Highly efficient SnS2-based photocatalyst: A green approach to biodiesel production

Abstract

Biodiesel, a promising alternative to traditional petroleum fuels, is a green energy solution. Photocatalysis is a facile, novel, economic, and efficient approach to biodiesel synthesis. Metal sulfides have been used extensively for various photocatalytic applications. The present study demonstrates, for the first time, the photocatalytic production of biodiesel using a novel metal sulfide-based heterogeneous photocatalyst under visible light irradiation.

A nano zero-valent silver doped hydroxyapatite (Ag/HAp) was synthesized using a green bio-reductant technique and decorated with tin sulfide nanoparticles (SnS₂/Ag/HAp or SAH) for photocatalytic biodiesel synthesis. The hydroxyapatite (HAp) was extracted from waste fish scales to minimize the use of chemicals and to utilize waste for useful applications. The prepared SAH photocatalyst was characterized through X-ray diffraction, UV-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, Fourier transform infrared analysis, energy dispersive X-ray analysis, scanning electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy analysis. The effect of reaction parameters was optimized, and under optimum conditions of 1 wt% photocatalyst loading, and 8:1 methanol-to-oleic-acid ratio, for 60 min, a high yield of 98.0 ± 0.61% could be achieved using a SAH photocatalyst.

Scavenger tests indicated the simultaneous generation of photoinduced electrons and holes necessary for photocatalytic biodiesel synthesis. A mechanism for the photocatalytic esterification reaction of oleic acid is proposed. The synthesized SnS₂-based photocatalyst could be easily recoverable and reusable for five consecutive runs, which can replace traditional industrial heterogeneous catalysts in the near future.