Green synthesis of CaO nanocatalyst using watermelon peels for biodiesel production

Biodiesel is becoming an alternative renewable energy source as it is safe, biodegradable, and eco-friendly. Biomass-based, heterogeneous CaO nanocatalyst, prepared using watermelon peel extract was exhibited to be an outstanding catalyst for biodiesel synthesis from the transesterification of soybean oil. The optimal reaction parameters were: methanol to oil molar ratio of 20:1, catalyst content of 8 wt.%, reaction time of 2.5 h, and temperature of 65 °C. Several analytical techniques such as XRD, XPS, FT-IR, BET, SEM, TEM, and TGA were used exhaustively to study the thermal stability, chemical composition, and morphology of the green CaO nanocatalyst. Furthermore, the prepared biodiesel was characterized by 1H NMR, 13C NMR, and GC. The catalyst showed admirable stability on repetitive reuse and was found to be stable up to 5th reused cycle where a decent biodiesel yield of 81.3% was obtained.