Polyethylene terephthalate (PET), a major plastic waste, was recycled into solid carbon by thermal decomposition under autogenic pressure. PET was carbonized at 500?1000 °C and the effect of temperature on the properties and yield of the synthesized carbons or char was studied and discussed using SEM, TEM, EDX, XRD, FTIR, and BET. The synthesized carbons (SC) exhibit a range of microporous to mesoporous structures with a pore volume and surface area ranging from 0.2029 to 0.0573 cm3 g?1 and 448.88 to 3.3 m2 g?1 respectively. SC was employed in the removal of methylene blue (MB) as a model dye and the effect of contact time was investigated. SC produced at 500 °C demonstrated the highest adsorption capacity of 77 mg g?1 due to its high surface area, porous structure, and surface functional groups.