Metal-TiO2 nanocomposites towards efficient solar-driven photocatalysis

Abstract

Water, together with energy and food, has been addressed as one of the main urgent problem of humanity. The reduction of fresh clean water sources will definitely lead to huge issues in the next future, especially in developing countries. The conventional wastewater treatments suffer some limitations related to the effectiveness in decontamination (mechanical filtration), in the heavy use of chemicals (chlorination), or in elevate operational costs and energy requirements (desalination and reverse osmosis). In this sense, new materials such as nanocomposites may overcome these issues taking advantage of the peculiar properties of materials at nanoscale. Research on novel nanotechnologies must bring advances in order to contrast and prevent water scarcity and pollution. In order to be effective, these nanotechnologies should run at low operational cost, even in places unequipped by strong infrastructures and in concert with conventional cheap methodologies. Among the alternative water purification methods, TiO2-based photocatalysis has attracted great attention due to material stability, abundance, non-toxicity and high decontamination efficiency. In this material, electron-hole pairs, generated by light absorption, separate from each other and migrate to catalytically active sites at the surface of the photocatalyst. Photogenerated carriers are able to induce the water splitting reaction and, consequently, to decompose organic pollutants. The main deficiency of this material, related to its large band gap, is that only the UV fraction of the solar spectrum is effective to this purpose. Several approaches have been proposed to overpass this issue and, among them, the use of metal-TiO2 nanocomposites with proper nanostructurarion seems very promising for water purification strategies. Aim of this work is to investigate the possibility to develop efficient solar-driven TiO2 photocatalyst taking advantage of metallic nanostructures to efficiently couple the incident light to the photoactive semiconductor. Two approaches have been followed: TiO2 nanoparticles obtained via pulsed laser ablation in liquid and optical engineering of multilayered metal-TiO2 thin films. The first approach maximizes the exposed surface, thus enhancing the photocatalytic efficiency. However, in this case nanomaterials is dispersed in the surrounding environment, and in order to avoid this drawback we have investigated, as second approach, the use of metal-TiO2 thin films.