Photosynthesis-inspired Materials Synthesis And Efficient Use Of The Photo-generated Carriers

Through billions of years of evolution,bioprocesses in nature have exquisite and efficient characteristics,and they are capable of either controlling the synthesis of biological materials with precise compositions and exquisite structures,or achieving high efficiency of material and energy conversion.By mimicking the unique structures in the biological systems,people have obtained bio-inspired materials with similar structures and functions,which is a hot spot in the past 20 years.In essence,these unique structures are all caused by the specific bioprocesses,and therefore it is beneficial for the development of new materials synthesis techniques by studying these bioprocesses.On the other hand,the bioprocesses are usually efficient due to the division of work and cooperation of multiple factors,which is of great significance for people to build bioinspired material and energy conversion systems with high efficiency.As a typical bioprocess,photosynthesis converts carbon dioxide and water to organics and oxygen under ambient conditions by using sunlight.By studying photosynthesis,we have an understanding of it from outside to the deep inside.The first impression of photosynthesis is that it can trigger chemical reactions to produce organic matter and oxygen under sunlight;by understanding the preliminary mechanism,the photo-excited carriers were found to be the driving forces of the reactions;further study shows that photosynthesis can efficiently use the absorbed photons to complete the conversion of light energy to chemical energy,and the multiple transfer intermediates play a very important role in this process.Based on the above understanding of photosynthesis,the present thesis studied photosynthesis from two aspects:one is to learn the process of chemical reaction initiation for material synthesis,and the other is to learn the role of carrier transfer intermediates to accelerate the separation of photo-excited carriers,and realize the efficient use of the carriers.Some results and conclusions have been obtained as follows:1.Au@Pt Au_m core-shell nanoparticles with controllable surface compositions have been obtained by photo-triggered reactions.The surface composition can be continuously controlled by tuning the addition amount of HAu Cl₄.The key is the coexistence of the galvanic replacement reaction between Pt and HAu Cl₄ and the coreduction of Au(III)and Pt(IV).As catalysts for methanol electro-oxidation,the surface composition plays a decisive role.Au@Pt Au_0.5 has the best catalytic activity and stability among the products,which can be ascribed to the following three aspects:(i)the introduction of Au atoms into the shell reduces the probability of formation of“3-fold Pt assembly”,thus decreasing the generation of CO and the poisoned Pt active sites,and therefore the catalytic performance is improved;(ii)Au atoms can modify the electronic structure of Pt and reduce the binding energy between Pt and CO,which is conducive to the oxidation of CO and thus improves the catalytic performance;(iii)the introduction of Au atoms can increase the oxidation potential of Pt and inhibit its oxidation dissolution during the electrocatalytic process,thereby improving the catalytic durability of the catalyst.2.Pt and MoS₂ were synthesized on the surface of K₄Nb₆O₁₇ nanosheets using photo-generated electron reduction method.The size of Pt and MoS₂ can be controlled by controlling the addition amount of H₂Pt Cl₆ and adjusting p H of the reaction solution,respectively.The experimental results showed that when the loading amount of Pt decreased from 1 wt.%to 0.05 wt.%,the average size of Pt decreased from 3.9 nm to less than 1 nm,the hydrogen evolution rate decreased by only 5%,and the mass activity of Pt increased by nearly 20 times.By adjusting the p H of the reaction solution,the average size of MoS₂ can be reduced from 4.2 nm to less than 1 nm without reducing the loading amount,and the hydrogen evolution rate can be increased by 2.7 times.Compared with the traditional nanoscale hydrogen production catalyst,the sub-nano Pt and MoS₂ are capable of promoting the transfer of photo-generated electrons and increasing the number of active sites for hydrogen production,so as to effectively improve the efficiency of hydrogen production.3.By learning the role of freely-moving carrier transport intermediates in natural photosynthesis,CO₃^2-ions were used as the hole vehicles to accelerate the hole transfer from photocatalysts to the sacrificial reagents and promote the efficient use of the photo-excited electrons,thus improving the photocatalytic activity of the photocatalysts.During the photocatalytic reactions,CO₃^2-ions could rapidly capture the photo-generated holes to generate CO₃^·-radicals,which can further transfer the holes to methanol and regenerate CO₃^2-ions.In this process,CO₃^2-ions accelerated the carrier separation.Moreover,they just served as hole vehicles without any consumption,therefore,the hydrogen evolution performance was significantly enhanced.4.An artificial photosynthetic system with multi-step hole transport processes is constructed by learning the synergistic effects of multiple carrier transport intermediates in natural photosynthesis to efficiently use the photo-generated electrons.Co-O-Ac,synthesized by a photo-generated hole oxidation method,serve as the anchored oxidation catalyst,and CH₃COO^-ions serve as hole vehicles to transfer the photo-excited holes from the cocatalysts to the sacrificial reagents.The synergistic transport of the holes by the Co-O-Ac and CH₃COO^-ions greatly accelerated the separation of the carriers,thus remarkably improved the photocatalytic activity of g-C₃N₄.