Tuning the size of photo-deposited metal nanoparticles via manipulating surface defect structures of TiO2 nanocrystals

Advances in photochemical deposition for controllable synthesis of heterogeneous catalysts

Photochemical deposition has been attracting increasing attention for preparing nano-catalysts due to its mild reaction conditions, simplicity, green and safe characteristics, and potential for various applications in photocatalysis, thermal catalysis, and electrocatalysis. In this review, we provide an overview of recent advances in photochemical deposition methods for fabricating heterogeneous catalysts, and summarize the factors that influence the nucleation and growth of metal nanoparticles during the photochemical process. Specifically, we focus on the various factors including surface defects, crystal facets, surface properties and the surface plasmon effect on the size, morphology and distribution control of metal and metal oxide nanoparticles on semiconductors. The control of the photogenerated charges and the triggered photochemical reactions have been proved to be significant in the photochemical deposition process. Besides, the applications of the obtained catalytic materials in thermal catalysis and electrocatalysis is highlighted, considering that many reviews have covered photocatalysis applications. We first introduce the principle of photodeposition, nucleation and growth theory, and factors affecting photodeposition. Then, we introduce photodeposition methods that can achieve "controlled" photodeposition from a strategic perspective. Finally, we summarize the fruitful results of controlled photodeposition and provide future prospects for the development of controlled photodeposition technologies and methods, as well as the deepening and expansion of applications.

Photo-assisted sequential assembling of uniform metal nanoclusters on semiconductor support

Dispersing metal nanoclusters on the oxide supports is attracting close attention in heterogeneous catalysis, but great challenges still lie in controlling the size and dispersion of nanoclusters due to the inevitable agglomeration. Here, we propose a sequential photochemical deposition strategy named “first store, and then release” to uniformly fabricate the size-controlling noble metal nanoclusters on semiconductor oxides. Using the typical semiconductor TiO₂, the photoexcited electrons can be first stored as reduced species (e.g. Ti³⁺) under irradiation and the Ti³⁺ species can optimize both the nucleation and growth processes in dark reaction, resulting in a uniform dispersing of various noble metals (Au, Pt, Ag etc.) with size diameters of ∼1 nm. The nanoclusters catalysts exhibited superior performance in catalytic oxidation of HCHO compared with that of nanoparticles. This work brings a new and useful strategy to construct size-controlling noble metals on the oxide supports for heterogeneous catalysis and the related fields.

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Metal nanoclusters were deposited on semiconductors via sequential photodeposition

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Ti³⁺ species store the photoelectrons and optimize the nucleation and growth processes

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The catalysts exhibit superior performance in catalytic oxidation of HCHO

A New Strategy to Regulate the Selectivity of Photo-Mediated Catalytic Reaction

Here we developed a new method for regulating the selectivity of photo-mediated catalytic reaction by manipulating the surface charge of Au/TiO₂ (gold/titanium dioxide) catalysts within chemical reaction timescales. Two kinds of photocatalytic reactions, hydrogenation of acetophenone and benzyl alcohol oxidation, have been applied to investigate the photocatalytic performance over Au/TiO₂ catalysts with tunable surface charges. We found that a suitable timescale of switching surface charge on Au would benefit for the enhanced quantum efficiency and play different roles in the selectivity of desired products in hydrogenation and oxidation reactions. Au/TiO₂ catalyst under 5 μs flashing light irradiation exhibits much higher selectivity of 1-phenylethanol in the hydrogenation of acetophenone than that under continuous light and 5 s flashing light irradiation; by contrast, Au/TiO₂ catalysts under both flashing light and continuous light irradiation exhibit a similar selectivity of benzaldehyde in benzyl alcohol oxidation. Our findings will benefit for a better understanding of electronic structure-mediated reaction mechanism and be helpful for achieving highly efficient photocatalytic systems.

Tuning the shape and crystal phase of TiO2 nanoparticles for catalysis

Synthesis of TiO₂ nanoparticles with tunable shape and crystal phase has attracted considerable attention for the design of highly efficient heterogeneous catalysts. Tailoring the shape of TiO₂, in the crystal phases of anatase, rutile, brookite and TiO₂(B), allows tuning of the atomic configurations on the dominantly exposed facets for maximizing the active sites and regulating the reaction route towards a specific channel for achieving high selectivity. Moreover, the shape and crystal phase of TiO₂ nanoparticles alter their interactions with metal species, which are commonly termed as strong metal-support interactions involving interfacial strain and charge transfer. On the other hand, metal particles, clusters and single atoms interact differently with TiO₂, because of the variation of the electronic structure, while the surface of TiO₂ determines the interfacial bonding via a geometric effect. The dynamic behavior of the metal-titania interfaces, driven by the chemisorption of the reactive molecules at elevated temperatures, also plays a decisive role in elaborating the structure-reactivity relationship.