PEI-Functionalized Surface Coating on Carbonized ZIF-8 for Enhanced Adsorption of Methyl Orange

The contamination of water resources by high concentrations of organic dyes poses severe threats to human health, making the removal of these pollutants critical. Metal–organic frameworks (MOFs) have shown promising potential in dye adsorption due to their high surface area and chemical stability. Zeolitic imidazolate framework-8 (ZIF-8), a typical MOF, is known for its thermal stability and is frequently used in removing organic dyes. To enhance its adsorption performance, ZIF-8 is often carbonized to form porous carbon-based materials. However, carbonized ZIF-8 (CZ) often demonstrates restricted adsorption capacity and sluggish kinetics. To address these limitations, we chemically modified low-temperature carbonized ZIF-8 (CZ-550) with polyethyleneimine (PEI) using cyanuric chloride (CC) as a crosslinking agent, producing a novel composite (CZ@PEI/CC-7) featuring abundant amine-rich active sites for adsorption. This study evaluated the adsorption performance of CZ@PEI/CC-7 in removing methyl orange (MO) dye. Our findings reveal that CZ@PEI/CC-7 exhibits accelerated adsorption kinetics aligning with the pseudo-second-order kinetic model, while its isotherms fit the Freundlich and Temkin models, highlighting a favorable multilayer adsorption. Significantly, CZ@PEI/CC-7 achieved an adsorption capacity of 3150 mg/g for MO, compared to 1100 mg/g for unmodified CZ-550. Furthermore, the composite demonstrated excellent acid-base stability across a broad pH range (2–12), retaining structural integrity and adsorption efficiency. These findings suggest that CZ@PEI/CC-7 is a promising candidate for efficient MO removal from water.