrections to account for solvent effects. The explicit waters have been found to be extremely important in providing additional stabilization of intermediates and transition states which are not accounted for properly by more conventional implicit solvent approaches, suggesting some of the known pathways are more facile than previously predicted. Additionally, a number of previously neglected bimolecular growth pathways such as dimer/dimer and monomer/cyclic trimer additions, and unimolecular cyclization steps such as branched 3-ring formation from branching tetramers and the formation of highly condensed bicyclic and tetrahedral clusters have been studied in detail. Many are found to be very energetically feasible and consequently could have considerable impacts on the initial stages of silica nucleation.

Implications of silica on biorefineries – interactions with organic material and mineral elements in grasses

“…11 Recently, ab initio studies have been conducted to elucidate the mechanism for polymerization of silicic acid into all forms of tetrameric silica. 12,13 Th e models show good correlation with experimental data in terms of dependency of polymerization reaction rates on pH and temperature. Despite mainly providing new fundamental knowledge about silica polymerization, such studies can provide valuable information about silica chemistry and reaction kinetics which can potentially be benefi cial for controlling silica in biorefi neries.…”

“…Recently, ab initio studies have been conducted to elucidate the mechanism for polymerization of silicic acid into all forms of tetrameric silica . The models show good correlation with experimental data in terms of dependency of polymerization reaction rates on pH and temperature.…”

Advances in theory and their application within the field of zeolite chemistry

“…43,44 In addition, McIntosh benchmarked a series of electronic levels of theory, selecting finally a hybrid approach as a good compromise between accuracy and computational cost. He initially argued that 8 water molecules suffice to converge the theoretical activation barriers and pre-exponential factors with respect to the number of water molecules.…”

“…44 For instance, explicit water molecules do raise the barriers of the trimer cyclization reaction, but lower the relative stability of the silica three-ring. 44 For instance, explicit water molecules do raise the barriers of the trimer cyclization reaction, but lower the relative stability of the silica three-ring.…”

Precipitation mechanism of amorphous silica nanoparticles: A simulation approach

“…These small units, called pre-nucleation clusters 49 , have been thoroughly studied in the case of silica-rich solutions, both experimentally [11][12][13][14][15][16][17][18] and theoretically 19,21,[50][51][52] . It has been shown that their average concentration depends on several factors such as temperature, initial silica concentration, pH and the presence of additional cations.…”