Hierarchically Porous
CuO Hollow Spheres Fabricated
via a One-Pot Template-Free Method for High-Performance Gas Sensors
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Abstract
CuO hollow spheres with hierarchical pores, that is,
quasi-micropores
(1.0–2.2 nm), mesopores (5–30 nm), and macropores (hollow
cores, 2–4 μm), have been synthesized via a simple one-pot
template-free method. The CuO hollow spheres also show a hierarchical
architecture, namely, the primary CuO nanograins, the quasi-single-crystal
nanosheets assembled by nanograins, and the spheres composed of the
nanosheets. A mechanism involving an “oriented attachment”
growth step followed by an “Ostwald ripening” process
has been proposed for the hierarchical structure and pore formation
of the typical CuO hollow spheres. With such unique hierarchical pores
and architecture, the CuO hollow spheres display excellent sensing
performance toward H<sub>2</sub>S as gas sensing material, such as
low detection limit of 2 ppb, high sensitivity at parts per billion
level concentration, broad linear range, short response time of 3
s, and recovery time of 9 s. The excellent performance is ascribed
to a synergetic effect of the hierarchical structure of the unique
CuO spheres: the quasi-micropores offer active sites for effectively
sensing, the mesopores facilitate the molecular diffusion kinetics,
and the macropores serve as gas reservoirs and minimize diffusion
length, while good conductivity of the quasi-single-crystal nanosheets
favors fast charge transportation, which contribute to the high sensitivity,
quick response, and recovery of the H<sub>2</sub>S sensor, respectively