Facile fabrication of hierarchical porous ZIF-8 for enhanced adsorption of antibiotics.

Aiming for improve mass transfer rate of antibiotics adsorption from water, a strategy of building larger pores (>2 nm) in microporous MOFs has been put forward. However, most of reported approaches are complicated and inefficient. Herein, a facile one-spot approach to fabricate hierarchical porous Zeolitic Imidazolate Framework-8 (HpZIF-8) was developed, where poly(diallyldimethylammonium chloride) (PDDA) was selected as structure-directing agent to modulate the growth of microporous ZIF-8 (mZIF-8). The final products with meso- and macropores exhibit hierarchical porosity. The mechanism was a two-step process: First, crystal nucleus aggregated initiated by electrostatic interaction between cationic PDDA and deprotonated 2-MI anions. Second, Ostwald ripening process and orientated growth occurred with further growth of crystals. For removing Tetracycline Hydrochloride (TH) and Chloramphenicol (CP) from water, hierarchical porous HpZIF-8-10(D) (D = 1.0, 1.5, 2.0) showed larger adsorption capacity than mZIF-8-10 despite of decreased BET surface area, which could be attributed to novel hierarchical porous structures. The adsorption kinetics and isotherms of TH and CP by HpZIF-8-10(1.5) were analyzed. The strategy present here may provide new thoughts for designing more abundant MOF structures and further expand their application range.