2D MXene Nanosheet-Stabilized CaO for Enhanced Cyclic CO2 Capture and Energy-Efficient Calcium Looping

Abstract CO2 capture using multi-cycle carbonation-calcination in calcium looping (CaL) is a promising strategy for reducing industrial carbon emissions; however, it suffers from rapid deterioration in CaO sorption capacity due to sintering and high energy requirements for regeneration. In this study, 2D-MXene nanosheet-modified CaO is proposed to enhance cyclic sorption performance and thermochemical behavior. 2D-MXene nanosheets (0.25−5 wt %) were incorporated using a simple dry-mixing approach to modify the CaO structure and evaluate its effect on cyclic stability. Structural and morphological analysis indicates that 2D-MXene incorporation is associated with reduced CaO crystallite size, improved preservation of textural characteristics, and higher accessible surface area, which are consistent with improved effective carbonation kinetics under the investigated conditions. The 1 wt % 2D-MXene-modified CaO (Ca-MX1) exhibits the best CO2 sorption performance, achieving ∼8.5 mol kg−1 in the first cycle and ∼4.9 mol kg−1 after 10 cycles at 650 °C, which is 69% higher than pure micron-sized CaO (m-CaO,∼2.9 mol kg−1). Thermochemical analysis shows that calcination and carbonation enthalpies follow sorption behavior, with m-CaO exhibiting a rapid decline in sorption capacity due to structural degradation, while the 2D-MXene-modified sample retains higher values over cycles. At comparable CO2 sorption capacities, Ca-MX1 exhibits approximately 20% lower normalized calcination enthalpy than m-CaO, indicating improved regeneration behavior at the material level under the investigated conditions. Kinetic analysis using the SCM and RPM indicates higher fitted reaction-rate and effective−diffusivity parameters for Ca-MX1, consistent with a greater contribution of reaction-controlled carbonation over the investigated conversion range and reduced apparent transport resistance compared with m-CaO. Overall, the incorporation of low-loading 2D-MXene improves the measured structural retention, cyclic CO2 capture performance, and material-level thermochemical behavior of CaO under the investigated laboratory conditions. These findings demonstrate the potential of low-loading 2D-MXene as a structural stabilizer for CaO-based calcium looping sorbents.