Design And Synthesis Of Metal-Organic Frameworks-based Hybrid Photocatalysts For Visible-Light-Induced H₂ Production

Energy shortage and environmental deterioration have raised scientist to search clean and renewable energy sources to replace the conventional fossil fuels. Hydrogen as a clean, renewable, and storable chemical energy shows great potential to power the future society. Among the techniques for hydrogen production, direct water splitting using solar energy over a photocatalyst is an ideal process to convert solar energy into chemical energy. In a large number of literature reports, many semiconductor photocatalysts materials activity was influenced because of the band gap is too wide or easy light corrosion and other reasons. Therefore, Study and design of highly efficient photocatalysts materials is the key to hydrogen production by water splitting.The morphology and structure of photocatalyst have important influence on the photocatalysts activity. Recently, some of the metal organic framework (MOFs) is used as new photocatalysts materials, metal organic framework materials with unique porous structure, large specific surface area and easy to modified. The research content of this paper is designing and preparing new type of highly active photocatalysts composite materials for hydrogen evolution based on MOFs, the main contents of the present research are as follows:(1) We prepared UiO-66 metal-organic framework octahedrons through a hydrothermal process, then CdS nanoparticles acting as photosensitizer was grown in situ upon UiO-66 octahedrons. The prepared CdS/UiO-66 nanoparticles were characterized by XRD, SEM, TEM, UV-vis, PL and so on. The photocatalytic activity of CdS/UiO-66 for hydrogen evolution was investigated under visible light irradiation (λ≥420nm), and the CdS/UiO-66 composite show remarkably active hydrogen evolution compared with CdS and UiO-66 alone. The improved photocatalysts hydrogen production over CdS/UiO-66 composite is due to the the excellent electron transfer effect between CdS and UiO-66. The optimum mass ratio CdS to UiO-66 was 16 wt.%.(2) We prepared a hybrid photocatalyst through coupling metal-organic framework UiO-66 octahedrons and graphitic carbon nitride (g-C3N4). The resultant hybrids show enhanced photoactivity for hydrogen evolution from water under visible light irradiation when compared to pristine g-C3N4 and UiO-66. The hybrid with optimum g-C3N4 content of 50 wt% shows the highest photocatalysts hydrogen production rate of 14μmol·h-1, which is nearly 18 times higher than that of g-C3N4 alone under the same experimental condition. The enhancement in photocatalysts hydrogen production could be ascribed to the improved charge transfer across the UiO-66/g-C3N4 interfaces, which effectively suppresses the recombination of photogenerated electron-hole pairs and thereby enhances the photocatalysts water splitting activity.(3) On the basis of MIL-101(Cr), we prepared an noble-metal-free photocatalysts hydrogen generation system consisting of MOFs MIL-101(Cr) as photocatalyst, Ni(dmgH)2 as co-catalyst, and Erythrosin B dye as photosensitizer. It is found that Ni(dmgH)2 can serve as an efficient co-catalyst to boost hydrogen generation in the presence of triethanolamine (TEOA) as electron donor under visible light irradiation. The optimal hybrid with 5 wt.% Ni(dmgH)2 coupled MIL-101(Cr) offers a stable hydrogen generation rate of 45.9μmol·h-1. The present study provides a new route for the rational design and preparation of active hydrogen generation system by combining non-noble metal molecular complex and MOFs photocatalysts.