MoO 3 is an important catalytic material, and there exist controversial viewpoints about its surface structure, oxygen vacancy, and hydrogen adsorption, which are crucial for rationalizing the catalytic properties and reaction mechanism. To clarify these disputes, we adopted the density functional plus U (DFT+U) method to investigate properties of MoO 3 bulk and surfaces and examined atomic hydrogen adsorption. Analyses reveal that the vibration peak at 820 cm −1 previously assigned to the vibration of asymmetrical oxygen is due to the vibration of symmetrical oxygen. On the other hand, the previously unassigned weak peaks at 899 and 723 cm −1 are caused by the asymmetrical oxygen stretching. Single hydrogen atom adsorbs favorably at asymmetric oxygen, while the terminal oxygen becomes the favorable position for accommodating two hydrogen atoms. The H atoms occupy preferentially asymmetrical oxygen at low coverage, whereas at high coverage they favorably reside on the terminal one. Our calculations indicate that different from the previous viewpoint, water binds to the terminal oxygen defective site relatively strongly. Furthermore, the controversial viewpoints about the stability ordering of oxygen vacancy under oxidation and reduction conditions is discussed on the basis of the formation energy of oxygen vacancy and water desorption energy on defect sites.

While metal is the most common conductive constituent element in the preparation of metamaterials, one-dimensional conductive carbon nanotubes (CNTs) provide alternative building blocks. Here alumina (AlO) nanocomposites with multi-walled carbon nanotubes (MWCNTs) uniformly dispersed in the alumina matrix were prepared by hot-pressing sintering. As the MWCNT content increased, the formed conductive MWCNT networks led to the occurrence of the percolation phenomenon and a change of the conductive mechanism. Two different types of negative permittivity (i.e., resonance-induced and plasma-like) were observed in the composites. The resonance-induced negative permittivity behavior in the composite with a low nanotube content was ascribed to the induced electric dipole generated from the isolated MWCNTs. The frequency dispersions of such negative permittivity can be fitted well by the Lorentz model, while the observed plasma-like negative permittivity behavior in the composites with MWCNT content exceeding the percolation threshold could be well explained by the low frequency plasmonic state generated from conductive nanotube networks using the Drude model. This work is favorable to revealing the generation mechanism of negative permittivity behavior and will greatly facilitate the practical applications of metamaterials.

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Solar vapor generation has attracted tremendous attention as one of the most efficient ways of utilizing solar energy. It is highly desirable to develop low-cost, eco-friendly, and high-efficiency solar absorbers for practical applications of solar vapor generation. Herein, a three-dimensional plasmonic covellite CuS hierarchical nanostructure has been synthesized as the light-absorbing material via a facile one-pot hydrothermal method for structurally integrated solar absorbers with microporous poly­(vinylidene fluoride) membrane (PVDFM) as the supporting material. A broadband and highly efficient light absorption has been achieved in the wavelength of 300–2500 nm, along with high water evaporation efficiencies of 90.4 ± 1.1 and 93.3 ± 2.0% under 1 and 4 sun irradiation, respectively. Meanwhile, stable performance has been demonstrated for over 20 consecutive runs without much performance degradation. To the best of our knowledge, this is the highest performance among the copper sulfide-based solar absorbers. With the additional features of low-cost and convenient fabrication, this plasmonic solar absorber exhibits a tremendous potential for practical solar vapor generation.

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