Construction Of Aluminum-based Ldhs Materials By In-situ Growth And Their Adsorption Performance For Cadmium

Cadmium is a heavy metal with high biological toxicity,which mainly pollutes water resources through cadmium-containing waste water produced by non-ferrous metal smelting and electroplating processing,and further enters the food chain thus causing harm to body.When cadmium is absorbed by body,it will lead to reduced immunity,bone softening and cell damage,which will seriously affect human growth and threaten human safety.Cadmium is stable in water and difficult to remove.Therefore,the efficient removal of heavy metal cadmium from water is one of the key concerns in the world today.As a typical two-dimensional layered material,layered double hydroxides（LDHs）possess a variety of adjustable parameters such as metal elements of laminate,metal ratio and interlayer anion species etc.Additionally,the literatures report that LDHs have a significant"super-stable mineralization"effect on various metal ions.Therefore,LDHs exhibit a good application prospect in heavy metal adsorption.However,LDHs possess a small specific surface area,and LDHs are likely to self-aggregation and self-assemble,thus causing a large number of adsorption sites to be buried,which limits the further practical application of LDHs in heavy metal adsorption.To deal with the above problems,two kinds of aluminum-based LDHs functional materials were constructed by in-situ growth strategy in this work,which showed excellent adsorption performance in the adsorption experiments of heavy metal cadmium.The main research of this paper was as follows:1.Construction of MIL-96（Al）@aluminum-based LDHs functional materials by in-situ growth strategy and its performance for heavy metal cadmium adsorption.Using MIL-96（Al）as the template and magnesium nitrate as the magnesium source,MIL-96（Al）@Mg Al-LDH with hierarchical structure was successfully constructed by in-situ growth strategy and hydrothermal method.The effects of magnesium salt concentration,alkali source concentration and solvent compositions on the morphology and crystallization of MIL-96（Al）@Mg Al-LDH were systematically investigated,and the growth process of MIL-96（Al）@Mg Al-LDH was illustrated.The morphology and chemical structure of MIL-96（Al）@Mg Al-LDH were analyzed by XRD,FT-IR,HRTEM,SEM and XPS characterization.The results showed that the Mg Al-LDHs were in-situ grown on the outer surface of the hexagonal structure of MIL-96（Al）.Additionally,MIL-96（Al）@Ni Al-LDH and MIL-96（Al）@Co Al-LDH were successfully prepared by in-situ growth strategy,indicating the excellent universal of synthetic method.MIL-96（Al）@Mg Al-LDH was selected as a representation to investigate its performance in adsorption of heavy metal cadmium.The results showed that the adsorption process of Cd²⁺by MIL-96（Al）@Mg Al-LDH was well fitted into pseudo-first-order kinetic equation and the Langmuir adsorption model.Compared with MIL-96（Al）(q_m=100.232 mg g^?1)and Mg Al-LDH(q_m=83.961 mg g^?1),MIL-96（Al）@Mg Al-LDH exhibited a higher maximum adsorption capacity(q_m=148.947 mg g^?1),which was attributed to the adsorption by CO₃^2?between the Mg Al-LDH layers,unique hierarchical structure and excellent porosity properties of MIL-96（Al）@Mg Al-LDH.2.Construction of magnetic core-shell structure Fe₃O₄@Si O₂@Mg Al-LDH and its performance for heavy metal cadmium adsorption.To deal with the problems of large size of powder adsorbent and difficulty in recycling,the Fe₃O₄@Si O₂@Mg Al-LDH with core-shell structure was constructed by using in-situ growth strategy and double-drop method with magnetic Fe₃O₄ as the core.The morphological and structural characterization of Fe₃O₄@Si O₂@Mg Al-LDH showed that it possessed a core-shell structure with a particle size of ca.400 nm and superparamagnetic properties.In the experiments of the adsorption of Cd²⁺,the adsorption process of Fe₃O₄@Si O₂@Mg Al-LDH was fitted into the pseudo-first-order kinetic equation and Freundlich adsorption model with a K_f value of 62.663 mg^1-n g^?1·L^?n.After the adsorption experiments,the adsorbed products can be quickly separated and recovered by magnetic field.Finally,the adsorption mechanism was proposed by XPS,FT-IR and XRD characterization.