摘要
为了开发一种新型的钍基碘吸附材料,本文通过溶剂热法合成了一种含喹啉配体的钍基金属有机框架(MOF)材料——[Th(C9H5NOCOO)4]·12H2O(Th-HQCA),表征分析了其结构、组分、光谱性质,并探究了该MOF材料对碘的吸附性能及其影响因素.结果表明:钍离子与4个喹啉上的羧基氧和另外4个喹啉上的羟基氧配位后,形成了 Th-HQCA的2,8-连接的新型框架结构.荧光光谱显示Th-HQCA受紫外光激发后,展现出发射蓝光的特性.碘吸附的实验结果表明Th-HQCA可从气相和环己烷溶液中捕获碘的最大吸附容量分别为535、295 mg/g.
Abstract
Radioactive nuclides such as129I are produced during the operation of nuclear facilities.129I is volatile and can induce radiation sickness.Capture of radioactive iodine can protect public health and facilitate the sustainable development of the nuclear industry.Preliminary studies on the synthesis and iodine adsorption properties of thorium based MOFs have shown that thorium-based MOFs usually have different structures and iodine adsorption performance when they contain different ligands.Quinoline derivatives containing both hydroxyl and carboxyl groups are a class of rigid ligands with strong coordination ability.Although these ligands have been used to synthesize transition metal complexes,their application in the preparation of thorium MOFs remains unexplored.To further investigate the effect of ligands on the structure and iodine adsorption performance of thorium-based MOFs,in this paper thorium-quinoline MOF(Th-HQCA)was synthesized using 2-hydroxyquinoline-4-carboxylic acid(HQCA)as the ligand via solvothermal method,and its structure,composition,thermal stability,spectral properties,and iodine adsorption performance were investigated through various characterization techniques,including single-crystal X-ray diffraction,powder X-ray diffraction(PXRD),scanning electron microscope-energy dispersive X-ray spectroscopy(SEM-EDS),Fourier transform infrared spectroscopy(FT-IR),ultraviolet-visible(UV-Vis)spectroscopy,thermogravimetric analysis(TGA),X-ray photoelectron spectroscopy(XPS),and fluorescence spectroscopy.Crystallographic analysis reveals that the coordination modes of thorium ions in the structure of Th-HQCA are the same,and each ion is coordinated with four carboxylate oxygen atoms from four HQCA and four hydroxyl oxygen atoms from another four HQCA.It is worth mentioning that thorium ions usually coordinate with carboxylate oxygen atoms in ligands,and rarely coordinate with hydroxyl group.The connections between thorium ions and HQCA ligands result in the formation of a novel 2,8-connected framework structure of Th-HQCA.The channels of the framework are filled with water molecules.Based on the crystallographic analysis,the ratio of thorium ions,HQCA,and water molecules is determined to be 1:4:1.However,further thermogravimetric analyses indicate that there may be twelve cocrystallized water molecules in the compound.Consequently,the chemical formula for Th-HQCA can be expressed as[Th(C9H5NOCOO)4]·12H2O.The solid-state fluorescence spectrum shows that Th-HQCA crystals emit blue light when they are excited by ultraviolet light.The adsorption experiments of Th-HQCA on gaseous iodine and iodine in cyclohexane solution show that their adsorption kinetic curves fit the pseudo-second-order kinetic equation,and the adsorption isotherm of the latter fits the Langmuir model.Through further calculations,the maximum adsorption capacity of Th-HQCA for iodine vapor is 535 mg/g,and the maximum adsorption capacity for iodine in cyclohexane solution is 295.63 mg/g.In summary,Th-HQCA is a thorium-quinoline MOF with a novel 2,8-connected topological structure,and it shows remarkable fluorescence properties and can effectively capture iodine in the gas phase and solution.
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