Preparation Of Novel Materials For Solid-phase Extraction And Their Separation Properties For Trace Heavy Metal Elements

Recent years,with the rapid development of science and technology,new challenges have been required for analytical chemistry in several subjects with the complexity of samples and lower content of analyte.Although many instrument analysis methods have been developed recently and reached trace level or super trace level sensitivity,the direct analysis is still difficult because of the high complexity of samples and severe interference caused by matrix effects.So,various pre-treatment procedures are necessary before the more accurate measurement by analytical instruments.There can be no doubt that solid-phase extraction(SPE)is the most popular sample preparation method with the high efficiency and reliability.This paper mainly described the preparation of several extractants based on the parameters of SPE technology such as selectivity,maximum adsorption capacity,equilibrium time etc..The more detailed novelty of this research can be categorized as following:1.4-(2-Pyridylazo)-resorcinol(PAR)-modified nanometer SiO₂ was prepared and confirmed by infrared spectra(IR)and scanning electron micrograph(SEM). Experimental results revealed that only two minutes were needed for the adsorption equilibrium,and the maximum adsorption capacity of this sorbent for Hg²⁺was 276μmol g^-1at pH 4.Under the selected conditions,Hg²⁺was successfully separated and pre-concentrated from real sample solutions.The modification process greatly increased the selectivity of nanometer SiO₂ particles and descreased the quantitative adsorption pH value compared with the blank materials.2.Using the excellent cooperation capability of 1,5-Diphenylcarbazide towards some heavy metal ions,Fe₃O₄-SiO₂ nanometer magnetic core-shell material having separation function was prepared by sol-gel and adulteration method.The material could be used as sorbent for effectual remove of Hg²⁺from aqueous solution.This composite preparation method resolved the problem of nanometer oxide particles in aqueous solution such as difficult dispersion or separation,et..Except Cr³⁺and Cu²⁺, 100-fold other common foreign ions did not interfere with the extraction.SiO₂ polymer enveloped on the surface of magnetic particles greatly increased the magnetism stability and acid-resistance of material.Finally,when they were used as solid phase extraction materials,nanocomposite magnetic particles exhibited several favourable properties such as simple operation,easy preparation and high application value.3.Methylmercury imprinted polymer was prepared based on the synthesis of (4-Ethenylphenyl)-4-formate-6-phenyl-2,2-bipyridyl methylmercury complex,and was used for the pre-concentration and determination of methylmercury from aqueous solution.The imprinted polymer exhibited favorable selectivity for target ion.The selectivity factor of imprinted sorbent for Hg²⁺,Cu²⁺,Zn²⁺and Cd²⁺reached 22.6, 75.2,98.8 and 53.1,respectively.The main parameters of solid-phase extraction were optimized and based on this a new determination method of methylmercury was developed.The detection limit and quantification limit of the method were 0.041 and 0.093μg L^-1,and the relative standard deviation was less than 3.5%.The method was applied to the separation and pre-concentration of trace methylmercury in human hair samples with satisfactory results.4.As the materials prepared by reaction of hydrophobic functional monomer and cross-linker having several disadvantages such as poor hydrophilicity and low adsorption rate,a new hydrophilic monomer,(2Z)-N,N'-bis(2-aminoethylic)but-2-enediamide, was synthesized and copolymerized with pentaerythritoltriacrylate for preparing novel Cd²⁺and Cu²⁺imprinted polymer sorbents.The new monomer and cross-linker which has three double bonds provided the sorbents high selectivity and great hydrophilicity.The equilibrium time of target ion adsorbed on the sorbents was obviously reduced comparing with similar literatures.The template ions extracted on the imprinted polymer followed the Langmuir isotherms model.Non-imprinted polymer was not suitable for enrichment and determination of trace Cu²⁺or Cd²⁺ because no quantitative adsorption was observed in any tested concentration.At the same time,a new method was developed for high selective separation and pre-concentration of trace Cu²⁺and Cd²⁺in aqueous solution.This work also indicated that the design of dual-ligand monomer was very suitable for further development of ionic imprinted polymers techniques.5.Zn²⁺-(2,2'-bipyridyl)imprinted polymer membrane with PVDF membrane as supporting material was prepared by using 4-vinylpyridine as monomer and ethyleneglycoldimethacrylate as crosslinker.The substrates permeated through the membranes followed the diffusion mechanism.The adsorption process of substrates decided the selectivity and permeation rates of membranes.With the mediation of small molecule,2,2'-bipyridyl,the imprinted polymer membranes exhibited higher selective adsorption and permeation for the template than the control and non-imprinted counterpart.This work further proved that the effectual three-dimensional interspace of imprinted sites and higher hydrophilicity of polymer materials were necessary for further improving the selectivity and permeation flux of separation membranes.