Synthesis Of Iron-Based Metal-Organic Frameworks And Their Catalytic Performance In Phenol Degradation

Metal-organic frameworks(MOFs),which are also called porous coordination polymers(PCPs),are a new class of molecular sieve materials composed of metal ions or metal oxide clusters coordinated by organic linkers to form highly regular porous networks.MOFs first came to our attention due to their permanent porosities and ultrahigh surface areas,which was considered to be advantageous for high-capacity gas storage.Owing to their high adjustability in both pore apertures and functionality,MOFs have offered unprecedented opportunities for efficient gas storage,gas separation,drug delivery,catalysis,and so on.This dissertation focused on the synthesis of iron-containing MOF catalysts(Fe(BDC)(DMF,F))and investigation of their performance in assisting phenol degradation.Increasing Fe(II)/Fe(III)ratio and introducing proper complementary metal ions in the MOF framework were found to be essential for catalytic performance improvement of Fe(BDC)(DMF,F).Main results are summarized as follows:(1)Agitation favored the formation of Fe(BDC)(DMF,F)catalyst.With the increase of crystallization hours,concentration,and HF addition,the obtained samples present a typical Fe(BDC)(DMF,F)structure,which contained Fe(II)and Fe(III)simultaneously.However,MIL-53(Fe)was favorably formed by reducing the crystallization time,concentration,and HF addition,which just included Fe(III)in its framework.Through adjusting the above factors,the highest content of Fe(II)was 20.8%,which was achieved in the sample prepared under agitation for 3 days.At 35 ? and pH 6.2,this sample performed favorable catalytic activity.(2)Increasing n(FeCl2)/n(FeCl3)ratio in the precursor solution was beneficial for increasing Fe(II)/Fe(III)ratio in the Fe-MOF materials.From FeCl3 to FeCl2,the structures of the synthesized samples transformed from MIL-53(Fe)to Fe(BDC)(DMF,F).Along with this structure transformation,the crystal morphology,went through a striking change from small irregular shape to big triangular prism.The catalytic behavior of these iron-containing MOFs was tested in the phenol degradation with hydrogen peroxide as oxidant at near neutral pH,35?.The degradation efficiency of these samples increased gradually from MIL-53(Fe)to Fe(BDC)(DMF,F).77Fe Mossbauer spectra revealed that Fe(II)and Fe(III)coexisted in the Fe(BDC)(DMF,F)framework,and the highest amount of Fe(II)in the sample prepared with mixed FeCl3 and FeC12 was up to 26.0%.The result illustrated that the amount of Fe(II)in the samples can be controlled by using varied n(FeCl3)/n(FeCl2)in the feed.The diverse amount of Fe(II)in this series of Fe-MOF materials exactly explained the distinction of reaction efficiency.The iron leaching tests,structures of the fresh and used catalysts,and the data of the recycling runs showed that the Fe-containing MOFs were stable in this liquid-phase reaction.(3)Complementary metal ions had been successfully introduced in the Fe(BDC)(DMF,F)framework.Moreover,the incorporation of Mn positively influenced the catalytic performance due to a cooperative effect.Partial isomorphic substitution of iron in the Fe(BDC)(DMF,F)framework by manganese,cobalt,and nickel was described for the first time.Specifically,different amounts of Mn,Co and Ni have been incorporated into the Fe-based framework during facile crystallization procedures.The catalytic performance of these materials was examined in liquid-phase degradation of phenol at mild conditions.Results present that the degradation efficiency can be evidently improved by the incorporation of Mn,while it can be inhibited by the incorporation of Ni.The incorporation of Co showed no remarkable influence on the degradation process.The reasons for this different catalytic activity were that Mn and Fe had synergetic effects,Ni was inbitory in the efficient decomposition of H2O2,and the contents of Co were quite low in the Fe/Co-MOFs samples.Moreover,the ratios of n(Fe)/n(Mn)in the bimetallic Fe/Mn-MOFs had strong impacts on the degradation process.The stability and reusability of these catalysts were also demonstrated in this study.The bimetallic Fe/Mn-MOF-71 showed excellent catalytic performance.