Hydrothermal Synthesis and Properties of Nanostructured Silica Containing Lanthanide Type Ln-SiO₂ (Ln = La, Ce, Pr,...

The nanostructured lanthanide-silica materials of the Ln-SiO₂ type (Ln = La, Ce, Pr, Nd, Eu, Gd, Dy, Yb, Lu) were synthesized by the hydrothermal method at 100 °C, using cetyltrimethylammonium as a structural template, silica gel and sodium silicate as a source of silicon, and lanthanide oxides, with Si/Ln molar ratio = 50. The resulting materials were calcined at 500 °C using nitrogen and air, and characterized by X-ray diffraction (XRD), Fourier-Transform infrared absorption spectroscopy, scanning electron microscopy, thermogravimetry (TG), surface area by the BET method and acidity measurements by n-butylamine adsorption. The XRD and chemical analysis indicated that the SiO₂ presented a hexagonal structure and the incorporation of lanthanides in the structure changes the properties of the Ln-SiO₂ materials. The heavier the lanthanide element, the higher the Si/Ln ratio. The TG curves showed that the decomposition of the structural template occurs in the materials at temperatures below 500 °C. The samples showed variations in specific surface area, mean pore diameter and silica wall thickness, depending on the nature of the lanthanide. The incorporation of different lanthanides in the silica generated acid sites of varied strength. The hydrothermal stability of the Ln-SiO₂ materials evaluated at high temperatures, evidenced that the properties can be controlled for application in adsorption and catalysis processes.