Facile tailoring of Co-based spinel hierarchical hollow microspheres for highly efficient catalytic conversion of CO2.

High-performance and low-cost photocatalysts are of significance to artificial photosynthetic systems for converting of CO2 into CO and other value-added products. In this work, we developed a controllable and scalable self-templated approach to fabricate hierarchical Co-base spinel hollow microspheres for visible light-driven CO2 reduction with a Ru-based sensitizer. The hollow microspheres are assembled by ultrathin nanosheets using Ni-Co-hydroxides as the morphology-conserved precursor. A series of characterization techniques were conducted to investigate structural features of the prepared Co-base spinel hollow spheres. Owing to the integration of the specific microstructure, functional Ni/Co species and oxygen vacancies, Co-base spinel hollow spheres possess enhanced CO2 adsorption ability, more active sites, and efficient transfer and separation of photoexcited electrons. The high CO-evolving rate (27.7 µmol h-1) and selectivity (84.4%) manifest desirable performance of Co-base spinel hollow spheres for CO2 photocatalytic reduction. The findings suggest that such spinel-structured bimetallic oxides hierarchical hollow spheres, facilely synthesized via the proposed self-templated method, are efficient for photocatalytic CO2 reduction.

Synergetic Effect of Facet Junction and Specific Facet Activation of ZnFe2O4 Nanoparticles on Photocatalytic Activity Improvement.

Crystal facet engineering has been proved as a versatile approach in modulating the photocatalytic activity of semiconductors. However, the facet-dependent properties and underlying mechanisms of spinel ZnFe2O4 in photocatalysis still have rarely been explored. Herein, ZnFe2O4 nanoparticles with different {001} and {111} facets exposed were successfully synthesized via a facile hydrothermal method. Facet-dependent photocatalytic degradation performance toward gaseous toluene under visible light irradiation was observed, where truncated octahedral ZnFe2O4 (ZFO(T)) nanoparticles with both {001} and {111} facets exposed exhibited a superior performance than the others. The formed surface facet junction between {010} and {100} facets was responsible for the improved activity by separating photogenerated e-/h+ pairs efficiently to reduce their recombination rate. Photogenerated electrons and holes were demonstrated to be immigrated onto {001} and {111} facets, separately. Intriguingly, electron paramagnetic resonance trapping results indicated that both •O2- and •OH were abundantly present in the ZFO(T) sample under visible light irradiation as major reactive oxygen species involved in the photocatalytic degradation process. Additionally, further investigation revealed that {001} facets played a predominant role in activating photogenerated transient species H2O2 into •OH, beneficially boosting the intrinsic photocatalytic activity. This work has not only presented a promising strategy in regulating photocatalytic performance through the synergetic effect of facet junction and specific facet activation but also broadened the application of facet engineering with multiple effects simultaneously cooperating.