The role of boric acid in the synthesis of Eni Carbon Silicates

Abstract

The influence of H₃BO₃ on the crystallization of hybrid organic–inorganic aluminosilicates denoted as Eni Carbon Silicates (ECS's) was investigated. Syntheses were carried out at 100 °C under different experimental conditions, using bridged silsesquioxanes of general formula (EtO)₃Si–R–Si(OEt)₃ (R = –C₆H₄– (BTEB), –C₁₀H₆– (BTEN) and –C₆H₄–C₆H₄– (BTEBP)), in the presence of equimolar concentrations of NaAlO₂ and H₃BO₃. The study, involving the synthesis of three different but structurally related phases (ECS-14 from BTEB, ECS-13 here described for the first time from BTEN, and ECS-5 from BTEBP), confirmed a catalytic role for H₃BO₃ which in general increased the crystallization rate and improved the product quality in terms of amount of crystallized phase (crystallinity), size of the crystallites and phase purity, while it was weakly incorporated in trace amounts in the framework of ECS's.