Chiral TiO₂‑Based Aerogels from Ligand-Imprinted Nanoparticles: Implications for Heterogeneous Asymmetric...

Aerogels composed of chiral nanoparticles combine the high surface area, extensive porosity, and low density of aerogels with the chiroptical and enantioselective properties of nanoscale chiral building blocks, thereby opening up potential applications in photonics, enantioselective catalysis, and molecular recognition. Here, we report the fabrication of a chiral TiO₂-based aerogel from l/d-threoninol-functionalized nanoparticles. Gelation was induced by controlled destabilization of the nanoparticle dispersion through the addition of a nonsolvent, leading to the formation of a highly porous three-dimensional network. Remarkably, nuclear magnetic resonance (NMR) spectroscopy, supported by Fourier-transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, thermogravimetric analysis (TGA), and elemental analysis, reveals that the chiral ligand interacting with the titania surface is largely removed during the gelation and solvent exchange processes. Despite the absence of the ligand, circular dichroism (CD) measurements demonstrate that the nanoparticles constituting the aerogel retain the chiroptical response with a g-factor comparable to that of the ligand-functionalized particles. These results indicate that the observed chirality arises from the inorganic TiO₂ nanoparticles rather than from threoninol, suggesting that chiral structural features were imprinted onto the nanoparticle surface during synthesis. This work demonstrates that chiral information can be preserved within an inorganic aerogel architecture, laying the groundwork for the use of such materials in heterogeneous asymmetric photocatalysis.