Porous carbons derived from polyethylene terephthalate (PET) waste for CO₂ capture studies

Oxygen augmented carbon adsorbent has been developed using polyethylene terephthalate (PET) waste by first carbonizing at different temperatures (500-800 °C) and then chemically activating using different ratios of KOH: PET (mass ratio 1 to 4). The textural characterization divulges the effect of activation in terms of the development of the high surface area and micropore volume of 1690 m² g^-1 and 0.78 cm³ g^-1 respectively, for the optimum sample (PET-3-700). Elemental analysis of PET-3-700 illustrates the presence of 34.33% oxygen and XPS results confirmed the occurrence of oxygen moieties which enhance the basicity of the adsorbent and promote CO₂ capture. The CO₂ adsorption capacity of prepared carbons was determined thermogravimetrically under dynamic conditions, at different concentrations of CO₂ (6-100%) and temperatures. The maximum CO₂ uptake capacity of 2.31 mmol g^-1 was exhibited by PET-3-700 at an adsorption temperature of 30 °C under 100% pure CO₂ flow. Four adsorption-desorption cycles corroborate almost complete regenerability of the prepared adsorbent. Adsorption kinetics at all adsorption conditions was described best by fractional order kinetic model. Freundlich isotherm fit indicates the surface of adsorbent being heterogeneous and low values of isosteric heat shows physisorption behavior of the process. Negative values of thermodynamic parameters indicate exothermic and feasible nature of adsorption process.