Advances in photocatalytic biodiesel production: Preparation methods, modifications and mechanisms

Abstract

The increased demand for fossil fuels, environmental pollution, and global warming calls for an alternative renewable energy source to power the world. Biodiesel has emerged as a potential candidate in place of petroleum-based diesel as a green and sustainable energy source. Biodiesel is the result of the (trans)esterification of oils or fats with single-chain alcohol. With the increasing demand for biodiesel, several new strategies have been proposed to synthesize biodiesel efficiently in less time. Several heterogeneous catalysts have been developed to enhance the rate of (trans)esterification reaction, but they still have drawbacks, such as harsh reaction conditions and high energy consumption. Photocatalytic biodiesel production is an eco-friendly, energy-efficient, new strategy for synthesizing biodiesel using semiconductor photocatalysts under light irradiation. Various metal oxide-based photocatalysts have been utilized for photocatalytic biodiesel production with efficiencies of over 95 %. However, metal oxides have a higher bandgap, which requires high-energy light to generate electron-hole pairs. Scientists are still working on the development of new photocatalysts for biodiesel production under visible light, and the field of photocatalytic biodiesel production is still in its initial stage. The present review article highlights the efficiency of various photocatalysts investigated for biodiesel production. The effect of various parameters affecting photocatalytic biodiesel production has been discussed. Based on the studies, strategies to enhance the photocatalytic biodiesel yield, limitations of the present photocatalysts and the scope of future research have also been proposed. The mechanism of photocatalytic biodiesel production has also been discussed to help readers design novel photocatalysts with enhanced properties for biodiesel synthesis.