| Concerning the rapid consumption of fossil fuels and the increasingly deteriorating environmental problems,it is urgent for mankind to find a low-cost,sustainable and environmentally friendly novel energy sources to replace the traditional fossil energy.Currently,solar energy,wind power,water power,geothermal energy and other novel energy sources have been exploited.Among which,solar energy is promising to be a powerful alternative to traditional energy forms of fossil fuels for its inexhaustible nature and high-power delivery.Theoretically,solar energy reaching the surface of the earth in 1 hour is comparable to the total energy consumption of the globe in one year.However,the intermittent property of solar irradiation makes solar energy difficult to be utilized directly and efficiently.Scientists are trying to transform solar energy into other enegy forms,such as electrical energy,thermal energy and even chemical energy.Much attention has been putting on the conversion of solar energy to hydrogen energy for its high caloricity,convenicence of storing and transporting.Natural hydrogenases embedding in photosynthetic organisms,such as green plants,cyanobacteria and algae can convert carbon dioxide and water to carbohydrate or hydrogen driving by solar energy.However,the high extraction cost of natural hydrogenase out of organisms and the easy deactivation of catalytic center after detaching from the protein environment of natural hydrogenses limit the mass-exploitation of natural hydrogenases.Numerous efforts have been paid to design and synthesize artificial hydrogenase mimics,and fabricate photochemical hydrogen evolution systems.Most of artificial hydrogenase mimics are hydrophobic metallic complexes made of iron ions,nikel ions and cobalt ions,not favorable for photocatalytic hydrogen production in aqueous solution.In order to enhance the water solubility of artificial hydrogenase mimics,various strategies,such as covalent linking of hydrophilic group like amino group and carboxyl group onto the artificial hydrogenase mimics,grafting hydrogenase mimics onto water-soluble synthetic polymers like poly(acrylic acid)and branched polyethylenimine,peptides like cytochrome,proteins like flavodoxin,ferredoxin and barrel-like Q96C-NB protein,membranous biomass like vesicles and A?16-22 peptide self-assembly,embedding hydrogenase mimics into the hydrophobic cavity of hydrogel,micelles and host/guest macromolecules like cyclodextrin,have been successfully applied.In this dissertation,we adopted a basic protein,histone H1,as the protein matrix.Its natural property of containg plenty of lysines and argines makes histone H1 an excellent platform to covalently link[FeFe]catalyst.We designed and prepared a series of protein catalysts Histone-g-Fe2S2(H-Fe)with different compositions,and explored the morphology,the photophysical and photoelectrochemical properties of these protein catalysts.We fabricated the optimal photochemical hydrogen generation systems using these protein catalysts and studied the effect of the concentration of photosensitizer,catalyst and electron donor,and the solution pH on the efficiency of hydrogen production.Finally,we synthesized four different[FeFe]catalysts and compared their difference in photophysical and photoelectrochemical properties,and also their performance in photocatalytic hydrogen generation.This work can be subdivided into the following two parts.Firstly,we covalently linked a common[FeFe]catalyst onto histone H1 via amidation reaction,producing a series of protein catalysts with different compositions.UV-vis spectra and FTIR spectra jointly proved the combination between histone and Fe2S2-NHS.Dynamic light scattering experiments and transmission electron microscope images indicated that protein catalysts self-assembled into large sized protein nanoparticles after modification of histone with Fe2S2-NHS?Zeta-potential experiments further verified this conclusion.Circular dichroism spectra showed that the modification of Fe2S2-NHS induced the conformational change of histone to more orderd state,which is more favorable for electron transferring.The results from cyclic voltammertry and photocurrent response suggested the efficient electron transferring between protein catalyst and photosensitizer.The electrochemical impedance spectra showed that histone possesses good electroconductivity to facilitate electron transfer and lower charge recombination.Photochemical hydrogen generation experiments indicated that protein catalyst with high loading capacity of Fe:2S2-NHS possessed the highest catalytic activity and could produce hydrogen over 1 millilitre during 6 hours.Which is comparable or even advanced than most reported hydrogen generation systems based on protein/peptide catalysts.Secondly,we synthesized four different[FeFe]catalysts and verified the validity of synthesis via NMR and HRMS.We also explored their photophysical and photoelectrochemical properties via UV-vis spectra,FTIR,Cyclic Voltammetry and Electrochemical Impedance Spectra.Finally,we fabricated photocatalytic hydrogen generation systems using these[FeFe]catalysts to study the effect of the difference in the structure of[FeFe]catalysts on hydrogen generation. |
PDF Full Text Request