Application of metal-organic frameworks and their composites in separation

Metal-organic frameworks (MOFs) are known to be an intriguing class of organic inorganic hybrid porous solids, synthesized by the assembly of metal ions with organic linkers. MOFs exhibit remarkable properties, such as ultrahigh surface areas, structural diversity, excellent thermal stability, tuneable pore size and the availability of framework functionality, which make MOFs promising for the separation applications. MOFs have shown great potentials as efficient adsorbents and novel stationary phases in adsorption and separation. However, due to the submicron or micron size of most MOFs particles as well as their irregular morphology, the applications of MOFs as stationary phases for sample pretreatment and liquid chromatography were greatly limited. To overcome these obstacles, an effective strategy was applied to fabricate MOF-based composites, combining the excellent separation ability of MOFs with the specific properties of substrates. The substrate materials combining with MOFs included metal nanoparticles, metal oxide nanoparticles, silica, carbonaceous materials, polymers, quantum dots and so on. This review summarizes the current progress in the application of MOFs and their composites for adsorption, sample pretreatment and chromatographic separation. The main contents involve the types and preparation methods of MOF-based composites, the applications of MOFs and their composites in vapor and liquid phase adsorption, solid-phase extraction, solid-phase microextraction, gas chromatographic separation and high performance liquid chromatographic separation. The prospects of MOFs in separation science are also discussed.