The impact of the reaction atmosphere on the additive-free growth of Mg2B2O5 nanorods

Abstract

Although many routes for the production of magnesium borates (Mg2B2O5, Mg3B2O6 and MgB4O7) are well known, the synthesis of single phases is still a challenge. Secondary phases such as other magnesium borates and MgO are commonly observed in the final product. In order to produce high quality Mg2B2O5 nanorods, we developed a study analyzing the influence of different reaction atmospheres on the synthesis of magnesium borate in a tubular furnace. Through this investigation, a strong correlation between the produced borate phases and the composition of the atmospheres was verified. The sample produced under Ar presented Mg2B2O5, Mg3B2O6 and MgO in molar percentages of 36.82%, 35.34% and 27.84% respectively, while the sample synthesized under H2 is composed of 18.9 mol% of Mg3B2O6 and 81.1 mol% of MgO. Mg2B2O5 nanorods with elevated structural homogeneity were successfully produced under hydrogen and acetonitrile. Under this atmosphere only Mg2B2O5 and Mg3B2O6 were produced, with the formation of Mg2B2O5 nanorods representing 87.5 mol% of the sample. The nanorods growth followed a solution-solid-solid (SSS) self-catalyzed mechanism. This synthesis was performed without the assistance of external agents such as catalysts or surfactants, guaranteeing elevated chemical purity for applications in the optical and electronic field. Reflectance and impedance analyses presented a wide range of light absorption and a dielectric character for the nanorods. The produced structure would be very interesting for theranostic applications.