Designing ZIF-8/hydroxylated MWCNT nanocomposites for phosphate adsorption from water: Capability and mechanism

In this study, ZIF8@MWCNT nanocomposite has been designed throughout in-situ growth of zeolitic imidazolate framework-8 (ZIF8) polyhedron on hydroxylated multi-walled carbon nanotube (MWCNT). In detail, three types of nanocomposites harvesting different nanostructures are obtained by varying the dosages of MWCNTs. Such nanocomposites are assessed as phosphate adsorbents via batch experiments to determine the adsorption capacity, reusability and stability. Among the three types of composites, the ZIF8@MWCNT120 affords the maximum phosphate adsorption capacity of 203.0 mg g(-1), which is 0.7-3.7 times higher than those of the other adsorbents at the same adsorption conditions. Experimental characterizations in combination with theoretical calculations reveal that the outstanding performance of ZIF8@MWCNT120 is mainly attributed to the enhanced Zn-O-P interaction and hydrogen bonding. In addition, high phosphate removal performance was observed in the real wastewater (residual effluent Conc.= 0.0-0.45 mg L-1) with initial concentrations of 0.63 mg L-1-6.32 mg L-1, which satisfied the A-level standard of phosphate effluent in China (0.5 mg L-1). This work offers a versatile solution to tailor the adsorption affinity of emerging metal-organic-frameworks (MOFs) toward phosphorous-based pollutants.