Reactive adsorption of NO2 over the NaCoO2–Co3O4 nanocomposite: experimental study and first-principles calculations

Abstract

We have fabricated a NaCoO₂–Co₃O₄ nanocomposite through high-temperature calcination of a Na,Co-MOF precursor. The resulting nanocomposite features Co₃O₄ polyhedral nanoparticles decorated over NaCoO₂ nanosheets. The composite possessed a surface area of 21.0 m² g⁻¹, surpassing that of the MOF. The composite was studied for its capacity to adsorb NO₂ gas (100 ppm) in ambient conditions, demonstrating a substantial capacity of 68.1 mg g⁻¹. However, this adsorption capacity was influenced negatively by factors such as moisture, increased gas flow rate, and reduced bed loading. Spectroscopic analysis and theoretical calculations revealed that NO₂ exhibited a higher tendency to adsorb onto the NaCoO₂ component than Co₃O₄. Apart from NO evolution, the adsorbed NO₂ molecules underwent redox reactions on the composite's surface, yielding nitrite and nitrate species. Thus, for the first time, we have confirmed that Na–Co oxide effectively cleans lean sources.