Niobium Doping in BiVO4 : Interplay Between Effective Mass, Stability, and Pressure

Oxygen Vacancies Regulated S-Scheme Charge Transport Route in BiVO4-OVs/g-C3N4 Heterojunction for Enhanced Photocatalytic Performance

Oxygen vacancies (OVs) are widely considered as active sites in photocatalytic reactions, yet the crucial role of OVs in S-scheme heterojunction photocatalysts requires deeper understanding. In this work, OVs at hetero-interface regulated S-scheme BiVO4-OVs/g-C3N4 photocatalysts are constructed. The Fermi-level structures of BiVO4 and g-C3N4 lead to a redistribution of charges at the heterojunction interface, inducing an internal electric field at the interface, which tends to promote the recombination of photogenerated carriers at the interface. Importantly, the introduction of OVs induces defect electronic states in the BiVO4 bandgap, creating indirect recombination energy level that serves as crucial intermediator for photogenerated carrier recombination in the S-scheme heterojunction. As a result, the photocatalytic degradation rate on Rhodamine B (RhB) and tetracyclines (TCs) for the optimal sample is 10.7 and 11.8 times higher than the bare one, the photocatalytic hydrogen production rate is also improved to 558 µmol g-1 h-1. This work shows the importance of OVs in heterostructure photocatalysis from both thermodynamic and kinetic aspects and may provide new insight into the rational design of S-scheme photocatalysts.

Enhanced photoactivity towards bismuth vanadate water splitting through tantalum doping: An experimental and density functional theory study

The activation of hole trap states in bismuth vanadate (BiVO4) is considered an effective strategy to enhance the photoelectrochemical (PEC) water-splitting activity. Herein, we propose a theoretical and experimental study of tantalum (Ta) doping to BiVO4 leading to the introduction of hole trap states for the enhanced PEC activity. The doping of Ta is found to alter the structural and chemical surroundings via displacement of vanadium (V) atoms that cause distortions in the lattice via the formation of hole trap states. A significant enhancement of photocurrent to ∼4.2 mA cm-2 was recorded attributing to the effective charge separation of efficiency of ∼96.7 %. Furthermore, the doping of Ta in the BiVO4 lattice offers improved charge transport in bulk and decreased charge transfer resistance at the electrolyte interface. The Ta-doped BiVO4 displays the effective production of hydrogen (H2) and oxygen (O2) under AM 1.5 G illumination with a faradaic efficiency of 90 %. Moreover, the density functional theory (DFT) study confirms the decrease in optical band gap and the activation of hole trap states below the conduction band (CB) with a contribution of Ta towards both valence and CB that increases the charge separation and majority charge carrier density, respectively. The findings of this work propose that the displacement of V sites with Ta atoms in BiVO4 photoanodes is an efficient approach for enhanced PEC activity.

n-Type doping of BiVO4 with different F-doped concentrations for improving the electronic character of BiVO4 as a photoanode nanomaterial for solar water splitting: a first-principles study

Atom doping has been realized as an effective way to improve the photocatalytic performance of the most promising photoanode material, BiVO4, but the effects of doping mass concentration still need to be explored. In this work, the effects of F-doping with different doping mass concentrations (1%, 2%, 5%, 10%, 15%, and 20%) on the electronic character of BiVO4 were examined theoretically using density functional theory (DFT) calculations. The thermal stability of BiVO4 with different F-doped mass concentrations was confirmed using formation energy (Ef) calculations though F-doped BiVO4 becomes harder as the mass concentration of induced dopants increases. n-Type doping effects on the electronic character of BiVO4 were observed upon F-doping, leading to the energy level of CBM shifting far away from the Fermi level and giving F-doped BiVO4 metallic character. Moreover, a linear relationship between the frontier energy level shifts and the total charge transfer amounts from doped F atoms to other atoms involved in F-doped BiVO4 was observed, which means the oxidizing capacity of the VBM is increased and the reducing capacity of the CBM is decreased upon increased F-doped mass concentration. Moreover, the recombination of photogenerated electron-hole pairs is suppressed by F-doping strategies, which will not change a lot with the increased F-doped mass concentration. This means atom doping is an effective strategy to improve the photocatalytic efficiency of the BiVO4, but the number of atoms introduced into BiVO4 should be appropriate.