Highly asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) with intense near-IR light (650–800 nm) absorption is utilized as a sensitizer to extend the spectral response region of graphitic carbon nitride (g-C3N4) from ∼450 nm to more than 800 nm. Ultraviolet–visible light (UV-vis) diffuse reflectance absorption spectra (DRS), photoluminescence (PL) spectra, time-resolved photoluminescence spectra (TRPS), and energy band structure analyses are adopted to investigate the photogenerated electron transfer process between Zn-tri-PcNc and g-C3N4 on both thermodynamics and dynamics aspects. After optimizing the photocatalytic condition and adding chenodeoxycholic acid (CDCA) as coadsorbent, Zn-tri-PcNc sensitized g-C3N4 photocatalyst shows a H2 production efficiency of 125.2 μmol h–1 under visible/near-IR-light (λ ≥ 500 nm) irradiation, corresponding to a turnover number (TON) of 5008 h–1 with an extremely high apparent quantum yield (AQY) of 1.85% at 700 nm monochromatic light irradiation. The present work should be the rarely fundamental investigation on the utilization of near-IR light of solar radiation for the photocatalytic H2 production from water splitting over a dye-sensitized semiconductor.

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Zinc phthalocyanine (ZnPc) derivatives with asymmetric (Zn-tri-PcNc-2) or symmetric (Zn-tetrad-Nc) structure, which possess wide spectral response in the visible/near-IR light region, are synthesized and utilized as a sensitizer of graphitic carbon nitride (g-C3N4) with 0.5 wt% Pt-loading for photocatalytic H2 production. The experimental results indicate that Zn-tri-PcNc-2 exhibits much better photosensitization on g-C3N4 than Zn-tetrad-Nc under visible/near-IR light although Zn-tetrad-Nc possesses wider and stronger optical absorption property than Zn-tri-PcNc-2. Zn-tri-PcNc-2-Pt/g-C3N4 exhibits an average H2 production rate of 132 μmol h(-1), which is much better than that (26.1 μmol h(-1)) of Zn-tetrad-Nc-Pt/g-C3N4 under visible-light (λ ≥ 500 nm) irradiation. Moreover, Zn-tri-PcNc-2-Pt/g-C3N4 also shows much higher apparent quantum yield (AQY) than Zn-tetrad-Nc-Pt/g-C3N4 under red/near-IR light irradiation. Especially, Zn-tri-PcNc-2-Pt/g-C3N4 exhibits impressively higher AQY (1.07%) than that (0.22%) of the Zn-tetrad-Nc-Pt/g-C3N4 under 700 nm monochromatic light irradiation. The much better photoactivity of Zn-tri-PcNc-2-Pt/g-C3N4 than Zn-tetrad-Nc-Pt/g-C3N4 is caused by the asymmetric structure of Zn-tri-PcNc-2, which can result in the electronic orbital directionality of its excited state, much faster photogenerated electron transfer to g-C3N4, and higher red/near-IR light utilization efficiency as compared to Zn-tetrad-Nc-Pt/g-C3N4. The present results provide an important insight into the effects of molecular structure and optical absorption property of phthalocyanine derivatives on the photoactivity of the dye-sensitized semiconductor, and also guide us to further improve the solar energy conversion efficiency by optimizing the molecular structure and effectively utilizing the visible/near-IR light of sunlight.

A series of carbon-coated Ni (Ni@C)-Cd0.8Zn0.2S nanocomposites were fabricated via a facile hydrothermal process using pre-prepared Ni@C as a starting material. The obtained products were characterized by X-ray diffraction, UV-Vis diffuse reflectance absorption spectroscopy, X-ray photoelectron spectroscopy and electron microscopy. It was found that the introduction of Ni@C nanoparticles can improve both the visible light-induced photocatalytic H2 production activity and stability of the Cd0.8Zn0.2S solid solution, and the Ni nanoparticles encapsulated by several graphite-like carbon layers show high chemical and thermal stability. Among those products with various Ni@C contents, the 5 wt% Ni@C-Cd0.8Zn0.2S nanocomposite exhibits the maximum photoactivity (969.5 μmol h(-1)) for H2 production, which is ∼3.10 times higher than that (312.6 μmol h(-1)) of pristine Cd0.8Zn0.2S. This significant enhancement in the photoactivity by loading Ni@C nanoparticles can be attributed to the metallic Ni in the Ni@C acting as a co-catalyst, while the graphite-like carbon shells acting as the Cd0.8Zn0.2S nanoparticles' support and electron acceptor, which causes an effective photogenerated carrier separation in space and an improvement in the photoactivity and stability for H2 production. The present findings demonstrate a cost reduction strategy by using a non-noble metal co-catalyst for efficient and stable light-to-hydrogen energy conversion.