Controlled Synthesis of Layered Double Hydroxide Nanoplates
Driven by Screw Dislocations
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Abstract
Layered
double hydroxides (LDHs) are a family of two-dimensional (2D) materials
with layered crystal structures that have found many applications.
Common strategies to synthesize LDHs lead to a wide variety of morphologies,
from discrete 2D nanosheets to nanoflowers. Here, we report a study
of carefully controlled LDH nanoplate syntheses using zinc aluminum
(ZnAl) and cobalt aluminum (CoAl) LDHs as examples and reveal their
crystal growth to be driven by screw dislocations. By controlling
and maintaining a low precursor supersaturation using a continuous
flow reactor, individual LDH nanoplates with well-defined morphologies
were synthesized on alumina-coated substrates, instead of the nanoflowers
that result from uncontrolled overgrowth. The dislocation-driven growth
was further established for LDH nanoplates directly synthesized using
the respective metal salt precursors. Atomic force microscopy revealed
screw dislocation growth spirals, and under transmission electron
microscopy, thin CoAl LDH nanoplates displayed complex contrast contours
indicative of strong lattice strain caused by dislocations. These
results suggest the dislocation-driven mechanism is generally responsible
for the growth of 2D LDH nanostructures, and likely other materials
with layered crystal structures, which could help the rational synthesis
of well-defined 2D nanomaterials with improved properties