Preparation Of Three-Dimensional Superhydrophilic Surface Imprinted Polymer And The Research Of Selective Adsorption Behavior And Mechanism For Heavy Metal Ions In Water

With the improvement of people’s living standards and the rapid development of industry,the discharge of heavy metal ions has increased year by year,leading to the increasingly serious problem of water pollution.Conventional heavy metal ion adsorbents usually suffer from poor selectivity and are unable to adsorb specific heavy metal ions in complex environments.Ion imprinted polymers have become excellent adsorbents for the adsorption of heavy metal ions in water due to their excellent selective adsorption ability for the target ions.However,the ion-imprinted polymers prepared by conventional methods usually suffer from poor hydrophilicity,poor selectivity,and high energy consumption in the polymerization process,resulting in increased side reactions,fewer adsorption sites,and lower adsorption capacity.Aiming at the above problems,this paper optimized functional monomers and matrix materials in the preparation process of surface ion-imprinted polymer,improved polymerization methods and induction methods,designed and prepared a series of superhydrophilic surface ion-imprinted polymers based on three-dimensional materials,investigated their physical and chemical properties,and studied their adsorption properties for heavy metal ions in aqueous phase.The adsorption mechanism was investigated by density functional theory（DFT）and frontier molecular orbital theory（FMO）.The specific research content includes the following three parts:（1）Controllable synthesis and adsorption properties of three-dimensional superhydrophilic cadmium ion-imprinted polymer based on POSS by synergistic interaction of bifunctional monomersIn this chapter,a hydrophilic bifunctional monomers prepolymerization system was designed,and a three-dimensional superhydrophilic cadmium ion-imprinted polymer（Cd（Ⅱ）-IIP）was prepared on the surface of octavinyl cage sessiloxane（OV-POSS）by reversible addition-fragmentation chain transfer（RAFT）polymerization technique.The structure,morphology and hydrophilicity of Cd（II）-IIP were characterized by various characterization methods,among which scanning electron microscopy（SEM）showed that the prepared three-dimensional microspherical Cd（Ⅱ）-IIP had more uniform and thinner imprinted layer distribution than the traditional free radical polymeric polymer（TRP-IIP）,water contact angle（WCA）test showed that the WCA of Cd（Ⅱ）-IIP was 0°,showed superhydrophilicity.Under the optimal adsorption conditions,Cd（Ⅱ）-IIP rapidly reached adsorption equilibrium within 40 min with a maximum adsorption capacity of 81.26 mg/g,which was significantly higher than that of TRP-IIP and single functional monomer imprinted polymers,and 4 times that of non-imprinted polymers（NIP）.The selectivity of Cd（Ⅱ）-IIP was superior to that of single functional monomer imprinted polymers.X-ray photoelectron spectroscopy（XPS）analysis proved that the adsorption mechanism was the coordination of Cd（Ⅱ）with O and N atoms.DFT and FMO calculations demonstrated that the coordination between functional monomers and Cd（Ⅱ）was more inclined to F2 and S3 types,that was,N and O atoms were coordinated to Cd（Ⅱ）simultaneously.（2）Microwave preparation of POSS/SBA-15 composite three-dimensional superhydrophilic copper ion imprinted polymer and adsorption propertiesIn this chapter,a three-dimensional superhydrophilic copper ion imprinted polymer（Cu（Ⅱ）-IIP）was synthesized by microwave initiated polymerization on POSS/SBA-15 surface.Microwave initiated polymerization was completed within 60min,which was 6 times higher than that of conventional thermoinitiated polymerization.The structure,morphology and hydrophilicity of Cu（Ⅱ）-IIP were characterized by various characterization methods,among which SEM tests showed that SBA-15improved the dispersibility of OV-POSS significantly,the WCA test showed that Cu（Ⅱ）-IIP WCA was 0°,had superhydrophilic properties.Under optimal adsorption conditions,the adsorption of Cu（Ⅱ）on Cu（Ⅱ）-IIP reached equilibrium within 60 min with a maximum adsorption capacity of 163.87 mg/g,which was 4 times higher than that of the non-imprinted polymer（NIP）and also higher than that of single SBA-15-based imprinted polymer（92.14 mg/g）.The adsorption of Cu（Ⅱ）-IIP was in accordance with the Langmuir and pseudo-second-order kinetics models,and was mainly chemisorption on the surface of monolayer.Thermodynamic studies showed that Cu（Ⅱ）-IIP adsorption was a spontaneous endothermic process.Binary and multi-component mixed ion competition experiments showed good selectivity of Cu（Ⅱ）-IIP.After 5 adsorption-desorption cycles,the adsorption capacity of Cu（Ⅱ）-IIP did not decrease significantly,and the imprinted factor remained above 2.21,which had good regeneration performance and good recovery for actual water sample determination.DFT and FMO theoretical calculations indicated that the type of adsorption of Cu（II）-IIP for Cu（II）was dominated by the tetra-coordination of N atoms with Cu（II）.（3）Preparation of three-dimensional superhydrophilic mercury ion imprinted polymers with dual recognition sites based on MoS₂/SBA-15 and adsorption propertiesIn this chapter,three-dimensional superhydrophilic mercury ion-imprinted polymers（Hg（II）-IIP）with dual recognition sites were prepared on MoS₂/SBA-15surface using N-allylthiourea（ATU）as the functional monomer.The dual recognition sites were constructed by S atoms on MoS₂ and ATU.The microstructure,morphology and hydrophilicity of Hg（Ⅱ）-IIP were characterized by various means,among which the SEM test showed that MoS₂ with three-dimensional nano-flower shape provided a good space medium for the dispersion of SBA-15,the WCA test showed that Hg（Ⅱ）-IIP had a WCA of 0°and had superhydrophilic properties.Under the optimal adsorption conditions,the maximum adsorption capacity of Hg（Ⅱ）-IIP for Hg（Ⅱ）was 567.78 mg/g,which was 6 times higher than that of the single SBA-15-based imprinted polymer（96.53 mg/g）,and also higher than that of the MoS₂/SBA-15 composite（322.74 mg/g）.The adsorption performance experiment showed that Hg（Ⅱ）-IIP reached adsorption equilibrium within 90 min,and the adsorption process was consistent with the pseudo-second-order adsorption kinetic model,which was chemisorption.The selectivity experiments showed that Hg（Ⅱ）-IIP had excellent selectivity and the regeneration experiments showed that Hg（Ⅱ）-IIP had good regeneration ability.The actual sample analysis experiments showed that Hg（Ⅱ）-IIP was satisfactory for the recovery of Hg（Ⅱ）in water samples.DFT and FMO theoretical calculations indicated that the adsorption of Hg（II）by S atoms on ATU was more likely to be the type of S-Hg tetrad adsorption.