Enhanced direct air capture by uranyl superoxide: a comprehensive study of the carbonation reaction of uranyl peroxide complexes†

Reactive oxygen species, such as superoxide, are known to engage in direct air carbon capture within strong base systems. Previous work has also suggested that U(VI) peroxide/superoxide solids may also engage in this process, although the phase behavior and kinetics of this system have not been explored. Herein, we report optimal conditions which promote carbonation of two potassium uranyl triperoxide phases and their analogous diperoxo superoxide forms. Raman spectroscopy and elemental analysis were used to monitor the carbonation reaction, and the data was subjected to Principal Component Analysis (PCA) to gain insight on the complex reactivity of these phases. These systems exhibited full carbon dioxide (CO₂) uptake at 22 °C when relative humidity is at least 45%. Further, carbonation of the uranyl peroxide complexes occurred under atmospherically relevant CO₂ concentrations, and we utilized a custom-built reaction chamber to evaluate the kinetics of this process. Our results identified conditions favoring the carbonation of uranyl peroxide complexes and provide insight on the mechanism of carbonate formation.