Towards low-cost and sustainable activated carbon production: Influence of microwave activation time on yield and CO2 uptake of PET-derived adsorbents

Microwave (MW) heating is proposed as a method to transform polyethylene terephthalate (PET) into porous adsorbents. The yield, textural properties, and CO₂ uptake of the PET-derived adsorbents irradiated at different durations (3 – 35 min) at 400 °C were assessed. MW activation time influenced both the physical properties and CO₂ uptake capacities of the resulting adsorbents. The yield decreased with activation time, but the surface area, total pore volume, micropore volume, and CO₂ uptake capacities all increased with MW activation time before declining. The optimal sample (produced with 5 min of MW activation time) showed improved textural properties as well as higher equilibrium and dynamic CO₂ uptakes than the commercial activated carbon used as reference. This adsorbent also possesses good selectivity for CO₂ in the binary 10:90%vol/vol CO₂: N₂ mixture. Additionally, an excellent recyclability over 20 cycles, (Regeneration Efficiency > 97%) was observed, and the CO₂ adsorption kinetics best fits Lagergren’s pseudo-second-order model. This study has shown that a low activation temperature (400 °C), a short MW activation time (5 min), and a low amount of chemical agent (KOH, 0.72 M) could produce CO₂ adsorbents from a cheap and abundant material (PET-waste) with better CO₂ uptake to that of a commercial activated carbon.