Characterization of Type I/II g-C3N4/MoS2 van der Waals Heterostructures: A New Theoretical Insight

Exploring the Role of Flexoelectric Effect in Band Modulation in 1D MoS2/Boron Phosphide Nanotube Heterostructures

Designing and discovering superior type-II band alignment are crucial for advancing optoelectronic device technologies. Here, we employ first-principles calculations to investigate the evolution of band edges in monolayer MoS2, boron phosphide (BP), and MoS2/BP heterostructures before and after their rolling into nanotubes. Our research results indicate that the intrinsic MoS2/BP vertical heterostructures exhibit a type-II direct bandgap, but this feature is not robust under strain. For MoS2/BP coaxial heterotubes, the type of bandgap is influenced by both chirality and diameter. Specifically, when the diameter exceeds 19 Å under zigzag chirality, the system undergoes a transition from a type-I direct bandgap to a type-II direct bandgap, which remains stable within a strain range of -6 to 6%. Furthermore, we delve into the alterations in band edge positions in single-walled nanotubes induced by curvature-driven flexoelectric effects and circumferential tensile strain. In coaxial heterotubes, the transfer of electrons between the inner and outer tubes forms a cylindrical capacitor-like structure. Incorporating the inherent flexoelectric voltage in single-walled nanotubes, we have derived a functional relationship between the counteracting voltage (Vhyb) and their diameter. Finally, the system was explored for its strong light absorption capabilities with absorption levels up to 105, and it was found that strain can effectively modulate the range of light absorption. The findings of this research contribute to new insights and theoretical foundations for the development of novel one-dimensional (1D) van der Waals (vdW) optoelectronic devices.

Coupling Z-Scheme g-C3N4/rGO/MoS2 Ternary Heterojunction as an Efficient Visible Light Photocatalyst for Hydrogen Evolution and RhB Degradation

Coupling heterostructures to synergistically improve the light adsorption and promote the charge carrier separation has been regarded as an operative approach to advance the photocatalytic performances. However, it is still challenging to construct heterostructures with appropriate optical properties and interfacial energy structures at the same time. In this work, a Z-scheme g-C3N4/rGO/MoS2 ternary composite photocatalyst is successfully synthesized via an effective hydrothermal method. The as-synthesized g-C3N4/rGO/MoS2 composite photocatalyst exhibited significant improvement for visible light absorption and boosted the separation efficiency of photoinduced electron-hole pairs. The g-C3N4/rGO/MoS2 system exhibited optimum visible-light-induced photocatalytic activity in hydrogen (H2) from water splitting and degrading pollutant rhodamin B (RhB), which is 22 times and 5 times higher than that of pure g-C3N4, respectively. The excellent photocatalytic activities are attributed to the synergetic effects of coupling rGO, g-C3N4, and MoS2 ternary structures to the composite photocatalyst. These combinations of intimate two-dimensional nanoconjugations can effectively inhibit charge recombination and accelerate charge transfer kinetics, forming a Z-scheme-assisted photocatalytic mechanism, thereby exhibiting superior photocatalytic activity.

Visible-Light Photocatalytic Overall Water Splitting on a B4C3/CxNy Z-Scheme Heterojunction: Role of Ultrafast Carrier Recombination-Transfer Kinetics

Herein, combining density functional theory (DFT) calculations with nonadiabatic molecular dynamics (NAMD), we built a computational framework to rationally screen from a series of 2D conjugated carbon nitrides (CNs) to match with B4C3, resulting in the excellent direct Z-scheme photocatalyst (B4C3/C6N6) for overall water splitting (OWS). Studies on interface engineering and ultrafast dynamics of carrier recombination-transfer show that in the B4C3/C6N6 system, compared with the slower interlayer migration process of carriers, strong nonadiabatic coupling and longer quantum decoherence time accelerates weak carrier interlayer recombination on a subpicosecond time scale, enabling simultaneous triggering of hydrogen evolution reaction (HER) with ΔG = -0.23 eV and spontaneous oxygen evolution reaction (OER) in the absence of sacrificial or cocatalysts. In general, our work will promote the design of efficient direct Z-scheme photocatalysts from an ultrafast dynamics perspective.