Research Of Micro Gas Chromatographic Columns With Metal-organic Framework Materials As Stationary Phases

Gas chromatographs are commonly used for the separation and detection of various volatile,semi-volatile and thermally stable compounds,and have a wide range of applications in petrochemical,energy exploration,biomedical and other fields.However,conventional gas chromatographs are bulky,energy-consuming,have long analysis cycles,are not portable,and are difficult to perform real-time detection in the field,therefore,the research of low-power portable gas chromatographs is of great importance.The use of microelectromechanical systems（MEMS）technology allows the preparation of tiny chromatographic devices,making it possible to micro gas chromatography systems.The large size of conventional gas chromatography columns leads to a large percentage of the column box volume,therefore,the miniaturisation of gas chromatography columns is of great significance.However,the separation of light alkanes is a challenge with the shorter length of micro gas chromatography columns（μGCC）compared to conventional gas chromatography columns.The stationary phase is one of the key factors determining the separation performance of the column.The current stationary phases ofμGCC mainly include polydimethylsiloxane（PDMS）,silicon oxide,gold particles and other materials,however they are more difficult for the separation of methane and ethane and cannot meet the quantitative requirement of separation R≥1.5.Metal organic frameworks（MOFs）materials have the advantages of large specific surface area,low density,high adsorption The use of MOFs as stationary phases in gas chromatography is expected to improve the separation performance of light alkanes,due to their large specific surface area,low density,high affinity and adjustable pore size.The main research of this paper is as follows:（1）TheμGCC with a serpentine channel layout and embedded four rows of elliptical micro-pillar arrays was prepared based on MEMS technology.In this paper,CPL-2 material was synthesized by hydrothermal method at room temperature,and CPL-2 was coated intoμGCC as stationary phase by dynamic coating method.ThisμGCC can not only effectively separate light alkane mixture（C1-C4）,where the resolution of C₁and C₂is 3.1,but also separate ethane,ethylene and acetylene.（2）HKUST-1 is a crystal structure formed by a BTC^3-ligand linked Cu paddlewheel cluster,also known as Cu₃（BTC）₂.In this paper,HKUST-1 was synthesised at room temperature and HKUST-1 was coated intoμGCC,which can effectively separate light alkane mixtures（C₁-C₄）,where the resolution of C₁and C₂was 7.3.This is due to the entry of the light hydrocarbon mixture into the HKUST-1 pore size and the different van der Waals interactions of the component molecules with the inner wall of HKUST-1,resulting in a good separation.（3）Since HKUST-1 is hydrophilic and collapses its structure in water,and the samples to be tested often contain water molecules,it is necessary to modify it hydrophobically.In this paper,hydrophobic FG-HKUST-1 composites were synthesized at room temperature based on the hydrophobic modification of HKUST-1 with multilayer fluorinated graphene（FG）,and the FG-HKUST-1 composites were used as stationary phases in gas chromatography.TheμGCC showed better separation of light alkane mixtures（C₁-C₄）,where the resolution of C₁and C₂was 9.3,and the difference in retention time between methane The difference in retention time between methane and ethane was 57.6 s,which effectively avoided the phenomenon of methane peaks overwhelming ethane peaks when separating methane and ethane in very different concentrations.This may be due to the perfect synergy between the C-F bond in FG and the free carboxylic acid group in HKUST-1,which changes the polar HKUST-1 into a non-polar FG-HKUST-1 composite and therefore provides better separation for non-polar methane and ethane.