Quantifying chiral handedness of core-shell inorganic nanotube photocatalysts via electron microscopy and diffraction

Abstract

Intrinsically chiral inorganic nanotubes (NTs) based on WS2 and MoS2 are promising visible-light-absorbing materials for heterogeneous enantioselective photocatalysis and, potentially, for fundamental studies of the chiral induced spin selectivity (CISS) effect. Accurate identification of chiral handedness is essential for advancing enantioselective applications of these materials, but existing imaging and diffraction-based protocols do not rapidly facilitate the identification of NT handedness. We present a combined transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) approach for determining the chiral handedness of WS2 NTs that contain WOx cores. We observe the WOx core lattice and WS2 atomic layers in the same TEM image. By comparing the lattice orientations of the WOx core relative to the WS2 layers, and confirming that relationship with the chiral angle revealed by SAED patterns, we can unambiguously identify the right- or left-handed structure of individual NTs. In addition, we show that moiré patterns formed from the WS2 shells and oxide core can also be used to characterize lattice orientation, chiral indices, and handedness. This approach requires no additional sample preparation, instrumentation, or experimental adjustments, and may be applied broadly to other core-shell nanotube systems such as MoS2, BN, and carbon NTs. The significance of this work is that it enables reliable handedness determination of chiral core-shell nanostructures and addresses a key difficulty in the existing characterization methods of multiwalled NTs. We envision that the single particle catalysis community can leverage these methods to study structure-activity relationships of this unique class of intrinsically chiral semiconductor nanostructures.