TiO2 Nanotubes as Photocatalyst for Biodiesel Production

Abstract

The use of semiconductors as catalysts in photocatalytic reactions is an alternative for the synthesis of esters with the potential to simplify the production process by enabling the use of ambient temperature and pressure. Photocatalysis is a process involving the use of a light source to trigger oxidation and reduction reactions through the formation of electrons and holes by excitation of the semiconductor. The use of photocatalysts with a high surface area such as TiO2 nanotubes (TNTs) can offer better photocatalytic performance. They have a higher surface area and a high number of hydroxyl groups versus oxide precursors (TiO2). The hydrothermal mechanism is a simple and effective method to synthesize TNTs, wherein the TiO2 reacts with a concentrated NaOH solution at high pressure. In the related esterification experiments with TNTs as a photocatalyst, the lowest band gap energy sample exhibited the highest rate of oleic acid esterification among all the investigated TNTs. In addition to the band gap, other factors such as the TNT crystalline phase and surface area were important in photocatalytic performance.