Preparation And Heavy Metal Adsorption Of PEI-modified Corncob Magnetic Gel Material

Heavy metal-contaminated wastewater has become an environmental issue that has attracted much attention because of its great harm.It was also a research hotspot for global researchers.There were many ways to treat heavy metal polluted wastewater and utilize it as a resource.Among them,the adsorption method was widely used because of its simple operation,high efficiency,and easy engineering application.The development of adsorption materials with excellent performance was the key prerequisite for the application of adsorption methods.Biomass-based adsorption materials were favored because of their excellent adsorption performance,environmental friendliness,low price and high quality,and a wide range of sources.In this study,corncob（CC）biomass was used as raw material.Alkali（NaOH）,acid（HAc）,and salt（ZnCl₂）solutions were used as activators,respectively.Used glutaraldehyde as the crosslinking agent,and polyethylene polyamine（PEI）as the chemical modifier.The modified corncob magnetic gel adsorption materials PEI-CC@Fe₃O₄（NaOH）,PEI-CC@Fe₃O₄（HAc）,and PEI-CC@Fe₃O₄（ZnCl₂）with excellent adsorption performance and high selectivity were prepared.And the laboratory preparation conditions were optimized.The structure was characterized by FT-IR,XRD,SEM-EDS,TGA,etc.The influence and regularity of the synthesis process on the molecular structure of the magnetic gel were elucidated.The adsorption process of Pb²⁺,Cu²⁺,and Ni²⁺on the corncob magnetic gel material was explored through adsorption kinetics,adsorption thermodynamics,and adsorption isotherm.The mechanism of adsorption of heavy metals by magnetic gel was studied by XPS.The research results provided experimental support and a theoretical basis for expanding the deep resource utilization of corncob biomass.Experimental results show that:（1）The corncob magnetic gel has a three-dimensional network porous structure and a large specific surface area,which significantly increases its saturated adsorption capacity of heavy metals.The maximum adsorption capacity of Pb²⁺,Cu²⁺,and Ni²⁺on the Corn cob magnetic gel prepared by NaOH,HAc,ZnCl₂ solution activation reached 160.2 mg/g,132.8mg/g,and 105.6 mg/g,respectively.This was significantly better than an unmodified corncob.The activator had an important influence on the adsorption performance of magnetic gel,and alkali>acid>salt.The adsorption performance relationship of the prepared corncob magnetic gel was PEI-CC@Fe₃O₄（NaOH）>PEI-CC@Fe₃O₄（HAc）>PEI-CC@Fe₃O₄（ZnCl₂）.The modification of PEI and the size of the PEI molecule greatly improved the adsorption performance of corncob magnetic gel.（2）Environmental conditions were an important influence on the adsorption of Pb²⁺,Cu²⁺,and Ni²⁺on corncob magnetic gel.The adsorption capacity was positively correlated with p H,temperature,and adsorbent dosage.The larger the initial concentration of heavy metal ions,the higher the adsorption capacity.With the increase of the adsorption time,the adsorption capacity of the heavy metals on the magnetic gel also increased,and it reached saturation in 3 h.（3）Competitive adsorption studies showed that with the increase of Na⁺and Ca²⁺concentrations,the adsorption capacity of heavy metals on magnetic gels decreases gradually.PEI-CC@Fe₃O₄（NaOH）exhibited good selectivity for Pb²⁺,and the order of adsorption strength is Pb²⁺>Cu²⁺>Ni²⁺.PEI-CC@Fe₃O₄（HAc）and PEI-CC@Fe₃O₄（ZnCl₂）had high selectivity to Cu²⁺,and the order of competitive adsorption was Cu²⁺>Pb²⁺>Ni²⁺.（4）The adsorption mechanism study showed that functional groups such as-NH₂ and-OH in the gel molecular structure played a major role.It was dominated by the coordination and complexation of O1s and N1s electrons with heavy metal ions.The adsorption process followed pseudo-second-order kinetics,and the adsorption process was mainly chemical adsorption.The adsorption process was consistent with Langmuir isotherm adsorption,which belonged to the characteristics of monolayer adsorption.Thermodynamic data confirm that the adsorption process was a spontaneous endothermic and entropy-increasing process.