Preparation Of PAN-based Monolithic Adsorbents For Ion Adsorption And Separation

This dissertation introduces a series of PAN-based adsorbents which perform better in the removing of heavy metals and the extracting of minerals from water.All adsorbents,prepared by sol-gel method under the thermodynamical control,are with monolithic and hierarchicalpore structures: the former solves the problem of difficult separation;the latter helps reduce the internal diffusion resistance as well as improve the adsorption capacity.Specific works are as follows:In the first part of the work,the PAN monolithic material with the hierarchical pore structure is prepared by the thermo-controlled sol-gel method,and then the functional groups that can adsorb heavy metals are grafted to the monolithic PAN materials,thus the three kinds of monolithic adsorbents are prepared,namely Diethyltriamine modified D-PAN,NaOH hydrolyzed H-PAN,and Hydroxylamine hydrochloride modified A-PAN.Here,the FTIR spectroscopy is used to confirm that the corresponding functional groups are successfully grafted.Then SEM and N2 adsorption and deadsorption isothermal analysis are used to confirm these adsorbents are hierarchically pore structured.Finally,these three adsorbents are used for lead ion adsorption tests.The adsorption capacity of D-PAN,H-PAN and A-PAN proves to be good with a saturation adsorption capacity of 144,206 and 242 mg·g^-1 respectively.In addition,the effects of kinetics,pH and ionic strength on the adsorption process are investigated in detail.At the same time the three adsorbents also show good regeneration performance,the adsorption capacity still remains more than 70% after four cycles of testing.In the second part of the work,firstly,nano-LiMn2O4 is prepared by one-step hydrothermal method,and then different proportions of LiMn2O4-PAN composites are prepared by thermo-controlled sol-gel method.Finally,The composites are washed by 0.5 M HCl to prepare a monolithic lithium ion sieve with hierarchical pore structures which is used for selective extraction of lithium ions.When the composite ratio of LiMn2O4/PAN is 1.2 g: 0.8 g,the saturated adsorption capacity of lithium ions reaches 27.3 mg·g^-1,and the adsorption kinetics is rapid.The adsorption equilibrium can be achieved in 4 hours.In addition,in order to test the regeneration performance of the adsorbents and to confirm that the monolithic material is easy to be separated,the monolithic material is filled in a adsorption column for lithium ion adsorption.Then,0.5 M HCl is used for the regeneration of the adsorbents.After three times of cyclic adsorption,the adsorption capacity still maintains more than 90%.In conclusion,the monolithic adsorbents prepared by this dissertation show good potential for industrial application,since they can be easily prepared in a short period,and most importantly,they demonstrate good ion adsorption and separation capacity.