A Cu O superstructure is constructed through a recrystallization-induced self-assembly strategy. Single Cu O superstructure particle exhibits an outstanding surface-enhanced Raman spectroscopy performance with the limit of detection as low as 10 mol L and metal comparable enhancement factor (8 × 10 ) due to the synergetic effect of vacancies defect-facilitated charge-transfer process and copper vacancies defect-induced electrostatic adsorption.

Mn-Fe Prussian blue analogs (PBAs) cathode materials suffer from poor cycling reversibility and capacity retention during phase transition from cubic to tetragonal phase, which is related to the large structural deformation of MnÀN 6 octahedra caused by Jahn-Teller distortion. Herein, we explore a controllable strategy for creating unconventional cation Mn vacancies (V Mn ) on the surface of Mn-Fe PBAs by utilizing a strong chelating agent-ethylenediaminet etraacetic acid disodium. The V Mn in Mn-Fe PBAs can restrain the movement of MnÀN bonds and thereby mitigate the Jahn-Teller distortion of MnÀN 6 octahedra, leading to highly reversible phase transitions of Mn-Fe PBAs as well as an outstanding long-term cycling stability and capacity retention for both the half-cell (72.3% after 2,700 cycles at 0.5 A g À1 ) and full cell (75.5% after 550 cycles at 0.1 A g À1 ). This work opens up a universal avenue to explore the relationship between vacancies and electrochemical performances, even in other materials beyond PBAs.

Shape‐dependent catalysis and sensing behaviours are primarily focused on nanocrystals enclosed by low‐index facets, especially the three basic facets ({100}, {111}, and {110}). Several novel strategies have recently exploded by tailoring the original nanocrystals to greatly improve the catalysis and sensing performances. In this Review, we firstly introduce the synthesis of a variety of Cu2O nanocrystals, including the three basic Cu2O nanocrystals (cubes, octahedra and rhombic dodecahedra, enclosed by the {100}, {111}, and {110} facets, respectively), and Cu2O nanocrystals enclosed by high‐index planes. We then discuss in detail the three main facet‐controlled synthetic strategies (deposition, etching and templating) to fabricate Cu2O‐based nanocrystals with heterogeneous, etched, or hollow structures, including a number of important concepts involved in those facet‐controlled routes, such as the selective adsorption of capping agents for protecting special facets, and the impacts of surface energy and active sites on reaction activity trends. Finally, we highlight the facet‐dependent properties of the Cu2O and Cu2O‐based nanocrystals for applications in photocatalysis, gas catalysis, organocatalysis and sensing, as well as the relationship between their structures and properties. We also summarize and comment upon future facet‐related directions.

Surface-enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid (4-MBA) have been investigated on the surface of Cu2O nanospheres. The SERS signals were believed to originate from the static chemical enhancement, resonant chemical enhancement and electromagnetic enhancement. The coupling between the adsorbates and the semiconductor, evidenced by the shift in absorption spectrum of modified Cu2O and the enhancement of non-totally symmetric modes of the 4-MBA and 4-mercaptopyridine (4-MPY) molecules, were invoked to explain the experimental results. Furthermore, simulations were employed to investigate the nature of the enhancement mechanisms operative between the molecules and the semiconductor. Density functional theory (DFT) calculations suggested a charge transfer (CT) transition process between the molecules and the Cu2O nanospheres. Three-dimensional finite-difference time domain (3D-FDTD) simulations were conducted to map out the electromagnetic field around the Cu2O nanospheres. The experimental and simulation results have revealed the promise of the Cu2O nanospheres as a good SERS substrate and the prospect of using the SERS substrate as a valuable tool for in situ investigation and assay of the adsorption behavior on semiconductor surfaces.

Semiconductor-based surface enhanced Raman scattering (SERS) has attracted great attention due to its excellent spectral reproducibility, high uniformity, and good anti-interference ability. However, its relatively low SERS sensitivity still hinders its further developments in both performance and applications. Since the SERS is a peculiar surface effect, investigating the facet-dependent SERS activity of semiconductor nanostructures is crucial to boost their SERS signals. Although the semiconductor facet-dependent SERS effect is predicted via numerical calculations, convincing experimental evidence is scarce due to complicated and undefined surface conditions. In this work, three facet-defined ({100}, {110}, and {111} facets) Cu O microcrystals (MCs) with clear surface atomic configuration are utilized to investigate the facet-dependent SERS effect. The results from the Kelvin probe force microscopy measurements on single Cu O polyhedron, demonstrate that the facet-dependent work function plays a crucial role in the interfacial charge transfer process. Comparing with the {110} and {111} facets, the {100} facet possesses the lowest electronic work function, which enables more efficient interfacial charge transfer. The simulation results further confirm that the {100}-facets can transfer the most electrons from Cu O MCs to molecules due to its lowest facet work function, resulting in the largest increment of the molecular polarization.