Anisotropy-Dependent Chirality Transfer from Cellulose Nanocrystals to β-FeOOH Nanowhiskers

Abstract

Chiral iron oxides and hydroxides have garnered considerable interest owing to the unique combination of chirality and magnetism. However, it remains elusive how to improve their g-factor, which is critical for optimizing the chiral magneto-optical response. We demonstrated that the g-factor of β-FeOOH could be boosted by enhancing the anisotropy of nanostructures during a biomimetic mineralization process. Cellulose nanocrystals were used as both mineralization templates and chiral ligands, driving oriented attachment of β-FeOOH nanoparticles and inducing the formation of highly aligned chiral nanowhiskers. Circular dichroism spectra and time-dependent density-functional theory proved induced chirality transfer from cellulose nanocrystals to β-FeOOH through the ligand-metal charge transfer. Interestingly, chirality transfer is significantly enhanced during the elongation of nanowhiskers. A nearly 34-fold increase in g-factor was observed when the aspect ratio of nanowhiskers increased from 2.6 to 4.4, reaching a g-factor of 5.7*10-3, superior to existing dispersions of chiral iron oxides and hydroxides. Semi-empirical quantum calculations unveiled that such remarkable improvement of g-factor could be attributed to the enhanced dipolar interactions. Cellulose nanocrystals exert vicinal actions on highly anisotropic β-FeOOH with a large dipole moment, increasing structural distortions of coordination geometry. This mechanism is accorded with the one-electron theory's static coupling principle, highlighting the large interaction potential from supramolecular templates. Furthermore, paramagnetic β-FeOOH nanowhiskers alter the magnetic anisotropy of cellulose nanocrystals, leading to a reverse response of helical photonic films to magnetic fields, promising for the real-time optical modulation.