Heterogeneous carbon dot catalysts for biodiesel production: A mini review

Biodiesel is a petroleum diesel substitute made by reacting oils and fats obtained from plants and animals with short-chain alcohols. The most common approach to biodiesel synthesis is transesterification, which, although a spontaneous reaction, is often catalysed by both homogeneous and heterogeneous catalysts. Homogeneous catalysts, typically very strong acids and bases, have the disadvantages of requiring special equipment and being very difficult to separate from the end product; therefore, heterogeneous catalysts, primarily metal and metal oxide nanoparticles, are preferred. However, conventional heterogeneous catalysts have several limitations, including poor industrial applicability. Recently, carbon-based nanoparticles, including carbon dots (C-dots), have been proposed as potential catalysts. A fledgling innovation, C-dots are a promising heterogeneous catalyst due to their easy, cost-effective synthesis; modifiability; high specific surface area; high specificity; and high conversion efficiency. Furthermore, unlike other catalysts, C-dots do not have to be removed after biodiesel production and can be included as an additive that improves fuel and engine performance and reduces greenhouse gas emission. This mini review aims to highlight the emerging role of C-dots in biodiesel synthesis via transesterification.