Performance And Mechanism Of Lead Adsorption From Water By Modified Chitosan-based Magnetic Nanomaterials

With the rapid development of economy and industrialization,the problem of heavy metal ions pollution has become increasingly serious.Among numerous treatment technologies,the adsorption method has received extensive attention in recent years due to its low cost,simple operation,rapid response and good treatment effect.Compared with other adsorbent materials,chitosan was an ideal adsorbent material because of its extensive source,low price,biodegradability and friendly to environment.In order to overcome the shortcomings of chitosan,such as its sensitivity to pH,single surface functional group and difficult separation,chitosan was modified by pyrrole-2-carboxaldehyde and 5-hydroxymethylfurfural respectively.Then the derivatives were coated onto Fe₃O₄,and were obtained two kind of magnetic nanomaterials?PACCS@Fe₃O₄ and HMFCS@Fe₃O₄?.The effects of various factors?initial solution pH,adsorbent dosage,initial fluoride concentration,contact time and temperature?were investigated to determine the two kinds of adsorbents performance.The adsorption mechanism was explored by characterization such as SEM,FTIR,XRD and XPS.The results showed that when the initial concentration was 50 mg Pb²⁺/L,the optimum adsorbent dosage of PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ was 0.30 and0.50 g/L,respectively.The adsorption process reaches equilibrium within 2 h.The adsorption capacities of the two kinds of adsorbents increased with the increase of initial concentration,and the effect of temperature on the adsorption performance was not significant.Adsorption kinetics studies have demonstrated that the pseudo-first order kinetics models and pseudo-second order kinetics models were both fitted well to the adsorption process on PACCS@Fe₃O₄ and HMFCS@Fe₃O₄,indicating that physical adsorption and chemical adsorption exists simultaneously in the adsorption process.The adsorption isotherm data of PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ were fitted well by the Langmuir isotherm model,indicating that adsorption of single molecular layer dominated.When the temperature was 303K,the maximum adsorption capacity of Pb²⁺by PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ was 213.91 and 142.30 mg/g,respectively.Thermodynamic tests indicated the spontaneous and exothermic adsorption process for both of the PACCS@Fe₃O₄ and HMFCS@Fe₃O₄.SEM,FTIR,XRD and XPS characterizations showed that the surface of the PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ was rough and the specific surface area was large,which was beneficial to the adhesion of adsorbate.The main adsorption mechanism of PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ was the complexation reaction of N and O with Pb²⁺.VSM analysis showed that the saturation magnetizations of PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ were 35.12 and 33.38 emu/g,respectively.The results showed that both PACCS@Fe₃O₄ and HMFCS@Fe₃O₄ can effectively adsorb Pb²⁺in water,providing technical support for the remediation of lead-contaminated water.