The Composite Material Of Metal-Organic Layers And Carbon Nanotubes For Electrochemical Organic Synthesis

As a kind of high atomic efficiency and environmentally benign process,electrochemical methods are widely used for conversion of various organic or inorganic substrates.During the process of electro-catalytic reaction,the generated electric current can act as reagents replacing the addition of toxic and dangerous oxidant or reductant reagents.Which can not only reduce the waste and simple to operate,but also simplify the experimental steps because of the special reaction process of electrochemical reaction.Therefore,the applications of electrochemical techniques show a very good application prospect and becomes more and more attractive.The indirect electrochemical synthesis method by modifying the electrode surface with appropriate materials can regulate the electrochemical process on the surface of electrode.Moreover,by adjusting the voltage between the electrodes can easily control the selectivity and reaction rates.Metal-organic frameworks(MOFs),as a new kind of functional material,has unique structural characteristics,such as high-density distribution of active sites.The high dispersion of active sites can avoid the decrease or deactivate the catalytic activity resulting from the agglomeration of active sites.MOFs are a novel class of highly crystalline materials with clear structure constructed by the coordination of inorganic metal clusiers or metal ions nodes and organic bridging ligands linkers.By post-synthetic modification strategies for inorganic SBU nodes or organic linkers,the obtained functional MOFs can act as the potential MOF-based electro-catalyst.However,because of the limited mobility of electrons on the MOFs skelleton,most MOFs are electrical isolation.And due to the poor stability of most MOFs in organic solvents and water,as well as the limited diffusion of substrates or products in the 3D MOFs skeleton,MOFs are barely used in the field of electro-catalysis.Considering the above limitations,we hope that we can usage some feasible strategy to solve the above problems.By using a simple solvothermal synthesis method,with formic acid or acetic acid and water as modulators to selectively block the growth of MOF crystals along the vertical direction without affecting the growth along the other two directions,we obtained the novel 2D Metal-organic layer(s)with the thinness of monolayer or several layers.Compared with 3D bulk MOFs,the 2D MOLs can greatly reduce the transport distance of electrons to the surface of the electrode.By modifying the 2D MOLs on the electrode surface,the electrons can directly jump from MOLs to the electrode.Moreover,because of overcome the limitations of pore size in 2D MOLs,the diffusivity of the large electrolytes cations and substrate on MOLs surface is completely unrestricted.Despite the poor conductivity ofMOLs,we can usage its unique structural characteristics to achieve its in-situ binding with carbon nanotubes to perfectly overcome its conductivity limitations.In addition,in the synthesizing process,high-valence Hf4+/Zr4+and carboxylate ligand were used as metal salts and linkers to construct the stable MOLs in most solvents and a higher temperature.Compared with the previously reported methods,we can obtain MOLs with high yield,good reproducibility and produced in volume by means of the bottom-up modulated synthesis method.The obtained MOLs can meet the practical application demands.The above design philosophy can solve the stability of materials,the diffusivity of electrolytes and substrates and the conductivity of materials problems.Based on the above consideration,the following research were carried out:First:By using the facile solvothermal synthesis method,with HfOCl2·8H2O as metal-salt,4,4',4"-nitrilotribenzoate(H3NNTB)as organic ligand,formic acid and water as modulators and N,N-dimethylformamide(DMF)as solvent,we obtained the monolayer 2D Hf6(?3-O)4(?3-OH)4(?1-OH)2(?1-OH2)2(HCO2)4(NTB)2 MOLs.The TR,TGA,NMR,AFM,TEM,PXRD,HRTEM and HAADF were used to determine the MOLs structure.Then,with the characteristics of the formate capping and the softness of the MOL thin film,the MOLs were grown on multiwalled carbon nanotubes(CNTs)as a coat to obtain CNT/MOL composite material to overcome conductivity constraint.The CNT/MOL assembly can act as electrocatalyst to oxidize benzyl alcohol.Because of the high overpotential,it leads to a poor selectivity.In order to reduce the potential and improve the selectivity,we further utilize the formate capping characteristic to obtain TEMPO functionalized 2D MOLs by exchanging TEMPO-CO2H/TEMPO-OPO3H2 with formate capping groups on the secondary building unit(SBU).Furthermore,the TEMPO derivatives functionalized MOLs can oxidize alcohols to aldehydes and ketones at a lower potential.The study on the reaction mechanism indicate that the presence of MOL endowed the selectivity for primary versus secondary alcohols.Second:The catalytic acceptorless dehydrogenationthe process of saturated N-heterocycles to generate unsaturated molecules with the release of hydrogen gas is a very important kind of chemical reactions and be widely applied in organic synthesis.In addition,these reactions are also applicable to the field of liquid organic hydrogen storage materials.The desaturation reaction of N-heterocycles is a thermodynamically unfavored process leading to the previous reports often carried out in harsh conditions.In this paper,we use TEMPO-OPO3H2 functionalized Hf6(?3-O)4(?3-OH)4(?1-OH)2(?1?OH2)2(HCO2)4(NTB)2 catalyst to catalyzes the conversion of N-heterocycles by electrochemical method under mild reaction conditions.The experiment results indicate that the hybrid material can act as an efficient electrocatalyst for the dehydrogenation of N-heterocycles.Third:Hydrogen evolution reaction,as a key step in the overall water splitting process,have received great attention.In the field of electroorganic synthesis,when a lot of organic compound transformed into the target product at the anode with the HER at the cathode.The ideal conditions are that only HER reaction occurs and without other side reactions at the cathode.However,because of the high cathode overpotential in the actual reaction process often lead to side reactions of substrate,products or other substance in the system,which does not seem to be attached enough importance.Considering the importance to reduce the overpotential of HER at the cathode,the excellent electrocatalytic HER activity of platinum-based catalysts and the inherent structural features of metal-organic layers,we try to load Pt nanoparticle onto the surface of metal-organic layers and carbon nanotubes composite as the HER electrocatalyst at the cathode.Based on the experiment results,the catalyst can reduce the cathode overpotential and improve the produce yield.Fourth:The first part and the second part mainly introduced to obtain the functional catalyst by modifying the SBU surface.The obtained material can act as excellent electrocatalyst to oxidize alcohols to aldehydes or ketones and catalytic acceptorless dehydrogenation of N-heterocycles.We know that one of component of MOFs is organic linker.And the functional MOF materials can be obtained by selecting the organic ligand easy to be metallized or poscess the redox property.The major work in this section is to usuage N-containing C3/C2-symmetry ligand or redox-active linkers to construct 2D MOL.And the electrocatalytic properties were investigated by assembling CNT/MOL composite material.Moreover,the single-site solid MOF catalyst can be prepared by metallizing N-containing organic linker.Based on the above consideration,we designed and synthesized the following three kinds of 2D MOLs:(a)we prepared CNT/Hf-TPY-MOL material by growing[Hf6(?3-O)4(?3-OH)4(HCO2)6(CO2)6(TPY)2]on CNTs.The TPY ligand in MOLs were metallized with various metal and explore their catalytic activity for different substrate.(b)we prepared CNT/Zr12-bpydc-MOLs material by growing Zr12(?3-O)8(?3-OH)8(?2-OH)6(BPYDC)9·2HCO2H on CNTs.The BPYDC ligand in MOLs were metallized with various metal and explore their catalytic activity for different substrate.(c)we prepared CNT/Zr12-L 1-MOLs material by growing Zr12-L1-MOLs(L1?4-(7-(4-acetylphenyl)-2-hydroxy-1,3-dioxoisoindolin-4-yl)benzoic acid)on CNTs and explore its electrochemical performance for benzyl alcohol.