Preparation of activated carbons from CD waste for the adsorption of SO2 and NOx: a study by adsorption calorimetry

Abstract Plastic waste from compact disks (CDs) poses a significant environmental issue. In this work, such waste was repurposed as a precursor to synthesize activated carbons via chemical activation with KOH and H 3 PO 4 . The resulting materials were further functionalized with amino and acidic groups to enhance their adsorption capacity for gaseous pollutants, such as sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ). Textural analysis showed surface areas up to 1.200 m 2 g −1 , primarily composed of microporous structures (~ 2 nm). The functionalized materials demonstrated adsorption capacities of up to 75 mg g −1 for SO 2 and 62 mg g −1 for NO x , significantly surpassing those of their unmodified counterparts. The Sips isotherm and pseudo-second-order kinetic models well described the adsorption behavior. Importantly, adsorption calorimetry played a key role in this study by directly measuring interaction enthalpies, which reached up to –120 kJ mol −1 , indicating the presence of specific chemical interactions. These results highlight the potential of functionalized activated carbons derived from plastic waste as a sustainable, high-performance solution for capturing atmospheric pollutants, while also emphasizing the importance of calorimetry in advancing the understanding of gas–solid interactions.