Preparation And Evaluation On The Adsorption Multifuctions Of A Silica Gel Modified With A Novel Aminocarboxylic Acid Ligand

With the increasing harm of dyes and heavy metal ion wastewater to the environment and humans,aminocarboxylic acids with ion exchange properties and metal chelation properties have also got more and more attention.Among them,biodegradable EDDS can provide 6 coordination atoms due to the structure of tetracarboxyl group&diimino group,so that it has metal chelating properties no less than EDTA and is widely used in the adsorption of heavy metal ions.However,in the past studies,EDDS was mostly directly applied in the form of liquid chelating agent,which is not conducive to its reuse.At the same time,the tetracarboxyl group&diimino group of EDDS are six dissociative groups,which can provide multiple anion exchange groups,making it have excellent ion exchange characteristics,which can be applied to the removal of cationic reactive dyes.In this study,the EDDS-Silica adsorbent was obtained by bonding EDDS as a ligand on the silica matrix for the first time,and the superiority of the indirect method was confirmed by the comparison between the direct and indirect synthesis methods.In order to demonstrate the excellent multifunctional properties of ion exchange and metal chelation of the new EDDS-Silica adsorbent,it was combined with other aminocarboxylic acid ligands to functionalize silica gel IDS-Silica,IDA-Silica were used as adsorbents to explore the treatment effect of methylene blue（MB）and heavy metal uranium（U）in wastewater.In order to evaluate the ion-exchange properties of EDDS-Silica adsorbents,the effect of the number of carboxylic acid groups on ligands on the adsorption of cationic dye MB in wastewater was investigated by comparing EDDS-Silica,IDS-Silica and IDA-Silica adsorbents.The research shows that the more carboxylate groups on the ligands,the better the removal of cationic dye MB.Under the same conditions,the EDDS-Silica adsorbent from both adsorption capacity and removal rate showed better cation exchange adsorption characteristics.On this basis,the adsorption kinetics and thermodynamics of MB on EDDS-Silica were further discussed,and the effects of experimental conditions such as concentration,temperature and rotational speed on MB adsorption were investigated,and the reusability of adsorbent was evaluated.The research shows that the pseudo-second-order model can describe the adsorption behavior of MB on EDDS-Silica well,and the rate-limiting step may be chemical adsorption;the Langmuir isotherm fitting of the adsorption isotherm is the best fit,and the adsorption is an endothermic.The spontaneous process of EDDS-Silica was studied by isosteric adsorption enthalpy,and the adsorption mechanism of EDDS-Silica to MB may be the synergistic effect of electrostatic and hydrogen bonding.In addition,the adsorbent has excellent regeneration and recyclability.This study proves that the novel EDDS-Silica has excellent cation exchange properties and can be used to remove cationic species,and also provides a theoretical reference for the development of other ligands.In order to evaluate the metal chelating properties of EDDS-Silica adsorbent,the adsorption effect of aminocarboxylic ligands on the heavy metal U（VI）in wastewater was explored by comparing with IDS-Silica and IDA-Silica,under the experimental conditions of different temperature,p H,adsorption time and coexisting ions,the adsorption effect of EDDS-Silica adsorbent on U（VI）in wastewater was preliminarily investigated,and the reusability of the adsorbent was evaluated.The study shows that under the same conditions,EDDS-Silica has the strongest adsorption capacity for U（VI）,showing excellent metal chelating properties.For 20 m L,10 mmol/L U（VI）solution,the saturated adsorption capacity can be as high as about 87 mg/g at p H=3;four metal ions such as Fe³⁺,Ni²⁺,Cu²⁺,Zn²⁺and Cl^-,SO₄^2-.The competition of ions to EDDS-Silica for the adsorption of U（VI）is not obvious.When the above cations and anions coexist with U（VI）,EDDS-Silica can still remove U（VI）efficiently;in addition,EDDS-Silica adsorbent has Good reusability.This study proves that the new EDDS-Silica has excellent metal chelation properties,and provides a new adsorption material for the removal of U（VI）and other metals in wastewater.The results showed that the newly developed EDDS-Silica adsorbent had better ion exchange and metal chelation properties than IDS-Silica and IDA-Silica because of the unique molecular structure of the modified ligand EDDS with multiple dissociative groups and multiple dentate coordination atoms.The study confirmed the suitability of EDDS-Silica adsorbents for the removal of other cationic substances and other metal ions from wastewater.The influence of the number of dissociated groups and the number of teeth on the ligand provided a theoretical reference for the development of other types of ligands,and also provides a theoretical reference for the development of such chelating resins.