The Synthesis Of Zif-8-based Hierarchical Co₂ Adsorbent

CO₂ capture by traditional amine-solution adsorbent has high efficiency,but it has problems of serious corrosion to equipment and low regeneration efficiency.However,CO₂ capture by solid adsorbent has the advantages of strong adsorption capacity,easy recovery,and stable physical and chemical properties.Metal–organic frameworks?MOFs?are the latest types of solid porous materials with special physical and chemical properties such as large specific surface area,high porosity,easy modification and adjustable structure.They have achieved excellent results in the field of CO₂ adsorbent.Post-thermal treatment technology is a simple and versatile approach by creation of a locally defective structure for enhancement of CO₂ capture.Moreover,the MOFs composite formed by doping with other materials is also the main method to improve CO₂ uptake.Zeolitic imidazolate frameworks?ZIFs?are important sub-family of metal-organic frameworks?MOFs?.Among these,ZIF-8 is one of the most studied potential gas adsorbent,which exhibited microporous structure.In this study,ZIF-8 and chitosan?CS?as raw material,a series of ZIF-8 based millimetre-scale hybrid material with hierarchical pores were synthesized by post-thermal treatment and doping mesoporous silica nanoparticles?MSNs?.The effects of different annealing temperatures on CO₂ capture and MSNs doping on structure were explored.The main contents are shown as follows.1.We prepared CS/ZIF-8 millimetre-scale spheres based on in situ self-assembly to form internal honeycomb structures.By post-thermal treatment,the annealed CS/ZIF-8spheres with 500°C exhibited mechanical stability,which maintained the internal honeycomb structure,shape and size of millimetre-scale spheres.Moreover,by comparison with as-synthesized CS/ZIF-8 millimetre-scale spheres,the annealed CS/ZIF-8 spheres exhibited hierarchical porous with macropores,micropores and mesopores and higher CO₂uptake after annealing process.Particularly,the CO₂ uptake of annealed CS/ZIF-8 spheres with 500°C was 0.99 mmol·g^-1,which obvious higher than that of as-synthesized CS/ZIF-8 spheres and samples annealed at 450°C,525°C and 550°C.And studies have shown that carbonization at 500°C is the most suitable temperature and can obtain the best CO₂ adsorption effect.After CO₂ adsorption-desorption recycling of 10 times,the annealed CS/ZIF-8 spheres exposed only minor change by comparing with the first cycle,suggesting the excellent stability and regeneration of annealed CS/ZIF-8 spheres for CO₂uptake,which was promising for the application of industry process.2.The amino-functionalized MSNs with uniform size and good monodispersity were incorporated into CS/ZIF-8 spheres,and new millimetre-scale hierarchical porous hybrid spheres were synthesized through one-pot self-assembly methods.Keeping the molar mass of the metal ions unchanged,the MSNs powder was mixed into the mixed solution according to different mass ratios,three kinds of hybrid spheres with different MSNs contents were prepared.After the incorporation of MSNs,the hybrid spheres preserved millimetre-scale macrostructure and honeycomb internal channels.In addition,the peak positions of the CS/ZIF-8/MSNs-1 spheres in X-ray diffraction spectrum were same as the characteristic diffraction peaks of as-synthesized CS/ZIF-8,indicating that the crystal structure of ZIF-8 in the hybrid spheres was maintained.Scanning electron microscopy,energy dispersive X-ray spectroscopy,infrared spectroscopy,and thermogravimetry analysis confirmed that MSNs and ZIF-8 in the spheres were successfully compounded.This synthesis method was facile and low in energy consumption,which provided a feasible way for preparing hybrid adsorbents with hierarchical pores.