Preparation And Functionalization Of Chitin In Ionic Liquids/Deep Eutectic Solvents

The extracted chitin from waste shrimp shells can be applied in various fields including medicine,agriculture,and textile industry,which is valuable and sustainable.However,the chitin and chitin-based products are usually prepared with acid,base and special organic solvents,which no long meets the environment requirement now.Ionic liquids(ILs),a new generation green solvent,has low vapor pressure,high thermostability,designable structure,and numerous hydrogen bonding net.They provide new options for chitin extraction and utilization.Currently,the literatures about chitin extraction and utilization using ionic liquid are still few.Unfortunately,the reported IL-based methods still have the problems such as high cost,high water consumption,and difficulty in recycle.Moreover,there is still no literature about direct preparation of chitin-based products from shrimp shells.Herein,this work used the shrimp shells as raw material to prepare chitin,chitin/Zn compsotie,and O-acylated chitin,providing alternation for waste shrimp shells utilization.The main innovative work and results are as follows.(1)Study on the preparation of chitin using combined inorganic salt aqueous solution-ionic liquid.In this part,NiSO4 aqueous solution(aq.)was employed to remove calcium carbonate by ion exchange,and the 1-butyl-3-methyl-imidazolium chlorine([Bmim]Cl)was used to remove protein and the introduced nickel in the first step through hydrogen interaction.Through the two steps,the high purity chitin was prepared.The results showed that the type of the inorganic aq.,and temperature,liquid/solid ratio affected the purity of the chitin.Finally,the chitin with purity 98.8 wt%was obtained by sequential treatment with NiSO4 aq.(20 wt%)and[Bmim]Cl at 130 ?for 24 h.It can be seen that ion exchange can remove calcium carbonate from shrimp shells and simultaneously load metal salts,which provides a new option for the preparation of chitin/metal composites.(2)Study on the preparation of chitin/Zn composite from shrimp shells using phosphate ionic liquid and inorganic salt aqueous solution.The employed ILs hold the ability of deproteinization,and the inorganic salt aq.has the ability of decalcification and zinc loading.Systematically,the effects of the IL type,experiment temperature,liquid/solid ratio,and time on the protein removal were explored firstly,then the concentration of Zn(OAc)2·H2O aq.,experiment time and temperature were explored for decalcification and zinc-loading.Under the optimal conditions,the chitin/Zn composite with purity 99.1 wt%and 13.4 wt%zinc was obtained,displaying a good catalytic effect on the PET glycolysis.The characterization of the chitin/Zn composite showed that the chitin kept ?-form,and the zinc existed as ZnCO3/Zn(OH)2 with forming interaction with chitin.It can be seen that the preferential solubility of protein and chitin in different ionic solutions is different.(3)Study on the chitin/Zn composite preparation with metal deep eutectic solvent.Based on the second part research,the multifunctional DES,namely urea/Zn(OAc)2·2H2O(1:2,U-Zn),was designed and synthesized.The U-Zn aq.can remove calcium carbonate,protein,and load zinc,simultaneously.The factors including the concentration of U-Zn aq.,liquid/solid ratio,experiment time and temperature were studied to determine their effect on the purity and Zn-loading of chitin.Under the optimal conditions,the chitin/Zn composite with purity 97.2 wt%and 34.7 wt%zinc was obtained,exhibiting high anti-bacterial effect on the Gram negative and positive bacterium.Moreover,the chitin/Zn composite was characterized,suggesting that the chitin kept a-form,and zinc was the Zn5(OH)2(CO3)6 with forming interaction with chitin.Importantly,experiments and spectroscopy results revealed the mechanism of chitin/Zn composite formation.The zinc ion with higher coordination ability can exchange with calcium ion in-suit forming zinc carbonate,which hydrolyzed to Zn5(OH)2(CO3)6 and CO2.Additionally,the protein was surrounded with U-Zn clusters resulting in dissolution and removal.It can be seen that the ion exchange capacity and aggregation of the U-Zn aqueous solution are the main reasons for the formation of the chitin/Zn composite.(4)Study on the O-acylated chitin with acid deep eutectic solvents.11 multifunctional DES composed of choline chloride and organic salt were designed and synthesized.These DESs have the ability of decalcification,deproteinization,and acylation.The influences of the chitin purity and degree of substitution(DS)were explored,which included DES type,experiment temperature,time,liquid/solid ratio,and water contents of DES.With the optimal NADES(choline chloride/DL-malic acid 1:2,ChC11-DL Mal 2)treatment under the optimal conditions,the highest purity O-malate chitin was obtained with purity 98.6 wt%and DS 0.46.The O-malate chitin showed an inhibitory on the Gram-positive bacterium and C6 glioma cells.Characterizations further proved that product was the O-malate chitin.Furthermore,process of O-acylated chitin was discussed.During the process,the H+ released from DES was reacted with the calcium carbonate,producing CO2 and soluble organic calcium salts.Meanwhile,the H+ was reacted with part of protein forming the amino acid.The rest part of protein was dissolving in the DES by hydrogen interaction.Additionally,the DES activated the chitin by swelling its stable structure firstly,then reacted with chitin under the acid conditions to produce the O-acylated chitin.Thus,the acidity and hydrogen bond forming ability of the used deep eutectic solvent are the main reasons for the formation of O-acylated chitin.