Study On The Preparation And Organic Dyes Adsorption/Separation Performance Of Anionic Metal-Organic Frameworks

Water is an indispensable resource for the progress and development of human society,but with the development of society,water environment has been seriously damaged.Water pollution is mainly caused by the waste water from industrial production,among which organic pollutants are the most important components of the waste water.At present,the existing water pollution treatment technology mainly includes membrane separation technology,oxidation treatment method,electrochemical method and adsorption method.Membrane separation,oxidation treatment and electrochemical treatment are associated with low efficiency,high cost and secondary pollution.Compared to other methods,adsorption method is simple to operate and friendly to the environment.However,currently commonly used adsorption materials such as zeolite and activated carbon have low adsorption efficiency and are difficult to have selective adsorption for different pollutants.As a new type of adsorbent,Metal-Organic Frameworks has large pore size.It can select and adsorb different charged pollutant molecules,so it has a good development prospect.In this paper,anionic metal-organic frameworks: TPHC-Cu,TPHC-In and TPTC-In was synthesized respectively.Different adsorption effects of different cationic organic dyes were realized.?1?A kind of anionic metal-organic framework with uncoordinated-COOH in pore channel was synthesized by using the organic compound with six carboxylic acids as organic ligand and Cu²⁺ as metal node.The single crystal X-ray diffraction shows that TPHC-Cu is R-3m space group,the crystal system is trigonal,it is Nb O topological space structure.It has two types of pore structure,among which the diameter of the hole is 9.4× 22 ??? in the shape of spindle-shape cage,and the diameter of the hole is 10 ??? in the shape of spherical cage.Because of the appropriate diameter of the pore and the uncoordinated-COOH in the pore TPHC-Cu has a good adsorption effect on cationic dye methylene blue.In the dye aqueous solution with 5 m L concentration of 4×10-5 M,the residual methylene blue content in the solution after adsorption for 12 h is about 2.27%,the methyl violet content is about 30.66%,and the residual dye content in rhodamine B and rhodamine 6G solutions are 86.30% and 76.49%.For the anionic dye methyl orange,because its charge is the same as TPHC-Cu,the remaining dye molecules in the solution after adsorption for 12 hours is about 92.45%.The selective adsorption effect of TPHC-Cu on methylene blue in the competitive adsorption experiment of mixed solution also reflects its separation ability of mixed dye.?2?A kind of anionic metal-organic framework TPHC-In with uncoordinated-COOH in pore channel was synthesized.The same organic ligand as TPHC-Cu was used and took In3+ as the metal node.The single crystal X-ray diffraction shows that TPHC-In is a P4?2?/nnm space group,the crystal system is tetragonal.The approximate diameter of the channel is 6.6 ???.In the 5 m L dye solution with a concentration of 4×10-5 M,the adsorption of TPHC-In on methylene blue in the solution can reach 100% after adsorpted for 5 h,and the residual contents of methyl violet,brilliant green,rhodamine B and rhodamine 6G In the solution after adsorption for 12 h are about 23.45%,60%,79.63% and 70.64%,respectively.For methyl orange solution,the residual dye content in the solution after 12 h adsorpted of TPHC-In is 72.02%,indicating that the adsorption capacity of TPHC-In for anionic dye is bad.At the same time,it was concluded that TPHC-In could adsorb and separate methylene blue from mixed dyes by competitive adsorption experiments.?3?A kind of anionic metal-organic framework TPTC-In with-NH2 in the pore channel was synthesized by using organic compound with four carboxylic acids as the organic ligand and In3+as the metal node.The single crystal X-ray diffraction shows that TPTC-In is a Cmmm space group,the crystal system is orthorhombic.The organic ligand and In3+are connected by the coordination bond to form a frame structure.This structure contains two types of channels,square and rectangle,in which the diameter of the square channel is 6.8???,and the length and width of one rectangular channel are 11???and 6.8???respectively,and the length and width of the other are 7.4???and 6.8???respectively.Because of its large channel size,it is speculated that it has excellent adsorption property for cationic dyes with large molecular weight.For the cationic dye methylene blue,the adsorption of TPTC-In can reach 100%after 8 h adsorption.For methyl violet and brilliant green solutions,TPTC-In achieves complete adsorption after 7 h.For rhodamine 6G,TPTC-In also achieves complete adsorption after 12 h of adsorption.It indicated that the adsorption of TPTC-In on 5 m L 4×10-5 M methyl violet,brilliant green,rhodamine 6G solution could reach 100%.