Preparation And Enrichment Properties Of Cd(II) Or Pb(II) Ion Imprinted Sorbents

The rapid development of economy in our country results in the serious polluting by heavy metals in the air, water and soil and it is becoming one of important factors influencing the social economy development and the people’s health. Heavy metal ion is; harmful for the living beings even at very low level in environment. Therefore, the separation and determination of trace heavy metal in environmental samples is significant., Molecularly imprinting technique （MIT） is merging interdisplinary methodology of molecular recognition that is developing in recent years. Molecularly imprinting polymers （MIPs） can discriminate template molecule and related analogs selectively. Because of their good affinity, sensitivity and stability, MIPs have been rapidly developed and used extensively in biotechnology, environmental monitoring, inartificial drugs, food industries, and so on. To establish new methods by which trace heavy metal can be separated completely and concentration availably and determined exactly, in this paper, three different methods were employed to prepare metal ion imprinted sorbents. These sorbents were characterized by FTIR and specific surface area and pore size distribution analyzer. The selective adsorption properties of imprinted sorbents were described. The dynamics and thermodynamics of recognition process were also studied. The properties of different sorbents were compared. Some novelty conclusions are as follows:1. The Cd（II）-ion imprinted and non-imprinted polymers were prepared by suspension polymer technique using methacrylic acid （MAA） as monomer. The effect of different crosslinking agent, reactive temperature and raw material configuration on the property of the Cd（II）-ion imprinted were investigated. The separation and preconcentration characteristics of the imprinted polymers for Cd（II） were researched by batch and column procedures. The results show that the imprinting polymer selected ethylene glycol dimethacrylate as crosslinking agent has the uniform particles and a certain mechanical strength. The imprinted polymer has the maximum capacity and high selectivity when the mole ratio of template ion, monomer and crosslinking agent is 1:4:20 and the reactive temperature is 70℃. The maximum adsorption capacity was 12.6 mg·g^-1. The relatively selective coefficient over Cu（II） and Zn（II） are 3.3 and 3.5, respectively. The preconcentrative separation and determination methods for Cd（II） was established using flame atomic absorption spectrometry （FAAS） with detection limits 0.76μg·L^-1 which can be used to determine the real water samples.2. The Pb（II） ion-imprinted mesoporous sorbent was prepared by surface imprinting technique in combination with sol-gel process. The imprinted mesoporous sorbents were characterized by FTIR and specific surface area and pore size distribution analyzer. The kinetics of adsorption, capacity and selectivity were investigated by batch procedure. The results show that the sorption process is very fast and the static maximum sorption of Pb（II） onto imprinted sorbent was about 221 mg·g^-1. The preconcentrative separation and determination methods for Pb（II） was established using flame atomic absorption spectrometry （FAAS） with low detection limit and high selectivity, which can be used to determine the complex environmental samples.3. The dynamics and thermodynamics in the recognition process of ion imprinting were studied. The main conclusions are as follows. （1） The adsorption process of lead ion in the aqueous solution by Pb（II） ion imprinted sorbents is a fast process which can be fitted by the Pseudo second-order model; the sorption rate under high concentration of Pb（II） ion was higher than that of under low concentration of Pb（II） ion; when the concentration of Pb（II） ion is high, the liquid film diffusion become the main control step for sorption rate, while the concentration of Pb（II） ion is low, the intraparticles diffusion become the main control step for sorption rate. （2） The Langmuir and Freundlich sorption models were applied to describe the isotherms and isotherm constants. Sorption isothermal data could be well interpreted by the Langmuir model. This indicates that the sorption process is a chemical sorption with single molecule layer. （3） The results of thermodynamics behavior in the recognition process of ion imprinting show that the values of△H⁰ is positive, which indicates the adsorption process is endothermic. The negative values of△G⁰ and the positive values of△S⁰ indicate that the adsorption reaction is a spontaneous process.4. The Pb（II） ion imprinted sol-gel sorbents was prepared by double imprinting method using lead ion and surfactant as double templates. The effects of various preparation conditions on the property of ion-imprinted sorbent were investigated. The double imprinted sorbent was characterized by FTIR and specific surface area and pore size distribution analyzer. The effects of pH and contact time were studied by batch procedure. The adsorption capacity and selective recognition ability of the double imprinted sorbent were also investigated by equilibrium-adsorption method. Results showed that the optimum pH value for quantitative enrichment is 5.0-7.0. The double imprinted sorbent possessed a fast kinetics for removal of Pb（II） from aqueous solution with satuation time about 10 min. Compared with other imprinted sorbents or non-imprinted sorbent, the double sorbent has higher sorption capacity and the selectivity. The related selective coefficient over Cd（II） is greater than 100. The adsorption capacity has no obvious decrease by five times of adsorption-desorption processe. Based on this double imprinted sorbent, a highly selective solid-phase extraction and preconcentration method for Pb（II） from aqueous solution was developed. The process of the determination demands less solvents so that the contamination and loss of samples can be reduced. The method can be directly used to analyze the complex environmental samples.