A review on plasmonic metalTiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

The titania based nanomaterials are an attractive candidates for energy and environmental applications. TiO2 is one of the most important photocatalyst for its special multiple characteristics like high reactivity, low toxicity, low cost, high flexibility, long term stability especially in aqueous medium, shows relatively high energy conversion efficiency, easy to prepare several modifications with various morphologies, with good recycle ability, favorable band edge positions and superior physicochemical and optoelectronic properties. However, large band gap of titania and massive charge carrier recombination impairs its wide photocatalytic applications. As an alternative to various strategies reported extensively in literature, noble metal deposition on the titania surface seems to be effective and reliable method for increasing the life time of excitonic pairs and to extend the band gap absorption to visible range of the solar spectrum. In this focused review, we discuss the fundamental and critical issues in the photocatalytic activity of metal deposited titania taking into consideration the influence of various parameters like preparation methods, metal dispersion on titania, formation of heterojunctions and optimum metal loadings on the interfacial charge carrier dynamics. The metal deposition onto the varied hierarchical morphology, crystal structure, defective surface of titania along with extended modification like simultaneous doping and heterostructure coupling with other semiconductors is also highlighted. It was revealed that deposited metal is involved in multiple crucial roles like; (i) it serves as passive electron sink with high capacity to store electrons to suppress photogenerated charge carrier recombination; (ii) it facilitates rapid dioxygen reduction to generate reactive free radicals; (iii) visible light response for titania can be achieved through surface plasmon resonance effect; (iv) direct excitation of metal nanoparticles especially under visible light and vectorial electron transfer to the TiO2 CB. This review attempts to provide a comprehensive update of design and fabrication of metallization on the surface of TiO2 semiconductor particles highlighting some of the advancements made in the energy and environment applications.