Preparation Of Nitrogen-Containing Graphene Oxide Composites And Their Adsorption Properties For Rare Earth Elements

With the fast development of industries,the increasing dependent in rare earth elements（REEs）is becoming more apparent.However,with the rapid increasing utilization of REE resources,the discharge of industrial wastewater containing REEs is also gradually increasing,causing serious ecological damage and water pollution.Moreover,REEs-containing wastewater will inevitably cause potential risks to human health.The reasonable treatment of REE-containing wastewater and recycling REEs has become a hot topic recently.To recover REEs from aqueous solutions,we attempt to construct novel graphene oxide（GO）-based composites.Nitrogen-containing graphene oxide composites with adsorption selectivity were prepared by introducing nitrogen-containing aromatic heterocyclic organic molecules as nitrogen sources and adjusting the types and numbers of surface functional groups.The structural morphologies,chemical compositions and elemental distributions of the composites before-and after-adsorption were characterized,and the interaction mechanism between the adsorbent and rare earth ions(REE³⁺)was elucidated.The main research contents are as follows:（1）Underappropriatehydrothermalconditions,N-benzyloxycarnylglycine（ZG）was non-covalently attached to GO through hydrogen bonding andπ-πstacking interactions.The construction of three-dimensional（3D）GO-ZG_x:ycomposites with different GO-to-ZG mass ratios was implemented.GO-ZG_x:ycomposites were easy to be separated from aqueous solution and possessed good stability.The characterization GO-ZG_{2:1/6h/120°C}composite by SEM,AFM,HR-TEM,XPS,FT-IR and other methods,confirming that the existence of surface functional groups such as-COOH,-OH and N-containing groups such as C-N and N-H,which could provide more active sites for adsorption of REE³⁺.The adsorption properties of GO-ZG_{2:1/6h/120°C}composite for REE³⁺in aqueous solution were systematically studied and the conditional parameters were optimized.GO-ZG_{2:1/6h/120°C}composite exhibited excellent reusability after 10 consecutive adsorption/desorption experiments.（2）To further enhance adsorption selectivity and stability of GO-based composites,a facile one-step amidation was carried out to introduceanitrogen-containingheterocycliccompound,4-（1,2,4-triazole-1-yl）aniline（TYA）,which possesses electron-rich and electron-poor areas to GO.The novel GO-TYA composite exhibited adsorption selectivity for REES and reduced dispersibility in aqueous solution.GO-TYA composite possessed excellent adsorption selectivity for Nd³⁺,which was 8.80,15.96,20.03 and 20.49 times of the adsorption capacities for La³⁺,Yb³⁺,Sm³⁺and Eu³⁺,respectively.GO-TYA composite pre-and post-adsorption of Nd³⁺were characterized by SEM,FT-IR and XPS.The adsorption mechanism was proposed,and the ion exchange and surface complexation might dominate the adsorption.GO-TYA composite retained high adsorption capacity and removal rate for Nd³⁺after 10 cycles of successive adsorption/desorption operations,indicating that GO-TYA composite was relatively more stable,further guaranteeing that GO-TYA composite could be used as a sustainable adsorbent for removal and recovery of REEs from aqueous solution.