Direct synthesis of zeolitic imidazolate framework-8/chitosan composites in chitosan hydrogels

Zeolitic imidazolate framework-8 (ZIF-8)/chitosan composites were prepared in the chitosan hydrogels. The concentrations of the chitosan and the alkaline solution were varied to the synthesis of the ZIF-8/chitosan composites. In the chitosan hydrogels with the addition of ammonium hydroxide solution, the resulting ZIF-8 crystals exhibited an unusual XRD structure that the XRD peak at about 18o (2 2 2) became the strongest. The XRD peak intensity ratio of (2 2 2)/(0 1 1) increased from 0.68 to 1.5–5.2 in the presence of chitosan hydrogels. ZIF-8/chitosan composites (FC2) were composed of aggregated nanosized particles, and exhibited a higher CO2 adsorption than normal ZIF-8 crystals. After removing chitosan from FC2, XRD pattern of the resulting ZIF-8 crystals returned to the normal state and the morphology kept the same as the composite.

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► ZIF-8/chitosan composites prepared in chitosan hydrogels.
► Unusual XRD patterns with the strongest peak at about 18o.
► Higher CO2 adsorption compared to the regular ZIF-8.