Structure-activity Relationship And Adsorption Performance Of Diatom-based Cd(?) Ion-imprinted Composites

In recent years,people have adopted different treatment methods and methods for Cd???ions,but it is difficult to recover and reuse the treated Cd???ions.Therefore,this paper designs a selective adsorption for Cd???ions s material.In this paper,diatoms were used as carriers,mercaptopropyltrimethoxysilane?MPS?as functional monomer,epichlorohydrin?ECH?as crosslinking agent,and Cd???ion as template ion to prepare diatomyl Cd???Ion surface imprinted composite adsorption material?SH/DE-?P?.The relevant research results are as follows:?1?Scanning electron microscope?SEM?images were observed throughout the preparation process of the blot.The diatom surface morphology changed from smooth to rough,and the modifier was more uniformly and regularly distributed on the diatom surface with the addition of crosslinking agent.The existence of S element was observed from the X-ray energy spectrum?EDS?,indicating that under the preparation conditions of the system,the functional monomer can be successfully loaded on the surface of the diatom,forming a good compound effect.The uniform distribution of functional groups?-SH?on the surface of diatoms meets the requirements of material design,increases the adsorbable sites of imprinted materials,and increases the adsorption capacity of Cd???ions.?2?Transmission electron microscopy?TEM?images show that the internal structure of pores in SH/DE-?P is more concentrated than that of diatom-based non-imprinted adsorbent materials?SH/DE-NIP?.The main difference is that there is a template in SH/DE-?P Cd???ion exists but not in SH/DE-NIP.Due to the cross-linking process,the distribution of Cd???ions and the homogeneity of the surface structure are also the same.On the SEM image of SH/DE-?P,the modified objects behave more uniformly and regularly.This phenomenon confirms that template ions play a crucial role in the preparation of imprinted materials.By analyzing the pore structure and surface area of the imprinted material,it can be found that the specific surface area of the imprinted diatom has increased to 38.8 m² g^-1.This result has significantly improved the adsorption capacity of activated diatoms.The average pore diameter of diatoms was reduced to 4.5 nm,indicating that after the grafting and cross-linking process,more microporous structures were formed on the imprinted diatoms.?3?The FTIR spectrum shows that 3708.4 cm^-1 is an active isolated hydroxyl peak on the surface of the diatom.MPS grafted diatoms at 2956.3 cm^-1,2854.1 cm^-1,and 2553.2 cm^-1.The characteristic peaks of the CH group and the C and-SH groups,combined with the appearance of Si-C bonds in the XPS fitting spectrum,proved that MPS was hydrolyzed with diatom isolated silanol groups to complete the grafting.ECH cross-linking agent,during the compounding process with the material,the intensity of the characteristic peak of the-SH group weakens.According to the occurrence of the peak position of the C-O binding energy,ECH is ring-opened and then cross-linked with the-SH group.According to the appearance of the binding energy peak of Cd-S indicates that the addition of the cross-linking agent fixes the composite structure of the functional monomer and the template ion.After elution of template ions by HCl,the characteristic peak of the-SH group in the FT-IR spectrum was enhanced,and a slight red shift occurred.The S-Cd interaction binding energy peak in the XPS spectrum disappeared,indicating that Cd???in the imprinted holes had Complete elution,the binding site with the same size and shape as Cd???was formed.?4?According to the SH/DE-?P grafting degree analysis,the grafting method of the thiol silane coupling agent to the diatom surface-active silanol group is mainly one-component hydroxyl condensation method,and two-component hydroxyl condensation method is auxiliary.The grafting degrees calculated by gravimetric method and XPS method were11.26 and 13.85,respectively.The diatom-based imprinted composite material can provide a good adsorption environment.Through a lot of experiments and structure analysis,we have well analyzed the complete structure-activity relationship of the diatom-based Cd???ion-imprinted composite adsorbent system.?5?Through the single factor analysis experiment,the optimal adsorption condition of Cd???ion by SH/DE-?P was determined.SH/DE-?P in the binary mixed system,the relative selectivity coefficient is greater than 1.5,showing a good selectivity for Cd???ion.After 5times of adsorption-desorption,the removal rate of Cd???ion can be maintained at 91%.It is a stable diatom-based Cd???ion surface imprinted composite adsorption material.