Ligand Substitution Of Dissolved Metal Ions And The Corresponding Mechanisms Of Their Application In Metal Ions Removal

Metallic element,existing widely in the nature,play important roles in a variety of fields in human society.Compared with solid metallic compound,hydrated metal ions are characterized by higher reactivity and higher probability in contacting with other compounds,as a result,their migration and transformation behavior are more complicated.At the meantime,the extensive usage of metallic mineral and inappropriate post processing method lead to the massive discharge of metallic compound-containing wastewater and cause server ecological threat.So,it is theoretically and practically important to research on coordination structure and their treatment of metal ions dissolved in water.In this work,the effects of metal ions on the structure of short-/long-range water cluster,and the precise structural parameters of the first coordination shell were studied with NMR,Raman spectra,viscosity measurement and MD.Meanwhile,thermodynamic data of the complex reaction between 2-methyl glutaric acid and 4 metal ions,and corresponding structural parameters were obtained with the help of ITC,viscosity measurement and XAS.What's more,a new superabsorbent polymer capable of adsorbing metal ions with high performance was prepared by making use of corn starch,acrylic acid,organo-modified zeolite 4A,potassium persulfate and MBA.At last,the microscopic mechanisms of metal ions adsorbtion by the polymer was discussed through a combined use of quantum-mechanical calculation and EXAFS fitting analysis.Within aqueous solution,metal ions can promote the association of water molecules adjacent to the center ions,but make distant water cluster less ordered,the influence ability followed the order Cr³⁺> Fe³⁺ >Cu²⁺ >Zn²⁺.The coordination number of the four metal ions were all 6,and the average distance between metal ion and coordination oxygen atoms were about 1.994-2.173 ?.Compared with water molecule,2-methyl glutaric acid had higher affinity for the four metal ions studied here,which made it replace water molecules and complex with metal ions.As for the stable complexes,the coordination number for Zn²⁺ and Cu²⁺ were 7.2 and 4.6,respectively,but the first coordination shell of Zn²⁺ was characterized by higher degree of disorder.By contrast,Fe³⁺ and Cr³⁺ could form similar bimetal core complex compound with 2-methyl glutaric acid and water molecules.The prepared polymer composite could adsorb and remove metal ions from aqueous solutions with high efficiency,and the adsorption capacity exceeded 907.97,651.42,911.15,589.45 mg·g^-1 for Fe³⁺,Cr³⁺,Cu²⁺,Zn²⁺,respectively,which stemmed from the joint coordination of water molecule and carboxyl group.The successful application on coordination structure study manifested that the combined use of DFT calculations and XAS analysis is a powerful mechanism study method suitable for metal ion adsorbtion by polymer.