Elucidating the carbochromism of K3[V(O2)4] with ab initio modeling

Abstract

Direct Air Capture (DAC) reactions are increasingly being studied for their potential role in climate mitigation strategy. Color transformations triggered by reactions with carbon dioxide---a phenomenon we term carbochromism---are a less considered aspect of DAC chemistry. We previously noted how the conversion of solid K₃[V(O₂)₄] into K₃[VO(O₂)₂(CO₃)] from CO₂ exposure is associated with a blue to yellow color change. Decomposition of the carbonate product produced K[VO₃] and a white coloration. Density-functional theory (DFT) simulations undertaken here reveal the chemical origin of this color change to be from hybridization between the vanadium-3d and oxo-2p orbitals that both widens the band gap from reactants to products and narrows the d-orbital splitting in the visible region. Powder samples of the three materials were independently synthesized and measured for optical absorption, corroborating the computationally predicted color coordinates. Our phenomenological description can inform the selection of next-generation DAC sorbents with favorable color-change properties.