Preparation And Adsorption Properties Of Thioamide Chelating Resins

The study of economical and efficient adsorbents is of great significance for the application of adsorption method.Thioamides have protonated amino groups,and the complexation of sulfur atoms can improve its interaction selectivity of metal ions.At the same time,its adsorption property can improve under the synergistic action of strong electron donor groups such as aromatic ring,amino and sulfhydryl group.However,available researches are relatively scattered,and lack of systematic comparison and in-depth discussion on the strengthening mechanism.In this study,a series of thioamide chelating resins containing strong electron-donating groups were prepared,and the adsorption processes of heavy metal ions and organic dyes was systematically studied,including adsorption capacity and selectivity.The relationship between their structure and properties and the strengthening mechanism were studied by combing with Gaussian theoretical calculation.The main results are as follows:(1)Six kinds of thioamide chelating resins were successfully prepared.The sulfure(S)content of thiourea(TMCR),ammonium thiocyanate(ATMCR)and carbon disulfide(CDMCR)modified chelating resins were3.94%,11.93% and 4.92%,respectively,and the N content of them were7.94%,9.21% and 6.81%,respectively.The resins were characterized by Fourier Transform Infrared spectroscopy(FTIR),Brunauer-Emmett-Teller(BET),scanning electron microscope(SEM)and X-ray photoelectron spectroscopy(XPS),and all were of mesoporous structure.(2)TMCR,ATMCR and CDMCR had good adsorption properties for Hg(Ⅱ)with the oder ATMCR > CDMCR > TMCR.The adsorption processes of three chelating resins accorded with the pseudo-second-order kinetic model.Their adsorption isotherms obeyed the Freundlich,Temkin and Temkin model,respectively.The maximum adsorption capacity of ATMCR could reach 636.9 mg/g at 318 K.ATMCR showed specificity for Hg(Ⅱ)adsorption in the multi-heavy metal system.The adsorption rate of ATMCR was still above 94% after ten regeneration cycle experiments.DFT theoretical calculations showed that the interaction between Hg(Ⅱ)and the chelating resin monomer may be dominated by electrostatic.ATMCR exhibited specific adsorption for Hg(Ⅱ)with stronger coordination than TMCR and CDMCR.(3)Ammonium thiocyanate(ATMCR),isothiocyanate(ITMCR)and polyethyleneimine(PEIMCR)modified chelating resins had good adsorption capacity for methyl orange(MO).The optimal adsorbents of the three chelating resins were all 1.5 g/L.Their adsorption processes all conformed to the pseudo-second-order reaction kinetic model.The correlation coefficients of linear fitting were all above 0.981.Their adsorption isotherms all accorded with the Temkin isotherm model indicated the adsorption processes of three resins were mainly chemical interactions.At 318 K,the maximum adsorption capacities of the three chelating resins were 398.4 mg/g,390.6 mg/g and 319.5 mg/g,respectively.