Pillared-layer Metal-organic Frameworks (mofs) As Photocatalysts For Degradation Of Dyes

Metal-Organic Frameworks (MOFs) are highly crystalline and porous materials. In thisrnthesis, three sets of work have been undertaken. The first two involve the synthesis andrncharacterization of pillared-layer MOFs and the third is a study of the photodegradationrnapplication of selected pillared-layer MOFs in the textile wastewater treatment sector.rnIn the first work, three pillared-layer Metal-Organic Frameworks (MOFs) werernsynthesized at room temperature in water/methanol mixed solvents and fully characterized.rnFumaric acid was converted to its sodium fumarate salt and used as a linker to form MOFsrnin combination with the pillar, 4, 4’-bipyridine. The powder x-ray diffraction (PXRD) ofrntwo MOFs were found to be in good agreement with simulated diffractograms from singlerncrystal data of related MOFs made at higher temperature using DMF as solvent. The studyrnshowed that room temperature synthesis (of such pillared-layer MOFs) could producernmesoporous MOFs in less toxic solvents. This could be an attractive approach to obtainrnMOFs in a greener way and will increase the applicability. Even though single crystalsrncouldn’t be obtained from all three newly prepared MOFs, quantitative amounts of MOFsrncould be obtained. Determination of the optical band gaps using Tauc plots revealed thatrn{[Ni2(Ox)2(BPY)]•3.75H2O}n is photo responsive in the visible region, whereasrnrn{[Zn2(Fu)2(BPY)]•1.5H2O}n and {[Cu2(Fu)2(BPY)]•H2O}n are responsive in the UVrnregion.rnEncouraged by the first set of the work, Zn (II) and Cu (II) based pillared-layer MOFs fromrnsodium oxalate linker (and also 2-aminotherephtalate) and 4,4’-bipyridine pillar inrnwater/methanol mixed solvents were synthesized at room temperature and characterized.rnPowdered MOFs were obtained and their crystallinity was studied using PXRD techniques.rnDICVOL06 in Expo2014 software was used to index PXRD patterns of the MOFs and itrnwas possible to have crystal parameters. All the MOFs obtained have porosities in thernmesoporous region. The optical band gap measurements showed that thern{[Zn2(ATA)2(BPY)]•H2O}n is active in the visible region whereasrn{[Zn2(Ox)2(BPY)]•3.5H2O}n and {[Cu2(Ox)2(BPY)]•0.5H2O}n are active in the UVrnregion. Magnetic property studies of the Cu and Ni-based MOFs revealed that there arernlong range cooperative spin exchange interactions between paramagnetic metal ionsrnthrough diamagnetic units implying that the MOFs behaved as low dimensional magneticrnmaterials.rnIn the last sets of the work, the photocatalytic performance of one of the pillared-layerrnMOF, {[Cu2(Fu)2(BPY)]•H2O}n, has been studied in detail towards degradation of methylrnorange as a model dye, which is toxic, nonbiodegradable, and discharged to thernenvironment through wastewater by textile industries. The degradation of this model dyernwas investigated with UV radiation in the presence of the semiconducting MOF,rn{[Cu2(Fu)2(BPY)]•H2O}n. The optimized conditions for the photodegradation efficiencyrnof the MOF were achieved after considering the effect of pH, and MOF loading at a fixedrndye concentration. 96 % of the 10-ppm methyl orange is photodegraded with 0.25 g/Lrnrnloading of the photocatalyst at pH 5.2 in 140 min of irradiation time. The photocatalystrnwas recycled five times with a 96 %, 88 %, 87 %, 80% and 53 % degradation efficiencies.rnThe PXRD analysis of the recycled photocatalyst showed that the crystallinity of the MOFrnis maintained in the five runs.

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