Synthesis of ZnO and SnO₂ catalysts using roselle flower extract for biodiesel production from waste cooking oil

¹ Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Islam Indonesia, Yogyakarta 55584, Indonesia
² Nanomaterials and Sustainable Chemistry Research Centre, Universitas Islam Indonesia, Yogyakarta 55584, Indonesia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

The development of biodiesel from waste cooking oil using green-synthesized heterogeneous catalysts offers a sustainable alternative to fossil fuels. In this study, ZnO and SnO₂ catalysts were synthesized using roselle flower (Hibiscus sabdariffa L.) extract and applied to transesterification. Characterization revealed that SnO₂ exhibited a surface area of 51.52 m²/g and a pore volume of 0.080 cm³/g, nearly 12 times higher than ZnO (4.11 m²/g; 0.009 cm³/g), resulting in superior catalytic activity. FTIR analysis of biodiesel catalyzed by ZnO showed ester-specific peaks at 1115 cm⁻¹ (C–O) and 1022 cm⁻¹ (C–O–C), while biodiesel from SnO₂ displayed a strong ester carbonyl band at 1744 cm⁻¹, confirming FAME formation. GC–MS results indicated that ZnO-catalyzed biodiesel consisted mainly of methyl oleate (60.23%), methyl palmitate (34.83%), methyl stearate (2.27%), and methyl myristate (0.34%), with a total FAME content of 97.34%. In contrast, SnO₂-catalyzed biodiesel contained methyl oleate (55.85%), methyl palmitate (37.12%), methyl stearate (4.50%), and methyl myristate (0.64%), yielding nearly 100% FAME. The dominance of methyl oleate and palmitate confirmed the production of high-quality biodiesel with balanced oxidative stability and combustion properties. Therefore, roselle- extract-based SnO₂ demonstrated greater potential than ZnO as an eco- friendly catalyst for biodiesel production from waste cooking oil.