Preparation And Adsorption Properties Of Chitosan-Based Thermally Responsive Rare Earth Metal Ion Imprinted Materials

With the rapid development of high-tech technologies,the global demand for rare earth metal resources is increasing.In order to meet the unbalanced supply of rare earth metal resources,the recovery of rare earth metal ions from waste resources has become an important area of concern.Among them,biomass adsorbents got a lot of attention.In this paper,biomass polysaccharide-chitosan（CS）is used as the matrix,and ammonium persulfate（APS）and N,N-methylenebisacrylamide（BIS）are used as the initiator and crosslinking agent of the reaction,respectively.Isopropylacrylamide（NIPAM）is used as a thermo-responsive monomer,and La³⁺and Y³⁺are used as template ions to prepare thermo-responsive ion imprinting materials CLIT and CYIT through gradient heating imprinting polymerization;and La³⁺and Y³⁺are used as ion imprinting template,the chitosan-based thermo-responsive double ion-imprinting material CNRD was prepared.The above-mentioned materials have shown good thermal responsiveness and adsorption performance in the process of characterization and application.（1）When the molar ratio of NIPAM to CS is 1:4 and the addition amount of La³⁺is1mg,the obtained CLIT shows good reversible thermal responsiveness.The phase transition temperature of CLIT is 37.24°C and 28.92°C,and after three cycles of heating and cooling tests,it still maintains good reversible thermal responsiveness.By investigating the influence of adsorption temperature,adsorption time,p H value of initial adsorption solution,La³⁺concentration and other factors on adsorption capacity,the optimal conditions for CLIT adsorption of La³⁺were obtained:adsorption temperature45°C,p H 5,adsorption time 60 min.The kinetic and adsorption isotherm model studies show that the adsorption process of CLIT on La³⁺conforms to the second-order kinetic model and the Freundlich isotherm adsorption model.By discussing the effects of desorption temperature,desorption time,and desorption times on the desorption rate of CLIT,the best desorption condition of CLIT on La³⁺was obtained:soaking in 20 m L 10°C deionized water for 25 min and repeating 4 times.In the mixed metal solution containing La³⁺,Y³⁺,Gd³⁺,Cu²⁺,Al³⁺,Fe³⁺,La³⁺/Y³⁺,La³⁺/Gd³⁺,La³⁺/Al³⁺,La³⁺/Fe³⁺,La³⁺/Cu²⁺are1.67,2.04,3.15,2.72,4.84,respectively,It can be seen that CLIT exhibits good selectivity to La³⁺;after 10 cycles of use,the adsorption capacity and desorption rate of CLIT to La³⁺are 84.33 mg/g and 82.99%,respectively.（2）When the molar ratio of NIPAM to CS is 1:3 and the amount of Y³⁺added is 1 mg,the prepared CYIT exhibits good reversible thermal responsiveness.The phase transition temperature of CYIT is:37.3°C and 29.24°C;after three passes After cyclic heating and cooling tests,CYIT still maintains good reversible thermal responsiveness.By investigating the effects of adsorption temperature,adsorption time,p H of the adsorption solution,Y³⁺concentration and other factors on the adsorption capacity,the optimal adsorption conditions for Y³⁺by CYIT were obtained:adsorption temperature was 50°C,p H 5,and adsorption time was 240 min.The kinetic and adsorption isotherm model studies show that the adsorption process of Y³⁺by CYIT conforms to the second-order kinetic model and the Langmuir isotherm adsorption model.By discussing the effects of desorption temperature,desorption time,and desorption times on the desorption rate of CYIT,the best desorption condition for Y³⁺by CYIT was obtained:soaking in 20 m L of15°C deionized water for 25 min,and repeating 3 times.In a mixed metal solution containing La³⁺,Y³⁺,Gd³⁺,Cu²⁺,Al³⁺,Fe³⁺,Y³⁺/La³⁺,Y³⁺/Gd³⁺,Y³⁺/Al³⁺,Y³⁺/Fe³⁺,Y³⁺/Cu²⁺are 1.66,1.59,1.75,1.67,1.88,respectively,It shows good selective adsorption;after 5 cycles of use,the adsorption capacity and desorption rate of Y³⁺by CYIT are124.76 mg/g and 90.02%,respectively.（3）When the ratio of NIPAM to CS is 1:3,and the addition amount of La³⁺and Y³⁺is0.5 mg,the prepared double imprinting material CNRD exhibits good reversible thermal responsiveness.The phase transition temperature of CNRD is:38.2°C and 32.6°C After three cycles of heating and cooling tests,CNRD still maintains good reversible thermal responsiveness.By investigating the effects of adsorption temperature,adsorption time,initial adsorption solution p H,initial La³⁺and Y³⁺concentration on the adsorption capacity,the optimal conditions for CNRD adsorption of La³⁺and Y³⁺bimetals are obtained:adsorption temperature is 50°C,p H 5,adsorption time 120 min.The study of kinetics and adsorption isotherm model showed that the adsorption process of La³⁺and Y³⁺by CNRD conformed to the second-order kinetic model and Freundlich isotherm adsorption model.By discussing the effects of desorption temperature,desorption time,and desorption times on the desorption rate of CNRD,the optimal desorption condition of CNRD for La³⁺and Y³⁺was obtained:soak in 20 m L of 20°C deionized water for 25 min,and repeat 3 times.In an environment where multiple metal ions(Fe³⁺,Cu²⁺,Pb²⁺,La³⁺,Y³⁺,Gd³⁺)coexist,the selective adsorption coefficients of CNRD for La³⁺&Y³⁺are La³⁺&Y³⁺/Gd³⁺3.02,La³⁺&Y³⁺/Pb²⁺5.99,La³⁺&Y³⁺/Fe³⁺4.11,La³⁺&Y³⁺/Cu²⁺4.30,showing good selective adsorption;after 10 cycles of use,the adsorption capacity of CNRD on La³⁺and Y³⁺is60.37 mg/g and 63.73 mg/g,The desorption rates were 80.45%and 79.77%respectively.