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

Xiaolei Hu; Mingyang Song; Shiyan Li; Yu Chu; Wei-Xian Zhang; Zilong Deng

doi:10.1016/j.chemosphere.2023.140212

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

Chemosphere. 2023 Dec:343:140212. doi: 10.1016/j.chemosphere.2023.140212. Epub 2023 Sep 22.

Authors

Xiaolei Hu¹, Mingyang Song², Shiyan Li¹, Yu Chu¹, Wei-Xian Zhang¹, Zilong Deng³

Affiliations

¹ State Key Laboratory for Pollution Control, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
² Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri, 63130, United States.
³ State Key Laboratory for Pollution Control, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China. Electronic address: zilongdeng@tongji.edu.cn.

PMID: 37742762
DOI: 10.1016/j.chemosphere.2023.140212

Abstract

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 Cr_xFe_1-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.

Keywords: Chromium; Modification; Nanocellulose; Nanoscale zero-valent iron.