Modified Titanium Dioxide for Photocatalytic Applications

Abstract

Titanium dioxide (TiO 2) has been widely used as a photocatalyst in many environmental and energy applications due to its efficient photoactivity, high stability, low cost, and safety to the environment and humans. However, its large band gap energy, ca. 3.2 eV limits its absorption of solar radiation to the UV light range which accounts for only about 5% of the solar spectrum. Furthermore, the photocatalytic activity of TiO 2 is also limited by the rapid recombination of the photogenerated electron-hole pairs. When used in water treatment applications, TiO 2 has a poor affinity toward organic pollutants, especially hydrophobic organic pollutants. Several strategies have been employed to reduce its band gap energy, its electron-hole recombination rates as well as enhance its absorption of organic pollutants. In this chapter, we review some of the most recent works that have employed the doping, decoration, and structural modification of TiO 2 particles for applications in photocatalysis. Additionally, we discuss the effectiveness of these dopants and/or modifiers in enhancing TiO 2 photoactivity as well as some perspective on the future of TiO 2 photocatalysis.

Hydrothermal Synthesis of Silver Decorated Reduced Graphene Oxide (rGO) Nanoflakes with Effective Photocatalytic Activity for Wastewater Treatment

“…In recent decades, inadequate availability of clean drinking water has presented itself as an unrelenting global concern. Rapid growth of the world's population and industrialization has led to increasing environmental pollution, such that around 750 million people face lack of access to clean water [2,3]. Water reservoirs are recurrently contaminated by various hazardous pollutants containing heavy metal ions, dyes, oil, and other chemicals that are released from different leather tanneries and industries related to textile, rubber, paper, cosmetics, dyeing, plastic, and food [4].…”

Application of Reverse Micelle Sol–Gel Synthesis for Bulk Doping and Heteroatoms Surface Enrichment in Mo-Doped TiO2 Nanoparticles

“…With the aim of improving TiO 2 photocatalytic activity, doping with heteroatoms, including transition metals (Cr, Co, Fe, Ni, Mn, V, Cu, Ni, and Zn) and non-metals (vide infra), has been subject to many studies, since it should allow narrowing the band gap and improving its solar light absorption [17,18,19,20]. Concerning doping with transition metals, the absorption edge shifts towards longer wavelengths due to charge-transfer transitions between d electrons of the transition metals and the CB (conduction band) or the VB (valence band).…”

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

“…Apart from Ti 3+ ions, other transition metals, such as copper (Cu), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe) and nickel (Ni), are typically employed to enhance the visible-light photocatalytic activity of titania [88][89][90][91][92][93][94][95][109][110][111][112][113][114][115]. The redshift effectiveness takes the following order: V > Cr > Mn > Fe > Ni [86]. The substitution of Ti 4+ in the TiO 2 lattice by transition metal ions creates a new energy state in the bandgap of TiO 2 .…”

“…Both Mn + and Mn 3+ species are unstable, and react with adsorbed O 2 and surface hydroxyl molecules to yield ROS [92]. Similarly, Fe 3+ ions of Fe-doped TiO 2 can also act as hole and electron traps in prohibiting the recombination of the electron-hole pair and promoting ROS generation [84][85][86]. These result in a red shift in the absorption edge and thus enhance photocatalytic activity ( Figure 3b) [95].…”