| As an important strategic resource,rare earth elements are increasingly used in modern high-tech fields and the demand of the global was increased as well.On the other hand,the accumulation of rare earth metal in the ecosystem will reduce soil fertility and stunt plant growth.Similarly,it causes irreversible toxic effects on the bones and nerves of animals and humans.Therefore,it is particularly important to develop and design new technologies for the separation and recovery of rare earth elements.In this thesis,N-isopropylacrylamide,maleic acid and graphene oxide were used to prepare a thermosensitive hydrogel by freeze polymerization and non-freezing polymerization methods,respectively.The effects of preparation method,monomer ratio and the content of graphene oxide on the morphology and internal structure,swelling/shrinking performance,volume phase transition temperature and mechanical properties of hydrogels were investigated.The hydrogels prepared by freeze polymerization possess hierarchical microporous internal structure while the non-freezing polymerization hydrogels have a smaller internal pore diameter.The non-freezing polymerization hydrogels have a higher equilibrium swelling ratio,but the freeze polymerization hydrogels have about 10 times swelling rate than the non-freeze polymerization ones.The mechanical properties of the hydrogels prepared by freeze polymerization were superior,and the higher the content of graphene oxide in the hydrogel is,the better the mechanical properties of the hydrogel will be.For the freeze polymerization hydrogels with a graphene oxide content was 1.01 mg/g,the compressive elastic modulus was 4.07 kPa,which is sufficient to support it for at least five swelling-shrinking cycles without significant damage.The compressive modulus of the non-freeze polymerization hydrogel was 2.93 kPa,which was broken during the third swelling/shrinking cycle.The effects of monomer ratio,initial La3+ concentration,adsorption time and initial pH on the equilibrium adsorption capacity of La3+prepared by both of the hydrogels were investigated,and the cyclic adsorption capacity of these hydrogels was calculated as well.For both of the hydrogels,the equilibrium adsorption capacity of La3+ increased as the MA molar ratio increased in the hydrogel.As for the effects of initial concentration of La3+and the contact time on the equilibrium adsorption capacity,both of the hydrogels showed the same tendency:with the increase of initial concentration,the equilibrium adsorption capacity increased gradually and the equilibrium adsorption capacity would increase along with extending the contact time to adsorption equilibrium.The Langmuir isotherm model fits the data very well,and the adsorption follows the pseudo-second kinetic equation.When the temperature was 25 ? and the initial concentration of LaCl3 was 0.36 g/L,the equilibrium adsorption of the hydrogels by freeze polymerization and non-freeze polymerization were 30.4 mg/g and 20.6 mg/g,respectively.The morphology of the hydrogels were characterized by scanning electron microscopy,differential scanning calorimetry,infrared spectroscopy and X-ray energy dispersive spectroscopy,and the adsorption mechanism of La3+ was discussed.Furthermore,using the thermosensitivity of hydrogels,the thermal-water purification capacity of the two hydrogels was explored.Both of the hydrogels can achieve further enrichment of La3+,but the hydrogel of freeze polymerization has excellent La3+ enrichment recovery ability.The adsorption selectivity of the hydrogel on La3+ and the effect of the introduction of stencil imprint on the adsorption selectivity of hydrogel were investigated.The adsorption of non-imprinted and imprinted hydrogels follows:La3+>Nd3+>Yb3+>Cu2+>Ni2+>Co2+.Both non-imprinted and imprinted hydrogels can convert La3+ from La3+-other metal ions binary solutions.The mixed solution was effectively separated,while the imprinted hydrogel has a higher adsorption selectivity coefficient. |
PDF Full Text Request