A Highly Active Titanium Dioxide Based Visible‐Light Photocatalyst with Nonmetal Doping and Plasmonic Metal Decoration

Abstract

Since the discovery of its photocatalytic activity under UV light, TiO 2 has been widely studied as a photocatalyst in applications such as water splitting and purification.[1] As pristine TiO 2 only absorbs UV light, much effort has been devoted to developing visible-light-active TiO 2 photocatalysts that can make use of both UV and visible radiation. Many strategies, including metal-ion [2] and nonmetal doping, [3] have been proposed to extend the absorption of TiO 2 to the visible spectrum, but, to date, new materials have typically suffered from low doping concentration and/or low stability against photocorrosion.[3d, 4] Noble-metal nanoparticles such as Au and Ag have also been used to enhance the activity of photocatalysts in visible light because of their plasmonic properties.[5] In any case, an improved absorption of photons may not necessarily guarantee significantly better photocatalytic performance because the efficiency of a photocatalyst is also determined by charge separation and transport. As most excited charges may recombine and quench before reaching the surface, small grain size and high crystallinity would be desirable for enhancing charge-separation efficiency that would result in a reduced migration distance of charges and, consequently, in a lower recombination rate.[6] Additionally, metal decoration has also been shown to enhance charge separation in TiO 2 photocatalysts by serving as an electron reservoir. [7] It is therefore expected that a composite of small doped TiO 2 nanocrystals decorated with metal nanoparticles may be a powerful photocatalyst, as all the features discussed above are combined. However, the incompatibility between the synthesis, doping, and decoration procedures means that the production of such nanocomposites has remained a great challenge.We report herein the design and synthesis, by combining simple sol-gel and calcination processes, of a highly efficient, stable, and cost-effective TiO 2 -based photocatalyst with the desired properties mentioned above. The new catalyst has a sandwich structure that comprises a SiO 2 core, a layer of gold nanoparticles (AuNPs), and a doped TiO 2 nanocrystalline shell. The sol-gel process allows for the convenient incorporation of AuNPs into the catalyst with controlled loading and location. TiO 2 is doped with both N and C using an unconventional method that involves introducing 3-aminopropyl-triethoxysilane (APTES), which originally acts as a ligand for immobilization of AuNPs on the surface of the SiO 2 support, but upon subsequent decomposition at high temperature serves as a source of both N and C for doping. Compared to traditional Au/TiO 2 composites, in which AuNPs are loosely attached to the surface of TiO 2 such that they are unstable during calcination and subsequent photocatalysis, the sandwich structures with the AuNPs embedded inside a TiO 2 matrix protects the former from moving together and coagulating.[8] The encapsulation also increases the contact area between the AuNPs and the TiO 2 matrix, and therefore allow...

Hot‐Electron‐Mediated Photochemical Reactions: Principles, Recent Advances, and Challenges

“…[38,[132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147] Several reports focused on the photocatalytic degradation of organic compounds. [132][133][134][135][136][137] In a typical degradation reaction, the photogenerated electrons convert oxygen (O 2 ) to superoxide radicals (HO 2 • ), with the photogenerated holes simultaneously forming hydroxyl radicals (OH • ) by reacting with H 2 O. [91] Subsequently, hydroxyl radicals oxidize the organic pollutants, degrading them into nontoxic small molecules, such as CO 2 , H 2 O, and NH 3 .…”

“…Based on the photocatalytic degradation of organic compounds, enhanced plasmon-assisted photodegradation reaction performance has been reported for plasmonic metal (such as Au, Ag)/semiconductor (such as TiO 2 , ZnO, CeO 2 , Fe 2 O 3 , SiO 2 , and ZrO 2 ) hybrid photocatalysts. [132][133][134][135][136][137] Several of them are widely applied to the removal of industrial pollutants, such as pharmaceutical drugs, perchlorethane, and pesticides.…”

Photoinduced electron transfer and photodegradation of malonic acid at Au/TiO2 investigated by in situ ATR-IR spectroscopy

“…Therefore, much effort has been devoted to efficiently separate the electron-hole pair. The use of metal-semiconductor heterostructures is a popular strategy for applications in photocatalysis because the metal in contact with the semiconductor greatly enhances the overall photocatalytic redox process [3][4][5]. However, corrosion or dissolution of the noble metal nanoparticles occurring during photocatalytic reactions is a challenge [6,7].…”

The impacts of nanotechnology on catalysis by precious metal nanoparticles

“…For example, in a recent study, Yin and coworkers designed a TiO 2 -based, sandwichstructured photocatalysts decorated with Au nanoparticles and found that Au played an important role in obtaining the high catalytic effi ciency in decomposition of organic compounds under light [85] . The Au nanoparticles were rationalized to enhance light harvesting and charge separation as well as boosting the role of implanted nitrogen dopants in TiO 2 [85] . In summary, the various types of nanostructures discussed in Section 3.3 remain to be further explored in future research.…”