Bismuth silicate (Bi4Si3O12 and Bi2SiO5) prepared by ultrasonic-assisted hydrothermal method as novel catalysts for biodiesel production via oleic acid esterification with methanol.

• Bismuth silicate as novel catalysts for biodiesel production via esterification. • Bi 4 Si 3 O 12 and Bi 2 SiO 5 catalysts prepared by ultrasonic-assisted hydrothermal method. • Catalyst acidity increase by increasing sonication time to 30 min then decreased. • Catalyst sonicated for 30 min (BS 30) exhibits the highest oleic acid conversion. • The most active catalyst (BS 30) exhibits good reusability till five runs. To date, there are no research in the literature on the esterification reaction for biodiesel production using bismuth silicate as catalyst. With the assistance of ultrasonication at different times, the bismuth silicate (BS) catalysts were successfully prepared by hydrothermal method and applied in oleic acid esterification with methanol for biodiesel production. The prepared catalysts were characterized by XRD, HR-TEM, BET, NH 3 -TPD and UV-vis/DR to reveal their physicochemical and optical properties. Further, the biodiesel sample was characterized by FT-IR analysis. The results of XRD and HR-TEM–EDS confirmed the preparation of Bi 4 Si 3 O 12 and Bi 2 SiO 5 phases by hydrothermal method at different ultrasonic irradiation times. Interestingly, the surface area, pore volume, total acidity and band gap energies of the prepared catalysts increase with increasing the ultrasonic irradiation time from 10 min to a maximum value at 30 min then decreased. It was observed that the catalyst sonicated for 30 min (BS 30) (Bi 2 SiO 5) exhibited the highest esterification conversion efficiency of 90% at optimized reaction conditions of 80 °C, molar ratio of methanol to oleic acid of 120, 0.3 g of catalyst and 2 h reaction time. The reusability of BS 30 catalyst was estimated by utilizing it for five runs with catalytic efficiency of 80%. [ABSTRACT FROM AUTHOR]