Structuring ZIF-8-based hybrid material with hierarchical pores by in situ synthesis and thermal treatment for enhancement of CO2 uptake

Abstract

This work demonstrated the design and synthesis of millimetre-scale hierarchical porous spheres based on ZIF-8 and CS (chitosan) by in situ assembly and post-thermal treatment technology. The ZIF-8/CS spheres have been synthesized according to the assembly method, which exhibited honeycomb internal structures and micropores of 0.77 nm. While the annealed ZIF-8/CS spheres exhibited obvious mesopores with a BET surface area of 626.85 m2 g−1 and maintained the honeycomb internal structures, which were obtained by calcinations in the tube furnace under nitrogen protection at 500 °C for four hours. The annealed ZIF-8/CS spheres exhibited hierarchical porous with macropores, micropores and mesopores after annealing process. The SEM image and the XRD pattern of annealed ZIF-8/CS spheres suggested the maintenance of shape and crystal structure of ZIF-8, indicated that the annealed ZIF-8/CS spheres were stable and robust. Particularly, the CO2 uptake of annealed ZIF-8/CS spheres with 500 °C is 0.99 mmol/g, which obvious higher than that of as-synthesized ZIF-8/CS spheres and samples annealed at 450 °C, 525 °C and 550 °C. The enhancement of CO2 uptake may attribute to the carbonization of CS and the enlarge micropores of ZIF-8 after annealing process. This approach could induce a simple way for industrial structuring ZIF-8-based adsorbents with improved CO2 uptake.