3.6. Effect of pore size
A big advantage of mesoporous materials is the possibility of
tuning their pore size by modifying synthesis parameters. In particular,
the pore size of the replicas of the KIT-6 silica template can be modified by filling one or two channels of its interpenetrated
network.
To study the influence of the pore size in the humidity sensing
properties, mesoporous CGO was synthesized by filling only one of
the two sets of interpenetrated channels and the fabricated sensor
is denoted as CGO-D. The micro-structural characterization of
the CGO-D synthesized powder is presented in the Supplementary
Information.
Fig. 12 shows a comparison of the response and recovery time
between the CGO and CGO-D mesoporous humidity sensors. The
response and recovery time of the CGO-D mesoporous sensor were
calculated to be 2.3 and 35.8 s. Both response and recovery times
are faster compared with the CGO sensor. The bigger pore size (over
∼10 nm) of the CGO-D seems to have a positive influence in the
dynamic response ofthe humidity sensors. The smaller pores ofthe
sensor CGO (∼4 nm) can limit the diffusion of the water molecules,
reducing the rates of the adsorption–desorption processes. Differences
shown in the impedance under dry conditions could be
explained by the non-normalized thicknesses of both sensing layers.
However the amplitude of the response (R) is very similar
for both sensors attributed to the similar surface area (BET) (see
Supplementary Information).