Visible light-driven photocatalytic biodiesel production using novel SnS2/Fly ash photocatalyst

The exponential depletion of fossil fuels urges humankind to explore alternative energy sources for petroleum products. Biodiesel is a greener and environmentally friendly alternative to petroleum diesel and could be used in diesel engines. Fly ash is powdery waste produced in overabundance by coal combustion in thermal power plants. Scientists are continuously searching for ways to provide a new dimension to the utilization of fly ash for creating “Best out of Waste”. The current study elucidates the synthesis of a pioneering visible light active SnS₂/Fly ash nanocomposite, emphasizing its photocatalytic activity in biodiesel production. Oleic acid was used as the test substrate since it is often found in several biodiesel feedstocks, such as waste soybean, waste frying, and palm oil. The optimization of the reaction conditions gives the highest biodiesel yield of 99.89 ± 0.10 % at photocatalyst loading of 3 wt%, methanol-to-oleic acid ratio of 8:1 at 338 K within 50 min light exposure. The reaction kinetics were observed to conform to a pseudo-first-order kinetic model, characterized by a rate constant of 0.1488 min⁻¹, and the activation energy necessary for the photocatalytic esterification of oleic acid was 29.16 kJ/mol. The scavenging tests suggested that the excitation of electrons is crucial to initiate the photocatalytic reaction, and the mechanism of the esterification reaction was proposed. The synthesized SFA photocatalyst was very stable and reusable, maintaining efficiency across five successive esterification cycles with a biodiesel yield of 82.07 ± 1.12 %, indicating the potential of SFA nanocomposite to replace existing heterogeneous thermal catalysts for biodiesel production.