Preparation Of Modified Cellulose In Ionic Liquids And Study On Its Adsorption Performance

Cellulose-based adsorbents has been found to be a kind of adsorption materials with great potential.However,the high crystallinity of cellulose,and the hydrogen bonds between cellulose molecules result in the low solubility of natural cellulose.Low accessibility makes it difficult to obtain uniformly modified products,which limits its industrial application.Ionic liquids,a kind of efficient green solvents,have great advantages in dissolving cellulose,which makes it possible to prepare new functional cellulose materials.In this work,1-butyl-3-methylimidazolium chloride was used as microcrystalline cellulose solvent,then modified materials were homogeneously synthesized with different functional groups.These modified cellulose materials were practiced to dyes adsorption.The main research contents and conclusions are as follows:(1)In order to prepare adsorbent with high adsorption capacity,cationic modified cellulose was obtained by introducing monomer acryloyloxyethyl trimethyl ammonium chloride into cellulose molecule.Firstly,1-butyl-3-methylimidazolium chloride was used to dissolve microcrystalline cellulose to form a transparent solution.With potassium persulfate as initiator,acryloxyethyl trimethyl ammonium chloride was grafted onto cellulose molecular chain by free radical polymerization.The effects of initiator amount,cationic monomer amount,temperature,and time were investigated on grafting ratio,and cationic content.Moreover,their structures and properties were characterized.Modified celluloses were applied to the adsorption of C.I.Acid Blue 40(AB 40).The results showed that under the optimum conditions,the grafting ratio and cation content of the sample were 32.36%,25.15%respectively.After dissolving and regenerating,the crystallinity of cellulose decreased,and the cellulose crystal form changed from type I to type II.Solvent exchange was put into effect by phase separation method.Regenerated cellulose presented three-dimensional porous aerogel structure.When it came to adsorption performance,the most suitable adsorption conditions were neutral and salt-free.Acid,alkali and Na₂SO₄reduced the adsorption rate of AB 40.The adsorption process conformed to Langmuir isotherm model,and the maximum monolayer adsorption capacity was 1052.29 mg·g^-1of cationic cellulose with cation content of25.15%.The adsorption process conformed to pseudo-second-order kinetics,The combination of adsorbent and AB 40 belonged to chemical adsorption,and electrostatic attraction was the main force.Using 2 mol·L^-1NaOH solution as desorption solution,the desorption equilibrium had been achieved in 28 hours.and the initial adsorption capacity were maintained at 59.71%after three desorption-adsorption cycles.(2)In order to improve the recycle performance of adsorbents,amino-terminated hyperbranched compounds were introduced to prepare amino-terminated hyperbranched compounds modified cellulose.Amino-terminated hyperbranched compounds were prepared with ethyl acrylate and diethylenetriamine as raw materials.Grafting of glycidyl methacrylate was completed by free radical polymerization in cellulose solution,and the ring-opening reaction between amino-terminated hyperbranched compound and epoxy group on branched chain was carried out to obtain modified cellulose.The chemical structure of modified cellulose was characterized to prove the formation of target product.The modified cellulose presented aerogel structure,and the crystallinity decreased.Meanwhile,the modified cellulose crystal form changed from type I to type II.The adsorption test showed that the modified cellulose had the ability to adsorb anionic AB 40 under acidic conditions,and the best adsorption condition of modified cellulose were pH 3 and no salt.The adsorption process accorded with Langmuir isotherm model and pseudo-second-order kinetics.The combination of adsorbent and AB 40 belonged to chemical adsorption,and electrostatic attraction was the main force.Desorption had been realized by NaOH solution of pH 12.The desorption equilibrium had been achieved in 24 h,and the concentration difference was the driving force of desorption.After the adsorbent was recycled for 5 times,the adsorption capacity still maintained 61.14%of the initial capacity.(3)In order to improve the applicable range of adsorbent,amphoteric cellulose was prepared by introducing L-lysine into cellulose molecule.L-lysine modified cellulose was prepared homogeneously in cellulose solution with the graft bridge of glycidyl methacrylate.The functional group characteristics of the product were determined by some measures,which proved the target product synthesis.The modified cellulose presented three-dimensional porous aerogel structure.the crystallinity decreased,and the crystal form changed from type I to type II.Acid-base controllability was given to modified cellulose by grafting L-lysine,thus giving the ability to carry different charges.The adsorption experiment results showed that the adsorbent CGL2.0 removed the anionic C.I.Reactive Red 2(RR2)in acidic solution under the condition of pH 3.The adsorption process accords with Langmuir isotherm model and pseudo-second-order kinetics.The theoretical monolayer adsorption capacity of CGL2.0 for RR2 can reach 1210.65 mg·g^-1.Adsorbent CGL2.0 removed cationic Methylene Blue(MB)in alkaline solution under the condition of pH 11.The adsorption process belonged to chemical adsorption,and electrostatic attraction was the main adsorption force.The adsorption process conforms to Langmuir isotherm model and pseudo-second-order kinetics,and the theoretical monolayer adsorption capacity of MB was 1077.91 mg·g^-1.The desorption of RR2 and MB was completed by NaOH solution with pH 12 and hydrochloric acid with pH 2,respectively.The desorption equilibrium had been reached in 90min.After 5 times of recycles,the adsorption capacity of RR2 remained 87.63%and that of MB remained 93.00%,respectively.Amphoteric cellulose took advantage of electrostatic attraction to complete the adsorption process,and electrostatic repulsion to complete the desorption process.Compared with concentration gradient drive,electrostatic repulsion played a more obvious role in desorption process.