Synthesis, structural characterization and optical properties of magnesium pyroborate nanoparticles

In this study, Pure Mg2B2O5 were successfully synthesized using different kinds of organic fuels (carbohydrazide, citric acid, glycine, HMDA, HMTA, tartaric acid and urea) via Solution Combustion Synthesis (SCS) method. The structural and optical properties of as-prepared products were comparatively characterized by Infrared spectroscopy (FTIR), X-Ray Powder Diffraction (XRD), Ultra Violet- Visible spectroscopy (UV-VIS) techniques. During the process of preparation, Mg(NO3)2.6H2O, 5wt% excess H3BO3, and fuel were used as the starting materials. The effects of fuels and temperature on the structural properties of the products were examined by XRD studies. It is shown that at low temperatures between 400 and 800°C, Mg2B2O5 was resulted in monoclinic phase except for carbohydrazide fuel. At 900°C, the transformation of monoclinic phase of Mg2B2O5 into triclinic phase was obtained. Most accurately, the single phase triclinic was acquired for all fuels at 1000°C. In the analysis of infrared spectra, the bands around 680 cm-1 and 720 cm-1 represent to the B-O-B bending and the bands assigned at 1175 cm-1, 1290 cm-1 and 1490 cm-1 belong to stretching vibrations of trigonal BO3 confirmed the formation of magnesium pyroborate. The effects of fuels and heating temperatures on optical properties of Mg2B2O5 were further examined using Ultra Violet- Visible spectroscopy (UV-VIS). It was found that the optical band gap energy of the products decreases as the temperature increases. The calculated optical band gap energy was attained at range of 4.66-4.91 eV for different fuels. The lowest band gap of Mg2B2O5 was detected for citric acid fuel whereas highest value was found for urea fuel.