Application Of Metal Nanoclusters And Their Composites In Photocatalytic Production Of H₂O₂

As new typed nanomaterials,thiolate-protected metal nanoclusters（MNCs）,which usually consist of several,dozens to hundreds of metal atoms（e.g.,gold,silver and platinum）,have recently attracted extensive attention in energy and catalysis.In addition to their ultra-small size（<3 nm）,ultra-high specific surface area and rich chemistry,MNCs exhibits unique molecular like properties,such as discrete electron energy levels,highest occupied molecular orbital（HOMO）-lowest unoccupied molecular orbital（LUMO）transitions,adjustable optical absorption and strong light luminescence.These unique properties make MNCs good candidates for diverse photocatalytic applications.Since hydrogen peroxide（H₂O₂）was firstly synthesized in 1818,it has received widespread attention and has been listed as one of the 100 most important chemicals in the world.At present,H₂O₂ has been widely used in organic synthesis,wastewater treatment,medical disinfection,and pulp papermaking.In the present industrial H₂O₂production,anthraquinone process is the primary method.However,this method not only consumes a lot of energy but also produces a large amount of organic waste liquid.Therefore,it is urgent to develop one H₂O₂production approach with low energy consumption and no pollution.As a green technology,photocatalysis has shown great potential in the production of H₂O₂.Therefore,given the unique physical and chemical properties of MNCs,the development of metal MNCs and their composite materials is expected to be used in photocatalytic H₂O₂ production.At present,the application of MNCs-based in photocatalysis is mainly limited by the following factors:（1）poor sunlight absorption,（2）high photocarrier recombination efficiency,（3）insufficient active sites.In summary,the main research contents of this paper are as follows:1)Given the poor light-harvesting ability as well as difficult diffusion of reactants onto active sites surface,we report the design of a high-performance photocatalyst based on decorating per-6-thio-β-cyclodextrin（SH-β-CD）protected platinum nanoclusters（Pt@β-CD NCs）on C₃N₄/MXene（Ti₃C₂）heterojunctions（C₃N₄-M for short）.The key to this design is the employment of the Pt@β-CD NCs,which not only serve as proper photoinduced e-acceptors for accelerating charge carriers’separation/migration and offer abundant active sites（i.e.,Pt core of the NCs）for reaction,but also provides plentiful“delivery channels”（i.e.,the hydrophobic cavity of the SH-β-CD ligand）to promote the diffusion of reactant（O₂）to active sites.In addition,the hybridization of MXene（Ti₃C₂）with C₃N₄ largely improves the visible（Vis）-light harvest of the photocatalyst.Leveraging on the complementary properties of Pt core,reactive SH-β-CD ligand,C₃N₄,and MXene（Ti₃C₂）,the as-designed Pt@β-CD/C₃N₄-M photocatalyst shows～6 times higher production of H₂O₂(147.1μM·L^-1)than pristine C₃N₄(24.2μM·L^-1).This interesting strategy and findings revealed in this work would provide a good platform to explore novel catalysts with high performance in photocatalytic H₂O₂ production.2)Given the high recombination rate of MNCs photogenerated carriers,insufficient active sites on the surface of metal NCs and difficult diffusion of substrates onto active sites surface.Ligand engineering is considered to be an effective way to solve the problem.We report the design of a Au NCs-based photocatalyst for photocatalytic hydrogen peroxide（H₂O₂）production based on the ligand engineering of Au NCs with porphyrin cobalt（Co-TCPP）.Besides enhancing the visible light absorption of Au NCs,the grafted Co-TCPP molecules on the Au NCs surface could serve as electron acceptors,which not only efficiently promotes charge carriers’separation of Au NCs,but also provides abundant active sites for photocatalysis.On the basis,the as-designed Au NCs-based photocatalyst exhibits excellent photocatalytic performance in H₂O₂ production(up to 235.93μM L^-1 with 1 h under visible light irradiation in the absence of any scavengers).This work provides new ideas for the design and application of MNCs-based photocatalysts.3)To study the influence mechanism of ligand on MNCs catalytic reaction,we synthesized a high luminescence Au Ag NCs with rich functional group GSH as the ligand,and explored the performance and mechanism of Au Ag NCs photocatalytic production of H₂O₂ via oxygen reduction reaction.According to the experimental results and theoretical calculations,we found that-COOH on the surface of the ligand could be used as the reaction site for H₂O₂ generation via oxygen reduction reaction.This study provides a theoretical basis for MNCs’interface design and interface reaction.