Capture of CO2 is a crucial process to achieve carbon neutrality. High-performance CO2 capture involves both physi- and chemi-sorption, with a transition between them. However, the underlying mechanistic insights required to produce the methods to tune the transition are poorly understood. Here, we describe a series of 1,2,4triazolate ionic liquids (TZ ILs) that capture > 0.7 mol CO2/mol TZ IL in a two-stage absorption process. Physiand chemi-sorption were studied by spectroscopy using (CO2)-C-13 and the transition between the two sorption modes has been identified. UV-Vis, FT-IR and NMR spectroscopy as well as density and viscosity measurements demonstrate that physisorption is initially the dominant process whereas later chemisorption predominates. Based on the identification of key species combined with theoretical modelling, a plausible molecular-level mechanism is proposed for the transition between the two sorption modes. These mechanistic insights enable the transition of CO2 capture to be tuned.