Synergistic Enhancement of Cyclic CO2 Capture Using MgO-Functionalised Coconut Shell Hydrochar: An Experimental, Economic, and DFT Investigation

Transforming biomass waste into stable, safe, and economical adsorbents represents a critical pathway toward scalable and sustainable carbon capture. This study presents a synergistic magnesium oxide (MgO)-functionalised activated hydrocar derived from coconut shells, evaluated through an integrated experimental, economic and density functional theory (DFT) for enhance cyclic CO 2 capture. To identify the most effective MgO functionalised route, hydrothermal treatment (HT), wet impregnation (WI) and solid-state dispersion (SS) were evaluated. SS method with CO 2 uptake of 2.05   mmol/g, proved techno-economically superior, reducing capture costs by 20% through minimized processing steps and energy requirements. Optimisation identified 15   wt.% MgO loading as ideal balance between surface basicity and microporosity preservation. The composite exhibited a high specific surface area of 721.05 m 2 /g with the introduction of Mg-O-Mg functional groups at 579   cm -1 . The CO 2 adsorption capacity of MgO-functionalised activated hydrochar was optimised at 109 °C and 3.3   bar, with maximum capacity of 2.48   mmol/g, retaining 94% efficiency after 10 adsorption-desorption cycles shows exceptional stability, safer and long-term process operation. Additionally, molecular modelling was conducted to confirm the interaction and binding energy between the MgO and activated hydrochar with CO 2 . The study confirmed the improved performance of the MgO-functionalised activated hydrochar compared to non-functionalised, attributed to enhanced charge transfer with decrement in binding distance by 24%. This study validates MgO hydrochar is a promising material, waste derived adsorbent for enhances performance, cost, and process safety consideration for post- combustion carbon capture.