【作者】 谢敏；

【导师】 邢航；

【作者基本信息】 湖南大学 ， 物理化学， 2020， 硕士

【摘要】 金属有机框架化合物(Metal-Organic Framework,MOF)是一种具有高比表面积的多孔晶体材料。普通MOF材料的形态一般是多晶固体粉末或大颗粒单晶,不具有流动性,限制了其作为运输介质在气体和小分子传输、能量传导以及物质交换等方面的应用。本论文基于纳米尺寸MOF粒子,提出了一种配位表面修饰的方法用于合成多孔液体。我们设计合成了阳离子和阴离子均具有配位位点的大体积离子液体(Coordination Ionic Liquid,COIL),通过合成的COIL与MOF纳米粒子表面不饱和金属配位点的配位作用,将COIL配体修饰在MOF纳米粒子表面,增强了溶剂化效应,显著提高了MOF纳米粒子在离子液体中的分散程度与胶体稳定性。合成的COIL配体的体积较大,由于空间位阻,无法进入MOF孔道,使得合成的MOF流体(MOF Fluid,MOFluid)既具有MOF材料纳米粒子的多孔吸附性质,又兼具离子液体的流动性质。除此之外,MOF流体还具备化学组成的高度可调性,可以从MOF结构、孔隙率、金属节点、尺寸大小、掺杂比例等方面精确调节,制备性能可控的多孔液体材料,为其作为介质用于小分子运输、能量传导等应用打下基础。(1)基于晶体生长的基本原理,通过控制调制剂的浓度,控制MOF纳米粒子的生长过程。本论文选取Ui O-66,Ui O-67,PBA,ZIF-8,MIL-101,HKUST-1等MOF结构作为研究对象,通过对调制剂的用量、反应时间、反应物浓度等MOF纳米粒子纳米晶体合成条件进行调控,成功得到一系列不同尺寸的MOF纳米粒子。我们对所合成的MOF纳米粒子进行了一系列的表征,例如使用扫描电子显微镜(Scanning Electron Microscope,SEM)和动态光散射(Dynamic Light Scattering,DLS)等技术表征其形貌及尺寸,使用X射线衍射(X-ray Diffraction,XRD)表征其晶体结构。所合成的MOF纳米粒子被用于制备具有不同孔隙率和不同力学性质的多孔MOF流体。(2)设计合成配位离子液体。为了合成孔隙率较高、流动性良好、且胶体稳定性高的多孔MOF流体,离子液体需要满足如下要求:(1)离子液体分子尺寸足够大,从而不能进入MOF孔道,保持较高的孔隙率。(2)离子液体本身流动性良好。(3)离子液体分子与MOF纳米离子具有较强纳米粒子相互作用,从而提高胶体稳定性。综合考虑后,我们设计并合成了含有多个配位点且尺寸大于大多数MOF结构孔道的离子液体(COIL)作为MOF纳米粒子的表面配体和分散介质。通过电离质谱(Electrospray Ionization Mass Spectrometry,ESI-MS)、核磁共振氢谱(Proton Nuclear Magnetic Resonance,~1H NMR)以及傅里叶变换红外光谱(Fourier Transform Infrared Spectroscopy,FT-IR)等表征手段,确定所合成的COIL分子的结构。所合成的配位离子液体被用于后续MOF流体的合成。(3)基于COIL和Ui O-66纳米粒子制备多孔流体。我们选择Ui O-66作为基础模型,通过MOF纳米粒子表面暴露的配位不饱和锆簇与COIL的相互作用,合成Ui O-66多孔流体,并对其理化性质进行了全面表征。我们通过FT-IR、X射线光电子能谱(X-ray Photoelectron Spectroscopy,XPS)、SEM、透射电子显微镜(Transmission Electron Microscope,TEM)、XRD、热重分析(Thermogravimetric Analysis,TGA)等表征手段分别对Ui O-66流体中纳米粒子的表面配位键变化、微观形貌、晶体结构及MOF含量进行了系统的理化性质分析。此外,我们利用室温高压甲烷气体吸附和Sudan II染料分子吸附证明了多孔Ui O-66流体具有接近初始Ui O-66材料的孔隙率,并利用蠕动泵证明了所合成的Ui O-66流体的流动性。我们进一步利用流变仪,系统研究了Ui O-66纳米粒子的纳米粒子质量分数和纳米粒子尺寸对所制备的Ui O-66流体的流变力学性质的影响。(4)利用COIL方法制备多种MOF流体。为了证明基于COIL制备多孔MOF流体的通用性,我们将这种方法应用在六种具有不同的结构特征的MOF中,进而合成六种MOF流体(Ui O-66、Ui O-67、MIL-101、HKUST-1、PBA、ZIF-8)。我们对以上六种MOF流体的进行了分子动力学(Molecular Dynamics,MD)模拟,结果表明COIL分子均无法进入这六种MOF孔道中,进一步说明了多孔流体中保留了MOF的多孔性。通过比较由COIL方法法合成的多孔MOF流体与先前报道中采用物理混合方法得到的多孔MOF流体的胶体稳定性,我们发现COIL方法得到的MOF流体具有更好的胶体稳定性,可以稳定更大尺寸的MOF粒子。综上所述,我们采用表面配位法将液体的流动性与MOF材料的多孔性有机结合,合成了多种稳定性好、孔隙率高、可调性强(孔道大小及孔隙率可调,金属中心及配体可调,力学性质可调)的多孔MOF流体。本论文合成的多孔MOF流体具有较好的吸附性能与流动能力,未来有望作为新型载体流动介质,在循环系统或运输系统中具有潜在的应用前景。更多还原

