In situ growth of ZIF-8 on mullite whiskers to form millimeter-sized composite beads for water treatment

Abstract

Metal–organic frameworks (MOFs) have been considered as promising adsorbents for eliminating organic contaminants from wastewater. However, their inherent fragile and particulate form renders them challenging to handle and recycle in practical applications. Herein, millimeter-sized porous mullite beads composed of interlocked mullite whiskers were selected as the substrate materials. ZIF-8 was synthesized in situ on the mullite whisker to create millimeter-sized ZIF-8@porous mullite composite beads. After three cycles of in-situ growth, the ZIF-8 fully enveloped mullite whiskers, forming a homogeneous core/shell structure. Furthermore, the loading mass of ZIF-8 in ZIF-8@Mullite-3 beads reached 22.18 wt%. The BET surface area of the ZIF-8@Mullite-3 porous beads samples is 244.23 m2/g. The obtained millimeter-sized ZIF-8@Mullite porous beads exhibited satisfactory adsorption of Congo red (61.29 mg/g) and displayed exceptional reusability and stability. The CR removal efficiency of the ZIF-8@Mullite beads remained above 90%, even after the fifth reuse. The MOFs based beads with enhanced mechanical strength can be recycled and easily handed, highlighting their superiority compared to MOF powders in water treatment applications.