Exotic Electronic Properties of 2D Nanosheets Isolated from Liquid Phase Exfoliated Phyllosilicate Minerals

Abstract

Spectrally inactive, electrically insulating, and chemically inert are adjectives broadly used to describe phyllosilicate minerals like mica and chlorite. Here, the above is disproved by demonstrating aqueous suspensions of liquid exfoliated nanosheets from five bulk mica types and chlorite schist. Nanosheet quality is confirmed via transmission electron and X‐ray photoelectron spectroscopies, as well as electron diffraction. Through Raman spectroscopy, a previously unreported size‐ and layer‐dependent spectral fingerprint is observed. When analyzing the high‐yield suspensions (≈1 mg mL−1) through UV–vis spectroscopy, all phyllosilicates present bandgap (Eg) narrowing from ≈7 eV in the bulk to ≈4 eV for monolayers. Unusually, the bandgap is inversely proportional to the areal size (A) of the nanosheets, measured via atomic force microscopy. Due to an unrecorded quantum confinement effect, nanosheet electronic properties scale toward semiconducting behavior (bandgap ≈3 eV) as nanosheet area increases. Furthermore, modeling X‐ray diffraction spectra shows that the root cause of the initial bandgap narrowing is lattice relaxation. Finally, with their broad range of isomorphically substituted ions, phyllosilicate nanosheets show remarkable catalytic properties for hydrogen production.

Ultrathin sillenite nanosheets with wide-spectrum response and high photocatalytic oxidation performance

“…The shifts may be the consequence of lattice relaxations of nanosheets and surface doping effects of residual Cr. 24,25 We conducted UV-DRS testing on Cr-doped nanoparticles (Fig. S7†) to investigate the impact of Cr residues and the nanosheet structure on the redshift of the absorption band.…”

A comprehensive review of atomically thin silicates and their applications

“…Layered silicates, also known as phyllosilicates, are naturally occurring inorganic layered compounds where stacks of 2D silicate sheets are held together by weak van der Waals forces [64,65]. As mentioned before, compared to intralayer bonds, the van der Waals forces between layers are relatively weak, allowing for easy exfoliation into a single or few layers [64].…”