【Abstract】 Metal-Organic Framework(MOF)is a type of porous crystalline material with high surface area.Conventional MOF materials are generally in the form of polycrystalline solid powders or large single crystals,which do not have fluidity.The lack of fluidity limits their application as delivery medium for gas and small molecule transportation,energy conduction,and material exchange.In this thesis,based on nano-sized MOF particles,a surface modification method based on coordination interactions is proposed to synthesize porous liquid.A type of bulky ionic liquid with coordination sites for both cations and anions(C ooridnation Ionic Liquid,COIL)is designed and synthesized.The coordination interactions between the unsaturated coordination sites on the surface of MOF nanoparticles(NPs)and the COIL ligands significantly enhance the solvation effect and improve the dispersion degree and colloidal stability of the MOF NPs in the ionic liquid.The synthesized COIL ligand also has a large size and cannot enter the pores in the MOF structure due to steric hindrance.Therefore,the synthesized MOF fluid,termed as MOFluid,posseses both the porosity of the MOF material and the mobility of the ionic liquid.In addition,the MOFluid also has a high degree of tunability in chemical composition.It can b e precisely tuned from the aspects of MOF structure,porosity,metal nodes,size,and loading ratio to prepare porous liquid material with controllable properties,laying the foundating as a medium for the application of small molecule transportation,energy conduction,etc.(1)Based on the basic principles of crystal growth,we control the growth process of MOF NPs by tuning the concentrations of modulator.In this thesis,MOF structures such as Ui O-66,Ui O-67,PBA,ZIF-8,MIL-101,and HKUST-1 are selected as model structures.By tuning the synthetic conditions of MOF nanocrystals such as modulator concentration,reaction time,reactant concentration,etc.,we successfully obtained a series of MOF NPs of different sizes.We then carried out a series of characterizations on the synthesized MOF NPs.For example,we used scanning electron microscope(SEM),dynamic light scattering(DLS)and other technologies to characterize the morphology and size of the MOF NPs.We used X-ray diffraction(XRD)to characterize their crystal structures.The synthesized MOF NPs were used to prepare porous MOFluids with tunalbe porosities and mechanical properties.(2)Design and synthesis of COIL.In order to synthesize porous MOFluids with high porosity,good fluidity,and high colloidal stability,the ionic liquid needs to meet the following requirements:(1)The molecular size of the ionic liquid should be large enough so that it cannot enter the MOF pores,researving the porosity;(2)Ionic liquid itself should have good fluidity;(3)Ionic liquid molecules should have strong interactions with MOF NPs,thereby improving colloidal stability.Having considered the above requirements,we designed and synthesized an ionic liquid(COIL)containing multiple coordination sites and having bulky size larger than the pores of most MOF structures.The COIL was used as the surface capping ligand and dispersion medium for MOF NPs.By using characterization methods such as electrospray ionization mass spectrometry(ESI-MS),proton nuclear magnetic resonance(~1H NMR),and Fourier transform infrared spectroscopy(FT-IR),the structure of the COIL was fully characterized.The synthesized coordination ionic liquid was used for the subsequent synthesis of MOFluid.(3)Preparation of porous liquid based on COIL and Ui O-66 NPs.We chose Ui O-66 as the model structure to synthesize the porous Ui O-66 MOFluid through the interaction of the coordination unsaturated zirconium cluster exposed on the surface of MOF NPs and the coordination moietie on COIL molecules.The physical and chemical properties of Ui O-66 MOFluid were then systematically characterized.We used FT-IR,X-ray photoelectron spectroscopy(XPS),SEM,transmission electron microscope(TEM),XRD,thermogravimetric analysis(TGA),etc.to characterize the surface coordination bond,morphology,crystal structure,and MOF loading percentage of the prepared porous Ui O-66 MOFluid.In addition,by testing the room temperature and high-pressure methane adsorption and Sudan II dye molecule adsorption properties,we proved that the porous Ui O-66 MOFluid maintained most porosity of the original Ui O-66 material.We also used the peristaltic pump to demonstrate the fluidity of the synthesized Ui O-66 MOFluid.We further used the rheometer to systematically study the effects of the mass loading and particle size of Ui O-66 on the rheological properties of the prepared Ui O-66 MOFluid.(4)Use the COIL approach to prepare different types of MOFluids.In order to demonstrate the versatility of the COIL approach to prepare porous MOFluid,we applied this approach to six different MOFs to synthesize six different corresponding MOFluids(Ui O-66,Ui O-67,MIL-101,HKUST-1,PBA,and ZIF-8).We performed molecular dynamics(MD)simulations on these six MOFluids.The simulation results showed that the COIL molecules cannot enter the pores of any MOFs,further indicating that the prepared MOFluids retained the porosity of the initial MOF NPs.By comparing the colloidal stability of the MOFluid synthesized by the COIL approach with the MOFluid obtained by the physical mixing method previously reported,we found that the COIL-MOFluid showed significantly improved colloidal stability,showing COIL can stabilize larger sized MOF particles.To sum up,by combining the fluidity of the ionic liquid with the porosity of the MOF material using surface coordination chemistry,we synthesized a series porous MOFluids with enhanced stability,high porosity,and good adjustability.The porous MOFluids synthesized in this thesis have sound adsorption properties and high mobility,which can be forseed to serve as a new class of carrier flow medium for potential applications in circulation systems or transportation systems in the near future.更多还原