In this study, a novel idea was proposed to convert the polyethylene terephthalate (PET) waste drinking-water bottles into activated carbon (AC) to use for waste cooking oil (WCO) and palm fatty acid distillate (PFAD) feasibility to convert into esters. The acidic and basic char were prepared by using the waste PET bottles. The physiochemical properties were determined by employing various analytical techniques, such as field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Brunauer–Emmett–Teller (BET) and temperature-programmed desorption – ammonia/carbon dioxide (TPD-NH₃/CO₂). The prepared PET H₃PO₄ and PET KOH showed the higher surface area, thus illustrating that the surface of both materials has enough space for impregnation of foreign precursors. The TPD-NH₃ and TPD-CO₂ results depicted that PET H₃PO₄ is found to have higher acidity, i.e., 18.17 mmolg⁻¹, due to the attachment of phosponyl groups to it during pretreatment, whereas, in the case of PET KOH, the basicity increases to 13.49 mmolg⁻¹. The conversion results show that prepared materials can be used as a support for an acidic and basic catalyst for the conversion of WCO and PFAD into green fuel.

In this study, black carbon derived from polyethylene terephthalate (PET) wastes was utilized as the precursor for heterogeneous bifunctional nanocatalyst, which successively catalyzed waste cooking oil into biodiesel. The nano-sized catalysts were prepared by impregnation method with different heat treatment techniques, such as reflux, hydrothermal, and microwave solvothermal, to provide good distribution of K₂O and NiO particles on PET activated carbon mesoporous surface. The sample treated with microwave solvothermal technique (MAC-K₂O-NiO) exhibited a high surface area of 120 m²/g with good dispersion of nanoparticles, as shown by FESEM image, large crystallite size of 62.2 nm, and consisted of a highest density of basicity (2.58 mmol/g) and acidity (1.79 mmol/g) for improving transesterification to a maximum yield. The catalytic transesterification of MAC-K₂O-NiO was optimized with 3 wt.% of catalyst loading, 18: 1 methanol-oil molar ratio, 65 °C for 3 h of reaction, with a maximum yield of 97.2%. The catalyst reusability was performed, and it was found to maintain the catalytic activity up to six reaction cycles, with a yield of 72.9%. The physiochemical quality of the optimized biodiesel was examined in accordance with the American Society for Testing and Materials, ASTM D6751 testing method.