Janus two-dimensional (2D) materials, referring to the layers with different surfaces, have attracted intensive research interest due to the unique properties induced by symmetry breaking, and promising applications in energy conversion. Based on the successful experimental synthesis of Janus transition metal dichalcogenides (TMDC), here we present a review on their potential application in photocatalytic overall water splitting, from the perspectives of the latest theoretical and experimental progress. Four aspects which are related to photocatalytic reaction, including the adsorption of water molecules, utilization of sunlight, charge separation and transport, and surface chemical reactions have been discussed, and it is concluded that the Janus structures have better performances than symmetric TMDCs. At the end of this review, we raise further challenges and possible future research directions for Janus 2D materials as water-splitting photocatalysts.

Harnessing solar energy to produce hydrogen through semiconductor-mediated photocatalytic water splitting is a promising avenue to address the challenges of energy scarcity and environmental degradation. Ever since Fujishima and Honda’s groundbreaking work in photocatalytic water splitting, titanium dioxide (TiO₂) has garnered significant interest as a semiconductor photocatalyst, prized for its non-toxicity, affordability, superior photocatalytic activity, and robust chemical stability. Nonetheless, the efficacy of solar energy conversion is hampered by TiO₂’s wide bandgap and the swift recombination of photogenerated carriers. In pursuit of enhancing TiO₂’s photocatalytic prowess, a panoply of modification techniques has been explored over recent years. This work provides an extensive review of the strategies employed to augment TiO₂’s performance in photocatalytic hydrogen production, with a special emphasis on foreign dopant incorporation. Firstly, we delve into metal doping as a key tactic to boost TiO₂’s capacity for efficient hydrogen generation via water splitting. We elaborate on the premise that metal doping introduces discrete energy states within TiO₂’s bandgap, thereby elevating its visible light photocatalytic activity. Following that, we evaluate the role of metal nanoparticles in modifying TiO₂, hailed as one of the most effective strategies. Metal nanoparticles, serving as both photosensitizers and co-catalysts, display a pronounced affinity for visible light absorption and enhance the segregation and conveyance of photogenerated charge carriers, leading to remarkable photocatalytic outcomes. Furthermore, we consolidate perspectives on the nonmetal doping of TiO₂, which tailors the material to harness visible light more efficiently and bolsters the separation and transfer of photogenerated carriers. The incorporation of various anions is summarized for their potential to propel TiO₂’s photocatalytic capabilities. This review aspires to compile contemporary insights on ion-doped TiO₂, propelling the efficacy of photocatalytic hydrogen evolution and anticipating forthcoming advancements. Our work aims to furnish an informative scaffold for crafting advanced TiO₂-based photocatalysts tailored for water-splitting applications.

Semiconductor photocatalysis via photogenerated electrons and holes can split water into H₂ and O₂, which is a promising way to utilize solar energy. However, the inefficient generation of oxygen severely restricts the catalytic efficiency for overall water splitting. Thus, it is necessary to find new photocatalysts for the oxygen evolution reaction (OER). In the present study, the electronic structure and related properties of one-dimensional blue phosphorene nanotubes (BPNTs) are systematically investigated using first-principle calculations to explore their photocatalytic activities. Our results demonstrate that the strain energy of BPNTs with a large diameter (larger than 8 Å) is nearly the same as that of carbon nanotubes, indicating that these BPNTs are stable. Due to their perfect band gaps and band energies for photocatalytic activity, BPNTs have potential for application in visible light photocatalysis for overall water splitting. More significantly, p-type zigzag BPNTs with good photooxidation capabilities, low electron–hole recombination, and high hole mobility (1729.53 cm² V⁻¹ s⁻¹) and photo-response coefficient (20a₀ ² per photon) are promising candidates as photocatalytic materials for OER. Besides, the band gap of BPNTs can be tuned monotonically by reasonable strain. We further report advanced strategies for designing and improving potentially efficient photocatalysts for overall water splitting.