Study On Nanocellulose Proton Conductive Materials Containing Purine Structure

In recent years,nitrogen-containing heterocyclic compounds have received attention in the field of proton exchange membranes and related fields.In nitrogen heterocyclic compounds,the basic nitrogen sites make them useful as donors and acceptors in proton transfer reactions.Purine molecules contain nitrogen heterocycles,the entire ring forms a conjugated system,and the nitrogen atom has strong nucleophilic activity.Its derivatives include adenine,adenosine monophosphate,2,6-diaminopurine and the like.In this thesis,cellulose nanocrystal was oxidized by sodium periodate,and the three types of purine derivatives were grafted onto the nanocellulose chain through chemical modification.Combined with the excellent characteristics of nanocellulose,environmentally friendly proton conductive materials were prepared.All modified membranes have improved proton conductivity,thermodynamic properties and oxidation stability.The prepared adenine-based nanocellulose membranes exhibited high proton conductivity,and could reach as high as 0.263 S·cm^-1 at 100?.In addition,the tensile strength of the membranes could reach up to 54.50 MPa,and the water absorption rate were high.However,the morphological stability at high temperatures needs to be improved.In order to further improve the mechanical properties and morphological stability of the membranes,adenosine monophosphate was selected to modify nanocellulose.The results showed that the tensile strength of this series of membranes could reach up to 95.92 MPa,and the mechanical strength was improved.In addition,the water absorption of the membrane was quite good,and the morphological stability was excellent.At 100?,its proton conductivity could reach 0.176 S·cm^-1.In order to improve the morphological stability and proton conductivity of the modified membranes,2,6-diaminopurine was used to prepare nanocellulose based proton conductive materials.Reseach showed that the proton conductivity of this type of modified membranes could reach 0.222 S·cm^-1 at 100?,which was close to the highest proton conductivity of adenine modified membranes.In order to further improve the mechanical properties of the modified membranes,a series of composite membranes were prepared by doping with oxidized nanocellulose.The results showed that the tensile strength of the composite membranes was increased to 2-3 times after doped with oxidized nanocellulose,which was equivalent to that of adenosine monophosphate modified membranes.And the composite membranes were not easy to swell and deform in water,which means the morphological stability was improved after doping.What's more,they had better antioxidant capacity than the first two modified membranes.The highest proton conductivity at 100?of the composite membrane was 0.207 S·cm^-1,which was higher than that of the adenosine monophosphate modified membrane.In addition,the methanol permeability of the composite membranes was about 13 times lower than that of Nafion 117,which means that they can better block methanol penetration and have the potential to be applied to methanol fuel cells.The research provides new ideas for solving the environmental pollution problem in the electronics industry,and has good environmental and social benefits.