Energy sources are necessary for human existence, comfort, and progress. Limited crude petroleum resources and increasing awareness of the environmental impacts of using fossil fuels motivate the search for new energy sources and alternate fuels. Herein, a low cost, fast, and green methodology for the synthesis of a hybrid solid base catalyst, strontium oxide coated millimetric silica beads (SrO@SiO 2 ), is designed for the transesterification of cooking oil into biodiesel in a domestic microwave oven. The cost reduction is due to the effective utilization of the catalyst by the homogeneous dispersion of the active sites on the silica beads and their reusability. The catalyst synthesis process was optimized with respect to the amount of glass beads, microwave irradiation time, calcination time, and calcination temperature. Several methods for synthesizing SrO by minimizing energy consumption were investigated, and an optimized process for designing SrO@SiO 2 was developed. The SrO@SiO 2 catalyst produced under optimum conditions was characterized by TGA, XRD, FTIR, ICP, SEM, and TEM. XRD analysis indicated peaks typical of SrO alone. ICP analysis indicated 41.3 wt % deposition of SrO on silica beads. The novel solid base catalyst thus generated was used for the transesterification of waste cooking oil. Conversion values as high as 99.4 wt % in 10 s irradiation were observed from 1 H NMR analysis using this composite catalyst, indicating the feasibility of economical biodiesel production from cooking oil waste in a very short time.

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The main goal of this study is to functionalize SrO with carbon dots (C-dots) and to explore the composite as a catalyst for fatty acid methyl esters (FAME) production using Chlorella vulgaris as feedstock. C-dots are synthesized by sonicating polyethylene glycol followed by sonochemical modification of Sr­(NO3)2 (precursor for SrO) with C-dots. Sonication facilitates the adhesion of C-dots to the surface of Sr­(NO3)2. The resulting material is calcined in an inert environment to form a SrO–C-dot composite. The effect of functionalizing SrO with C-dots on the transesterification of the lipids in the alga with methanol is studied. The optimization of a one-stage process of conversion of the lipid fraction of microalga Chlorella vulgaris into FAME using direct transesterification under microwave irradiation is illustrated. A lipid conversion value of 45.5 wt % is achieved using the SrO–C-dot catalyst after 2.5 min of microwave (MW) irradiation. The catalyst displayed better activity than commercial SrO. Microwave irradiation accelerates the disruption of the microalgal cells and facilitates the release of lipid content into the reaction medium. The catalyst is characterized by a variety of physicochemical techniques. The FAME product obtained from the alga is quantified using 1H NMR spectroscopy. The new catalyst, namely, SrO–C-dot nanoparticles (NPs), yielded 97 wt % FAME from Chlorella vulgaris in 2.5 min of MW irradiation.

Biodiesel is a renewable and environmentally friendly alternative to fossil fuels. Despite nearly 3 decades of research in the field of biodiesel, there remains major obstacles for large-scale production. In the search for an active, selective, and reusable solid base catalyst, strontium oxide (SrO) is emerging out as a preferred choice for the transesterification reaction under various methods of activation. SrO exhibits the highest activity among processable alkaline earth metal oxides as a result of its strong basicity. SrO nanoparticles (NPs) and hybrids showed improved performance. Recent progress achieved in the development of synthetic methods of SrO NPs is reviewed. Advantages of SrO-based nanocomposites for biodiesel production are discussed. Finally, potential support materials for enhancing the catalytic performance of SrO NPs with commercial implications are elaborated.