Research On The Amino Acid Ionic Liquid Modified Chitosan Gel Adsorbents For Adsorption Of Pb (?)

Heavy metal lead is widely applied in various industries,and its application range can be from ore mining to people's daily life.The toxicity of lead to the environment is very serious,and it is also very harmful to human's physical and mental health.Lead ions can be separated from waste water by precipitation method,biological method,adsorption method,electrochemical method and membrane technology.Adsorption method is widely applied and has good effect.Chitosan molecules are rich in amino and hydroxyl groups.These adsorption groups can be well combined with lead ions through potential neutralization and complexation.Besides,chitosan is easy to be functionalized by other polymer materials which can be introduced more functional groups.The amino acid ionic liquid has a strong hydrogen bond network structure,which can solve the problem of chitosan dissolution,especially amino and carboxyl groups in amino acid molecules.In addition,amino acid molecules have many amino and carboxyl groups,which are propitious to preparation of amino polycarboxylic acid structure.The amino acid ionic liquid modified chitosan gel adsorbents are prepared by alanine acid(Ala),aspartic acid(Asp),glutamic acid(Glu)and chitosan(CS).The static adsorption of lead ions in the wastewater are conducted with modified gel.The experimental results are shown as follows.(1)Ala-IL-CS on the removal rate of Pb2+is about 78.96%,Asp-IL-CS on the removal rate of Pb2+ is about 84.54%,Glu-IL-CS on the removal rate of Pb2+ is about 92.09%.(2)The adsorption efficiency of modified gels is positively correlated with the degree of functional groups of amino acid ionic liquids participating in the reaction.That is Glu-IL-CS > Asp-IL-CS > Ala-IL-CS.(3)The best adsorption conditions for Pb2+in simulated wastewater by Ala-IL-CS gel adsorbent are as follows: the dosage is 6g,the p H is 4~5,the initial concentration is 40mg/L,the temperature is 30?,the time is 20 h,and the number of regeneration is 3 times.The characteristic functional groups such as hydroxyl groups and carboxyl groups containing in Ala-IL-CS can be found through FTIR,indicating that the modification is successful.SEM shows that the surface and interior of Ala-IL-CS exist pore structure,and it has adsorption effect of Pb2+,and the XRD spectrogram analysis proves that the alanine ionic liquid modified chitosan is successful.After fitting the experimental data,the adsorption data of Ala-IL-CS on Pb2+ conforms to the Langmuir adsorption isothermal model(R2=0.9942)and the pseudo-second-order rate equation(R2=0.9905).It shows that the adsorption of single molecule layer and chemical adsorption are the dominant factors of Ala-IL-CS to Pb2+,and the saturated adsorption capacity is 90.91mg/g.(4)The best adsorption conditions for Pb2+in simulated wastewater by Asp-IL-CS gel adsorbent are as follows: the dosage is 8g,the p H is 4~5,the initial concentration is 40mg/L,the temperature is 30?,the time is 20 h,and the number of regeneration is 3 times.The characteristic functional groups such as hydroxyl groups and carboxyl groups containing in Asp-IL-CS can be found through FTIR,indicating that the modification is successful.SEM shows that the surface and interior of Asp-IL-CS contain pore structure and it has the adsorption effect on Pb2+.The movement of the peak value of XRD indicates that the amino acid ionic liquid is successfully modified the chitosan.At different temperatures,the adsorption data of Asp-IL-CS on Pb2+ conformed to the Freundlich adsorption isothermal model(R2 > 0.99),indicating that the multi molecular layer adsorption is the leading factor of the adsorption behavior.The maximum adsorption capacity under four temperature conditions of 15,20,25 and 30 ?are 100.60,99.26,129.53 and 136.63 mg/g respectively.The results of the thermodynamic equation fitting shows that the value of delta G is less than 0,indicating the surface adsorption process carries out spontaneously.And the delta S is less than 0,the degree of freedom is reduced and the entropy also decreases after the adsorption of the lead ion in the solution,and delta H is less than 0,indicating that the adsorption process is the exothermic process.In addition,the value of delta H is-79.59KJ/mol,shows the adsorption behavior of Asp-IL-CS on Pb2+ belongs to chemical adsorption.The adsorption of Asp-IL-CS on Pb2+ conforms to the pseudo-second-order rate equation(R2=0.9907),indicating that chemical adsorption is the dominant factor in the adsorption process.(5)The best adsorption conditions for Pb2+in simulated wastewater by Glu-IL-CS gel adsorbent are as follows: the dosage is 8g,the p H is 4~5,the initial concentration is 40mg/L,the temperature is 30?,the time is 20 h,and the number of regeneration is 4 times.The characteristic functional groups such as hydroxyl groups and carboxyl groups containing in Glu-IL-CS can be found through FTIR.SEM and EDS show that the surface and interior of Glu-IL-CS contain pore structure and it has adsorption effect on Pb2+;XRD has been proved to be successful and has a adsorption effect on Pb2+ through the comparison of the spectra before and after adsorption.After fitting the experimental data,the adsorption data of Glu-IL-CS on Pb2+ conforms to the Freundlich adsorption isothermal model(R2=0.9693)and the pseudo-second-order rate equation(R2=0.9898).It shows that the adsorption of multi molecular layer and chemical adsorption of Glu-IL-CS to Pb2+ are the dominant factors in the adsorption process of Pb2+,and the saturated adsorption capacity is 149.25mg/g.