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Metal-Organic Frameworks for Liquid Phase Adsorption and Separation

Author: YangChengXiong
Tutor: YanXiuPing
School: Nankai University
Course: Analytical Chemistry
Keywords: metal-organic framework high performance liquid chromatography fullerene adsoption
CLC: O647.31
Type: PhD thesis
Year: 2012
Downloads: 44
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Abstract


Diverse structures and pore topologies, high surface areas, excellent thermal andsolvents stability, semi-organic frameworks, and the availability of in-porefunctionality and outer-surface modification make metal-organic frameworks (MOFs)attractive as novel media in separation sciences. In the past decade, MOFs have beenwidely explored as the advanced adsorbent or stationary phases in gas adsorption andgas chromatographic separation. However, researches on the applications of MOFs inliquid phase adsorption and high-performance liquid chromatography (HPLC) havelagged behind. This dissertation focused on the developing of novel MOFs-basedstationary phases or adsorbents for HPLC separation and liquid phase adsorption. Themain contents are summarized as follows:(1) HPLC separation of substituted aromatics was investigated on MIL-101(Cr).High resolution separation of ethylbenzene (EB) and xylene, dichlorobenzeneand chlorotoluene isomers, and EB and styrene was achieved on a slurry-packedMIL-101(Cr) column (5cm long×4.6mm i.d.). The typical impurities of tolueneand o-xylene in EB and styrene mixtures were also efficiently separated on theslurry-packed MIL-101(Cr) packed column. The column efficiencies for EB,m-dichlorobenzene, and m-chlorotoluene are20000,13000, and10000plates m-1,respectively. The relative standard deviation for five replicate separations of thesubstituted aromatics was0.2-0.7%,0.9-2.9%,0.5-2.1%, and0.6-2.7%for theretention time, peak area, peak height, and half peak width, respectively. TheMIL-101(Cr) offered high affinity for the ortho-isomer, allowing fast andselective separation of the ortho-isomer from the other isomers within3minusing dichloromethane as the mobile phase. The effects of the mobile phasecomposition, injected sample mass, and temperature were investigated. Insummary, MIL-101(Cr) was demonstrated to be a promising stationary phase forHPLC separation of substituted aromatics.(2) Metal-organic framework MIL-53(Al) was explored as the stationary phase forHPLC separation of position isomers using a binary and/or polar mobile phase. Baseline separations of xylene, dichlorobenzene, chlorotoluene and nitrophenolisomers were achieved on the slurry-packed MIL-53(Al) column with highresolution and good precision. The relative standard deviations for nine replicateseparations of EB and xylene, dichlorobenzene, chlorotoluene, and nitrophenolisomers are0.1-0.4%,1.1-2.9%,0.5-2.7%and0.6-1.8%for the retention time,peak area, peak height and half peak width, respectively. The MIL-53(Al) columnoffered a column efficiency of10200plates m-1for EB. The effects of mobilephase composition, injected sample mass and temperature were also investigated.(3) The first example of the utilization of MOFs (MIL-101(Cr)) as the stationaryphase for HPLC separation of fullerenes was developed. High resolutionseparation of C60and C70was achieved on a5cm long MIL-101(Cr) packedcolumn by using CH2Cl2/CH3CN (98:2) as the mobile phase at a flow rate of1mL min-1. Such high performance separation of C60and C70was achieved onlywithin3min with the selectivity of αC70/C60=17.1and the column efficiency of13000plates m-1for C70. Thirteen replicate separations of C60and C70gave agood reproducibility of the MIL-101(Cr) packed column with relative standarddeviations of0-0.2%,1.2-1.8%,1.4-1.7%, and0-0.7%for retention time, peakarea, peak height, and half peak width, respectively. MIL-101(Cr) packed columnnot only gave high resolution separation for C60, C70, C76, and C78, but alsooffered baseline separation of the other high fullerenes C82, C84, C86, and C96in the complex carbon soot. The results show that MIL-101(Cr) is very attractivefor specific recognition and separation of fullerenes. This work may bring abright future for MOFs in the specific adsorption, purification, and separation ofcarbon materials.(4) The adsorption and extraction of fullerenes on MIL-101(Cr) were studied indetail in terms of kinetics, thermodynamics, adsorption isotherm, competitiveadsorption, and breakthrough curve. The adsorption of C60and C70onMIL-101(Cr) follows a pseudo-second-order kinetic model. The adsorption rateconstant for C70is3to5times that for C60, showing faster and easier adsorptionof C70over C60on MIL-101(Cr). Intraparticle diffusion model analysis revealsthat the adsorption of C60and C70on MIL-101(Cr) proceeds by two phases, surface sorption and intraparticle/pore diffusion. The adsorption of fullerenes onMIL-101(Cr) is controlled by entropy change. The maximum adsorption capacityfor C70at30oC (198.4mg g-1) is29times that for C60(6.76mg g-1).MIL-101(Cr) shows much more favorable adsorption of C70and higherfullerenes than C60with a high selectivity (αC70/C60=24). Selective extraction ofC70and higher fullerenes from crude carbon soot can be easily achieved onMIL-101(Cr) via a simple adsorption-desorption process. The used MIL-101(Cr)can be easily regenerated by washing with o-dichlorobenzene underultrasonication. The high selectivity, fast adsorption, easy desorption, andexcellent reusability makes MIL-101(Cr) attractive as a novel adsorbent forenrichment and extraction of C70and higher fullerenes.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > The physical chemistry of surface phenomena > Adsorption > Adsorption theory
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