Study On Removal Of Perchlorate From Aqueous Phase By Cationic Metal-Organic Frameworks (MOFs) Based On Sulfonic Group

Perchlorate ion is a kind of inorganic anion with tetrahedral structure,which containing four oxygen atoms and a chlorine atom.The chlorine atom is in the center of tetrahedron?Cl??.The major source of perchlorate in environment is rocket fuel,firework,rubber product and so on.Due to its special physicochemical properties such as highly solubility,kinetic inertness and non-volatility,it was difficult to remove perchlorate from water effectively and cheaply.In fact,excessive perchlorate intake can hamper the adsorption of iodine ion,interfere with the synthesis and secretion of thyroid hormones,which directly affect on a normal metabolism and causing stunted growth and abnormal decreases in brain development,particularly for children and pregnant woman.Therefore,for the sake of environment and human beings,this problem should be solved as soon as possible.Metal organic frameworks?MOFs?,as a new type of porous material with regular net works contain both metal atom and inorganic moietie linked by coordination bonding.Due to its special physicochemical properties,it was widely used in energy gas adsorption,separation and catalysis,and environmental pollutions removal.As the production of synthesis technology development of MOFs,the cationic MOFs have more advantages on environmental protection field.Thus,Cationic MOFs might be promising candidate for removal of perchlorate anion in aqueous phase.The main contents of this paper include: Firstly,Two kinds of novel cationic MOFs such as ?,?-ethanedisulfonic-Cu-?4,4'-bipy?2?ESC?and amino sulfonic-Cu-?4,4'-bipy?2?ASC?,were synthesized to remove perchlorate anion in aqueous phase.In order to analysis physical and chemical properties and crystal structure of both materials,associated with some modern characterization techniques.Secondly,evaluating the ability of both materials to remove perchlorate anion from aqueous phase,the adsorption process was demonstrated by kinetics and isotherm model.Meanwhile,the potential reaction mechanisms were investigated by comparing the characteristics of both materials before and after reaction.Thirdly,to figure out the selective mechanism of perchlorate ion on ASC and ESC,a series of explored experiments were conducted in various anions coexisting solution.Similarly,the potential selective mechanism was analyzed by comparing the characteristics of both materials before and after reaction.Finally,tentative exploration on regeneration was carried out.The results of research have shown that both of cationic MOFs were established by sulfonic acid groups linking together with 1D Cu-4,4-bipyridyl chains under solvothermal conditions.The topological surface and crystal structures were revealed in scanning electron microscope-energy dispersive analysis?SEM-EDS?,Fourier transform infrared spectrometer?FTIR?and X-ray diffraction?XRD?suggested that both materials were triclinic system with regular layer structure.Meanwhile,the ASC and ESC have shown good performance on adsorption capacity in perchlorate removal.An adsorption dosage of 2.0g/L was selected as optimum dosage.The perchlorate could be removed effectively over a broad range of p H value?from 2 to 11?at room temperature.The removal rate of perchlorate ion onto ASC and ESC reached about 98% and 80%,respectively.The adsorption capacity of perchlorate and phosphate ion on ASC was higher than that of ESC,and the amino group contained in sulfonic acid ligand of ASC might provided more sites for tetrahedral oxoanion trapping.The perchlorate adsorption on both cationic MOFs can be well described by the pseudo-first-order kinetic model and Langmuir adsorption isotherm.The thermodynamic parameters,negative values of Gibbs free energy and enthalpy,indicated the spontaneous and exothermic nature of the process.The characterizations before and after reaction were demonstrated that the potential mechanisms were the co-effect of electrostatic force and ion-exchange between the perchlorate ions and cationic MOFs,which improved the adsorption capacity greatly.In various anions coexisting solution,only tetrahedral structure oxoanion was trapped effectively by ASC and ESC,and the affinity was found to obey the order of ClO₄^->PO43-.In binary system?ClO₄^-and PO43-?,when the p H value was in a range of 2¹1,the adsorbed amount of phosphate ion first increased slightly and then declined,and the tendency of perchlorate uptake capacity was just the opposite.It was indicated that there was a competitive relationship between ClO₄^-and PO43-.The adsorption process of perchlorate and phosphate ion on ASC and ESC followed the pseudo-first-order model.The adsorption isotherm results were fitted well with Langmuir model.The thermodynamic constants were shown that the adsorption process was spontaneous and exothermic reaction,and relative low temperature was benificial to spontaneity of reaction.The compared results of characterization before and after reaction suggested that the sulfonic acid ligand was very likely replaced by ClO₄^-and PO43-.Regeneration experiment has shown that the organosulfonate solution regeneration method was feasible and efficacious,and the regeneration ability of ASC and ESC were about 80% and 60%,respectively,which demonstrated that water stability is still a chief limiting factor in the development of MOFs.