TEMPO oxidized cellulose nanocrystal (TOCNC) scaffolded nanoscale zero-valent iron (nZVI) for enhanced chromium removal

• Published in: Chemosphere (Oxford) Vol. 343; p. 140212
• Main Authors: Hu, Xiaolei, Song, Mingyang, Li, Shiyan, Chu, Yu, Zhang, Wei-xian, Deng, Zilong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2023
• Subjects: Chromium; Modification; Nanocellulose; Nanoscale zero-valent iron; Chromium; Nanoscale zero-valent iron; Modification; Nanocellulose
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2023.140212

The conventional carboxymethyl cellulose (CMC) stabilization hampered available active sites of adsorption and reduction, due to irregular shape of nanoscale zero-valent iron (nZVI) particles with augmented average size and passivated surface, leading to insufficient removal and poor resistance against complex environmental conditions. Herein, we presented (2,2,6,6-Tetramethylpiperidine-1-oxyl)-mediated (TEMPO-mediated) oxidation of cellulose nanocrystal (TOCNC) scaffolded nZVI (nZVI@TOCNC) with enhanced efficiency for chromium removal in comparison with CMC stabilized nZVI (nZVI@CMC). The anchoring of nZVI at the functional sites of TOCNC was initiated by liquid-phase chemical reduction method. The nZVI@TOCNC showed improved nZVI distribution with uniform particle size and thinner shell (∼1 nm). Characterizations using FT-IR, XPS and XRD demonstrated that bindings between TOCNC and nZVI were through hydrogen bonds, electrostatic attractions, coordination-covalent bonds and bidentate chelation. TOCNC with shorter branch-chain (–COC–) surrounding the nZVI could potentially form a porous and compact “mesh” to rigidly encapsulate nZVI, while CMC wrapped around nZVI in the way of traditional polymeric stabilizers. Thus, 0.5 g/L nZVI@TOCNC achieved 99.96% Cr (Ⅵ) removal efficiency (20 mg/L) at pH = 7 and the removal capacity were up to 55.86 mg/g. The nZVI@TOCNC consistently presented higher removal efficiency than nZVI@CMC under wide pH range (3–7). Cr (Ⅵ) was reduced to Cr (Ⅲ) by nZVI@TOCNC with deposition of CrxFe1-x (OH)3 and Cr2O3. The predominant mechanisms of removal probably consisted of electrostatic attractions, reduction, co-precipitation and surface complexation. The pseudo-second-order kinetic model well-fitted the sorption kinetic, indicating TOCNC scaffold stabilized nZVI for efficient reduction of Cr (Ⅵ) through multi-layer adsorption. As a template and delivery carrier, TOCNC shows promising potential to further improve the capability and practice of nZVI for in situ treatment of industrial waste water with heavy metal pollution. [Display omitted] •TEMPO-mediated oxidation of cellulose nanocrystal (TOCNC) with shorter branch-chain formed a compact “mesh” to rigidly encapsulate nano zero-valent iron (nZVI).•TOCNC scaffold resulted in enhanced nZVI dispersion and wide-pH applicability (3–7).•The nZVI@TOCNC possessed effective mass transfer at solid/liquid interface.•The nZVI@TOCNC exhibited superior Cr (Ⅵ) removal efficiency (99.96%).•TOCNC acted as a corrosion inhibitor apart from being template during the nZVI formation.