Multilayer van der Waals (vdWs) heterostructures assembled by diverse atomically thin layers have demonstrated a wide range of fascinating phenomena and novel applications.Understanding the interlayer coupling and its correlation effect is paramount for designing novel vdWs heterostructures with desirable physical properties. Using a detailed theoretical study of 2D MoS 2 -graphene (GR)-based heterostructures based on state-of-the-art hybrid density functional theory, we reveal that for 2D few-layer heterostructures, vdWs forces between neighboring layers depend on the number of layers. Compared to that in bilayer, the interlayer coupling in trilayer vdW heterostructures can significantly be enhanced by stacking the third layer, directly supported by short interlayer separations and more interfacial charge transfer. The trilayer shows strong light absorption over a wide range (<700 nm), making it very potential for solar energy harvesting and conversion. Moreover, the Dirac point of GR and band gaps of each layer and trilayer can be readily tuned by external electric field, verifying multilayer vdWs heterostructures with unqiue optoelectronic properties found by experiments. These results suggest that tuning the vdWs interaction, as a new design parameter, would be an effective strategy for devising particular 2D multilayer vdWs heterostructures to meet the demands in various applications.

2D amorphous transition metal oxides (a‐TMOs) heterojunctions that have the synergistic effects of interface (efficiently promoting the separation of electron−hole pairs) and amorphous nature (abundant defects and dangling bonds) have attracted substantial interest as compelling photocatalysts for solar energy conversion. Strategies to facilely construct a‐TMOs‐based 2D/2D heterojunctions is still a big challenge due to the difficulty of preparing individual amorphous counterparts. A generalized synthesis strategy based on supramolecular self‐assembly for bottom–up growth of a‐TMOs‐based 2D heterojunctions is reported, by taking 2D/2D g‐C3N4 (CN)/a‐TMOs heterojunction as a proof‐of‐concept. This strategy primarily depends on controlling the cooperation of the growth of supramolecular precursor and the coordinated covalent bonds arising from the tendency of metal ions to attain the stable configuration of electrons, which is independent on the intrinsic character of individual metal ion, indicating it is universally applicable. As a demonstration, the structure, physical properties, and photocatalytic water‐splitting performance of CN/a‐ZnO heterojunction are systematically studied. The optimized 2D/2D CN/a‐ZnO exhibits enhanced photocatalytic performance, the hydrogen (432.6 µmol h−1 g−1) and oxygen (532.4 µmol h−1 g−1) evolution rate are 15.5 and 12.2 times than bulk CN, respectively. This synthetic strategy is useful to construct 2D a‐TMOs nanomaterials for applications in energy‐related areas and beyond.

Structural defects can greatly inhibit electron transfer in two-dimensional (2D) layered polymeric carbon nitride (CN), seriously lowering its utilization ratio of photogenerated charges during photocatalysis.

Designing a mediator-free direct Z-scheme heterojunction photocatalyst is a highly effective strategy for environmental purification and hydrogen generation from water. Herein, hierarchical g-C 3 N 4 /CeO 2 Z-scheme heterojunctions are successfully prepared via a facile calcination method without using any templates. This feasible strategy combines the morphology control with the formation of direct Z-scheme heterojunction. The resultant hierarchical g-C 3 N 4 /CeO 2 heterojunction is much more active than the commercial Degussa P25 under visible light irradiation, validated by the high methylene blue degradation rate of 0.246 h −1 , which is about 4.8, 8.8 and 30.8 times higher than that of commercial Degussa P25 (0.051 h −1 ), bulk g-C 3 N 4 (0.028 h −1 ) and hierarchical CeO 2 (0.008 h −1 ), respectively. The Z-scheme charge transfer mechanism across the heterojunction is verified by the active species trapping and producing experiments, as well as ab initio calculations. The hierarchical structures with large exposure surface, more efficient light harvesting, and a direct Z-scheme heterojunction for efficient photoinduced charge carriers transfer and separation across the interfacial domain of g-C 3 N 4 /CeO 2 heterostructures, are the key to attractive photocatalytic performance. This work provides a promising approach to design high-efficient mediator-free direct Z-scheme photocatalysts by morphology control and heterojunction engineering.

The enhanced photocatalytic performance of various MoS2-based nanomaterials has recently been observed, but the role of monolayer MoS2 is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS2/SnO2 nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS2 as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ∼0.49 eV exists between monolayer MoS2 and SnO2 with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO2, thus enhancing the reduction activity of latter, indicating that the monolayer MoS2 is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS2, turn into catalytic active sites, making the monolayer MoS2 to be a highly active co-catalyst in the composite. The dual role of monolayer MoS2 is expected to arise in other MoS2-semiconductor nanocomposites. The calculated absorption spectra can be rationalized by available experimental results. These findings provide theoretical evidence supporting the experimental reports and pave the way for developing highly efficient MoS2-based photocatalysts.