Based on first-principles calculations, we study the dependence of topological phase on anisotropic interactions in Bi${}_2$Se${}_3$-type materials. By applying different strains in order to vary interactions, we reveal that the topological phase is insensitive to lateral interaction but can be effectively tuned by longitudinal interaction. Longitudinal strain is inhomogeneous in the studied systems. The interquintuple interaction plays a dominant role in determining the topological phase. We explain the puzzling band-topology difference between Sb${}_2$Se${}_3$ and Bi${}_2$Se${}_3$ and propose an approach to tuning the topological phase by strain. It is found that Sb${}_2$Se${}_3$ can be converted into a topological insulator by applying compressive longitudinal strain while the converse strain can turn Bi${}_2$Se${}_3$ into a normal insulator. We have studied thin films of Sb${}_2$Se${}_3$ and Bi${}_2$Se${}_3$ and also observed a strain-induced topological phase transition.

Graphyne, a new allotrope of carbon, is a current topic of focus in the nanomaterial research community. We investigate the thermal transport property of graphyne nanoribbons (GYNRs) by using the nonequilibrium Green's-function method. The thermal conductance of GYNRs is only approximately 40$\%$ that of graphene nanoribbons. A distinct width dependence of the thermal property is observed in GYNRs as well. The conductance of armchair-edged GYNRs (A-GYNRs) shows a linear width dependence, while a steplike width dependence is displayed in the conductance of zigzag-edged GYNRs (Z-GYNRs). Moreover, the conductance of an A-GYNR is larger than that of a Z-GYNR of the same width, indicating obvious anisotropic transport in graphyne (twice that in graphene). In addition, the thermal transport in graphyne family nanoribbons is also explored. The results show that the conductance of graphyne family nanoribbons is insensitive to the acetylenic linkages, but depends on the number of benzene rings. These findings could offer useful guidelines for the design and performance improvement of the graphyne-based nanodevices.

Herein, a new nanocomposite consisting of up-conversion (UC) material (YF₃:Yb³⁺,Tm³⁺), TiO₂ (P25) and graphene (GR) has been prepared and shown to be an advanced sunlight activated photocatalyst. During the facile hydrothermal method, the reduction of graphene oxide and loading of YF₃:Yb³⁺,Tm³⁺ and P25 were achieved simultaneously, and the functionalities of each part were integrated together. The as-prepared ternary UC–P25–GR nanocomposite photocatalyst exhibited great adsorptivity of dyes, a significantly extended light absorption range, efficient charge separation properties and superior durability. Indeed, the photocatalytic activity of this novel ternary nanocomposite under sunlight was improved compared with those of P25–GR nanocomposites and bare P25. Overall, this work could provide new insights into the fabrication of ternary composites as high performance photocatalysts and facilitate their application in environmental protection issues.

Using first-principles method within the framework of the density functional theory, we study the influence of native point defect on the structural and electronic properties of Bi₂Se₃. Se vacancy in Bi₂Se₃ is a double donor, and Bi vacancy is a triple acceptor. Se antisite (Se_Bi) is always an active donor in the system because its donor level (ɛ(+1/0)) enters into the conduction band. Interestingly, Bi antisite (Bi_Se1) in Bi₂Se₃ is an amphoteric dopant, acting as a donor when μ_e < 0.119 eV (the material is typical p-type) and as an acceptor when μ_e > 0.251 eV (the material is typical n-type). The formation energies under different growth environments (such as Bi-rich or Se-rich) indicate that under Se-rich condition, Se_Bi is the most stable native defect independent of electron chemical potential μ_e. Under Bi-rich condition, Se vacancy is the most stable native defect except for under the growth window as μ_e > 0.262 eV (the material is typical n-type) and Δμ_Se < −0.459 eV (Bi-rich), under such growth window Bi_Se1 carrying one negative charge is the most stable one.

We successfully developed a simple electrophoretic deposition (EPD) method to decorate the MoSe₂ nanosheets on the carbon fiber surface of carbon cloth (MoSe₂/CC). With this process, MoSe₂ nanosheets can be uniformly and tightly deposited on this flexible conductor to form a 3D binder-free electrode for hydrogen evolution reaction (HER). The film thickness can also be controlled by the EPD time. Directly used as binder-free electrodes for hydrogen evolution reaction, the as-prepared 3D MoSe₂/CC samples exhibit excellent catalytic activity in an acidic electrolyte (21 mA/cm² at an over-potential of 250 mV). Variation of MoSe₂ nanosheets film thickness in the electrodes could affect the catalytic activity and it was found that the MoSe₂/CC sample prepared with 60 min EPD time shows the highest HER activity amongst these different thickness samples. Moreover, stability tests though long-term potential cycles (no degradation after 1000 continuous potential cycles) and extended electrolysis confirm the exceptional durability of the catalyst. This development offers us an attractive and active 3D electrode for electrochemical water splitting.