Based On Fluoride Carboxylic Acid Ligands To Construct Highly Stable MOF And The Adsorption Research Of Gold Ions

Metal-organic frameworks（MOFs）possess large specific surface areas and tunable pore structures,which make them potentially useful in many fields.As a porous material,in order to be widely used in practice,the MOFs need to have good hydrothermal stability.More and more MOF materials have been reported,but only a few materials can withstand a period of heating after removal of the guest or end-group-coordinated solvent molecules,and some even collapse at room temperature.The hydrothermal stability of porous materials plays an important role in industrial chemical processing.Fluorinated ligands can greatly improve the thermal and hydrothermal stability of organic ligands.Therefore,stable MOF materials can be obtained by using fluorine-containing ligands.On the one hand,the stability of porous materials constructed with fluorine-containing ligands against light and oxidants will be greatly enhanced.On the other hand,the channel fluorination of MOF materials can enhance the channel hydrophobicity,making it have good water stability.Based on the above background,this thesis selected three organic ligands of tetrafluorophthalic acid,2,2-bis（4-carboxyphenyl）hexafluoropropane and 4,4-（hexafluoroisopropene）diphthalic acid,respectively with 1,2,4-triazole and Cr（NO₃）₃·9H₂O for solvothermal reaction.Tfpa-Cr-TA,H₂hfdc-Cr-TA and H₄hfpd-Cr-TA were prepared to recover Au（Ⅲ）.For recovery of Au（Ⅲ）.Through the characterization of MOFs,adsorption performance and adsorption mechanism,the following main conclusions are obtained:1.A new MOF material Tfpa-Cr-TA was synthesized by solvothermal reaction of Cr（NO₃）₃·9H₂O,1,2,4-triazoles and tetrafluoro-phthalic acid,which was used to recover Au（Ⅲ）from aqueous solution.In the synthesis process of Tfpa-Cr-TA,the solvents used are water and isopropanol,which is different from the DMF solvent synthesis commonly used in the previous solvothermal method.It greatly improves the environmental protection.The experimental results show that Tfpa-Cr-TA didn’t dissolve even after being placed in an acidic solution for a long time.Also,it could accurately capture and 100%adsorb Au（Ⅲ）at low concentrations in a complex environment.After three desorption and adsorption experiments,the adsorption performance of Tfpa-Cr-TA for Au（Ⅲ）did not decrease.Tfpa-Cr-TA’s maximum adsorption capacity reached 156 mg/g.The main adsorption mechanism was electrostatic attraction and coordination.2.Cr（NO₃）₃·9H₂O,1,2,4-triazoles and 2,2-bis（4-carboxyphenyl）hexafluoropropane were used as raw materials for solvothermal reaction to synthesize a novel MOF material H₂hfdc-Cr-TA for recovery of Au（Ⅲ）in aqueous solution.Based on the research of the previous material,H₂hfdc-Cr-TA maintains good selectivity,but further improves the acid-base stability.It can adsorb 100%of Au（Ⅲ）with low concentration in water,and the maximum adsorption capacity is 270 mg/g.During the adsorption process,Au（Ⅲ）was reduced to Au（0）,which was then attached to the surface of H₂hfdc-Cr-TA material.The adsorption mechanism included partial reduction.And the adsorption performance of the material for Au（Ⅲ）did not decrease after five desorption adsorption experiments.3.Solvothermal reaction of 4,4-（hexafluoroisopropene）diphthalic acid,Cr（NO₃）₃·9H₂O and1,2,4-triazole to synthesize H₄hfpd-Cr-TA material for recycling Au（Ⅲ）in aqueous solution.The experimental results show that H₄hfpd-Cr-TA has an excellent fast adsorption effect on Au（Ⅲ）and good stability.The complete adsorption time at low concentration is 20min and 1min,respectively.The optimum p H value is 1.60,the total adsorption rate is mainly determined by the liquid membrane diffusion step,and it has an excellent affinity for Au（Ⅲ）.The adsorption isotherm conformed to the Langmuir model,and the adsorption process was an endothermic spontaneous process.The adsorption performance of the material for Au（Ⅲ）did not decrease after five desorption-adsorption experiments.