Deep Eutectic Solvent Assisted Extraction Of Wool Keratin And Its Application

Wool keratin is a typical renewable biomass resource.The development of keratin resources in waste wool is a topic worthy of researchers’attention.Deep eutectic solvent（DES）,as a new solvent,shows a good potential in the field of protein fiber dissolution,and meets the requirements of green chemistry,is the optimal solvent for wool pretreatment and keratin regeneration.Regenerated keratin can be used as a carbon and nitrogen source to make carbon electrode materials for supercapacitors by compounding with polymers,carbonization,etc.The regeneration and electrochemical applications of keratin are of great significance to the utilization of waste biological resources,the protection of ecological environment and the development of new energy storage devices.Therefore,this paper explored a type of DES suitable for wool pretreatment,and combined it with L-cysteine/urea reduction system to extract wool keratin and prepared the electrode material of keratin-based supercapacitor,with a view to realizing the application of wool keratin in the electrochemical field.The research contents and results are as follows:（1）Binary or ternary DES were synthesized by using choline chloride（ChCl）as hydrogen bond acceptor,citric acid（CA）,oxalic acid dihydrate（OA·2H₂O）,L-cysteine（L-cys）and urea as hydrogen bond donors.The synthesis of DES and its dissolution effect on wool were investigated.The results showed that ChCl and L-cys were difficult to synthesize DES under ordinary conditions,while other combinations could synthesize DES under certain conditions.In the successfully synthesized DES,ChCl/CA could hardly dissolve wool,while ChCl/Urea/L-cys and ChCl/OA·2H₂O/L-cys could all decrease the overall dissolving ability due to the introduction of L-cys.In general,the synthesis effect of ChCl/OA·2H₂O was the best.The dissolution rate of wool reached 60.2%and the extraction rate of keratin reached 30.74%when the molar ratio was 1:2 and temperature was 110℃,which were suitable for pretreatment of wool.（2）The wool was pretreated by ChCl/OA·2H₂O DES,and then the wool was dissolved by L-cysteine/urea reduction system.The optimization degree of the l-cysteine extraction method parameters by DES pretreatment was explored from five factors,namely,dissolution time,urea concentration,L-cysteine concentration,dissolution temperature and p H of the solution.Compared with the L-cysteine/urea reduction method,the dissolution time was shortened from 5 h to 1 h,and the urea concentration was reduced by 50%.The optimum extraction conditions of keratin were as follows:the mass fraction of L-cysteine was 1.5%,the concentration of urea was 4 mol/L,the post-treatment time was 1 h,the temperature was 75℃,the p H value was 10,the dissolution rate of wool reached 85.1%and the extraction rate of keratin was 55.85%.FTIR and XRD analysis showed that DES pretreatment can increase the fracture of disulfide bond in wool and destroy theα-helix structure to promote the wool dissolution.Using DES pretreatment and L-cysteine/urea reduction system to dissolve wool is a new efficient and green keratin regeneration scheme.（3）Wool keratin and polyvinylidene fluoride（PVDF）were used as raw materials to prepare WK/PVDF composite nanofibers of different proportions by electrostatic spinning process,and WK/PVDF carbon nanomaterials were prepared through pre-oxidation and carbonization,and were used as electrode materials of supercapacitors to explore their electrochemical properties.SEM test showed that the diameter distribution of WK/PVDF composite nanofibers was relatively uniform,and there were a few bonding points with the increase of WK content.Thermogravimetric test results showed that WK could improve the yield of fiber pyrolysis.After carbonization,WK/PVDF composite nanofibers were generated by gas generation and melting at high temperature,resulting in pore structure and no fiber morphology remained.XRD,Raman and XPS tests showed that the addition of WK could improve the graphitization degree of carbon materials and the content of C,N,O and other elements to a certain extent.The electrochemical tests showed that WK/PVDF carbon nanometer materials all showed double layer capacitance characteristics,WF-C-10-90 had the best electrochemical performance,the highest specific capacitance value reached 201.1 F/g,and the internal resistance was small,showing good electrochemical performance and certain application potential.（4）WK/PAN composite nanofiber films and carbon nanomaterials of different proportions were prepared using wool keratin and polyacrylonitrile（PAN）as raw materials and using the same spinning and carbonization process as WK/PVDF.The results showed that the diameter of WK/PAN composite nanofiber membrane fiber was uniformly distributed without beads,and WK had a great contribution to the fiber pyrolysis yield,which reached 42%after the pyrolysis of WN-20-80.After carbonization,WK/PAN carbon nano-material remained a fiber morphology,XRD,Raman,XPS test results showed that the WK/PAN carbon nano-material showed a typical structure characteristics of carbon materials,amorphous carbon characteristic was obvious and graphitization degree was higher.With the increase of WK,C and N content increased after the first decline trend,on the other hand,the change trend of O content was opposite.This was related to the denitrification of PAN at high temperature and the increase of amorphous region caused by WK.