| Precious metals are very important resources in human industrial production and life because of their unique physical and chemical characteristics.With the development of industrial technology,precious metals are becoming scarcer.So,it is very important to recover precious metals from secondary resources.At present,adsorption is considered to be the most powerful means for the enrichment and separation of noble metal ions.In this paper,three new MOFs adsorbents were prepared for the enrichment and separation of noble metal ions.The influences of pH,reaction time,initial ion concentration and reproducibility were studied.The adsorption behavior and mechanism were studied by adsorption kinetics and isotherm.The main research contents are as follows:（1）Preparation of three new MOFs adsorbents:（1）Pd（II）adsorbent（UIO-66-PEA）was prepared by modifying UIO-66-NH2 with homophthallic acid;（2）An Au（Ⅲ）adsorbent（UIO-66-ATU）was synthesized by modifying UIO-66-NH2 with thiosemicarbamide.（3）An Au（Ⅲ）adsorbent（ZT-MOFs）was synthesized by using tripolythiocyanate as an organic ligand.The three adsorbents were characterized by means of FESEM,XPS,FT-IR and XPS.（2）The effects of pH,adsorption time,initial concentration of metal ions,repetition times and interference ions on the adsorption performance were studied.The maximum adsorption capacity of UIO-66-PEA on Pd（II）was 226.1mg/g when pH=2.0and adsorption time was 300 min.The maximum adsorption capacity of UIO-66-ATU for Au（Ⅲ）was 227.68 mg/g when the pH was 3.0 and the adsorption time was24h.The maximum adsorption capacity of Zt-MOFs for Au（Ⅲ）was 333.34 mg/g when pH=7.0 and adsorption time was 480 min.All three kinds of MOFs adsorbents have good repeatability and selectivity..（3）Adsorption kinetics and adsorption isotherm were used to study the adsorption behavior.The adsorption process of the three MOFs adsorbents to noble metal ions conforms to the pseudo-second-order kinetic model,which belongs to chemisorption.The isotherm model for the adsorption of Pd（II）by UIO-66-PEA and Au（Ⅲ）by ZT-MOFs is consistent with Freundlich model,indicating that the adsorption process of the two adsorbents is heterogeneous and multi-layer adsorption process.The adsorption isotherm model of Au（Ⅲ）by UIO-66-ATU conforms to Langmuir model,indicating that the adsorption process belongs to monolayer homogeneous adsorption.（4）The adsorption mechanism of three adsorbents for noble metal ions was studied by means of XPS and Zeta potential.Chelation plays a dominant role in adsorption process.In addition,the adsorption of Pd（II）by UIO-66-PEA and the adsorption of Au（Ⅲ）by UIO-66-ATU also had an ion exchange effect.In summary,three kinds of MOFs adsorbents with large adsorption capacity and can be reused for enrichment and separation of noble metal ions were prepared.The adsorbents prepared in this paper have broad prospects in the enrichment and separation of noble metal ions. |
