Construction Of Magnesium Based Three-dimensional Classification Materials And Their Performance In Removing Heavy Metal Ions

With the acceleration of industrialization and urbanization,heavy metal pollution has gradually become one of the issues that humans need to pay attention to.Heavy metals have the characteristics of strong fluidity,non biodegradability,and high toxicity in the ecological environment.It flows between lower animals and plants,and accumulates in higher animals to a certain concentration,which can cause functional damage and organ damage.Therefore,developing efficient,low-cost,and easy to operate heavy metal adsorption materials is of great significance for human health and sustainable environmental development.Layered double metal hydroxides（LDHs）are a kind of clay materials,which are composed of positively charged brucite like laminates and anions between the laminates.LDHs,as a supramolecular assembled 2D structure,have many advantages in removing heavy metal ions:1)interlayer anion species can be regulated through methods such as anion exchange;2)the metal cations on the laminates are flexible and adjustable,such as fixing heavy metal ions into LDHs laminates through metastable mineralization;3)the LDHs laminates are rich in hydroxyl groups,which result in many heavy metal binding sites on the surface of LDHs.However,due to the self-assembly effect and abundant hydroxyl groups on the surface of LDHs,they are prone to self aggregation and stacking during synthesis.The heavily stacked LDHs have large mass transfer resistance during adsorption and catalysis,and less active site are exposed,which limits the application of LDHs.In response to the above issues,this work employed template method to construct two different forms of Mg based LDHs,which exhibit excellent heavy metal adsorption and fixation abilities in both water and soil.The research content of this article is as follows:1.Use MIL-101（Fe）with a large specific surface area and high porosity as a template,and partially etch MIL-101（Fe）with an additional alkali source.Then the added Mg²⁺and the etched released Fe³⁺coprecipitation on the surface of MIL-101（Fe）to generate MgFe-LDH,and successfully constructed MIL-101（Fe）@MgFe-LDH three-dimensional hierarchical functional material.Subsequently,a systematic study was conducted on the adsorption behavior and mechanism of heavy metals Pb²⁺,Cd²⁺,Cu²⁺and Ni²⁺by MIL-101（Fe）@MgFe-LDH in solution.The results showed that MIL-101（Fe）@MgFe-LDH had excellent adsorption capacities for Pb²⁺,Cd²⁺,Cu²⁺and Ni²⁺ions,reaching1408.57 mg g^-1,568.18 mg g^-1,366.30 mg g^-1and 152.91 mg g^-1,respectively.The excellent adsorption performance of MIL-101（Fe）@MgFe-LDH for Pb²⁺and Cd²⁺ions is attributed to the interlayer anion adsorption of MgFe-LDH and the excellent porosity of MIL-101（Fe）@MgFe-LDH.For Cu²⁺and Ni²⁺,the three-dimensional structure of MIL-101（Fe）@MgFe-LDH increases the isomorphic substitution sites of MgFe-LDH.Moreover,the results of MIL-101（Fe）@MgFe-LDH in column leaching experiments indicate that it has excellent performance in fixing heavy metal ions in actual soil adsorption.2.Using Fe₃O₄as the core,Fe₃O₄@Mg Al-LDH magnetic nano adsorbent with core-shell structure was synthesized by in-situ growth of Mg Al-LDH on the surface of Fe₃O₄by adding Mg²⁺and Al³⁺.The structure of the adsorbent was characterized by means of SEM,XRD,and EDS et.al.Subsequently,we studied the performance and mechanism of the magnetic nano adsorbent adsorption of heavy metals Cd²⁺,Cu²⁺,and Ni²⁺in solution.The results indicate that the magnetic adsorbent conforms to Langmuir and pseudo second-order adsorption models,and its theoretical maximum saturated adsorption capacities for heavy metals Cd²⁺,Cu²⁺,and Ni²⁺are 152.67 mg g^-1,86.96 mg g^-1,and 76.81 mg g^-1.Furthermore,a column leaching experiment was designed to investigate the adsorption performance of Fe₃O₄@Mg Al-LDH for heavy metal ions in soil by simulating actual rainfall.The results indicate that the magnetic adsorbent has a good fixation effect on heavy metals in actual soil environments,and can be separated and recovered after adsorption is completed.