Porous ZIF-8@ magnetic chitosan nanocomposite for ultrahigh adsorption capacity and fast filtration removal toward Congo red.

Conventional chitosan-based adsorbents suffer from limitations including narrow pH tolerance, poor recoverability, low adsorption efficiency, hindering their practical applications. Herein, a porous ZIF-8@magnetic chitosan nanocomposite (ZIF-8@mCS) was synthesized through in-situ crystallization of zeolitic imidazolate framework-8 on a magnetic γ-Fe2O3/chitosan substrate. Comprehensive characterization (SEM, TEM, FT-IR, XRD, XPS, etc.) confirmed the successful synthesis of hierarchical porous ZIF-8@mCS with structural integrity. The composite exhibited both ultra-high adsorption capacity (qe,exp, 2486.56 mg·g-1) and efficient magnetic separability. The adsorbent maintained exceptional performance under various conditions, achieving removal rates of 99.78% for the original CR solution, 98.21% in 1 M NaOH, and 99.67% in 1 M HCl within 30 min. Notably, the column sustained a CR removal efficiency of >94.5% after 1200 min, corresponding to a treatment capacity of approximately 1166 bed volumes (BV) at an influent concentration of 20 mg·L-1. Furthermore, the ZIF-8@mCS composite demonstrated exceptional recyclability, retaining 99.6% of adsorption efficiency after five cycles using 0.1 M NaOH/ethanol mixture (1:1 v/v). The ZIF-8@mCS composite developed in this study achieves higher adsorption capacity, stability, wider pH adaptability and operational convenience, demonstrating its potential as a reliable water treatment platform.