Polymer/Metal Nanohybrid Systems:Design,Synthesis And Catalytic Applications

Catalysis plays an important role in both chemical reactions in nature and industrial manufacturing applications.The design and development of catalysts with high conversion rate and selectivity are faced with great challenges.In recent years,new catalysts based on polymer/metal nanohybrid systems have attracted extensive attention.The diversity of building blocks,variable and adjustable structures,and easy introduction of functional units make polymer materials showing great application prospects in the field of catalysis.On the one hand,conjugated polymer materials can regulate semiconductor properties such as band gap at the molecular level and the abundant surface sites are easy to hybridize with metal catalysts to improve photocatalytic activity.On the other hand,polymer materials with unique mechanical response can also be combined with metal catalysts to regulate the heterogeneous catalytic reaction.This doctoral thesis mainly focuses on the design and synthesis of polymer/metal nanohybrid systems,and develops their applications in photocatalytic carbon dioxide reduction,photocatalytic formic acid dehydrogenation and regulating heterogeneous catalysis with polymer mechanochemistry.The main research results are summarized as follows:1.We have successfully demonstrated that ultrathin graphdiyne oxide nanosheets with rich oxygen-containing groups can effectively anchor and stabilize Cu2+ ions,which then serve as active sites towards CO2-to-CH4 photoconversion in aqueous solutions with selectivity up to 87%.The GDYO nanosheets possess a suitable LUMO level and the H2 evolution is completely suppressed when the photocatalytic CO2 reduction is conducted in aqueous solutions.The atomically anchored Cu2+ ions can effectively trap photogenerated electrons and facilitate charge separation in the GDYO nanosheets.In addition,since Cu2+ ions can preferably enhance the adsorption and activation of the CH3OH*intermediate,CH4 can be produced via a continuous hydrogenation process by accepting more electrons and protons during the photoreduction of CO2.The methodology presented in this study can be extended to prepare various polymer/metal nanohybrid photocatalysts with precisely engineered metallic centers towards a wide range of photocatalytic applications.2.We report a highly efficient room-temperature photocatalytic formic acid dehydrogenation system,where ultrathin aza-CMP nanosheets are employed to activate coordinated Pd sites.The aza-CMP/Pd delivers 100%selectivity for hydrogen and the turnover frequency number of 167.2 h-1 under visible light irradiation without any additives.Significantly,it was found that the remarkable improvement of hydrogen production performance is attributed to the interaction between Pd and N on aza-CMP.Highly dispersed Pd can enrich photogenerated electrons from aza-CMP,and furthermore act as an active center to reduce formic acid to form hydrogen.The photogenerated holes directly participate in the oxidation reaction to generate carbon dioxide.Our study provides a feasible approach towards preparing various polymer-based photocatalysts with precisely engineered metallic centers for efficient and sustainable photocatalytic formic acid dehydrogenation system under mild conditions.3.We for the first time demonstrated that polymer-grafted gold nanoparticles can be developed as mechanically responsive catalysts for heterogeneous catalysis of the hydrogenation of 4-nitrophenol.Polymer chains can be mechanically ruptured from the surface of gold nanoparticles exerted by sonication-generated elongational flow.The breakage of Au-Au bonds at the heterointerfaces is responsible for the mechanical activation.With the reduced grafting densities,the newly exposed surfaces are thus catalytically active toward desired chemical reactions.The mechanical activation of polymer-grafted gold nanoparticles only occurs when the grafted polymer chains exceed a threshold molecular weight.This mechanical behavior is similar to those mechanophore-linked polymers.Our study unveils an unprecedented catalytic characteristic of polymer-grafted metallic nanoparticles in response to external mechanical stress and has implications in the design and synthesis of stress-responsive polymer composites and stretchable polymer conductors containing metallic nanofillers.