Albumin/[FeFe]-Hydrogenase Mimics For Photochemical Hydrogen Evolution

Energy shortage and environmental pollution are major risks by countries around the world in economic development.Devoloping clean,sustainable and carbon-free energy to break through the dependence on traditional fossil fuels has become important strategic goals and social responsibilities of all countries.The sun is the largest supplier of renewable energy on the planet.Capturing solar energy and converting it into hydrogen energy is considered the most ideal energy solutions.To achieve efficient hydrogen production by photocatalytic water splitting,it is crucial to find a catalyst with high catalytic activity,high stability and low cost.Natural microorganisms contain hydrogenase that can efficiently catalyze the hydrogen production by protons,but its active center is deeply buried in the protein matrix and is difficult to extract,limiting its use.Many researchers have developed more than 1,000 artificial hydrogenase mimics by simulating its structure and function,and combined them with peptides/proteins,micelles,organic polymers,polysaccharides,metal-organic framework and semiconductors,which provides a broad research space for the development of inexpensive and efficient photocatalytic hydrogen production systems.This research paper focuses on two artificially synthesized[FeFe]hydrogenase mimetics.One of which is incorporated into ovalbumin?OVA?gel by non-covalent self-assembly to construct OVA@FeFe-1 composite nanogel.By adjusting the preparation conditions,combining morphological structure,photophysics and photoelectrochemical performance analysis,we have described the photocatalytic hydrogen production performance of OVA@FeFe-1 composite nanogel in aqueous environment and a series of influencing factors.The other is covalently linked the small molecule compound?4-aminobenzyl?phosphonic acid or ovalbumin OVA and then complexed with TiO₂ nanoparticles.This study completed the characterization and comparison of the morphology,structure and optical properties of the two compounds,and also explored the performance of the aqueous phase photocatalytic hydrogen production.The specific research content and results of the paper can be explained in detail in the following two aspects:The first work used[Fe₂??-SCH₂CH₂CH₂S??CO?₆]?FeFe-1?as a catalyst for proton reduction and hydrogen production,and incorporated it in situ in the assembled OVA nanogel by amino acid coordination,hydrophobic and electrostatic interactions,successfully constructing the artificial simulated hydrogenase simulant of OVA@FeFe-1 composite nanogel.Maintaining a uniform and strable macro appearance,its loading efficiency of FeFe-1 is about 54%,which is?3 times that of a direct mixture of OVA and FeFe-1.In the process of heat-induced gelation,the change of internal and external fluorescence indicates that the hydrophobic group inside OVA molecule is reversed and undergoes reorganization.Circular dichroism chromatography confirms that the secondary structure is converted from a tight?-helix to a loose?-fold.The microscopic morphology in TEM is transformed from a spherical-like shape with a particle size of6-8 nm of the original OVA to linear or random spherical accumulations with a particle size of 50-100 nm.After that,the cyclic voltammetry and static fluorescence quenching experiments jointly verified that the reduction potential of FeFe-1 embedded in the OVA gel matrix was positively shifted,which is possible to interact with the external Ru?bpy?₃Cl₂ photosensitizer via OVA protein to achieve more efficient electron transfer Finally,the optimized OVA@FeFe-1 photocatalytic hydrogen production system can achieve a high conversion efficiency of 35.6±2.8,which is?15 times larger than the free FeFe-1 photocatalytic hydrogen production system,and has good storage stability.However,after the photocatalytic hydrogen production reaction,the OVA@FeFe-1 in this system undergoes a conformational change from?-helix to?-sheet due to the influence of p H environment.Although FeFe-1catalyst is exposed to a certain extent,it is also expected to obtain more effcient exlectron transfer to improve photocatalytic hydrogen production.The second work used FeFe-NHS as the catalyst for proton reduction and hydrogen production.It is first covalently linked to the small molecule compound?4-aminobenzyl?phosphonic acid or ovalbumin OVA through amidation reaction,and then combined TiO₂ through the coordination of phosphonic acid groups or amino acids and electrostatic interaction,successfully assembling hybrid hydrogenase mimics of TiO₂-Ap-Fe₂S₂ and TiO₂-OVA-Fe₂S₂.XRD analysis shows that modified TiO₂ still retains the original crystal structure,and the absorption range of the ultraviolet-visible absorption spectrum is expanded to the visible region.In an aqueous photocatalytic system with ascorbic acid?H₂A?as a sacrificial electron donor,compared with a single TiO₂ produced less than 2?L of H₂,the photocatalytic hydrogen production performance of TiO₂-Ap-Fe₂S₂ and TiO₂-OVA-Fe₂S₂ hybrid hydrogenase mimics both have improved by several tens of times,relatively releasing about 30 and 100?L of hydrogen after 5 h light irritation.