Melamine-doped plastic-derived adsorbents for carbon capture: the influence of plastic type on textural properties and CO2 uptake.

Melamine-doped adsorbents were synthesized from single PET and mixed plastics (MP) via the 2-pot method involving co-carbonisation with melamine, followed by KOH impregnation, and thermal activation. Under dynamic conditions at 25 °C and 1 bar, the PET- and MP-doped adsorbents exhibited CO₂ adsorption capacities of 1.98 and 1.59 mmol g −1 , respectively, representing 10.6 and 17.8 % increase over their N-free counterparts (PET: 1.79 mmol g −1 ; MP: 1.35 mmol g −1 ). This also indicates that melamine doping had a greater impact on the adsorptive properties of the material derived from mixed plastics. Both doped adsorbents also showed excellent cyclic stability, maintaining regeneration efficiencies above 85 % over ten cycles, although slightly lower than the > 90 % seen in N-free adsorbents tested under the same regeneration conditions (100 °C with 50 mL min −1 of N 2 ). Elemental analysis revealed higher nitrogen incorporation in N-MP (1.37 wt%) than in N-PET (0.24 wt%), despite an identical added amount of melamine, suggesting more efficient N-doping in the mixed plastics compared with PET. Although doped adsorbents exhibited lower surface area, total pore volume, and micropore volume compared to their N-free versions, they showed higher ultra-micropore volumes, which can enhance affinity for CO₂ adsorption at the pressure tested. Lastly, the type of plastic precursor had minimal effect on the adsorption mechanism or kinetics, as all adsorbents followed the Sips isotherm and Avrami’s kinetic models. • N-doped plastic-ACs were prepared through carbonisation and activation. • Single and mixed plastic samples doped with melamine show improved CO 2 adsorption. • Melamine doping has a stronger impact on mixed rather than single plastic-derived ACs. • Doped-ACs show greater CO 2 capture, explained by the higher ultra-micropores and N-content. • N-doping yields greater CO 2 adsorption enhancement in mixed plastic-based adsorbents (17.8 %) than single plastic-derived AC (10.6 %).