Synthesis and Study of La2O3–SiO2 Systems Obtained from Kaolin and Tetraetoxysilane

Abstract

La₂O₃–SiO₂ systems are synthesized from kaolin and tetraethoxysilane. The thermal decomposition of images after freeze-drying when heated to 1000°C is studied using thermogravimetry and differential scanning calorimetry. The morphology of the samples is studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS); the acid–base properties of the surface are determined by the indicator method. During the heating of samples in the temperature range of 25–600°C, endothermic effects are discovered, accompanied by weight loss. The structure of the kaolin sample is heterogeneous; nanoparticles (10 nm) of lanthanum oxide are located on the surface of microparticles (220–270 nm) of silicon oxide. The sample obtained from tetraethoxysilane has a homogeneous nanostructure with particle sizes of 5–13 nm, but is characterized by less intense sorption values at Brønsted acid sites (pK_a 1.7; 3.46) compared to the sample from kaolin. This is due to the production of the La₂O₃–SiO₂ system already in solution and the blocking of silanol groups on the surface of silicon oxide. A significant increase in specific adsorption at pK_a 9.2 for both the kaolin and tetraethoxysilane samples proves the existence of La³⁺ metal ions and OH^– hydroxyl groups on the surface of silicon oxide.