In Situ STEM Determination of the Atomic Structure and Reconstruction Mechanism of the TiO₂ (001) (1 × 4) Surface

The widely studied anatase TiO₂ (001) surface usually shows a (1 × 4) reconstruction, which may directly influence its physical and chemical properties. Although various atomic models are proposed, the debates regarding the models and the formation mechanism of such reconstruction remain until now due to the lack of direct experimental evidence at the atomic level. Herein, we report the atomic-scale determination of the atomic structure and the reconstruction mechanism of the TiO₂ (001) (1 × 4) surface by in situ spherical aberration corrected scanning transmission electron microscopy (STEM) at elevated temperature. The atomic features of the reconstructed surface are unambiguously identified in our experiments, providing a solid evidence to verify the ad-molecule model, which was predicted by the calculations 15 years ago. Furthermore, the mysterious reconstruction route is revealed by our real time STEM images, which involves a new metaphase of the (001) surface. These results are expected to help resolve current dispute concerning the reconstruction models and understand the true performances of the anatase TiO₂ (001) surface

Real-Time Observation of Reconstruction Dynamics on TiO₂(001) Surface under Oxygen via an Environmental Transmission Electron Microscope

The surface atomic structure has a remarkable impact on the physical and chemical properties of metal oxides and has been studied extensively by scanning tunneling microscopy. However, acquiring real-time information on the formation and evolution of the surface structure remains a great challenge. Here we use environmental transmission electron microscopy to directly observe the stress-induced reconstruction dynamics on the (001) surface of anatase TiO₂. Our in situ results unravel for the first time how the (1 × 4) reconstruction forms and how the metastable (1 × 3) and (1 × 5) patterns transform into the (1 × 4) surface stable structure. With the support of first-principles calculations, we find that the surface evolution is driven by both low coordinated atoms and surface stress. This work provides a complete picture of the structural evolution of TiO₂(001) under oxygen atmosphere and paves the way for future studies of the reconstruction dynamics of other solid surfaces

Early Stage Growth of Rutile Titania Mesocrystals

Exploring the crystallization process of metal oxide mesocrystals has attracted enormous attention recently. However, due to the lack of insight into the behaviors of short-lived species at initial growth stages, there is currently a gap in understanding the underlying growth mechanism. Here, a combination of a preseeded hydrothermal method and transmission electron microscopy allows us to witness the rapid crystallization by particle attachement (CPA) in the early growth stage of capsule-shaped rutile titania mesocrystals. The presence of the embryonic form of nanocapsules, the slight misalignment of the primary particles, and, most importantly, the atomic interface between primary particles during attachment strongly indicate the existence of CPA mechanism. Furthermore, we rationalize our findings in terms of the free energy landscapes that govern nonclassical formation pathways. Our study provides a practical approach to explore the formation mechanism of fast-growing crystals at their initial growth stages

Biodegradable Grubbs-Loaded Artificial Organelles for Endosomal Ring-Closing Metathesis

The application of transition-metal catalysts in living cells presents a promising approach to facilitate reactions that otherwise would not occur in nature. However, the usage of metal complexes is often restricted by their limited biocompatibility, toxicity, and susceptibility to inactivation and loss of activity by the cell’s defensive mechanisms. This is especially relevant for ruthenium-mediated reactions, such as ring-closing metathesis. In order to address these issues, we have incorporated the second-generation Hoveyda–Grubbs catalyst (HGII) into polymeric vesicles (polymersomes), which were composed of biodegradable poly(ethylene glycol)-b-poly(caprolactone-g-trimethylene carbonate) [PEG-b-P(CL-g-TMC)] block copolymers. The catalyst was either covalently or non-covalently introduced into the polymersome membrane. These polymersomes were able to act as artificial organelles that promote endosomal ring-closing metathesis for the intracellular generation of a fluorescent dye. This is the first example of the use of a polymersome-based artificial organelle with an active ruthenium catalyst for carbon–carbon bond formation