Influência do ph na síntese de titanatos de sódio obtidos via síntese sonoquímica

Abstract

The rapid advancement of energy storage technologies to meet the growing demands of the industry, renewable energy, and the household sector drives researchers to seek more advanced and cost-effective materials for new devices. While lithium-ion batteries are predominant, their high cost and scarcity of lithium in the Earth's crust motivate exploration of alternatives, such as sodium-ion batteries. These batteries show similar potential in energy density and power, prompting research into innovative synthesis methods and chemical modifications to optimize their production. This study focuses on obtaining sodium titanates through the sonochemical method at room temperature of 25°C, over a time interval of 15 minutes, altering the synthesis pH under various conditions: pH~02, pH~04, pH~06, pH~08, pH~10, pH~12, and pH~14. X-ray diffraction (XRD) results and structural refinement using the Rietveld method confirmed the presence of the main phase Na2Ti6O13 in all samples, except for the pH~14 sample. The Na2Ti3O7 phase was obtained as a secondary phase in samples obtained in a basic environment: pH08, pH~10, pH~12, and pH~14. For samples obtained in an acidic environment, pH~02, pH~04, and pH~06, in addition to the main phase Na2Ti6O13, the presence of secondary phases TiO2 and NaCl was found. Infrared vibrational spectroscopy confirmed the presence of active modes related to the phases found in the XRD analysis. Characterization by diffuse reflectance UV-Vis spectroscopy made it possible to calculate the energy gap (Egap) of the synthesized samples, with the lowest value for the pH~08 sample (Egap = 3.41 eV); pH~02, pH~04, and pH~06 samples exhibited two Egap regions, caused by the presence of the NaCl phase. Scanning electron microscopy (SEM) images revealed that the morphology of the obtained materials presented in the form of micrometer-scale rods. The electrical properties of the samples were investigated by complex impedance spectroscopy (EIS); the pH~10 sample exhibited the highest conductivity value compared to the other samples, with σdc = 9.52 x 10-4 S cm-1; whereas, for the pH~02 sample, the lowest conductivity value was identified, with σdc = 9.85 x 10-6 S cm-1. The establishment of pH in the synthesis of the samples provided an alternative route to obtain materials in this study, achieving electrical conductivity values between 10-4 to 10-6 S cm-1, positioning them as alternative materials for energy storage device applications.