Effect of hydrothermal and deep eutectic solvent solvothermal pretreatments on the structural evolution of corncob-derived activated carbons for enhanced hydrogen storage and CO2 capture.

Agricultural residues are promising precursors for sustainable porous carbons, but their activation efficiency strongly depends on precursor chemistry. Here, corncob-derived activated carbons were prepared through three routes: direct KOH activation, hydrothermal carbonization followed by KOH activation, and acidic deep eutectic solvent (DES) solvothermal carbonization followed by KOH activation. The acidic choline chloride/phosphoric acid DES pretreatment substantially transformed the lignocellulosic precursor by promoting dehydration, deoxygenation, aromatic condensation, mineral removal, and precursor stabilization. Compared with direct activation and hydrothermal pretreatment, DES pretreatment produced a more carbon-rich and thermally stable precursor, enabling more effective KOH activation and ultramicropore development. The resulting DES-derived activated carbon showed the highest BET surface area of 3084 m2 g-1, total pore volume of 1.35 cm3 g-1, and micropore volume of 1.08 cm3 g-1. This structure delivered 3.08 wt% H2 uptake at 77 K and 1 bar, along with CO2 adsorption capacities of 8.98, 7.27, and 5.74 mmol g-1 at 273, 288, and 298 K, respectively. CO2 isotherm modeling, isosteric heat analysis, and adsorption-desorption cycling confirmed heterogeneous ultramicropore-filling physisorption with favorable reversibility. These results demonstrate that acidic DES-assisted precursor engineering is an effective strategy for converting corncob waste into high-performance activated carbon for hydrogen storage and carbon capture.