Microwave-Assisted Synthesis Of Inverse Cadmium Ion Imprinted Polymer And Study On Adsorption And Extraction Cd(Ⅱ) In Wastewater

Cadmium is a kind of toxic heavy metal,which could cause serious harm to the environment and human beings.Ion imprinted polymer as a new adsorbent material could be used for separation and removal of heavy metal ions from water with high selectivity,good stability,excellent reuse ability and wide range of application.Compared to the traditional heating method,microwave assisted synthesis method has the advantages of fast heating rate.In this paper,Cd（Ⅱ）ion imprinted polymers were prepared by microwave assisted two kinds of polymerization methods with different functional monomers.The adsorption and solid phase extraction performance of Cd（Ⅱ）ion imprinted polymers were investigated.Cadmium ion imprinted polymers（IEIIP）were prepared by microwave assisted inverse emulsion polymerization method using β-cyclodextrin and acrylamide as functional monomers,epichlorohydrin as crosslinking agent and ammonium persulfate as initiator.IEIIP was characterized by SEM,FTIR and TG.The effects of initial concentration of Cd（Ⅱ）,pH value,temperature,time and competitive ions on adsorption capacity and recognition properties of IEIIP were studied.Under the optimal adsorption conditions,the adsorption capacity of IEIIP reached 107mg/g.The adsorption capacity of non-imprinted polymer was less than that of the imprinted polymer.The selectivity coefficients k of IEIIP for Cd²⁺/Pb²⁺、Cd²⁺/Cu²⁺ and Zn²⁺ were 2.7624,3.8154 and 1.1500,respectively.While,selectivity coefficients of IENIP were 0.4521,0.5024 and 0.3747,respectively.The results showed that IEIIP had good selectivity for Cd（Ⅱ）in aqueous solution.Moreover,the adsorption kinetic behavior of IEIIP was described using pseudo first order kinetic model,pseudo second order kinetic model and intra-particular diffusion model.The results showed that the pseudo second order model could describe the adsorption behavior well.The Langmuir isotherm model had agreement with the experimental data,suggesting that adsorption was mainly monolayer adsorption.The results indicated that the bingding sites of IEIIP to Cd（Ⅱ）was equal class under the studied concentration range.The analysis of Scatchard plot showed that the dissociation constant KD and the maximum apparent binding capacity Qmax were 72.99mg/L and 130mg/g,respectively.The results indicated that the bingding sites of IEIIP to Cd（Ⅱ）was equal class under the studied concentration range.The thermodynamic parametersΔG0<0,ΔH0>0 and ΔS0>0 indicated that the adsorption process was spontaneous and endothermic.The influence fators including eluent concentration,the concentration of Cd（Ⅱ）,pH values and competitive ions were investigated using IEIIP as solid-phase extraction adsorbent to optimize solid-phase extraction conditions.The repeatability and precision of solid phase extraction column were tested.The results showed that the enrichment effect was best when the ratio of methanol and acetic acid was 7:1.The extraction efficiency was the highest at the concentration of Cd（Ⅱ）of 10μg/L and pH 7.The extraction efficiency of IEIIP solid phase extraction column was more than 70% after five recycles of adsorption elution.The extraction efficiency of IEIIP solid phase extraction column for Cd（Ⅱ）was higher than that of other competing ions in ionic mixed solutions.The precision of the method was analyzed by 11 replicate measurements of standard solutions.The relative standard deviation（RSD）and detection limit（3σ）of the method were about 2.699% and 0.8094μg/L（n=11）,respectively.The recovery rates for Cd（Ⅱ）in waste water samples were 93.58%-101%.Microwave assisted inverse emulsion-suspension polymerization method was used to prepare Cd（Ⅱ）ion imprinted polymer（IESIIP）using salicylic aldehyde ethylene diamine Schiff base as functional monomer,EGDMA as crosslinking agent and AIBN as initiator.SEM and FTIR were used to characterize IESIIP.The influences of initial concentration,pH value,temperature,time and competitive ions on adsorption capacity of IESIIP were studied by the static adsorption experiments and competitive adsorption experiments.Under the optimal adsorption conditions,the adsorption capacity of IESIIP was 179.04mg/g.The relative selectivity coefficient of k’ for Cd²⁺/Pb²⁺,Cd²⁺/Cu²⁺ and Cd²⁺/Zn²⁺ were 2.1061,4.7306 and 4.5602,indicating that the selectivity of IESIIP for Cd（Ⅱ）was much higher than that of IESNIP.The pseudo two second order kinetics equation and Langmuir isotherm（R2>0.99）could describe the adsorption process of IESIIP.The dissociation constants KD of two kinds of binding sites on IESIIP calculated by Scatchard model were 16.89mg/L and 39.84mg/L,respectively.The maximum apparent adsorption bingding capacity Qmax of two kinds of bingding sites were 105.15mg/g and 171.84mg/g,respectively.The thermodynamic parameters showed that the adsorption process was a spontaneous and endothermic process.The effects of eluent concentration,the initial concentration of Cd（Ⅱ）,pH values and competitive ions on extraction efficiency were studied by IESIIP solid phase extraction column to optimize the conditions of IESIIP solid phase extraction.The stability and precision of IESIIP solid phase extraction column were evaluated.The results showed that the optimum elution condition was 0.5mol/L hydrochloric acid.The extraction efficiency decreased with the increase of Cd（Ⅱ）concentration.The optimum pH condition was 7.The extraction efficiency of the IESIIP solid phase extraction column was reduced by 9.9% after adsorption and elution for 5 times recycles.The extraction efficiency for Cd（Ⅱ）was higher than that of other competing ions when the solution containing competitive ions was extracted by IESIIP solid phase extraction column.The relative standard deviation（RSD）and the detection limit（3σ）of this method were 2.699% and 0.288μg/L（n=11）.Under the optimum conditions of solid phase extraction,the recovery rates of Cd（II）in waste water samples were 95.22%-104%.