Upcycling PET waste into porous activated carbon via KOH activation using microwave-assisted and conventional direct thermal approaches

The increasing accumulation of plastic waste, especially polyethylene terephthalate (PET), raises serious environmental concerns. This study investigates the conversion of PET waste into activated carbon using Direct Thermal Activation (DTA) and Microwave-Assisted Activation (MAA) methods. Production was optimized by varying the KOH to PET mass ratio (1:1 to 3:1) in DTA, and microwave power (600–900 W) with irradiation times (30–60 min) in MAA. The resulting carbons were characterized by BET, TGA/DSC, FESEM-EDX, FTIR, zeta potential, and X-ray fluorescence (XRF). MAA yielded higher carbon production efficiency (57% vs. 29%), whereas DTA achieved a much larger surface area (2035 vs. 371 m 2 /g). Morphological analysis showed that MAA produced smaller and more uniform pores. Elemental analysis confirmed increased carbon content and decreased oxygen in both methods, indicating effective carbonization. XRF analysis verified the high elemental purity of the synthesized carbons, revealing low concentrations of inorganic impurities (e.g., Si, Al, Fe, and Sb). TGA results indicated higher thermal stability for MAA samples, with a decomposition peak at 607–624 °C compared to DTA samples (600 °C). Zeta potential measurements indicated acidic surface groups, with higher microwave power enhancing reactivity and lowering the pH pzc . Consequently, while DTA produces carbons with superior surface area and microporosity, the MAA method is a more efficient alternative due to its significantly reduced processing time and higher product yield. Therefore, the choice of method depends on the target application and its priorities.