Preparation of alumina–titania nanofibers by a pH-swing method

Fibrillar Al2O3–TiO2 were obtained by a pH-swing method by varying the pH from 2 to 8, and repeating this range (e.g. a cycle) several times, in combination with different ways to incorporate titanium oxisulfate. Depending on the stage in which Ti-oxisulfate is added to the alumina, large anatase aggregates or very dispersed TiO2 domains were obtained on/in alumina nanofibers. Thus, when using a co-precipitation method in combination with pH-swing between pH 2 and 8, with six pH cycles, a high TiO2 dispersion can be obtained, as indicated by Raman spectroscopy and X-ray diffraction. On the other hand, when adding Ti-oxysulfate at the end of the pH-swing procedure, though alumina nanofibers were formed, anatase was predominantly located as large particles in the interfibrillar voids. Specific surface area and total pore volume of nanofibrillar Al2O3–TiO2 were around 300 m2/g and 1 cm3/g, respectively, after calcining at 500 °C. The highly disordered intertwined fibrils favored high pore volume values, even upon calcinations at 500 °C.