Surface properties, dielectric, and Ac-conductivity studies of nano-mesoporous LaAlO3 synthesised by the chitosan template method

Abstract

Nano-mesoporous lanthanum aluminium oxide (LaAlO₃) was successfully synthesised using the chitosan template method. The use of chitosan, a biodegradable and renewable biopolymer, as a templating agent adds a green chemistry dimension to the synthesis approach. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy confirmed the formation of LaAlO₃. The morphology of LaAlO₃ was analysed using transmission electron microscopy (TEM). Surface area, pore size, and pore size distribution were determined via Brunauer-Emmett-Teller (BET) analysis, which confirmed its mesoporous nature. Surface acidity and basicity of nano-mesoporous LaAlO₃ were examined using temperature-programmed desorption (TPD-NH₃ and TPD-CO₂) techniques. TPD analysis revealed a higher number of surface acidic groups and a moderate presence of surface basic groups. Surface and bulk oxygen reducibility was assessed using temperature-programmed reduction (H₂-TPR) analysis. The results indicated that LaAlO₃ remains stable under reduction up to 500 °C and contains a limited number of reducible surface groups. The frequency dependence of capacitance, dissipation factor, and dielectric constant was analysed at room temperature. To better understand the conduction mechanism, the variation of AC conductivity with frequency was also measured. Nano-mesoporous LaAlO₃ exhibited a high capacitance and dielectric constant, along with low AC conductivity and a low dissipation factor in the low-frequency region. These properties suggest that nano-mesoporous LaAlO₃ holds significant promise for multifunctional applications, particularly in catalysis, energy storage devices such as supercapacitors and solid-state capacitors, gas sensing, and dielectric components in electronic devices.