Morphology preservation and crystallinity improvement in the thermal conversion of the hydrothermal synthesized MgBO₂(OH) nanowhiskers to Mg₂B₂O₅ nanowhiskers

Preservation of one-dimensional (1D) morphology and improvement of crystallinity in the thermal conversion route to magnesium borate (Mg₂B₂O₅) nanowhiskers at a relatively low temperature as 650-700 °C (200-350 °C lower than that of the literature) based on the hydrothermal synthesis of magnesium borate hydroxide (MgBO₂(OH)) nanowhiskers were investigated; the results indicated that thermal conversion at appropriate temperature with a slow heating rate was favorable for the morphology preservation and crystallinity improvement. A specific heating procedure was developed according to the recrystallization phenomenon existing in the thermal conversion of the MgBO₂(OH) nanowhiskers to produce Mg₂B₂O₅ nanowhiskers with uniform morphology, improved crystallinity and fewer pores, in which Mg₂B₂O₅ nanowhiskers (15.0-45.0 nm in diameter, 0.2-2.0 μm in length) were synthesized by heating MgBO₂(OH) nanowhiskers (1.0 °C min^-1) to 650 °C for 2.0 h of isothermal condition first to preserve the 1D morphology, and thereafter to 700 °C (1.0 °C min^-1) for another 2.0 h of isothermal state to recrystallize. The designed specific heating procedure to reduce the mesopores and deformation could also benefit synthesis of other 1D anhydrous nanostructures via the wet chemistry-based thermal conversion route.