Photocatalytic hydrogen evolution reaction (HER), which can convert solar energy into hydrogen energy, offers a viable green energy solution to the current energy shortages. Herein, Cu^II-tetrapyridylporphyrin (CuTPyP) molecules are decorated onto an amino-functionalized Ti-based metal organic framework (NH₂-MIL-125(Ti) MOF) to form CuTPyP/NH₂-MIL-125(Ti) precursor via an impregnation method, which is then pyrolyzed to fabricate a novel single-atom CuN_x cluster-modified TiO₂ composite (CuN_x/TiO₂). Under the full spectrum irradiation of Xe-lamp, the resultant CuN_x/TiO₂ exhibits slightly better photocatalytic performance than the Pt-loaded TiO₂ product, with an optimal HER activity of 581 μmol h^-1, which is 38 and 20 times higher than that of the TiO₂ (15 μmol h^-1) pyrolyzed from of the bare NH₂-MIL-125(Ti) and the N_x/TiO₂ (28 μmol h^-1) pyrolyzed from the H₂TPyP/NH₂-MIL-125(Ti) precursor, respectively. The characterization results confirm that the Cu species in CuN_x/TiO₂ can maintain the single-atom dispersed CuN_x clusters, thereby extending the spectral absorption region, promoting the photoexcited charge separation, and then enhancing the activity of TiO₂. These results demonstrate that the CuN_x clusters exhibit comparable effectiveness to Pt cocatalyst, providing a feasible approach for developing efficient non-precious metal single-atom photocatalysts.

It is highly desirable to simulate natural photosynthesis by using sunlight to drive the overall water splitting without using external bias and sacrificial agent. Herein, few-layer monoclinic BiVO₄ nanosheets (BVNS) with a thickness of ~4.3 nm, exposed (010) facets and abundant oxygen vacancies are fabricated using graphene oxide dots as templating reagent. After decorating with asymmetric chromium porphyrin derivative bearing one benzoic acid and three phenyls as meso-position substituents (chromium-5-(4-carboxyphenyl)-10,15,20-triphenylporphrin, CrmTPP) and PtO_x cocatalyst, the obtained two-dimensional (2D) hybrid nanocomposite (BVNS/CrmTPP/Pt) with an optimal component ratio delivers a robust overall water splitting performance with a relatively high apparent quantum yield (8.67%) at 400 nm monochromatic light. The ultrathin structure and widely distributed oxygen vacancies on the exposed (010) facets of BVNS not only endow strong and intimate contact with the decorated CrmTPP molecules to promote a two-step excitation Z-scheme charge transfer mechanism for preserving the high redox ability of the photogenerated charge carriers, but also alleviate their recombination, and thus causing the robust overall water splitting performance of the 2D hybrid nanocomposites. The present results provide a novel strategy to construct highly efficient artificial photosynthetic system for overall water splitting.

A TiO₂ heterostructure modified with carbon nitride nanosheets (CN-NSs) has been synthesized via a direct interfacial assembly strategy. The CN-NSs, which have a unique two-dimensional structure, were favorable for supporting TiO₂ nanoparticles (NPs). The uniform dispersion of TiO₂ NPs on the surface of the CN-NSs creates sufficient interfacial contact at their nanojunctions, as was confirmed by electron microscopy analyses. In comparison with other reported metal oxide/CN composites, the strong interactions of the ultrathin CN-NSs layers with the TiO₂ nanoparticles restrain their re-stacking, which results in a large specific surface area of 234.0 m²·g^-1. The results indicate that the optimized TiO₂/CN-NSs hybrid exhibits remarkably enhanced photocatalytic efficiency for dye degradation (with k of 0.167 min^-1 under full spectrum) and H₂ production (with apparent quantum yield = 38.4% for λ = 400 ± 15 nm monochromatic light). This can be ascribed to the improved surface area and quantum efficiency of the hybrid, with a controlled ratio that reaches the appropriate balance between producing sufficient nanojunctions and absorbing enough photons. Furthermore, based on the identification of the main active species for photodegradation, and the confirmation of active sites for H₂ evolution, the charge transfer pathway across the TiO₂/CN-NSs interface under simulated solar light is proposed.