Preparation And Mechanism Research Of Thermoresponsive Metal-Ion Imprinted Adsorption Material From Quaternary Ammonium Salt Modified Polysaccharide

With the over-exploitation and utilization of fossil fuels,the energy crisis and environmental problems were increasingly severe.As efficient and clean energy,nuclear energy is one of the most promising future energy sources for mankind.Uranium,as the most important nuclear fuel at present,its mining and recovery have gradually become the focus of research in recent years.In this paper,we used natural biomass—chitosan（CS）as the matrix,N-isopropylacrylamide（NIPAM）as the thermosensitive monomer,quaternary a0mmonium salt as the antibacterial component,useing the Gradient Heating Imprinting Polymerization（GHIP）proposed by our team,prepared UO₂²⁺-imprinted thermosensitive antibacterial chitosan derivatives（UITAC and UITDC）.The structure of the materials was characterized.The antibacterial properties,adsorption and desorption properties,and recycling properties of the materials were tested.（1）Using CS as the matrix,NIPAM as the thermosensitive monomer,allyl trimethyl ammonium chloride（TMAAC）as the antibacterial monomer,and UO₂²⁺as the template ion,using gradient heating imprinting polymerization,prepared UO₂²⁺-imprinted thermosensitive TMAAC modified CS derivatives（UITAC）under the best material ratio(n _CS:n _NIPAM=1:4,n _CS:n _TMAAC=1:2,1mg UO₂²⁺).UITAC had reversible phase transition temperatures at 37.85℃and 32.39℃,respectively.Put UITAC（dry whight 0.1 g）into 20 m L 1.05 mg/m L UO₂²⁺solution,adjusted the p H to10.0,and absorbed at 50℃for 2.5 h,the maximum adsorption capacity can reach199.2 mg/g.The adsorption of UITAC to UO₂²⁺can be better fitted with the pseudo-second-order equation and Langmuir adsorption isotherm model,and the theoretical maximum adsorption capacity was 216.9 mg/g.UITAC(adsorbed UO₂²⁺)was washed with 40 m L 0.4 mol/L HNO₃ solution for 25 min,and the desorption rate can reach 94.32%.After five cycles of adsorption-desorption experiments under optimal adsorption and desorption conditions,UITAC still has adsorption capacity of150.8 mg/g and desorption rate of 81.6%.The flat colony counting method was used to characterize the antibacterial performance of UITAC.The results showed that the antibacterial rate against Escherichia coli（E.coli）was 98.76%and the antibacterial rate against Staphylococcus aureus（S.aureus）was 89.14%.（2）Using CS as the matrix,NIPAM as the thermosensitive monomer,dimethyl diallyl ammonium chloride（DMDAAC）as the antibacterial monomer,and UO₂²⁺as the template ion,using gradient heating imprinting polymerization,prepared UO₂²⁺-imprinted thermosensitive DMDAAC modified CS derivatives（UITDC）under the best material ratio(n _CS:n _NIPAM=1:4,n _CS:n _DMDAAC=1:2,1mg UO₂²⁺).UITDC had heating phase transition temperature at 45.90℃and 54.42℃,and a cooling phase transition temperature at 35.06℃.Put UITDC（dry whight 0.1 g）into 20 m L 1.90mg/m L UO₂²⁺solution,adjusted the p H to 10.0,and absorbed at 50℃for 25 min,the maximum adsorption capacity can reach 376.9 mg/g.The adsorption of UITDC to UO₂²⁺can be better fitted with the pseudo-second-order equation and Langmuir adsorption isotherm model,and the theoretical maximum adsorption capacity was495.1 mg/g.UITDC(adsorbed UO₂²⁺)was washed with 60 m L 0.5 mol/L HNO₃solution for 20 min,and the desorption rate can reach 98.26%.After five cycles of adsorption-desorption experiments under optimal adsorption and desorption conditions,UITDC still has adsorption capacity of 328.6 mg/g and desorption rate of91.0%.The flat colony counting method was used to characterize the antibacterial performance of UITDC.The results showed that the antibacterial rate against E.coli was 71.84%and the antibacterial rate against S.aureus was 71.84%.（3）Adsorption materials were prepared with BC,CS,and regenerated chitosan（RCS）as the matrix,respectively,and the difficulty of gel formation under different initiator dosages was analyzed.The results showed that the matrix of gel state was easier to exchange with the free radicals in solution,making the polymerization reaction easier to occur;the matrix of powder state required more initiators to increase the reaction probability.By analyzing the change of p H of the solution with the change of temperature during the gradient heating process and the monomer polymerization degree of the phased products（70℃1 h;70℃2 h;70℃3 h）,the reaction mechanism of thermosensitive imprinting material prepared by GHIP was proposed.Material Studio software was used to establish unit models of NIPAM,BC,CS,and adsorbents.Combined with the VASP software,the models of two polysaccharide matrices for UO₂²⁺adsorption were simulated and calculated according to the First-Principles,and the adsorption energy was-2.4237 e V（BC）and-2.1601 e V（CS）,indicating that the two substrates both have strong adsorption force to UO₂²⁺.Through Amorphous Cell module,the adsorption material-water mixture model was established,and the systems were simulated at different temperatures.The results showed that temperature can affect the conformation of the adsorption material molecules in the aqueous solution,which confirmed the temperature sensitivity of the material.