Catalytic efficiency and stability of biomass-derived sulfonated graphene catalysts in microwave-enhanced biodiesel production

•Embarks on novel bio-based graphene catalysts syntheses from biomass.•Unfolds their potential for microwave-assisted transesterification of palm oil.•Exceeding EN14214, the highest 97.45% FAME yield is achieved.•Demonstrate lower catalyst usage, temperature, and time than prior studies. The strategic integration of bio-based catalytic design principles and the intricacies of microwave irradiation offers a viable path to improving the sustainability and efficiency of biodiesel production. In this work, we produced novel biomass-derived sulfonated graphene oxide (bGO-SO3H) and reduced graphene oxide (brGO-SO3H), examining their collaborative effects with microwave irradiation on reaction efficacy. Sulfonation in catalysts was evident through 1) reduced mass loss during thermal decomposition (bGO-SO3H: 34.5 %; brGO-SO3H: 29.4 %) compared to precursors (bGO: 55.6 %; brGO: 20.3 %), indicating decreased oxygen-containing functional groups; 2) higher TPD-acidic sites (bGO-SO3H: 3.17 mmol g−1; brGO-SO3H: 3.24 mmol g−1), supported by titration-acid density (bGO-SO3H: 2.97 mmol g−1; brGO-SO3H: 3.83 mmol g−1); and 3) additional C1s peaks attributed to C-S bonds in sulfonic moieties and a significant increase in sp2 carbon content compared to their precursors, confirmed by ID/IG ratio reduction (bGO-SO3H: 1.09 to 0.98, brGO-SO3H: 0.99 to 0.95). Despite modest surface areas (18–44 m2/g), both catalysts exhibited significantly elevated acid densities (0.05–4.83 mmol g−1) post-sulfonation. Under optimized conditions (2 wt% catalysts, 25:1 methanol-to-oil ratio, 25 min at 75 °C), bGO-SO3H yielded 90.97 % FAME yield, while brGO-SO3H achieved 97.45 % with a reduced dosage (1.5 wt%), shorter time (20 min), and less methanol (20:1). Despite catalytic deactivation, our study demonstrates reduced catalyst consumption, a lower reaction temperature, and a shortened conversion time compared to prior findings, thereby enhancing the efficiency of biodiesel production.