van der Waals (vdW) heterostructures have attracted immense interest recently due to their unusual properties and new phenomena.

The enhanced photocatalytic activity of SrTiO 3 (STO), a promising photocatalyst for decomposing organic compounds and overall water splitting for H 2 /O 2 evolution, has been experimentally demonstrated by coupling the graphene(GR) sheet. Here, we reveal the mechanism of the enhanced photocatalytic activity of STO/GR composites using ab initio calculations.Due to C 2p states forming the bottom of conduction band or the top of valence band, the band gap is reduced to about 0.6 eV, resulting into a strong absorption in the visible region. The composites of STO coupled with reduced graphene oxide(RGO) and graphane(GRH) are also explored to investigate their potential photocatalytic activity. We demonstrate that the surface termination layer of STO(100) surface plays an important role in determining the formation energy, interfacial distance, band gap and optical absorption of these composites. Moreover, the GR sheet is a sensitizer for STO with termination layer TiO 2 , on the contrary, it is to be an electron shuttle to carry excited electrons from the STO with termination layer SrO.Interestingly, a type-II, staggered band alignment is formed in the interface, thus improving photoexcited charge separation. The negatively charged O atoms in the RGO are considered to be active sites in photocatalytic reactions, leading to the enhanced photocatalytic activity.The calculated results can rationalize the available experimental reports and provide design principles for optimizing the photocatalytic performance of the STO-based composites.

The coupling of carbon nanomaterials with semiconductor photocatalysts is a promising route to improve their photocatalytic performance. Herein, density functional theory was used to investigate the electronic structure, charge transfer, photocatalytic activity, and stability in a series of hybrid fullerene (C20, Li@C20, C26, Li@C26)/Ag3PO4(100) composites. When a Li atom is incorporated in fullerene, the adsorption energies significantly increase, although the change of interface distance is negligibly small due to the weak interface interaction. The charge transfer between constituents decreases with the C atom number of fullerene. Compared to pure Ag3PO4, the band gap of the composites is smaller, which enhances the visible-light absorption and photoinduced electron transfer. Most importantly, a type-II, staggered band alignment could be obtained in the C26-Ag3PO4(Li@C26-Ag3PO4) interface, leading to significantly reduced charge recombination and thus enhanced photocatalytic activity. These results reveal that fullerene modification would be an effective strategy to improve the photocatalytic performance of Ag3PO4 semiconductor photocatalysts.

Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) heterostructures have recently attracted growing interest due to their massive potential in solar energy applications due to their band gap in the visible spectral range and extremely strong light-matter interactions. Herein, heterostructures composed of WS2 and MoS2 monolayers, as representative TMDCs, with small fullerenes (B12 and C20) are investigated to explore their applications in solar energy conversion using first principles calculations based on density functional theory (DFT). The WS2 (MoS2) monolayer and fullerene form a van der Waals (vdW) heterostructure. Compared to pure monolayers, the heterostructures have a smaller band gap, which favours enhancing visible light absorption. The amount of charge transfer at the interface induced by vdW interactions depends on the type of fullerene. Most importantly, a type-II staggered band alignment is formed between WS2 (MoS2) and fullerene with the latter possessing the higher electron affinity which results in the robust separation of photoexcited charge carriers between them. These results indicate that the electronic properties and photoactivity of TMDCs monolayers can be tuned by non-covalent coupling with small fullerenes, thus meeting the needs of various applications.