Metal-Organic Framework Materials For Gas Chromatography Stationary Phases

Metal-organic framework(MOF) is represented by connecting two or more metal ion/ion clusters with oxygen, nitrogen and other polydentate organic ligand. Most of MOFs possess much more porosity, good chemical stability, high surface area,structural diversity and tailoring and so on, which can applied for catalysis, gas storage, sensing, bio-imaging and drug delivery, etc. In this paper, some MOFs which have been synthesized by hydrothermal method were selected as stationary phases to prepare the capillary gas chromatographic column via a verified dynamic coating procedure. Moreover the chromatographic performance of these MOFs were studied as well. The contents of the paper are divided into the following three parts:1. More attention has been given to developing microporous material MOFs with high surface area as an advanced media for separation in the field of separation science. In this work, a novel metal–organic framework, {[Sm(L)(DMF)]﹒2(DMF)﹒5(H2O) }(MOF-Sm-L), with a one-dimensional channel and active amido groups was chosen as stationary phase to prepare a capillary gas chromatographic column via a verified dynamic coating procedure to study the separation of liner alkanes, linear alcohols and substituted aromatic aspect of performance. The column offered good separations for linear alkanes, linear alcohols, as well as aromatic positional isomers(cresol, hydroquinone, bromobenzonitrile, chloronitrobenzene and nitrotoluene). It is worth noting that excellent resolution and separation for cresol and hydroquinone isomers is shown on MOF-Sm-L column. Elution sequence of most of the analytes followed an increasing order of their boiling points. Separation behavior of the column upon different organic substances may be related to the 1D pore structure of MOF-Sm-L, in which the van der waals forces between the compounds without hydroxyl and the hydrophobic inner surfaces might have great effect on separation of the compounds without hydroxyl, whereas the separation of the hydroxyl compounds were affected by(OH…O or OH…N) hydrogen bonds formed between the analytes and the active amido groups on the pore wall except for the van der waals forces. Theeffects of temperature on separation of aromatic positional isomers were investigated to elucidate entropy and enthalpy controlling of the separation process.2. A chiral metal- organic framework [Cu(mal)(bpy) ? H2O(mal = s-malic acid)(bpy = 4,4-bipyridyl)] was synthesized by hydrothermal method, and used as stationary phase to prepare the capillary gas chromatographic column via a dynamic coating procedure. The images of scanning electron microscopy(SEM) showed that the chiral MOF had been coated on the inner wall of the capillary column. And the thermal gravimetric analysis showed that MOF-Sm-L has good thermal stability within 230 ℃ and is, suitable for gas chromatography stationary phase. Grob reagent,n-alkanes, positional isomers, and some enantiomers were selected to evaluate the separation performance of the chiral MOF colunm. The experiment indicates that the chiral column can obtain good separations for linear alkanes, linear alcohols, as well as aromatic positional isomers. Especially, the most important advantage of this this stationary phase in GC is its enantioselective and resolving abilitiy for the enantiomer of α-pinene.3. The polyethylene glycol 20000(PEG-20) mixed with MOF-Sm-L was used as stationary phase to prepare the capillary column. The impact of different percent of PEG-20 and MOF-Sm-L on the separation performance of Grob reagent, n-alkanes,aromatic isomers and other organic compounds was investigated. The result indicated that the column of PEG-20 mixed with MOF-Sm-L can obtain much better selectivity than the column of PEG-20. But the elution sequence of aforementioned organic compounds on the column of PEG-20 mixed with MOF-Sm-L is as same as the column of PEG and is based on the boiling point.