A new strategy of building covalently MOF–COF core–shell heterostructure with MOFs without –NH ₂ group for improved photocatalytic hydrogen evolution under visible light irradiation.

The electronic structures and transition properties of three types of triangle MoS₂ clusters, A (Mo edge passivated with two S atoms), B (Mo edge passivated with one S atom), and C (S edge) have been explored using quantum chemistry methods. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of B and C is larger than that of A, due to the absence of the dangling of edge S atoms. The frontier orbitals (FMOs) of A can be divided into two categories, edge states from S_3p at the edge and hybrid states of Mo_4d and S_3p covering the whole cluster. Due to edge/corner states appearing in the FMOs of triangle MoS₂ clusters, their absorption spectra show unique characteristics along with the edge structure and size.

The doping effect of graphene nanoplatelets (GNPs) on electrical insulation properties of polyethylene (PE) was studied by combining experimental and theoretical methods. The electric conduction properties and trap characteristics were tested for pure PE and PE/GNPs composites by using a direct measurement method and a thermal stimulated current (TSC) method. It was found that doping smaller GNPs is more beneficial to decrease the conductivity of PE/GNPs. The PE/GNPs composite with smaller size GNPs mainly introduces deep energy traps, while with increasing GNPs size, besides deep energy traps, shallow energy traps are also introduced. These results were also confirmed by density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) method calculations. Therefore, doping small size GNPs is favorable for trapping charge carriers and enhancing insulation ability, which is suggested as an effective strategy in exploring powerful insulation materials.

The transport and photoelectric properties of four two-dimensional (2D) silicene/MX₂ (M = Mo, W; X = S, Se) heterostructures have been investigated by employing density functional theory, nonequilibrium Green’s function, and Keldysh nonequilibrium Green’s function methods. The stabilities of silicene (SiE) are obviously improved after being placed on the MX₂ (M = Mo, W; X = S, Se) substrates. In particular, the conductivities of SiE/MX₂ are enhanced compared with free-standing SiE and MX₂. Moreover, the conductivities are increased with the group number of X, i.e., in the order of SiE < SiE/MS₂ < SiE/MSe₂. An evident current oscillation phenomenon is observed in the SiE/WX₂ heterostructures. When a linear light illumination is applied, SiE/MSe₂ shows a stronger photoresponse than SiE/MS₂. The maximum photoresponse with a value of 9.0a₀²/photon was obtained for SiE/WSe₂. More importantly, SiE/MS₂ (M = Mo, W) heterostructures are good candidates for application in designing solar cells owing to the well spatial separation of the charge carriers. This work provides some clues for further exploring 2D SiE/MX₂ heterostructures involving tailored photoelectric properties.