Preparation Of Porous Organic Frameworks And Their Applications In Uranium/Copper Ions Adsorption And Detection

Radioactive and highly chemically toxic uranium is an important element in the nuclear industry.The ocean is a huge potential resource which contains approximately 4.5 billion tons of uranium.So,the detection and extraction of uranium is of great significance for human health and nuclear fuel production.However,the high acidity and high radiation of wastewater,and biological fouling in the ocean are the main challenges currently faced by adsorbents,so it is still necessary to develop adsorbents with high stability and multifunctionality.In addition,copper is widely used in energy,construction,electricity and other fields.Excess copper from industrial waste and domestic sewage in the environment will threaten human health.Therefore,it is important to provide a simple,fast and highly sensitive method for detecting copper ions.Recently,emerging crystalline porous organic framework materials,covalent organic frameworks and metal organic frameworks,have attracted widespread attention due to their excellent chemical stability,designability,and porosity which have broad application prospects in environmental protection related fields.This paper designed and prepared porous organic framework materials for uranium and copper detection and adsorption applications.The main research contents are as follows:1.Sp2 carbon conjugated covalent organic framework materials with excellent stability and fluorescence properties were for the first time used for the detection and adsorption of uranium in radioactive wastewater.A covalent organic framework(named COF-PDAN)with C=C bond linkages was first prepared by using 1,3,6,8-tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile.Then,the cyano groups of COF-PDAN were converted into the amidoxime groups via reacting with hydroxylamine to afford COF-PDAN-AO.On the one hand,COF-PDAN-AO has good fluorescence characteristics.When UO22+ is present,the photo-induced electron transfer between COF-PDAN-AO and UO22+leads to fluorescence quenching of COF-PDAN-AO,enabling selective detection of UO22+in wastewater with a detection limit as low as 6.5 nM.On the other hand,COF-PDAN-AO has abundant uranium chelating groups,excellent regular pore structures and chemical stability,and can be used for the efficient adsorption of UO22+.At pH 4.0,the absorption equilibrium can be reached within 25 minutes and the maximum adsorption capacity is 410 mg g-1.After seven regeneration experiments,the crystal structure remained good,and the adsorption rate only decreased by only 7.48%.These results prove that this method has the potential for practical application in detection and adsorption of uranium in radioactive wastewater,which can effictively solves the problem that the instability of adsorbents in radioactive wastewater.In addition,by designing the target ligand,this strategy can also be extended to detection and extraction of other contaminants.2.For the first time,an anti-fouling sp2 carbon conjugated covalent organic framework material(Anti-COF-BAO)was designed and prepared by covalent crosslinking for the extraction of uranium from natural seawater.Compared with an adsorbent(COF-BAO)without anti-fouling property,Anti-COF-BAO with excellent stability,abundant amidoxime groups and antibacterial property significantly improves the extraction capacity of uranium in seawater.2,2',2"-(Benzene-1,3,5-triyl)triacetonitrile and(1,1'-biphenyl)-4,4'-dicarbaldehyde are integrated to prepared a sp2 carbon conjugated COF(COF-BA),and then antibiotics are covalently crosslinked via bonding defects functionalization approach and oximated to abtain Anti-COF-BAO.Because of its low reversibility C-.C linkage,Anti-COF-BAO displays remarkable stability in chemical and radiation condition.Anti-COF-BAO modified with antibiotics can inhibit bacterial growth by more than 86%,indicating that Anti-COF-BAO has excellent resistance to biological fouling.In addition,Anti-COF-BAO is rich in amidoxime groups.Compared with COF-BAO,which is rich in amidoxime groups and has no anti-fouling properties,Anti-COF-BAO's adsorption capacity for uranium in actual seawater has increased by 26.1%,and the adsorption capacity for uranium in actual seawater has reached 5.3 mg g-1.Moreover,Anti-COF-BAO still maintains 96.9%high sterilization performance and 90%uranium adsorption capacity after five consecutive cycles,and its crystal structure remains intact.This study provides a promising type of adsorbents for uranium extraction from seawater,which can effectively solve the problems of poor stability and low anti-fouling ability of commonly used adsorbents.In addition,the strategy of covalently modifying small molecules by the bonding defects functionalization approach can be widely used in the design of multifunctional ultra-stable COF based adsorbents.3.A new method for detecting Cu2+based on aminated cobalt metal organic framework fluorescence is proposed.Selecte 2-amino-terephthalic acid as the functional ligand,through the effective coordination between the carboxyl group on the aromatic ring and Co2+,to form a cobalt metal organic framework(NH2-CoMOF)with excellent fluorescence properties.When Cu2+is present,Cu2+interacts with the amino group on the amino-terephthalic acid ligand,which reduces the fluorescence of NH2-CoMOF.Therefore,using NH2-CoMOF as a fluorescent probe,a new method for selective detection of Cu2+was constructed,and the detection limit of Cu2+was as low as 30 nM.This method not only has simple operation,wide linear range and low detection limit,but also realizes quantitative detection of Cu2+in environmental water samples,and by designing ligands,the sensor can be further expand to other areas of environmental analysis.