Sri Rahmawati, Akhmad Faruq Alhikami, Ahmad Taufiq, Ria Aniza, Moh Ansori, Ahmad Alan Yanuarta
The development of high-performance catalysts from waste-derived, circular economy precursors is crucial for the advancement of renewable energy systems. This study reports a novel, energy-efficient magnetic Fe₃O₄/CaO nanocatalyst synthesized entirely from waste and natural resources: iron sand and eggshell waste. Unlike traditional methods, a synchronous impregnation strategy was utilized to introduce CaO during the formation of the Fe₃O₄ phase. This approach successfully modified the Fe₃O₄ crystalline structure, embedding strong basic catalytic sites while maintaining high magnetic susceptibility for rapid recovery. Structural characterization confirmed that this synergistic integration prevents CaO leaching and enhances stability. Catalytic performance was evaluated for the transesterification of soybean oil using a Taguchi L16 design to minimize energy expenditure. The system achieved a 91.8% biodiesel conversion under significantly milder conditions than existing literature (60 °C, 1 wt% total catalyst loading, and 60 min reaction time) using the optimal 3 g CaO-loaded magnetic nano-catalyst (FeCa3). By reducing operating severity, this catalyst addresses the limitation of high energy consumption in biodiesel production. The Fe₃O₄/CaO system facilitates rapid magnetic separation, which simplifies catalyst recovery and downstream processing. This work presents a scalable, waste-to-catalyst platform that bridges the gap between material sustainability and process intensification, offering a viable pathway for cost-effective, low-carbon biofuel manufacturing. © 2026 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/
Department of Mechanical Engineering, Universitas Kristen Cipta Wacana, Jl. Karel Satsuit Tubun 28A, Malang, 65149, Indonesia; Department of Mechanical Engineering, Faculty of Engineering, Universitas Islam Malang, Jl. Mayjen Haryono 193, Malang, 65144, Indonesia; Agro-Renew Centre for Energy, Water, and Environment Technologies, Faculty of Engineering, Universitas Islam Malang, Jl. Mayjen Haryono 193, Malang, 65144, Indonesia; Department of Physics, Faculty of Mathematics and Natural Science, Universitas Negeri Malang, Jl. Semarang 5, Malang, 65145, Indonesia; Université de Lorraine, INRAE, LERMAB, Epinal, F88000, France; International Doctoral Degree Program in Energy Engineering, National Cheng Kung University, Tainan, 70101, Taiwan
