Tuning the Morphology of Spray-Coated Biohybrid Beta-lactoglobulin:TiBALDh Films with pH for Water-Based and Nanostructured Titania.

The whey protein beta-lactoglobulin (β-lg) is used as a biotemplate for the water-based synthesis of nanostructured and foam-like titania films based on its variation in supramolecular structure when denatured at different pH values. Acting as a matrix, β-lg is mixed with the water-soluble titania precursor Ti(IV) bis(ammonium lactate)dihydroxide (TiBALDh) to promote biotemplated titania precipitation. Since TiBALDh is in chemical equilibrium with anatase titania nanoparticles and Ti(IV)-lactate complexes, and this equilibrium shifts with varying pH, the influence of the pH value on the final film morphology becomes essential. This work investigates this influence for three pH values: pH 7, pH 5, i.e., close to the isoelectric point of β-lg, and pH 2. Spray coating, a method of industrial relevance, is used to fabricate biohybrid β-lg:TiBALDh foam-like films. The obtained films are calcined to combust biotemplate β-lg and achieve nanostructured titania films. To understand the influence of pH on the film morphology, grazing-incidence small-angle and wide-angle X-ray scattering (GISAXS/GIWAXS) and grazing-incidence small-angle neutron scattering (GISANS), in combination with scanning electron microscopy (SEM), are applied to both the biohybrid and biotemplated titania films. With these techniques, information about domain sizes, porosity, and crystal structure is obtained with high statistical significance. Fourier-transform infrared spectroscopy (FTIR) probes the interaction of TiBALDh and β-lg on the molecular level as a function of pH. The results underline pH as a suitable tool for tuning the morphology in biotemplated titania films.