Simultaneous
Photodeposition
of an Ag–Co Cocatalyst
in Different pH Conditions To Improve the Activity of Calcium Titanate
Photocatalyst for Carbon Dioxide Reduction with Water
posted on 2023-11-07, 14:11authored byHongxuan Qiu, Akira Yamamoto, Eri Fudo, Atsuhiro Tanaka, Hiroshi Kominami, Hisao Yoshida
Photocatalytic CO2 reduction
with water has
been recognized
as an emerging technology in view of atmospheric CO2 mitigation.
Hence, further development of photocatalysts has been desired, where
especially the suitable design of cocatalysts should be considered.
In this work, it is revealed that solution pH adjustment in a simultaneous
photodeposition (SPD) method to load Ag–Co cocatalysts on calcium
titanate (CTO) photocatalyst surface provides various compositions
and structures of cocatalysts, and both the optimal basic and acidic
conditions provide highly efficient cocatalysts in contrasting ways
compared to a neutral condition. In an optimal alkaline condition
(pH = 10.5), redox chemical reaction between Ag and Co cations naturally
provides Ag–Co3O4 composites on the CTO
surface, and successive photoirradiation fabricates Ag–Co3O4 species with a unique core–shell structure
on the reduction facet while it does not change the state of Ag–Co3O4 composites on the oxidation facet. The unique
Co3O4 shell of the former structure assists
the Ag nanoparticle (NP) core to catalyze the CO2 reduction
with photoexcited electrons and protons while the latter species promoted
the generation of oxygen compared to single Co3O4 and Co(OH)2 species. These two types of cocatalysts jointly
worked to accelerate the photocatalytic CO2 reduction to
form CO about 4 times. On the other hand, an acidic condition (pH
= 1.0) of the SPD procedure prevents the Co cocatalyst from depositing
on the CTO surface and provides larger spherical Ag NPs, which is
responsible for the nearly 2 times enhancement of CO evolution rate.
Overall, this study proposed the benefit of adjusting the pH conditions
in the SPD method to form the corresponding structures of cocatalysts
for the improvement of the efficiency of photocatalytic CO2 reduction.