Site Sensitivity of Interfacial Charge Transfer and Photocatalytic Efficiency in Photocatalysis: Methanol Oxidation on Anatase TiO 2 Nanocrystals

In situ and Operando Spectroscopies in Photocatalysis: Powerful Techniques for a Better Understanding of the Performance and the Reaction Mechanism

In photocatalysis, a set of elemental steps are involved together at different timescales to govern the overall efficiency of the process. These steps are divided as follow: (1) photon absorption and excitation (in femtoseconds), (2) charge separation (femto- to picoseconds), (3) charge carrier diffusion/transport (nano- to microseconds), and (4 and 5) reactant activation/conversion and mass transfer (micro- to milliseconds). The identification and quantification of these steps, using the appropriate tool/technique, can provide the guidelines to emphasize the most influential key parameter that improve the overall efficiency and to develop the "photocatalyst by design" concept. In this review, the identification/quantification of reactant activation/conversion and mass transfer (steps 4 and 5) is discussed in details using the in situ/operando techniques, especially the infrared (IR), Raman, and X-ray absorption spectroscopy (XAS). The use of these techniques in photocatalysis was highlighted by the most recent and conclusive case studies which allow a better characterization of the active site and reveal the reaction pathways in order to establish a structure-performance relationship. In each case study, the reaction conditions and the reactor design for photocatalysis (pressure, temperature, concentration, etc.) were thoroughly discussed. In the last part, some examples in the use of time-resolved techniques (time-resolved FTIR, photoluminescence, and transient absorption) are also presented as an author's guideline to study the elemental steps in photocatalysis at shorter timescale (ps, ns, and µs).

Identifying Photocatalytic Active Sites of C2H6 C-H Bond Activation on TiO2 via Combining First-Principles Ground-State and Excited-State Electronic Structure Calculations

The activation of C-H bonds at low temperatures has attracted widespread interest in heterogeneous catalysis, which involves complex thermocatalytic and photocatalytic reaction processes. Herein, we systematically investigate the photothermal catalytic process of C-H bond activation in C₂H₆ dehydrogenation on rutile TiO₂(110). We demonstrate that the photochemical activity of the C₂H₆ molecule adsorbed on TiO₂(110) is site-sensitive and that C₂H₆ is more easily adsorbed at the Ti_5c site with a lower dehydrogenation energy barrier. The first C-H bond activation of the C₂H₆ adsorbed at the Ti_5c site tends to occur in the ground state, whereas O_br-adsorbed C₂H₆ is more photoactive during the initial adsorption. During the dehydrogenation of C₂H₆, the photogenerated electrons are always located at the Ti⁴⁺ sites of the TiO₂ substrate while the photogenerated holes can be captured by C₂H₆ to activate the C-H bond.

Surface-Terminated Hydroxyl Groups for Deciphering the Facet-Dependent Photocatalysis of Anatase TiO2

Understanding the relation between a crystal facet and photocatalytic performance is of great importance for the development of effective catalysts. In this work, we focus on anatase TiO₂ with controllable exposed facets toward photocatalytic hydrogen evolution by water splitting. By combining temperature-programmed desorption (TPD) and diffuse reflectance infrared spectroscopy (DRIFTS), we obtain that the adsorption of hydroxyl groups and the photo-driven breaking of hydroxyl groups depend strongly on the exposed facets. As a result, the higher catalytic hydrogen evolution activity of TiO₂ enclosed with (101) facets than that of (001) facets should be ascribed to the more favorable depletion of hydroxyl groups. Moreover, graphene quantum dots (GQDs) with rich surface functional groups are deliberately deposited on the TiO₂ surface. The determination of the states and dynamics of surface hydroxyl groups suggests that GQDs facilitate the reaction of hydroxyl groups on (001)TiO₂, thus leading to the activity enhancement. By contrast, the already active (101)TiO₂ become apparently less efficient after GQD deposition due to the restricted reaction of hydroxyl groups. Overall, our findings not only provide a unique guidance for understanding the crystal-plane-dependent photocatalysis but also present a powerful approach by which to tailor the photocatalytic performance.

An efficient catalyst of CuPt/TiO2 for photocatalytic direct dehydrogenation of methanol to methyl formate at ambient temperature

CuPt alloy nanoparticles on TiO2 are highly effective for photocatalytic direct dehydrogenation of methanol to methyl formate at ambient temperature.

Preparation of Ag3PO4/TiO2(B) Heterojunction Nanobelt with Extended Light Response and Enhanced Photocatalytic Performance

Photocatalytic degradation, as an emerging method to control environmental pollution, is considered one of the most promising environmental purification technologies. As Tibet is a region with some of the strongest solar radiation in China and even in the world, it is extremely rich in solar energy resources, which is ideal for applying photocatalytic technology to its ecological environment protection and governance. In this study, Na₂Ti₃O₇ nanobelts were prepared via a hydrothermal method and converted to TiO₂∙xH₂O ion exchange, which was followed by high-temperature calcination to prepare TiO₂(B) nanobelts (“B” in TiO₂(B) means “Bronze phase”). A simple in situ method was used to generate Ag₃PO₄ particles on the surface of the TiO₂ nanobelts to construct a Ag₃PO₄/TiO₂(B) heterojunction composite photocatalyst. By generating Ag₃PO₄ nanoparticles on the surface of the TiO₂(B) nanobelts to construct heterojunctions, the light absorption range of the photocatalyst was successfully extended from UV (ultraviolet) to the visible region. Furthermore, the recombination of photogenerated electron–hole pairs in the catalyst was inhibited by the construction of the heterojunctions, thus greatly enhancing its light quantum efficiency. Therefore, the prepared Ag₃PO₄/TiO₂(B) heterojunction composite photocatalyst greatly outperformed the TiO₂(B) nanobelt in terms of photocatalytic degradation.