Synergistic Adsorption and Reduction of Cr( <scp>VI</scp> ) in Wastewater Using Polydopamine‐Functionalized Cellulose Nanocrystals Loaded With <scp>FeS</scp> Nanoparticles

ABSTRACT Chromium (Cr) ions, as a critical pollutant in industrial wastewater, posed a persistent challenge for research aiming to realize their efficient removal alongside detoxification. Here, we presented a novel cellulose‐based nanoadsorbent, PDA@CNCs/FeS, obtained via dopamine (DA) self‐polymerization onto cellulose nanocrystals (CNCs) and subsequent FeS nanoparticle immobilization. Experimental results demonstrated that the adsorbent achieved a high removal capacity of 837.9 mg/g for Cr(VI) and exhibited efficient removal under mildly acidic conditions (pH 5.0), which outperformed the majority of cellulose‐based adsorbents. The adsorption followed the Langmuir isotherm model and fitted well with the Pseudo‐second‐order kinetic. FTIR and XPS analyses confirmed the adsorption mechanism, which revealed that electrostatic attraction was involved in Cr(VI) removal, while the synergistic effect between reductive PDA and FeS on the nanoadsorbents facilitated the detoxification of toxic Cr(VI) to less harmful Cr(III). Nearly 70% of the adsorbed Cr(VI) was reduced to Cr(III), with a final ratio of 31.4%:68.6% for Cr(VI):Cr(III). Furthermore, PDA@CNCs/FeS also demonstrated excellent reusability, with over 80% of its Cr(VI) removal efficiency remaining after four adsorption–desorption cycles; these findings implied that PDA@CNCs/FeS held great promise as an adsorbent for Cr(VI) remediation in water treatment.