The
ability to dictate the assembly of quantum dots (QDs) is critical
for their integration into solid-state electronic and optoelectronic
devices. However, assembly methods that enable efficient electronic
communication between QDs, facilitate access to the reactive surface,
and retain the native quantum confinement characteristics of the QD
are lacking. Here we introduce a universal and facile electrochemical
gelation method for assembling metal chalcogenide QDs (as demonstrated
for CdS, ZnS, and CdSe) into macroscale 3-D connected pore-matter
nanoarchitectures that remain quantum confined and in which each QD
is accessible to the ambient. Because of the redox-active nature of
the bonding between QD building blocks in the gel network, the electrogelation
process is reversible. We further demonstrate the application of this
electrogelation method for a one-step fabrication of CdS gel gas sensors,
producing devices with exceptional performance for NO2 gas
sensing at room temperature, thereby enabling the development of low-cost,
sensitive, and reliable devices for air quality monitoring.
Control
of nanoparticle assembly is a critical enabler for fabricating
nanostructures capable of complex, system-level functionality. Here,
we report a facile electrochemical method for assembling quantum dots
(QDs) into mesoporous gels directly onto an electrode surface using
localized, in situ generated metal ion crosslinkers (Ni2+, Co2+, Ag+, or Zn2+) within a colloidal
solution of metal chalcogenide nanoparticles capped with ligands featuring
pendant carboxylate groups. A mechanistic study reveals a critical
stoichiometry of 0.5 metal ions: 1 QD in solution is required to trigger
metal ion-mediated electrogelation (ME-gelation), representing a much
lower concentration of metal ions than is needed for initiating crosslinking
throughout an entire volume of solution (>26 metal ions: 1 QD in
solution).
The application of the ME gelation approach for the fabrication of
QD-based electronic devices is demonstrated by electrochemical patterning
of QD gels onto a printed circuit board chip.
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