The bovine whey protein ß-lactoglobulin (ß-lg) forms distinct supramolecular structures from spheres to amyloid fibrils by denaturation at different conditions. As a result, the non-toxic biopolymer is used in the food industry as a texture and foaming agent.

In the context of biotemplating, the texture and foaming properties of ß-lg attend attention also in nanotechnologies. The abundant biopolymer can replace synthetic copolymers in sol-gel chemistry to increase the sustainability of material synthesis. For instance, it was successfully employed as a biotemplate for TiO$_\text{2}$ morphologies. The performance in photocatalysis depends on the surface-to-volume ratio and the crystalline phase of TiO$_\text{2}$. Introducing ß-lg in the sol-gel synthesis of TiO$_\text{2}$ yields foam-like nanostructures of a high surface-to-volume ratio. Moreover, it enables water-based processing that matches the conditions for low-temperature crystallization of TiO$_\text{2}$.[1,2]

In this work, we present a low-temperature route towards crystalline TiO$_\text{2}$ films by water-based ß-lg biotemplating. For this, biohybrid ß-lg:TiO$_\text{2}$ films are prepared by spray deposition. Subsequent UV-light exposure combusts the ß-lg template and reveals foam-like TiO$_\text{2}$ films. We investigate the biohybrid film formation with in situ grazing incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) during spray deposition to understand the templating role of ß-lg. Electron microscopy complements GISAXS/GIWAXS with surface imaging. We identify a hierarchical morphology in the biohybrid film: The condensing ß-lg biomatrix act as a steric template, in whose pores the TiO$_\text{2}$ crystallites are forming. The results highlight the potential of ß-lg for water-based and sustainable biotemplating.

References
[1] S. Yin et al. Small Methods, 2020, 4, 1900689.
[2] S. Bolisetty et al. Adv. Funct. Mater., 2012, 22, 3424-3428.