Preparation Of Fluorinated Metal-Organic Polymers And Adsorption Of Au(?)

Precious metals play an important role in all kinds of human activities.However,precious metals not only belong to non-renewable resources,but are face to the problem of scarcity,especially for the less industrial storage of Au and Ag.Due to the fact that the large number of secondary resources are increasing since precious metals are put into use in the industry and life activity during the years,the recycle of precious metals from the secondary resource could realize the idea of changing the electronic waste into treasures as well as alleviating the situation of precious metals scarcity.Nowadays,adsorption is regarded as the most premising method in precious metal recycle for the advantages of easy performance,low cost,being suitable for the low concentration metal adsorption.Therefore,it is significant and valuable for the designing and synthesizing a high-performance adsorbent with fast adsorption rate,high adsorption capacity,selectivity,reusability and easy desorption.Tetrafluoroterephthalonitrile and Cu?NO₃?₂·3H₂O selected as the raw material react with two kinds of N-content group pyridine and imidazole,respectively,to synthesize two novel F-containing metal-organic polymers.The morphologies,surface chemical components and states of the material were analyzed by series relative characterizations.The as-synthesized materials were developed as the high-performance adsorbent for Au?III?recycle from aqueous solutions.The effect of initial p H in solutions,adsorption kinetics,adsorption isotherms,adsorption thermodynamics,adsorption selectivity in mixture metal ions solutions,reusability of the material and the stability of before-and-after adsorption materials were investigated.The potential adsorption mechanisms were studied intensively by combining experimental investigation and series characterization analysis.The specific contents and results of the work are as follows:1. A novel metal-organic polymer?material I?with the raw material containingone N-containing pyridine and Tetrafluoroterephthalonitrile and Cu?NO₃?₂·3H₂O is successfully synthesized by solvothermal reaction and developed as an efficient adsorbent for recycle Au?III?from aqueous solutions.The thermostability,Cu containment,crystallinity of the materials with different solvothermal reaction temperature were characterized and investigated adsorption performance toward Au?III?.Among them,the amorphous material obtained at 140 ^oC with only the suitable amount of Cu has the optimal activity for Au?III?adsorption.Then,spherical morphology,the component of the C,N,O,F,Cu elements and important functional groups retained from raw material?C-F,C=N,C?N?were known by correlative characterizations.In the study of Au?III?adsorption,the material I have an optimal adsorption capacity in p H=4.5 Au?III?solutions.The adsorption ratio can reach up to100%with rapid adsorption rate at low concentration solutions and the maximum adsorption capacity is up to 1317 mg/g.In batch adsorption experiments and flow-through experiments,the material displays excellent selective adsorption of Au?III?in the mixed solution containing Au?III?,Cu?II?,Ni?II?,Zn?II?,and Cd?II?.Besides,the adsorbed Au could be eluted completely by 0.52 mol/L thiourea solution at p H 2.5,and the adsorption capacity of material could maintain,indicating splendid reusability.During the adsorption process,adsorption isotherm fits the Langmuir model and adsorption kinetics can be described by a pseudo-second-order kinetic model.The adsorption mechanism could be attributed to reduce Au?III?to Au?0?according to XPS analysis.2. As pyridine is volatile liquid with low boiling point,low flashing point and large consumption,there might be large dangerous in the synthesis process.Therefore,in order to increase the security of synthesis and decrease environmental pollution and real consumption,the one-N-containing pyridine in material I was replaced by two-N-containing imidazole to synthesize the second F-containing metal-organic polymer?material II?with Tetrafluoroterephthalonitrile and Cu?NO₃?₂·3H₂O in 120 ^oC solvothermal reaction.Material II is the same as the material I,showing the excellent adsorption performance towards Au?III?and wonderfully potential application.The material has a high adsorption capacity for Au?III?removal and the maximum adsorption capacity reached up to 1253 mg/g at 45 ^oC.In low concentration Au?III?solutions?9 mg/L?,Au?III?could be removed rapidly within 7 min.The material displays perfect affinity towards Au?III?and shows 100%adsorption capacity in extreme mixture solutions including 8 mg/L Au?III?and 1200 mg/L Cu?II?,Zn?II?,Co?II?,Cd?II?,Ni?II?.It can recycle selectively Au?III?in multiple competing cations solutions.The adsorbed Au could realize 100%desorption ratio by 0.52 mol/L thiourea solution at p H 2.5,and the adsorption ratio is maintained at a comparatively high level of 92%after three regeneration cycles.By adsorption isotherm study and adsorption kinetics study,Langmuir adsorption isotherm and pseudo-second-order kinetics models could describe the adsorption process,exhibiting chemical adsorption and single-layer adsorption process.Several mechanisms are involved in the adsorption process including redox,complexation mechanism and electrostatic interaction by a series of characterization analysis.