Role of a waste-derived polymeric biosurfactant in the sol–gel synthesis of nanocrystalline titanium dioxide

An inexpensive polymeric biosurfactant isolated from urban bio-wastes is shown to be a useful chemical aid in the synthesis of nanostructured materials with tunable pore size and surface hydrophilicity. Photocatalytic active TiO2 powders were prepared by sol–gel reaction in the presence of variable amounts of a waste-derived polymeric biosurfactant. The products were characterized for morphology, crystal structures and surface hydrophilicity. The porosity data indicate that an increase of the biosurfactant amount in the reaction medium causes a decrease of pore size, pore volume and specific surface area in the synthesized oxide, whereas TEM and XRD data indicate that particle size decreases by increasing biosurfactant amount. These results suggest that biosurfactant molecules play a role in the nucleation step, during the formation of the titanium dioxide particles. The biosurfactant amount in the synthesis mixture affects also the hydrophilicity of the titanium dioxide surface, as demonstrated by water-adsorption microcalorimetry measurements, but the results suggest that this aspect is also connected to crystal nucleation and growth during the oxide formation.