Synthesis And Adsorption Properties Of Organic-inorganic Hybrid Materials Based On Dawson-type Polyoxometalates

With the rapid social and industrial development,the applications of dyes are becoming more and more widespread,its pollution has become the important environmental problem,therefore,it is urgent and necessary to find a suitable treatment strategy.So far,adsorption technology is one of an effective method of solving the environmental problem.With the rapid development of materials science and polyoxometalates?POMs?,organic-inorganic hybrid materials,based on Dawsontype polyoxometalates,have promising applications and widely used in many areas due to its rigidity of inorganic materials,the flexible of organic materials and the strongly acidic and structural diversity of heteropolyacid,especially its application in the field of adsorption receives much attention,in recent years.At this thesis,Dawson-type polyoxometalates,transition metal ion and organic ligand 2,2?-bipyridine were chosen as materials to synthesize organic-inorganic hybrid materials to explore its liquid-phase adsorption performance as methylene blue?MB?the target dye.In Chapter 2,POMs framework [Co?2,2?-bipy?3]3(P₂W₁₈O₆₂)were synthesized from reactions of Dawson-type phosphotungstic acid with CoCl2�6H2O and 2,2?-bipyridine by the hydrothermal method,and characterized by FT-IR,EDS,TG and BET,showed the hybrid materials have good thermal stability and big surface area.The experimental effect factors of the MB adsorption onto [Co?2,2?-bipy?3]3(P₂W₁₈O₆₂)were systematically explored,the result indicated that the watersoluble of [Co?2,2?-bipy?₃]Cl₂�5.5H2 O could be effectively overcame,and it could be used to liquid adsorption,the maximum uptake capacity of the composite was 80.97mg/g after composite with the phosphotungstic acid,the results also showed that the alkaline condition and higher temperature benefited MB adsorption.In Chapter 3,[Cu?2,2?-bipy?3]3(P₂W₁₈O₆₂)was synthesized by the facile chemical coprecipitation method as Cu was the metal ion.The results of the absorption experiment showed that the lower pH and higher temperature benefited MB adsorption,and from the experiment data,the adsorption process fitted by the Langmuir isotherm and kinetic?pseudo-sencond-order?model,respectively.Theadsorption was a spontaneous and exothermic process??G < 0,?H > 0?.Besides,this adsorbent towards other cationic dyes such as methylene blue and rhodamine B had good adsorption properties.Hybrid materials were prepared as the cobalt and copper was metal ion and Dawson-type phosphotungstic acid was material,found that the composite materials have better liquid phase adsorption performance of MB.In order to study the adsorption property of the composite based on other Dawson-type polyoxometalates and organic-inorganic complexes,in Chapter 4,the different types of Dawson type heteropoly acid and [Ni?2,2?-bipy?₃]Cl₂�5.5H2 O were investigated to synthesize the organic-inorganic hybrid materials [Ni?2,2?-bipy?3]3(P₂W₁₈O₆₂),[Ni?2,2?-bipy?3]3?P2Mo18O62?and [Ni?2,2?-bipy?3]3(P₂W₉Mo₉O₆₂)by chemical coprecipitation method and to expore their adsorption properties.The results showed that the three compounds thermal stability were could be greatly improved after that composition,and the surface area were larger than polyoxometalates,and the maximum adsorption capacity could reach 172.71,245.10 and 149.92 mg/g,respectively.It was suggested that the adsorption ability had been enhanced after composition.From the experiment datas,the three adsorption process fitted by Langmuir isotherm as well as kinetic?pseudo-sencond-order?model,and were spontaneous and exothermic towards MB,they also had good adsorption properties to cationic dyes.These results showed that organic-inorganic hybrid material was a quite promising strategy to handle this problem.