Efficient Adsorption Of Lanthanum And Lutetium Based On ZIF-8 Composite/Derivative Materials

Rare earths as raw materials play a key role in the research and development of many high-tech products,especially in the field of new materials,aerospace,military defense and other areas of particular importance.As far as the strategic resource of rare earths is concerned,China has great advantages in the world.However,in recent years,the amount of rare earth mining in China has been increasing year by year,and the vicious development of rare earth industry over the years has led to the over-exploitation of resources and the loss of many low concentration of rare earths in the tailing sludge to the surrounding water system,which not only causes waste of resources but also pollutes the environment.Therefore,the enrichment and recovery of low concentration rare earth ions from secondary resources such as wastewater has become an important research direction to achieve high quality utilization of rare earth resources,and adsorption method is one of the best methods to enrich and recover rare earth elements because of its multiple advantages.In this work,ZIF-8 nanomaterials and ZIF-8-derived carbon materials were studied.Since these two materials suffer from easy agglomeration,difficult separation,weak dispersion due to large amount of void space and poor adsorption effect in adsorption studies,three adsorption materials were obtained by in situ growth method in combination with other substrates or by functionalization of their material surfaces.The successful preparation of the materials was confirmed by FT-IR,XRD,SEM,TGA,BET,Raman,and XPS characterization methods.The adsorption performance of the three adsorbent materials was investigated under various conditions using lanthanum（Ⅲ）and lutetium（Ⅲ）as adsorbents,and the adsorption types and mechanisms of the adsorbent materials were analyzed,and finally the regenerative use performance and the selective performance of the adsorbents were investigated.The details are as follows:（1）ZIF-8@GO composites were synthesized by a simple and rapid in situ growth method using graphene oxide as a substrate and methanol as a solvent at room temperature.Lanthanum（Ⅲ）was used as the adsorbent to study the adsorption properties of ZIF-8,GO and ZIF-8@GO composites on La³⁺.The results showed that the adsorption performance of the ZIF-8@GO composites was improved compared with that of the single GO material and ZIF-8 material,which were 3 and 1.27 times higher than those of the GO and ZIF-8 materials,respectively.The adsorption process is consistent with the PSO model and Langmuir model,which are spontaneous heat absorption processes,and the composites have good regeneration performance.（2）Using ethanol and water as a mixed solution as a solvent,the substrate g-C₃N₄and Fe₃O₄ were composited into a magnetic graphitic carbon nitride material by an alcohol-thermal method,and then ZIF-8 was grown in-situ in the aqueous phase at room temperature to form a ternary composite.Material g-C₃N₄/Fe₃O₄@ZIF-8.Using lanthanum（Ⅲ）as the adsorbate,the adsorption properties of the adsorbent for La³⁺were studied.The results show that under the optimal conditions,the adsorption capacity of g-C₃N₄/Fe₃O₄@ZIF-8 composite is 176.68 mg/g and the adsorption rate is as high as88.34%,which is much higher than that of ZIF-8 and g-C₃N₄/Fe₃O₄ materials.From the analysis of experimental data,the adsorption process can be described by the PSO model and the Langmuir model.（3）Highly ordered ZIF-8-derived carbon material NPC@ZnO was obtained by high-temperature pyrolysis under N₂ atmosphere using ZIF-8 as a sacrificial template,and P-NPC@ZnO was successfully introduced by surface modification with phosphoric acid treatment.The adsorption of Lu³⁺by P-NPC@ZnO and the control NPC@ZnO was studied using lutetium（Ⅲ）as the adsorbent.performance.The results showed that the adsorption performance of P-NPC@ZnO material on Lu³⁺was significant under the optimal conditions,and the maximum adsorption amount could reach 230.21 mg/g,which was twice as much as that of NPC@ZnO material.Fitting the experimental data shows that the rate-limiting step is controlled by surface adsorption and lutetium（Ⅲ）forms a single molecular layer adsorption with the adsorption sites on the surface of the adsorbent material.The P-NPC@ZnO material has good stability and regeneration performance and is selective for lutetium ions.