Self-templated synthesis of Co3O4 hierarchical nanosheets from a metal–organic framework for efficient visible-light photocatalytic CO2 reduction

Abstract

Efficient photocatalytic conversion of CO₂ into energy-rich chemicals is of great significance for both environmental conservation and alleviating the energy crisis. However, convenient synthesis of low-cost, durable and eco-friendly photocatalysts with a novel morphology or structure for highly selective photocatalytic CO₂ reduction remains a challenge. Herein, Co₃O₄ hierarchical nanosheets were synthesized by calcination of novel cobalt metal–organic framework (MOF) nanosheets prepared by a facile oil bath method. In such Co MOF nanosheets, 1,4-naphthalenedicarboxylic acid was chosen as the organic linker, rather than the commonly used 2-methylimidazole for ZIF-67. After thermal treatment in air, the obtained Co₃O₄ inherited the 2D morphology of its MOF template and evolved into hierarchical nanosheets which were composed of small nanoparticles. Benefiting from the large surface area, abundant mesoporous structure and good capability towards the separation and transfer of photo-generated charge carriers induced by less internal oxygen vacancies, the Co₃O₄ hierarchical nanosheets showed a CO generation rate of 39.70 μmol h⁻¹ in visible-light photocatalytic CO₂ reduction, which was superior to that of Co₃O₄ nanoparticles and commercial Co₃O₄. What's more, a CO selectivity of 77.3% was achieved, which is among the highest of cobalt-based spinel oxide photocatalysts for CO₂ conversion.