[2011年06月28日]

Photocatalytic H2 production and transfer hydrogenation on hybrid catalyst system composed of inorganic semiconductor and molecular catalysts

 

   Artificial photosynthetic H2 evolution and visible light driven organic synthesis have attracted much attention of scientists. Over past decades, the usually used photosensitizers were the organometallic complexes such as Ru complexes or organic compounds. However, this type of photosensitizers can only absorb a light of particular wavelength or a narrow region of light, and furthermore suffer the problem of instability or even degradation under photoirradiation condition. On the other hand, the spectral absorption range of semiconductors is usually broad and continuous, and this is potentially beneficial for the efficient collection of solar energy. Therefore, we wonder that whether we can use semiconductor to replace the traditional photosensitizer to combine with molecular catalyst for photocatalytic H2 evolution or visible light driven organic synthesis. If this strategy is feasible, the utilization ratio of light and stability for artificial photosynthetic system would be obviously enhanced.

 

The UV-Vis absorbance of semiconductor CdS and Ru complex photosensitizer

 

Herein we report an inexpensive and stable hybrid artificial photocatalytic system to mimic photosystem I (PSI) using semiconductor (CdS) as photosensitizer, cobaloximes (CoIII complexes, functional biomimetic hydrogenase) as the catalysts for H2 evolution. Under visible light irradiation (λ > 420 nm), photocatalytic H2 evolution with more than 171 turnover numbers (based on CoIII(dmgH)2pyCl 1) can be achieved, which is comparable with the highest TON obtained from homogeneous Co complexes based photocatalytic systems. The stability of this hybrid system is much superior to homogeneous system. The interfacial electron transfer from photoexcited CdS to CoIII complexes is very efficient through the weak adsorption of CoIII complexes on CdS. In fact, we found that the photocatalytic activity of CoIII(dmgH)2pyCl/CdS is even higher than that of Pt/CdS catalyst which has been considered as a highly active photocatalyst for H2 evolution. The present work demonstrates the feasibility of using semiconductors as photosensitizers and molecular complexes as H2 evolution catalysts. The combination of semiconductor with molecular catalyst may provide an alternative strategy in the design of novel stable and inexpensive artificial photosynthetic system. Corresponding research is published on J. Catal. (2011, 281, 318-324, Fuyu Wen, Jinhui Yang, Xu Zong, Baojun Ma, Donge Wang, Can Li*).


   For visible light driven organic synthesis, we report an example of photocatalytic transfer hydrogenation of carbonyl and C=C compounds under visible light irradiation, by coupling the semiconductor CdS with iridium complexes. The iridium complexes are activated by the photoexcited electron from CdS, and they play dual functions, acting as the acceptor of electron as well as the catalytic sites for organic transformation. Results show that this hybrid system is a highly selective and active photocatalytic system for organic reduction reaction under visible light irradiation (TOF = 100 h-1, TON > 500). In the hybrid systems, the semiconductor harvests light energy, and complexes are activated by the photo-driven electron, and catalyze the subsequent reactions. The strategy of activating catalysts by photoexcited electron-transfer provides a promising method for various photocatalytic organic reactions, particularly for reductions and oxidation reactions. Furthermore, the strategy can be expanded to the utilization of solar energy to produce H2 and chemicals from H2O and CO2. This research is published on Chem. Commun. (2011, 47, 7080-7082, Jun Li, Jinhui Yang, Fuyu Wen, Can Li*).

 

Article

Photocatalytic H2 production on hybrid catalyst system composed of inorganic semiconductor and cobaloximes catalysts

Fuyu Wen, Jinhui Yang, Xu Zong, Baojun Ma, Donge Wang, Can Li*

J. Catal., 2011, DOI:10.1016/j.jcat.2011.05.015

http://dx.doi.org/10.1016/j.jcat.2011.05.015

 

A visible-light-driven transfer hydrogenation on CdS nanoparticles combined with iridium complexes

Jun Li, Jinhui Yang, Fuyu Wen, Can Li*

Chem. Commun., 2011, 47, 7080-7082

http://pubs.rsc.org/en/content/articlelanding/2011/cc/c1cc11800e

 

 

 

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