Photoinduced Hydrogen Production From Water By Organic Photosensitizer/Non-noble Metal Catalyst Systems

Hydrogen is known as an efficient and environmental friendly energy source with high combustion value, which is considered as a promising alternative to fossil fuels. Conversion of solar energy into molecular hydrogen has attracted more and more attention in recent years. Two types of catalytic systems based on inexpensive metals were studied in this dissertation:(i) On the basis of the principle that positively and negatively charged ions possess electrostatically attractive interaction in solution, the negatively charged xanthene dyes (Rose Bengal, RB2-; Eosin Y, EY2-and Eosin B, EB2-) were chosed as photosensitizers and the positively charged [Co(bpy)3]2+(1) as proton reduction catalyst to build new noble-metal-free homogeneous catalytic systems for photochemical H2production. The electrostatically attractive interaction of RB2-and1may improve the efficiency of photochemical H2production,(ii) In order to develop durable catalytic systems, the organic polymeric semiconductor graphitic carbon nitride (g-C3N4) was used as photosensitizer and in situ self-assembled complexes [M(TEOA)2]Cl2(M=Ni, Co, Fe; TEOA=triethanolamine) were used as catalysts for photocatalytic H2production in aqueous solution; In addition, the MoSx (x=2or3) nanoparticles as cocatalyst was deposited on the surface of g-C3N4and the high stability of g-C3N4/MoSx (x=2or3) were found for photocatalytic H2production from water.The readily obtained noble-metal-free homogeneous catalytic systems, with xanthene dyes as photosensitizers and1as catalyst in acetonitrile/water solution, are highly active for visible-light-driven hydrogen production from water. The TON is up to631versus1and2076versus RB2-under optimal conditions over2h irradiation of visible light, which was the highest TOF of hydrogen evolution by fully noble-metal-free photocatalytic systems until then. The experimental results indicate that the deactivation of the systems is mainly due to the decomposition of the organic photosensitizer. The electron transfer pathway from the singlet excited state1*RB2-to1is presumed to be the major electron transfer pathway for hydrogen production, due to the electrostatically attractive interaction of RB2-and1.In order to develop durable catalytic systems that rely exclusively on earth-abundant and environmentally benign elements for photocatalytic H2production in aqueous solution, the catalytic systems were constructed by replacing organic dyes with g-C3N4as photosensitizer and in situ self-assembled complexes [M(TEOA)2]Cl2(M=Ni, Co, Fe; TEOA=triethanolamine) as catalysts. The TEOA in the reaction solution acts not only as an electron donor but also as a catalyst ligand, which apparently enhance the stability of the system. The H2evolution lasts more than60h and the TON is up to281versus [Ni(TEOA)2]Cl2. The lifetime of H2production of the g-C3N4/[Ni(TEOA)2]Cl2/TEOA system is considerably longer than that of previously reported systems based on earth abundant elements in aqueous solution. Sensitization of g-C3N4by acriflavine through π-π interaction made the absorption band edge of g-C3N4/acriflavine red-shifted by130nm and the efficiency of photocatalytic H2production was significantly improved.As part of efforts to design and examine new systems based solely on earth-abundant elements, MoSx (x=2or3) nanoparticles were deposited on the surface of g-C3N4to replace noble metals (Pt, Pd, Au etc) as cocatalysts. The hydrogen production rate of g-C3N4/MoS2and g-C3N4/MoS3systems are19.96μmol/h and7.48μmol/h, respectively, under optimal conditions. The stability of g-C3N4/MoSx (x=2or3) was tested for photocatalytic H2production over20h irradiation. The g-C3N4/MoS3system proved to have good stability for photocatalytic H2production. The possible pathways for electron transfers were studied by steady and transient fluorescence spectroscopy.