Preparation And Performance Study Of Precious Metal Supramolecular Gel/aerogel Based On Ligand Self-assembly

Self-assembly of noble metal nano-building blocks(NBBs)to hierarchical self-suported porous monoliths provides a great potential for achieving their wonderful properties along with practical applications,including energy storage,electronic devices,sensors,and catalysis.The current preparation methods mainly involve sol-gel,template approaches and 3D printing.However,assembly process of sol-gel method was limited in complex drying process,weak strength of monoliths,and little interest has been paid to the role of ligands in the self-assembly process in order to grasp the control of the structure and properties.Although the template method can accurately control its structure,however the process of removing the template is complicated and the material structure is damaged greatly.3D printing method can accurately prepare regular,uniform structure,but the cost is high,so it is not suitable for large-scale production.Therefore,it is urgent to develop a simple,universal strategy for the preparation of noble metal aerogels.In recent years,the method based on self-assembly of nanoparticles has become an effective method for“bottom-up,preparing porous materials,which has attracted much attention in the preparation of noble metal aerogels.The interaction between ligand and noble metal was used to modify the surface of nanoparticles and cross-linking agent was added to assemble into the 3D nanostructures by coordination.Or the nano-unit self-assembled to create a 3D nanostructure by using the dense stacking action between the exposed crystal surfaces on the surface of nanoparticles modified by ligand.Based on the research of supramolecular gel,it is proposed to introduce abundant weak interaction forms in supramolecular chemistry(hydrogen bond interaction,van der Waals interaction,π-π interaction)in the design and synthesis of ligands capped onto NBBs.The formation of noble metal aerogels based on self-assembly of noble metal NBBs.This preparation strategy,which is simple and universal,can precisely control its structure and properties by exchanging various NBBs and adjusting different type of dirving forces.It would be an ideal strategy to greatly expand the types of noble metal aerogels and broaden the application field of precious metal aerogels.This dissertation mainly carried out the following two aspects of work:In the first part,we designed and synthesized ligand with glutamic acid molecule as self-assembly unit and mercaptan as anchor position.Two ligands(LI and L2)were synthesized by adjusting the linker and hydrogen binding sites,and characterized by FT-IR,1H NMR,MS etc.Ligands were grafted onto surface of platinum nanowires successfully by XPS,TEM and TGA,and the packing density was calculated as 3.43 molecules/nm2(L1)and 7.71 molecules/nm2(L2).Based on this,gelation behaviors and properties of functionalized Pt nanowires were investigated,which can gel toluene,dichloromethane chloroform and teralydrofuran with a wide gelation range(1.5-7.5%w/v).Interestingly,these gels displayed both thermo and shearing reversible gelation that has remained unreported with noble metal gels so far.Furthermore,the corresponding aerogels can easily be prepared through supercritical drying and their density and porosity were regulated by adjusting the NBBs concentration,SEM measurement demonstrated the aerogel networks as 3D continuous wound nanowires having hierarchical porosity.In addition,hydrogen bonds were main driving force of Pt aerogel formation by FT-IR.Owing to tihe 3D network and hierarchical pores,Pt aerogels prepared by the present strategy exhibited low overpotential,effective electrochemical active surface and long-term stability in hydrogen evolution reaction.In second part,different fimctionalized noble metal NBBs(morphology,colrPosition,metal)were synthesized and their self-assembly behavior in solvent was investigated.The results showed that functionalized Pt/Co nanowires,Au nanowires and Au nanoparticles could form stable gels in dichloromethane and trichloromethane etc.SEM and TEM measurements demonstrated that the noble metallic aerogels formation based on self-assembly of NBBs as hierarchical porous structure.This section folly proved that the novel self-assembly strategy is universal,and is expected to be applied to the preparation of other types of nano-aerogels.