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Titanium dioxide (TiO2) has received extensive attention for photocatalytic hydrogen peroxide (H2O2) production, with the d-band center related to the adsorption performance, which affects the photocatalytic reaction process. Herein, an ingenious strategy to lower the antibonding-orbital occupancy in the Ti 3dorbital by fluoride ion (F−) doping is proposed, with density functional theory calculations predicting that F-doping into TiO2induces a non-uniform charge distribution and enables an upshift of the d-band center in F/TiO2. This manipulation provides accessible active centers with favorable d-band energy levels, which can improve the charge-transfer behavior, strengthen the interaction between the adsorbed oxygen and the photocatalyst, and reduce the adsorption energy of oxygen, eventually promoting the photocatalytic H2O2production rate. The experimental results further confirm that a lower antibonding-orbital occupancy can intensify the adsorption of atomic oxygen at the Ti sites. Electron paramagnetic resonance experiment reveals that the presence of F−ions in the lattice induces the formation of Ti3+centers that localize the extra electron needed for charge compensation. Femtosecond transient absorption (fs-TA) spectroscopy suggests that photogenerated electrons are transferred from the conduction band of F/TiO2to the Ti3+surface states and surface F−ions, expediting the separation of electrons and holes. Consequently, with F−doping in TiO2, the photocatalytic H2O2production yields improved from 277 to 467 μmol·g−1·h−1, with ethanol as a sacrificial reagent. This study provides a new strategy for regulating the d-band center to optimize the adsorption strength between the photocatalyst and oxygen atoms and achieve enhanced photocatalytic H2O2production performance.

Covalent organic frameworks (COFs) are porous crystalline materials with promising applications in photocatalysis, but their performance is greatly hampered by the fast recombination of photogenerated carriers. Herein, a hollow spherical COF was synthesized via the condensation polymerization of 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarbaldehyde, and Au nanoparticles were in-situdeposited onto the COF through NaBH4reduction to ameliorate the photocatalytic performance. The composite exhibits impressive photocatalytic H2O2-production performance with the highest H2O2-evolution rate of 6067 μmol g−1h−1under visible light irradiation, which is about 1.9 times that of the pristine COF. The enhanced photocatalytic activity was ascribed to improved light absorption, abundant active Au sites, and efficient transfer and separation of photogenerated carriers in space. This work provides an avenue for designing high-performance H2O2-production photocatalysts by decorating porous COFs with active noble-metal sites.

• The PdS@NH 2 -MIL-125(Ti)@ZnS heterostructure is designed for the first time. • The abundant reactive sites and smooth charge channels are provided by the MOFs. • An analogous type-II heterostructure is constructed by NH 2 -MIL-125(Ti) and ZnS with defect levels assisted by PdS co-catalyst. • The comprehensive effects can effectively realize the spatial charge separation. • The optimal sample exhibits an excellent H 2 evolution rate of 1164.2 μmol/g/h. A new photocatalyst, PdS@NH 2 -MIL-125(Ti)@ZnS (PdS/M125/ZnS) heterojunction is fabricated for photocatalytic H 2 generation for the first time, where PdS nanoparticles are anchored in the pore of M125 by utilizing its confinement effect, and the ZnS is closely wrapped on the surfaces of the MOFs. The optimal photocatalyst exhibits a significantly enhanced H 2 generation rate of 1164.2 μmol/g/h, while the pure M125 only displays a H 2 generation rate of 16.7 μmol/g/h. The resultant improvement can be ascribed to the following comprehensive advantages. The hierarchical structure built by PdS, M125, and ZnS can form lots of intimate interfaces, offer abundant sites for reaction, and smooth channels for charge carriers due to the porous characteristics of MOFs. Moreover, M125 and ZnS with inner defect levels form an analogous type-II heterojunction assisted by PdS co-catalyst, which greatly promotes charge separation. This work may supply a new avenue to design MOFs photocatalysts for energy conversion. [ABSTRACT FROM AUTHOR]

Herein, a new photocatalyst PdS@UiOS@CZS is successfully synthesized, where thiol-functionalized UiO-66 (UiOS), a metal–organic framework (MOF) material, is used as a host to encapsulate PdS quantum dots (QDs) in its cages, and Cd0.5Zn0.5S (CZS) solid solution nanoparticles (NPs) are anchored on its outer surface. The resultant PdS@UiOS@CZS with an optimal ratio between components displays an excellent photocatalytic H2evolution rate of 46.1 mmol h–1g–1under visible light irradiation (420∼780 nm), which is 512.0, 9.2, and 5.9 times that of pure UiOS, CZS, and UiOS@CZS, respectively. The reason for the significantly enhanced performance is that the encapsulated PdS QDs strongly attract the photogenerated holes into the pores of UiOS, while the photogenerated electrons are effectively migrated to CZS due to the heterojunction effect, thereby effectively suppressing the recombination of charge carriers for further high-efficiency hydrogen production. This work provides an idea for developing efficient photocatalysts induced by hole attraction.

In recent years, ternary heterostructures (HSs) composed of three semiconductors have attracted significant attention because of the effective separation and transfer of photogenerated electrons and holes in these materials. In this work, new ternary CdS/ZnS/ZnO (CZZ) HSs with one-dimensional (1D) nanofiber morphology have been successfully fabricated for the first time by a series of processes: electrospinning ZnO nanofibers, sulfurizing ZnO in situ to form ZnS/ZnO binary HSs, and depositing CdS quantum dots in situ on the ZnS/ZnO HSs. Benefiting from the efficient separation and transfer of photoinduced charge carriers, the optimized CZZ ternary HSs exhibit a hydrogen evolution rate of 51.45 mmol h−1g−1(quantum efficiency: 26.88% at 420 nm) without any co-catalyst, which is 93.54 and 2.28 times higher than those exhibited by pristine ZnO and ZnS/ZnO binary HSs, respectively, under the same conditions. Furthermore, the rate of hydrogen evolution over the 1D CZZ nanofibers is significantly higher than that over 2D CZZ nanosheets (27.25 mmol h−1g−1, in the presence of a Pt co-catalyst) prepared by the same sulfurization and deposition procedures. This can be ascribed to the significantly smaller geometric sizes of 1D nanofibers compared to those of 2D nanosheets, resulting in effectively suppressed recombination of photogenerated charge carriers and promotion of photocatalytic H2evolution performance.