BC@LDH-EDTA Adsorption Removal Of Methyl Orange And Cr(Ⅵ) In Aqueous Solutions

In this study,the liquid-phase co-precipitation method was used to obtain the bamboo shavings biomass loaded with layered double hydroxides（LDH）.And then bamboo shavings were calcined at 480°C to prepare a novel adsorbent material BC@LDH-EDTA.Throughout the whole process,the effects of initial pH,initial concentration and coexisting anion on removal of methyl orange or Cr（Ⅵ）in aqueous solution by BC@LDH-EDTA were investigated.The morphologies of the material and the adsorption mechanism were investigated by various characterization methods such as SEM.The novel adsorbent material BC@LDH-EDTA has the ability to rebuild into a new LDH due to its surface attached to layered double oxides（LDO）formed by calcination,which is called"memory effect".Meanwhile,it also shows that the original loaded nanomaterial LDH has better thermal stability.The BET surface area of BC is 48.894 m²/g,while the BET surface area of BC@EDTA-LDH is 8.831 m²/g.The LDO formed after calcination may be filled into the larger pore position of biochar,which greatly reduced BET specific surface area of BC@EDTA-LDH.The LDO structure accompanying the surface of the biochar in the adsorption reaction was constructed to a new LDH.A clear layered structure can be seen in the SEM image of BC@EDTA-LDH after adsorption.At 480℃,the material just changed the structure.The BC@LDH-EDTA had very low intensity of characteristic diffraction peaks on the（003）,（006）,（009）,（010）and（113）crystal planes in the XRD pattern.The diffraction pattern after adsorption of methyl orange or Cr（Ⅵ）showed obvious characteristic diffraction peaks on the（003）,（006）,（009）and（110）crystal planes of LDH,respectively.This further validated the appearance of LDH with the intercalation of methyl orange or Cr（Ⅵ）anions by the XPS and FTIR spectra.The effect of pH on removing the methyl orange by BC@EDTA-LDH was not significant.Even at higher pH,the adsorption amount of methyl orange by BC@EDTA-LDH was as high as 613.79 mg/g.However,pH had a greater effect on the removal of Cr（Ⅵ）by BC@EDTA-LDH.A little LDH may be dissolved during the reaction,and BC@EDTA-LDH has a certain buffering effect on the pH of solution,and the equilibrium pH was greater than the initial pH.At different pH values,the zeta potential of BC@EDTA-LDH was always greater than zero,it meaned that the surface of BC@EDTA-LDH was always positively charged,and that between BC@EDTA-LDH and methyl orange or Cr（Ⅵ）anions always had an electrostatic attraction.However,too high pH value will lead to OH^-competition for adsorption sites.The effect of coexisting anions on the removal of methyl orange or Cr（Ⅵ）by BC@EDTA-LDH were very different.Under different ionic strengths,the effect of methyl orange removal was low.However,the ionic strength had a great influence on the removal of Cr（Ⅵ）by BC@EDTA-LDH.The interference followed the order of SO₄^2->Cl^->NO₃^-,and the low concentration of sulfate could influence largely.The pseudo second-order kinetic model could well fit the process of BC@LDH-EDTA adsorption removal of methyl orange or Cr（Ⅵ）,indicating that the adsorption process may be chemical adsorption,and the maximum equilibrium adsorption capacity were 727.04 mg/g and 38 mg/g,respectively.The Langmuir isotherm adsorption model showed good fitting effect on the adsorption process of methyl orange or Cr（Ⅵ）by BC@LDH-EDTA,indicating that the adsorption process may the single-layer adsorption with a maximum adsorption capacity of 1782.30 mg/g and 38 mg/g,respectively.In summary,the novel adsorbent BC@EDTA-LDH has a good removal effect on methyl orange or Cr（Ⅵ）.Biochar is used as a support frame for nanomaterials in the research process.The application of nanomaterials has a good application prospect.