Metallosalen-Covalent Organic Frameworks:Designed Synthesis And Catalytic Properties

Covalent-Organic Frameworks(COFs)are a class of porous organic crystal materials formed by organic ligands connected through reversible covalent bonds.Metalated COFs are obtained by anchoring the metal species by specific site within the COFs’ framework.Key metal coordination sites mainly include pyrine,phthalocyanine,pyrimidine,and N,N’-bis(salicylidene)ethylenediamine(Salen).Metallosalen complexes(M-Salen),known for their broad application as efficient homogeneous catalysts in various catalytic reactions,can be integrated into the COFs backbone.This integration not only achieves heterogenization of the M-Salen catalytic groups but also endows the catalysts with characteristics of ordered porosity.As an emerging M-COF material,research on the structure and performance of Metallosalen-COFs(M-Salen-COFs)is in its initial stages.This thesis primarily focuses on the design and synthesis of M-Salen-COF catalysts,discussing the structural design and synthesis methods of M-Salen-COFs,as well as their optical,electrical,and thermal catalytic properties.The main research content and outcomes are organized as follows:In Chapter 1,an overview of the main types and research advancements in M-COFs is provided,focusing on the representative work conducted by scholars,both nationally and internationally,in the structural design and performance exploration of various M-COF types.The chapter also reviews the structural characteristics and research progress of M-Salen-COFs.In Chapter 2,the instrument types,reagent purity and sources,and ligands utilized in this dissertation are enumerated.In Chapter 3,the influence of pore enrichment on the catalytic performance of porous materials is investigated.Theoretical simulation results guide the synthesis of Zn-Salen-COF-1,a material that possesses the optimal pore enrichment effect.The bonding modes,stacking modes,and pore structures of Zn-Salen-COF-1 are determined,with the results revealing a consistency between the synthesized structure and theoretical simulation.The catalytic performance of Zn-Salen-COF-1 in the CO2 cycloaddition reaction under ambient temperature and pressure is subsequently evaluated.Zn-Salen-COF-SDU11 shows catalytic activity with a yield of 97.3%and a turnover number(TON)value of 760.16.Moreover,we also test the catalytic activity towards internal epoxides(2,3-epoxybutane)with a substantial yield of 74.4%and a TON value of 533.9 at ambient conditions,which have never been achieved under ambient conditions by other porous materials.Experimental results demonstrate that the pore enrichment effect in porous materials promotes catalytic reactions.This study contributes an effective strategy for designing cost-effective catalysts for the chemical fixation of CO2.In Chapter 4,the electrocatalytic oxygen evolution performance of conjugated microporous polymer materials containing Salen(M-Salen-CMPs)and M-Salen-COFs is examined.Metal ions such as Sc4+,Ti4+,V4+,Mn2+,Fe2+,Co2+,Ni2+,Cu2+,and Zn2+ions are coordinated into Salen-CMP-1,and their electrocatalytic activities are investigated.Additionally,Fe-Salen-CMP-3 demonstrates exceptional electrocatalytic activity for the electrocatalytic oxygen evolution reaction,through the optimization of ligands and the addition of conductive carbon black.Building upon these findings,M-Salen-COF-2,with high crystallinity and a chemical structure similar to M-Salen-CMP-3,is synthesized.The linkages,stacking modes,and coordination environments of the active metal center in M-Salen-COF-2 are characterized.The studies of electrocatalytic activities confirm that Ni-COF is comparable with the best reported COF-based OER catalysts.The current density reaches 10 mA cm-2 at a low overpotential of 335 mV.Furthermore,Ni-COF is stable for over 65 h during electrochemical testing.In Chapter 5,two synthetic methods of M-Salen-COFs and their applications in photocatalytic CO2 reduction are discussed.Initially,two-dimensional M-Salen-COFs with different metal coordination environments(M-N2O2 and M-N2O2-M-N2O2)are prepared using a one-step synthesis strategy.The coordination environment of metal active centers is effectively verified by synchrotron radiation X-ray absorption spectra.When compared to the two-step synthesis of M-Salen-COFs,the one-step synthesized M-Salen-COFs exhibit enhanced crystallinity and more extensive self-assembly structures.The improved crystallinity and novel self-assembly structures collectively promote the photogenerated charge separation and migration within M-Salen-COFs.For instance,Co-TAPT-COF-1 displays a unique microtubule structure and exhibits the highest activity for producing syngas via photoreduction of CO2.In particular,Co-TAPT-COF-1 nanotubes exhibit a CO production rate of 8.39 mmol g-1 h-1 and H2 rate of 11.31 mmol g-1 h-1.Experimental results and spectral characterization uncover the effects of synthesis routes,metal species,coordination environment,and structural composition on the photocatalytic reduction of CO2,further providing a reference basis for understanding structure-activity relationships and designing high-efficiency photocatalysts.Additionally,six crystalline porous materials,namely,M-Salen-MOF-5 and M-Salen-COF-5(M=Zn,Co,and Ni)with identical three-dimensional interlocking structures,are synthesized.The relationships among corresponding structures and photocatalytic activities of these six interlocked crystalline frameworks are explored.This work offers an example for synthesizing crystalline materials with the same topological structure.In Chapter 6,M/Zn-Salen-COF-6(M=Zn,Fe,Co,and Ni)are designed and synthesized,featuring M-Salen as the molecular catalyst and pyrene as the light-absorbing group.M/Zn-Salen-COF-6(M=Zn,Fe,Co,and Ni)demonstrate photocatalytic hydrogen evolution reactions without the addition of noble metal co-catalysts.Co/Zn-Salen-COF-6 exhibit the highest hydrogen evolution rate of 1378μmol g-1 h-1.The distribution and coordination environment of cobalt atoms in Co/Zn-Salen-COF-6 materials are characterized by synchrotron radiation X-ray absorption spectroscopy and spherical difference electron microscopy.The results indicate that the efficient transfer and utilization of photogenerated charges are promoted by the close connection between pyrene and M-Salen catalytic active centers,as well as the formation of a conjugated system within the framework.Additionally,DFT calculations reveal that the Gibbs free energy changes the least during the adsorption of*H in the Co-Salen-Py model catalyst,resulting in its superior photocatalytic activity.This study proposes a novel strategy for designing efficient COF photocatalysts by incorporating molecular catalysts,offering new insights for devising effective active sites within COFs.