Research On Adsorption Behaviors Of The Amino Acid Modified Layered Double Hydroxides

In recent years,layered double hydroxide(LDH)has been attracted more and more attentions due to its better adsorption capacities of verious pollutions.In this study,cysteine intercalation modified LDH materials(Cys-LDH)was synthesized via a simple coprecipitation method and the removal of radionuclide and organic pollutions were investigated under various environmental conditions.The adsorption kinetics,thermodynamics and the effects of different environmental factors on uranyl and methyl orange(MO)were studied.The adsorption mechanism of U(?)and MO were investigated by using FT-IR,XRD,XPS spectroscopy techniques.The results of this study as follows:(1)The effects of pH and coexisting ions on U(?)adsorption on the two adsorbents suggested that the removal percentage of U(?)on Mg/Al-LDH or Cys-LDH increased with increasing of pH.Interestingly,the elimination of U(?)on Mg/Al-LDH was improved with the increase of NaNO3 concentration at pH>5.0,which inplied that the elimination of uranium on Mg/Al-LDH was ascribed to the outer-sphere surface complexation.In contrast,at all pH values,uranium adsorption on Cys-LDH was independent of electrolyte ionic strength,suggesting that the main interaction mechanism was inner-sphere surface complexation.The results of co-existing ions on U(?)adsorption on the two adsorbents showed various anions(such as NO3-,Cl-,ClO4-and SO42-)did not affect U(?)adsorption on Cys-LDH obviously,while CO32-could significantly influence U(?)elimination.(2)The effects of Humic acid(HA)showed that HA could decrease U(?)elimination on Cys-LDH or Mg/Al-LDH at high pH but increase U(?)removal at low pH.Intristingly,the effect of HA on the U(?)adsorption on Cys-LDH was weakly than thay on Mg/Al-LDH.This was due to that adsorption of U(?)on Mg/Al-LDH was mainly surface complexation,while on Cys-LDH the U(?)was mainly formed Cys-U(?)-Cys complexes with Cys molecules in the Cys-LDH interlayers.And thereby,the influence of HA on the adsorption of U(?)on Cys-LDH was weakly than Mg/Al-LDH.(3)The adsorption of MO on the two adsorbents were significantly influenced by the pH and ion intensity,indicating that the adsorption of MO on Mg/Al-LDH and Cys-LDH were the outersphere surface complexation.Adsorption isotherm and thermodynamic data implied that the adsorption of MO on Mg/Al-LDH and Cys-LDH were the spontaneous and exothermic process,and thereby the higher temperature,the lower sorption capacity of MO on Mg/Al-LDH and Cys-LDH.The cyclic regeneration experiments suggested that Cys-LDH had a stronger regeneration ability which also indicated that Cys-LDH could be a suitable adsorbent for the treatment of dye pollutions in the actural application.