Design,Synthesis and Energy Coversion Applications of Two-Dimensional Polymers

Author:Zhang Xin Lei

Supervisor:xu hang xun


Degree Year:2019





The diversity of building blocks and synthetic routes provide two-dimensional(2D)polymers with highly adjustable structures and precisely editable functions.Therefore,2D polymers can not only be directly utilized in many fields such as catalysis,adsorption and energy conversion,but also able to serve as promising precursors for preparing high-efficiency catalysts.Ultrathin 2D polymers are even more favorable when compared to their bulk counterparts for their larger specific surface area,more exposed active sites and better processability,which make them hold greater promise in a wide range of applicationsThis doctoral thesis mainly focuses on the fabrication of ultrathin N-containing 2D conjugated polymer nanosheets,the applications of ultrathin aza-CMP nanosheets assembled membranes and the synthesis of 2D coordination polymers derived carbon-based electrocatalyst.The details are as follows:1.A protonation-assisted liquid-phase exfoliation method was demonstrated for the highly efficient exfoliation of various 2D N-containing conjugated polymers such as g-C3N4,C2N,and aza-CMP in acidic media.Combining solid-state NMR techniques and Hansen solubility parameter test,we further revealed that protonation was critical in establishing strong hydrogen bonding between the polymer surfaces and water molecules,facilitating the exfoliation of polymers into liquid phase.Molecular dynamics simulations and first-principles calculations indicate that protonation of the heterocyclic nitrogen sites can promote the capture of surrounding solvent molecules and the formation of hydrogen bonds with the polymer surfaces,leading to improved exfoliation yields.2.Ultrathin aza-CMP nanosheets were prepared on large scale through protonation-assisted liquid-phase exfoliation,and further deposited on a polycarbonate(PC)filter membrane through vacuum filtration to prepare aza-CMP@PC membrane.The prepared film can achieve selective permeation of polar/non-polar solvents and high-efficiency selective retention of organic dyes.For large-sized Congo Red and Methyl Blue,the rejection could reach~100%.Self-cleaning could be realized by photo-degradation of residual dyes under visible light irradiation,so that water permeability could be restored to the original level,achieving reuse of this separation membrane.When used as light-induced actuator,aza-CMP@PC composite film could offer fast response,large deflection,and reversible actuation as a result of the prominent solar-thermal conversion ability.This research takes full advantage of the structural and functional properties of aza-CMP molecules and greatly expands the application range of N-containing 2D conjugated polymers.3.An NHC-Co coordination polymer was synthesized and served as single-component precursor for the fabrication of Co-NHC-900 electrocatalyst for oxygen reduction reaction(ORR),in which Co merely existed as metallic nanoparticles.The obtained electrocatalyst exhibited comparable catalytic activity and much better stability to commercial Pt/C catalyst.By combining electrochemical measurements and X-ray absorption studies,we found that the obtained catalyst was free of Co-N species,thus the prominent activity was ascribed to outer C-N shells.The density functional theory(DFT)calculations indicated that the enhanced ORR activity could be attributed to the charge redistribution and decrease of the work function,which resulted from the electron transfer from Co nanoparticles to the N-doped carbon sheets.