Morphology- and composition-controlled synthesis of aluminium borate nanowires without catalysts

Abstract

To depress evaporation of boron oxide during the high-temperature synthesis of borates, a sol–gel route followed by calcination was used to grow various aluminium borate nanowires. The morphology and structure of Al4B2O9 and Al18B4O33 nanowires could be controlled by adjusting the boron oxide content in the sol–gel derived precursors and the calcined temperature. Fine Al4B2O9 nanowires with an average diameter of ∼20 nm were obtained by the calcination of Al2O3–2B2O3 xerogel at 1100 °C, whereas heat treatment at the same temperature for Al2O3–B2O3 xerogel gave rise to Al18B4O33 nanowires with an average diameter of ∼30 nm. The morphology and composition dependence were investigated by x-ray diffraction, thermogravimetric and Brunauer–Emmett–Teller surface area analyses, and various microscopy techniques. A possible growth mechanism was also proposed based on high-resolution transmission electron microscopy observations.