Constructing ultramicropore-rich coal-based carbon materials via co-carbonization of heterogeneous carbon for efficient CO₂ capture

Coal-derived porous carbons are promising adsorbents for cost-effective CO₂ capture, yet their adsorption performance remains limited by low micropore volume, which is related to weak coal’s intrinsic activity during thermochemical conversion. Herein, a structural regulation strategy based on the co-pyrolysis of bituminous coal (BC) and polyethylene terephthalate (PET) is proposed, which aims to modulate the development of defects and microcrystalline structures within the coal matrix through interactions with exogenous free radicals, thereby optimizing potassium-based activation reactivity. Ultimately, this approach enables the targeted construction of activated carbon materials characterized by abundant ultramicropores and significantly enhanced CO₂ adsorption capacity. The results demonstrate that the incorporation of PET significantly facilitates the cleavage of oxygen-containing groups, increases aromaticity and defect density, and enhances the responsiveness to KOH activation. Concurrently, a short-range ordered microcrystalline structure is formed, leading to reduced oxygen content and lower adsorption heat of the resulting carbons. Under optimal conditions with pre-carbonization at 400 °C, activation at 750 °C, and a PET addition of 20 wt%, the obtained sample (AC-20PETBC) exhibits a high micropore fraction of 91.41%, a micropore volume of 0.49 cm³ /g, and a CO₂ uptake of 4.12 mmol/g at 25 °C (5.65 mmol/g at 0 °C). This work demonstrates that PET-coal co-pyrolysis not only provides an effective route for tailoring the ultramicroporous structure of coal-based carbons, but also enables the environmentally benign and resource-efficient valorization of plastic waste.