Mercury Adsorption Performance And Mechanism Using Copper Sulfide Nanoclusters Anchored Magnetic Nanoparticles

In this work,Cu_xS/PDA@Fe₃O₄ and Zn_xS/PDA@Fe₃O₄ adsorbents were synthesized using interfacial self-assembly method.Supported by magnetic Fe₃O₄ nanoparticles,Fe₃O₄was surface modified by dopamine hydrochloride（PDA）.Cu_xS and Zn_xS were loaded on PDA@Fe₃O₄ surface in aqueous environment respectively.The stable loading of adsorbent and the recovery and reuse of adsorbent using magnetic Fe₃O₄ magnetic separation performance are realized.The optimum Cu_xS/PDA@Fe₃O₄ nanosorbents were prepared by controlling the molar ratio of Cu Cl₂,synthesis temperature and solution p H.The adsorption properties of Cu_xS/PDA@Fe₃O₄nanosorbents were investigated under different initial p H,different adsorbents dosage and different anion coexistence conditions.The Cu_xS/PDA@Fe₃O₄ nanosorbents were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM+Mapping）,Zeta potential,Raman spectroscopy（Raman）,X-ray photoelectron spectroscopy（XPS）,X-ray diffrotometry（XRD）and hysteresis curve（VSM）Structural characteristics and adsorption mechanism of mercury.Then,the adsorption effect of Cu_xS/PDA@Fe₃O₄ adsorbent on large-volume and low-concentration mercury-containing wastewater was studied,and the selective adsorption performance of Cu_xS/PDA@Fe₃O₄ adsorbent on different metal cations in water was explored.Finally,the Cu_xS/PDA@Fe₃O₄ adsorbent after mercury adsorption test was desorbed with HCl as eluent to explore the cycling stability of the adsorbent.The results are as follows:（1）The prepared Cu_xS/PDA@Fe₃O₄ has clear surface morphology,good crystallinity and better adsorption effect.Under the conditions of 0.03 g/50 mL adsorbent dosage,p H=5,initial concentration of mercury 10 mg/L,after 24 min reaction time,the removal rate of Hg²⁺by Zn_xS/PDA@Fe₃O₄ is 99.79%.The removal rate of Hg²⁺by Cu_xS/PDA@Fe₃O₄ was close to 100%,and the adsorption effect was better than that of Zn_xS/PDA@Fe₃O₄.（2）The optimum preparation conditions were as follows:molar ratio of Cu Cl₂ was 0.04mol/L,synthesis temperature was 20℃,and reaction p H was 3.0.At this time,the initial concentration of mercury containing solution of 10 mg/L was absorbed by the adsorbent for24 min,and the mercury concentration of water was reduced to 0.0012 mg/L,and the removal rate was 99.98%.（3）The optimum adsorption conditions for mercury were as follows:the dosage of adsorbent was 0.03 g/50 mL,and the reaction p H was 6.The influence of different anions on the adsorption of mercury was small,and the removal rate was close to 100%after 24min.Hg²⁺in 20μg/L low concentration mercury containing wastewater can be removed in a short time and meet the discharge standard（2 ppb）.The adsorbent has adsorption effect on Hg²⁺Ag⁺,Mo²⁺,Pb²⁺,Cr⁶⁺/Cr³⁺,among which,the adsorption effect on Hg²⁺is the best,and the removal rate is close to 100%.（4）The adsorption capacity of the adsorbent increased with the concentration of mercury.At 500 mg/L,the adsorption capacity was 1394.61 mg/g,which was still not up to its saturation adsorption capacity,which was better than the adsorbents for inorganic materials reported in the literature.The adsorption data accords with Freundlich model,and the adsorption of Hg²⁺belongs to multilayer adsorption.（5）TEM characterization observed the microstructure evolution of the material before and after the adsorption,Mapping characterized the changes in the content of each element component and mercury content before and after the adsorption,Raman spectrum showed the existence of Cu-S bond and acted on the adsorption of mercury,indicating that mercury was successfully captured by Cu_xS/PDA@Fe₃O₄.XPS analysis showed that S existed in S^2-and S^1-forms and combined with Cu to form Cu_xS,indicating that the synthesized Cu_xS were mainly Cu₂S and Cu S.（6）Cyclic stability of the adsorbent:after 6 sorption-desorption cycles,the adsorption and desorption efficiency are still 44.76%and 74.26%,and the eluent HCl does not destroy Cu_xS/PDA@Fe₃O₄ surface,but still retains the adsorption property of mercury,indicating that the adsorbent is well prepared and has good cyclic stability.The green,economical,and effective Cu_xS/PDA@Fe₃O₄ nano-sorbents proposed in this work can provide a new strategy for Hg²⁺remove from wastewater.