Direct and Indirect Effects of Fluorine on the Photocatalytic Performance of Titania‐Based Photocatalysts

Abstract

TiO2 used as a light‐absorbing semiconductor represents the classic benchmark for photocatalytic solar energy conversion and many other photocatalytic reactions. Various strategies are developed to improve the photoresponse of TiO2‐based materials, such as bandgap engineering or surface sensitization in combination with nanostructuring and geometry optimization. The present feature article is focused on direct and indirect approaches involving bulk or surface fluorine used to tune the surface chemistry, electronic structure, and the morphology of TiO2 photocatalysts. A comprehensive overview is provided on fluorine effects on TiO2, involving morphology modifications, and how surface or bulk fluorine affect the photocatalytic performance of TiO2. After outlining some basic interaction principles of F and TiO2, characterization techniques for different fluorine species are discussed. It is reviewed how fluorine during crystal growth mediates the morphology of TiO2; then how surface fluorination and doping fluorine effects can be beneficially utilized in photocatalysis are discussed. Finally, synergistic effects between fluorine and cocatalyst are discussed, for example, the use of lattice fluorine species to stabilize Pt single‐atom cocatalysts. Finally, the challenges and outlook on further advancing the development of fluorine effects are highlighted.

Photocatalytic Hydrogen Peroxide Production through Functionalized Semiconductive Metal–Organic Frameworks

“…Specifically, we hypothesized that the primary reason that EFB-MOF shows the highest photocurrent and H 2 O 2 generation efficiency is due to a prolonged exciton lifetime resulting from fluorine. Given the high electronegativity of fluorine, the fluorine sites could act as electron trap sites . They facilitate electrons’ separation from photogenerated holes, expand their charge lifetime, and reduce charge recombination, promoting the participation of electrons and holes in target redox reactions.…”

“…Given the high electronegativity of fluorine, the fluorine sites could act as electron trap sites. 53 They facilitate electrons' separation from photogenerated holes, expand their charge lifetime, and reduce charge recombination, promoting the participation of electrons and holes in target redox reactions.…”

Spontaneous Dewetting of Au‐Thin Layers on Oxide‐ and Fluorine‐Terminated Single Crystalline Anatase and Efficient Use in Photocatalytic H2 Production

“…[47] Mostly, such effects have been ascribed to the high electronegativity of fluorine that aids trapping of photogenerated electrons; and thus, reduces the overall charge recombination. [24,48] In order to better understand this remarkable effect of Ftermination, we studied the photoelectrochemical behavior and light reflectance properties for the different samples. Figure 4a provides the comparison of F-terminated (as formed) and oxidized surface in an aqueous and in an MeOH containing solution.…”

Disclosing the true atomic structure of {001} facets in shape-engineered TiO2 anatase nanoparticles

“…[8][9][10] The synthesis of TiO 2 "nano-sheets" (n-sh) with dominant {001} facets requires the use of suitable capping agents (usually uoride ions), which are able to stabilize the (001) surface during the crystal growth. 11,12 Therefore, the surface of the NPs aer the synthesis is terminated with Ti-F groups and F − is also normally present in the bulk. [13][14][15][16] To completely remove these capping agents, the NPs are usually calcined at high temperature (generally between 773 and 873 K), [17][18][19] but this procedure can lead to a reconstruction of the unstable {001} facets, which can dramatically modify their functional properties.…”