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Cationic regenerated nanocellulose hydrogel for efficient Cr(VI) removal
This work was published in Carbohydrate Polymers in 2021.
(YunJin Kim, Junsik Bang, Jungkyu Kim, June-Ho Choi, Sung-Wook Hwang, Hwanmyeong Yeo, In-Gyu Choi, Hyoung-Joon Jin, Hyo Won Kwak, 2021, Cationic surface-modified regenerated nanocellulose hydrogel for efficient Cr(VI) remediation, Carbohydrate Polymers, Volume 278, 118930, DOI: 10.1016/j.carbpol.2021.118930.)
Cellulose is the most abundant biomass on earth and eco-friendly biological macromolecules among diverse nature’s polymeric kingdoms. In particular, nanocellulose has a nanofibrillar morphology, so it is a material that can expand the range of applications such as biomaterials and adsorption materials. However, the excellent aqueous dispersibility of nanocellulose is a fatal disadvantage in the water treatment process.
Fig 1. Optical images of dissolved, regenerated cellulose in lithium bromide solution. (A) Cellulose solution, (B) regenerated cellulose, (C) mechanically stirred regenerated cellulose. (D) FE-SEM images of the lyophilized RC hydrogel. (E) Optical images of RC and P/RC hydrogel. (F) FE-SEM image of lyophilized P/RC hydrogel.
Therefore, our research team produced a regenerated cellulose hydrogel using a novel and environmentally friendly solvent system. The aqueous solution-based solvent system reduces intermolecular hydrogen bonding of cellulose so that a polymer solution can be easily obtained. In this way, a stable regenerated cellulose hydrogel was prepared.
To impart superb Cr(VI) adsorption capacity, a cationization modification process was performed on the surface of the cellulose hydrogel. The cellulose hydrogel was immersed in cationic polyethyleneimine (PEI) solution, coated and cross-linked to introduce a cationic PEI layer on the surface. After crosslinking, we confirmed the introduction of PEI and changes in the physical properties of hydrogel’s cationic nature through FTIR, XPS, zeta potential, and UTM. In addition, the cationized regenerated cellulose hydrogel exhibited remarkably superior Cr(VI) removal performance among PEI-modified adsorbents.
Fig 2. (A) Compressive stress-strain curves, (B) zeta potential results, (C) Cr(VI) removal efficiency and optical images of RC and P/RC hydrogels. (D) Effect of initial Cr(VI) concentration on Cr(VI) removal capacity, (E) Langmuir and Freundlich isotherm fit curves, and (F) comparison of the Cr(VI) removal capacity of PEI-modified adsorbents in the reported studies.
Fig 3. XPS results of Cr(VI) removal with P/RC hydrogels to analyze mechanism. (initial concentration of Cr(VI) 200 mg/L, adsorption time 4 hour). (A) Total survey spectrum, (B) high resolution Cr 2p spectra of P/RC before and after adsorption, (C) N 1s spectra, (D) chromium species changes before and after remediation with P/RC hydrogels. (E) Mechanism of Cr(VI) adsorption and reduction by P/RC
Isotherm adsorption analysis showed that this adsorption was close to heterogeneous adsorption, and XPS, ICP analysis revealed the adsorption mechanism. The first acting factor of the adsorbent prepared in this study is the electrostatic attraction between -NH3+ on the hydrogel surface and the dichromate anion. The second is the reduction of Cr(VI) to Cr(III). The last is a chelate bond between the reduced Cr(III) and the nitrogen of the amine group.
These findings emphasize that nanocellulose manufactured by an eco-friendly solvent process effectively maintains the nanomorphology and has endless possibilities as a water restoration material. We are expanding research to increase the application fields of diverse lignocellulosic biomass.