Preparation Of Co-MOFs Materials And Removalof Mercury Ions

With the rapid growth of industrial technology,the removal of heavy metal ions in the wastewater of the power plant has grown increasingly important,and the mercury ions have been listed as important contaminants in many international organizations due to the obvious durability,the biological retention and the toxicity.In July 2011,the ministry of environmental protection of China promulgated the"standards for the emission of flue gas from thermal power plants"GB13233-2011,which took mercury as the new control index for the first time.The standard clearly stipulated that from 2015,the concentration limit of mercury and mercury compounds in all coal-fired boilers was 0.03mg·m^-3.As a new type of functional molecular material,MOFs?Metal Organic Framework material?has the characteristics of controllable structure and easy functionalization that other material can't match.In this paper,by trying different preparation conditions and referring to the current more mature preparation methods of several MOFs materials,three new MOFs materials were successfully prepared.The original material was modified with mercaptan,and got successfully the modified MOFs material with excellent ability of mercury removal.Mercury ions in desulphurization wastewater of coal-fired power plants were taken as the research objects and MOFs materials before and after modification were taken as the research objects.The adsorption test of solutions containing mercury ions was conducted.The influences of adsorption time,temperature,initial concentration,initial pH value of solution and other factors on adsorption performance were investigated and the differences in adsorption performance of different materials were compared and analyzed.The adsorption mechanism of the prepared MOFs materials was studied by fitting the thermodynamic,dynamic and isothermal equations of the experimental data.?1?With cobalt ions as metal ions and terephthalic acid and isobenzoic acid as organic ligands,three new MOFs materials with regular microscopic morphology were successfully prepared by solvent thermal method,which were respectively expressed as D-MOFs,F-MOFs and Q-MOFs.-SH was modified on the three prepared materials by stirring at room temperature and were respectively expressed as SH-D-MOFs,SH-F-MOFs and SH-Q-MOFs.?2?Modern analytical techniques?SEM,XRD,EDS,BET,TG and FTIR,etc.?were used to analyze and characterize the morphology,phase,crystal shape and element composition of the materials before and after modification.The results show that the original material has regular microstructure and excellent thermal stability;Cobalt ions were successfully assembled into organic ligands by solvent thermal synthesis.Mercaptan functional groups were successfully introduced by stirring at room temperature.After modification,the thermal stability of the modified material decreased but the specific surface area increased.With the increase of modifier,the microstructure of the material was damaged gradually,but the whole material remained intact.?3?Three raw MOFs materials were tested to find a relatively poor mercury removal capability,but the adsorption capacity was significantly improved upon modification by-SH.SH-D-MOFs materials in mercaptan content of 0.5ml,pH=5.5,T=35?,is the best reaction conditions.The maximum adsorption reached 412.8mg·g^-1;SH-F-MOFs and SH-Q-MOFs materials in-SH added quantity to 1ml,pH=6,T=30?,is the best reaction conditions;The maximum adsorption capacity reached 614 mg·g^-11 and 507.2mg·g^-11 respectively.?4?Thermodynamic,kinetic and isothermal fitting of the experimental data after adsorption showed that the adsorption process of Hg²⁺in the three modified materials conforms to the quasi-secondary kinetic model.The adsorption process is mainly a diffusion process dominated by surface adsorption,and the adsorption process is mainly controlled by the chemical adsorption mechanism.Thermodynamic fitting results show that?G⁰<0,indicating that the adsorption process is a spontaneous process;?H⁰>0,indicating the adsorption process is exothermic reaction;?S⁰>0,indicating that in Hg²⁺adsorption process,solid-liquid surface confusion increased;Through isothermal simulation results show that the material of Hg²⁺adsorption process conforms to the Langmuir model,showed the material to Hg²⁺adsorption belongs to single molecular layer adsorption.