| Iodine is an essential element for the maintenance of normal metabolism and life activities in the human body and is known as the"element of life"and the"element of wisdom".The iodide ion is usually oxidised to iodine monomers and then recycled,but the oxidation process is slow,the yield is low and the production costs are high.Studies have shown that Keggin-type polyoxometalates are superior in catalyzing the oxidation of iodide ions by hydrogen peroxide,but cannot be recycled due to the water solubility of the polyacid.However,Keggin-type polymetallic oxides have an abundance of oxygen atoms on their surfaces that can coordinate with the metal centres of the coordination compounds and form stable Keggin-type heteropolyacid-modified coordination non-homogeneous catalysts through strong coordination bonds.Based on this property,a series of polyoxometalates were synthesized by hydrothermal coordination polymer and characterized by X-ray single crystal diffraction,IR,XRD,TG,SEM,BET and elemental analysis,it is used as a catalyst to catalyze the oxidation of iodine ions by hydrogen peroxide.The main conclusions are as follows:1.Two novel and rare calix[6]arene-modified Keggin polyoxometalates were synthesized by the reaction of triazole and its derivatives with H3PW12O4and H3PMo12O40 using copper as transition metal source.Both compounds consist of two classical Keggin type polyacid anions,six[Cu（C2H4N4）]+coordination polymer similar to calix[6]arene,the three-dimensional（3D）structure is formed by supramolecular interaction between the components.The results show that the catalytic reaction of 3-atrz-Cu-PW12 with two heterogeneous catalysts for the oxidation of iodine ions by hydrogen peroxide takes only30.25 min to reach the end point,the formation rate of iodine was 6.89×10-7 mol·L-1·s-1,and the catalytic reaction of 3-atrz-Cu-PMo12took only1.85 min to reach the end point.The formation rate of iodine was 1.126×10-5 mol·L-1·s-1,it is 16.34 times of the reaction rate of 3-atrz-Cu-PW12.The catalyst was reused for 9 times and the conversion was still as high as 99.96%,showing excellent catalytic activity and good repeatability,the results show that the mo-containing polyoxometalate-based catalyst has bettercatalyticperformancethantungsten-containing polyoxometalate-based catalyst in the oxidation of iodine ions by hydrogen peroxide.[2(C6H12N12Cu3PW12O40)]3-atrz-Cu-PW12[2(C6H12N12Cu3PMo12O40)]·0.5H2O 3-atrz-Cu-PMo122.Based on the above studies,the catalytic performance of molybdenum-containing polyoxometalate-based catalysts for the oxidation of iodine ion by hydrogen peroxide is much better than that of Keggin-type heteropolytungstate.Using 1,2,4-triazole-3-formic acid as organic component,Cu（CH3COO）2·H2O as transition metal source,Keggin-type heteropoly molybdate-based metal-organic framework compounds were synthesized by one-pot reaction of1,2,4-triazole-3-formic acid with H3PMo12O40 and 1,2,4-triazole by in-situ decarboxylation under hydrothermal conditions.The compound consists of one classical Keggin-type[PMo12O40]3-and two[Cu6Cl0.5（C2H2N3）4]1.5+in a nearly central symmetric manner,and the three-dimensional（3D）structure is formed by supramolecular interaction between the components.The results show that the heterogeneous catalyst has a high reaction rate of 4.55×10-6 mol·L-1·s-1 after 4.58 min in the oxidation of iodine ions by hydrogen peroxide,the rate of iodine formation increased about 551 times.The catalyst was reused for 8 times and the conversion was still as high as 99.6%,showing excellent catalytic activity and good repeatability.[Cu6Cl0.5（C2H2N3）4][PMo12O40][Cu6Cl0.5（C2H2N3）4]trz-Cl-Cu-PMo123.Two cases of POMOFs modified by pyrazine and pyrazine were synthesized from H3PMo12O40,pyrazine with different steric hindrance and 2-aminopyrazine as organic unit and Cu2+as transition metal source.In the two compounds,the molybdenum atom are+6 valence and the copper atom are+1 valence.The Cu+of the two compounds are coordinated with one terminal oxygen atom of two polyacids and one nitrogen atom of two pz in the form of four coordination.The results show that the formation rate of iodine,respectively,when the end point was reached under the catalysis of PZ-Cu-PMo12 and 2-a PZ-Cu-PMo12,the formation rate of iodine was 1.47×10-5 mol·L-1·s-1 and 2.16×10-5mol·L-1·s-1,respectively,the formation rate of iodine was increased by942.31 times and 1384.62 times respectively,and the catalytic rate of2-a PZ-Cu-PMo12 was 1.47 times of that of PZ-Cu-PMo12.After 13 times of repeated use of the two crystal catalysts,the conversion was still as high as 99.97%,the conversionηof the two catalysts is very close to each other at the same reaction time,and the two catalysts have higher conversion under the catalysis of 2-a PZ-Cu-PMo12 than at the same reaction time.2-a PZ-Cu-PMo12 with large specific surface area,pore size and pore volume has good catalytic performance and is a potential excellent catalyst.2[(C12H7N6Cu3)(PMo12O40)]·5H2O PZ-Cu-PMo12[3（C4H5N3Cu）(PMo12O40)]2-a PZ-Cu-PMo12... |
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