Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry

Abstract

Common throughout sol-gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments.

Setting and nanostructural evolution of metakaolin geopolymer

“…Such condensation between aluminosilicates is expected, as the formation of Si–O–Al bonds is thermodynamically more favorable than formation of Si–O–Si bonds . White et al . found thermodynamics of reactions involving aluminate monomer depend on charge state, but they did not provide results for reactions involving aluminosilicate reactants.…”

High hydrothermal stability of Cu–SAPO-34 catalysts for the NH3-SCR of NOx

“…White et al [29] indicated that zeolite synthesis is the process of inorganic oxide polymerization and deprotonation which depend greatly on the pH value using density functional theory (DFT). Lower pH value led to decreased solubility of amorphous silica in the silicate dimerisation reactions.…”

Computational modelling of interactions between gold complexes and silicates

“…Because Si(OH) 3 O -is the conjugate base of a weak acid, it is observed only in appreciable quantities above pH 12 [19,20], and the second deprotonation requires even more highly alkaline conditions. To validate the structures of different silicate monomer species, the Gibbs free energies were calculated for deprotonation reactions of silica monomers, and the results were compared with experimental and theoretical data reported in the literature in Table 3.…”

“…Hydrolysis and deprotonation of the silicate monomer have been studied extensively [18][19][20]. At a pH below 2, which is the point of zero net charge of silica, protonation of silanols forms cationic species [Si(OH) n (OH 2 ) 4-n ] (4-n)+ (n < 4) [19].…”