Ting Song

Stable and improved visible-light photocatalytic hydrogen evolution using copper(II)–organic frameworks: engineering the crystal structures

Relatively high photocatalytic H2 production activities can be exhibited by metal–organic framework (MOF) materials using a compulsory cocatalyst or photosensitizer. However, no study has focused on the effect of the crystal structures of MOF materials on the photocatalytic H2 evolution activity when using the same organic ligand and metal ion. Therefore, by connecting the 4′-(2,4-disulfophenyl)-3,2′:6′,3′′-terpyridine (H2DSPTP) organic ligand with CuSO4·5H2O, different MOF photocatalyst crystalline structures, (1) and (2), were obtained. These products were then respectively characterized and employed for photocatalytic H2 evolution. In the absence of any photosensitizer and cocatalyst, compounds 1 and 2 exhibited efficient visible-light-driven photocatalytic H2 production at maximum rates of 5.77 μmol h−1 and 6.99 μmol h−1. Interestingly, compounds 1 and 2 also exhibited photocatalytic H2 generation when irradiated with near-infrared light. Compound 2 showed outstanding long-term stability, as evidenced by eight-cycle tests over 24 h. The charge separation and transfer process of the compounds were verified using PL, time-resolved PL spectroscopy, and photocurrent measurements.

Enhancement of hydrogen production of a Cu–TiO2 nanocomposite photocatalyst combined with broad spectrum absorption sensitizer Erythrosin B

A broad spectrum absorption photocatalytic system has been expected for a long time, especially for catalysts where the absorption mainly concentrates on the ultraviolet region, like TiO2. Here, dye sensitization was used to realize this expectation for TiO2. Anatase TiO2 was prepared by a hydrothermal method and then modified with Cu nanoparticles (NPs) by chemical reduction reaction. The highest H2 production rate was 3.33 mmol g−1 h−1 for Cu(3%)–TiO2 (content of Cu NPs was 3 wt%) and for pure TiO2 was only 0.356 mmol g−1 h−1. Next, the Cu(3%)–TiO2 photocatalyst was sensitized with various amounts of Erythrosin B (ErB) and the highest H2 production rate was 13.4 mmol g−1 h−1 with 3 mg of ErB in the photoreaction system. Under monochromatic light irradiation (500, 550, 600 and 650 nm), no photocatalytic activity was detected for Cu(3%)–TiO2 and some photocatalytic activities were obtained for sensitized Cu(3%)–TiO2, indicating that ErB sensitization can extend the visible light harvesting ability efficiently. Through photoelectrochemical analysis, electron–hole separation and transfer processes were promoted significantly by modification with Cu NPs and then sensitization by ErB. A possible ErB sensitization mechanism is proposed between ErB and Cu–TiO2 for the improvement of the photocatalytic activity.

Fabrication of a non-semiconductor photocatalytic system using dendrite-like plasmonic CuNi bimetal combined with a reduced graphene oxide nanosheet for near-infrared photocatalytic H2 evolution

The field of photocatalytic hydrogen evolution has almost exclusively concentrated on semiconductor photocatalysts, with few reports of non-semiconductor photocatalytic systems due to the small number of non-semiconductor catalysts and their poor photocatalytic ability. Herein, dendrite-like plasmonic CuNi bimetal was prepared by a hydrothermal method, followed by modification with reduced graphene oxide (rGO) nanosheets to facilitate the separation of the electron–hole pair and improve the photocatalytic H2 evolution rate. The electron–hole pair originates from the surface plasmon resonance (SPR) effect of Cu in CuNi bimetal. Importantly, a near-infrared photocatalytic activity was confirmed with monochromatic light irradiation at a wavelength of 800 and 900 nm in the photocatalytic system due to the broad-spectrum response of plasmonic Cu. In addition, this photocatalyst exhibited favorable stability and repeatability in five consecutive runs of accumulatively 30 h. This study provides a new and significant approach for the development of a non-semiconductor photocatalytic system, which could effectively broaden the scope of the photocatalyst field.

In Situ Construction of Globe‐like Carbon Nitride as a Self‐Cocatalyst Modified Tree‐like Carbon Nitride for Drastic Improvement in Visible‐Light Photocatalytic Hydrogen Evolution

Photogenerated carriers possess high recombination efficiency in carbon–nitrogen materials, which results in lower photocatalytic H2 evolution activity. By reviewing the literature, it was concluded that relying only on a structure‐controlled technique was insufficient to reduce the combination of photogenerated carriers without introducing a foreign material or element. Hence, bulk‐like g‐C3N4 [CN (B)], globe/strip‐like g‐C3N4 [CN (G/S)], and globe/tree‐like g‐C3N4 [CN (G/T)] were in situ obtained through a facile calcination method. Similar to platinum (Pt) as a cocatalyst, globe‐like carbon nitride as a self‐cocatalyst was found to improve the separation efficiency of photogenerated carriers effectively. Interestingly, the hollow‐tree‐branch morphology of CN (G/T) effectively transmitted photogenerated holes, which thereby enhanced the photocatalytic H2 evolution activity. The H2 production rates of CN (G/S) and CN (G/T) were almost 10.7 and 18.3 times greater, respectively, than that of CN (B) without the addition of Pt as a cocatalyst. Notably, CN (G/S) and CN (G/T) displayed considerable rates of H2 production in water relative to that shown by CN (B) (no activity) without the use of any sacrificial agent and by using Pt as a cocatalyst. CN (G/T) showed outstanding long‐term stability, as evidenced by seven cycle tests performed over 28 h. The charge separation and transfer process of the compounds were verified by photoluminescence (PL), time‐resolved PL spectroscopy, and photocurrent measurements.