Design,Synthesis Of Metal-Organic Frameworks And Their Performance In Luminescent Sensing And Selective Adsorption Of Metal Ions And Small Molecules

Environmental pollutants such as metal ions,dyes,and organic compounds have become a critical and vicious issue,restricting human development and posing a serious threat to human survival.Therefore,mankind urgently needs to search for cheap,safe,efficient,and reliable ways for the detection and decontamination of such environmental pollutants.To resolve this environmental crisis,the most promising strategies are the photoluminescent detection of invisible contaminants and the adsorptive removal of pollutants via physical or chemical interactions.Recently,metal-organic frameworks（MOFs）comprising of bridging organic ligands and metal ions through coordinate bonds or supramolecular interactions,are extensively used for sensing,adsorption,and removal of toxic metal ions and other chemical pollutants.Particularly,MOFs with luminescent properties such as lanthanide-MOFs（Ln-MOFs）,and transition metal-based MOF materials have gained ample attention due to their possible applications in fluorescent materials,electroluminescent devices,and photoluminescent sensors along with many other applications.Among luminescent MOFs,transition-metal organic frameworks are more cost-effective and possess a lot of interesting characteristics than lanthanide-MOFs.By bearing this in mind,in this dissertation,a variety of modified porous MOFs have been synthesized and applied for the separation of transition metal cations,selective adsorption of organic dyes,and white light emission.Besides,photoluminescent sensing of metal ions,small molecules,nitroaromatic compounds,and fused aromatic hydrocarbons have also been explored.The mechanism involved in sensing and selective adsorption phenomena have been studied in detail.The main points and topics in this dissertation are summarized as follows:1.Transition-MOF-based selective and sensitive detection of trace amounts of metal ions and nitroaromatic compounds in the presence of other interfering analogs is still a challenge due to their electron affinities and absorption capacities,which leads to false responses and poor selectivity for analytes.For this purpose,by using a multi-carboxyl triazine-based ligand,5,5’,5’’-（（1,3,5-triazine-2,4,6-triyl）tris（azanediyl））tris（3-methylbenzoic acid）,a new porous material MOF1 was obtained,which exhibits strong blue luminescence.This framework contains a lot of possible chelating sites for analytes to conquer the desired selectivity.The structural analysis discovered that MOF1 possesses a three-dimensional framework with a monoclinic C2/c space group.Experimental results disclosed that the strong emission of MOF1 can be effectively quenched by traces of copper ions（3 ppm）as well as nitrobenzene（NB）（0.6 ppm）.The detection limits of analytes in this work are much better than the previously reported MOFs,which is triggered by the fact that massive carboxylic O atoms and N atoms are anchored in the framework.Interestingly,MOF1 shows a highly selective and sensitive quenching effect towards nitrobenzene in the vapor phase as well,which is quite rare.The amazing solvatochromic phenomenon of MOF1 is witnessed by incorporating acetonitrile guest molecules due to host-guest interactions provided by the carboxyl groups of ligands and amino triazine backbone.Thus,owing to the highly selective and sensitive quenching effect in fluorescence and solvatochromic behavior,MOF1 can be used as a potential sensor for Cu²⁺,NB,and acetonitrile.2.At present,an important environmental safety concern is the extensive use of mercury-based lighting materials to achieve white light emission.Due to the lethal effects of mercury,it is vital to discover safe alternatives.Keeping this important issue in mind,solvothermal synthesis of a nanoporous triazine-based MOF2 was carried out,by using tricarboxyl ligand,5,5’,5’’-（（1,3,5-triazine-2,4,6-triyl）tris（azanediyl））tris（2-methylbenzoic acid）).Interestingly,MOF2 was found to be a proficient blue light-emitting material with（0.18,0.15）calculated CIE coordinates.MOF2exhibits the property of tunable white light emission by combining three emissions(blue emission from MOF2,green emission from Tb³⁺,and red emission from Eu³⁺)through lanthanide ions encapsulation.These results establish that MOF2 is a potential solid-state light-emitting material with high color quality.Also,owing to the porous nature of MOF2 with potential chelating nitrogen moieties,it can separate cationic dyes by selective adsorption from other organic dyes depending on charge selectivity instead of size selectivity.3.Detection and removal of an excessive amount of copper ions are of great significance for human life.Due to size and charge similarity,transition metal ions could not be selectively adsorbed and separated effectively by only adjusting the pore size of MOFs but it requires some interactions.There are only a few reported MOFs which can selectively adsorb copper ions from other transition metal ions.Hence,upon these considerations,well designed multifunctional MOF1 and MOF2,with suitable channels based on the heterocyclic tricarboxyl triazine ligands L1 and L2,were prepared.These frameworks with abundant N-active sites and carboxylate oxygen groups were applied for the studies of adsorption and extraction of heavy metal ions in DMF.Interestingly,MOF1 can selectively adsorb Cu²⁺ions among other transition metal ions(Mg²⁺,Mn²⁺,Ni²⁺,Co²⁺,Zn²⁺,Fe^2+,and Cr³⁺)with 90.5 mg/g adsorption capacity.Similarly,MOF2 also shows the ability to selectively adsorb and separate Cu²⁺ions from other metal ions.However,selectivity was found to be more in MOF2 as compared to MOF1.Thus,we used MOF2 for column chromatographic separation of metal ions.ICP results showed that copper ions can be completely separated from cobalt,nickel,manganese,and zinc ions after passing through MOF2 based column.These results established that MOF1 and MOF2 are the most promising materials for the adsorption and selective removal of Cu²⁺ions from organic solvents.4.Fused aromatic hydrocarbons（FAHs）are very harmful to the environment and have been studied by some research groups through photoluminescent based detection.However,there are only a few reports on photoluminescence sensing of naphthalene.Therefore,this field still needs exploration.We used N-heterocyclic multi-carboxylic acid ligand,5,5’,5’’-（（1,3,5-triazine-2,4,6-triyl）tris（azanediyl））tris（2-methylbenzoic acid）,and Zn²⁺ions to synthesize MOF3 architecture with nanoporous channels.Due to the suitable porous apertures and hydrophobic conditions,this framework shows enhancement in luminescent intensity by the inclusion of FAH molecules such as naphthalene,anthracene,and phenanthrene.Different degree of enhancement in photoluminescent intensity was observed due to different sizes and conjugation in FAHs which suggest that MOF3 is a potential probe material for recognizing naphthalene,anthracene,and phenanthrene.MOF3 also exhibits the ability to sense the acetone molecule via solvatochromism.5.Since the past few decades,various adsorbents have been developed and used for dye adsorption such as activated carbons.However,these adsorbents have a problem of poor specificity towards dyes,which makes them less effective.Thus,it is the need of time to explore such materials that can selectively adsorb and remove dyes.In this report,we used paddle-shaped BTB as a 3-connected ligand with C3 symmetry and Mn Cl2 to design and synthesize a new Mn-BTB based MOF4 structure having the 3,6-connected network.We have discussed the structural aspects and gas adsorption behaviors.This MOF4 has been found to exhibit the ability to selectively adsorb cationic dyes in the presence of other dyes.