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Xuefeng Zhang and EI Barbary Hassan's group at Mississippi State University have made progress in making nanocellulose and nanochitin composite hydrogels
2019-12-24 Source: Polymer Technology

Aerogels are generally obtained from hydrogels by supercritical drying or freeze-drying and dehydration, so it is important to develop simple and effective methods for preparing cellulose and chitin hydrogels. Hydrogels can be obtained by directly dissolving cellulose and chitin, but currently there are only a few solutions that can dissolve cellulose and chitin, and these solutions have certain risks and toxicity, so this method is difficult to be widely used. On the other hand, nanocellulose and nanochitin dispersions can also be converted into hydrogels by suitable gel reactions. The chemical gel method can prepare high-strength hydrogels, but chemical cross-linking agents also have danger and toxicity problems. Physical gel methods such as ultrasound, solution pH adjustment, solution replacement, and heat treatment can also be used to prepare hydrogels, but this method has a series of problems such as complex operations and time and energy consumption. Therefore, how to design and develop a simple and easy method for making cellulose and chitin hydrogels is very important.

In response to this problem, Assistant Professor Zhang Xuefeng and associate professor EI Barbary Hassan of Mississippi State University have developed a simple and effective solution for obtaining cellulose and chitin composite hydrogels. Nanocellulose with negative charge on the surface is obtained through TEMPO oxidation treatment; nanochitin with positive charge on the surface is obtained through partial deacetylation reaction. Depending on the electrostatic attraction between nanocellulose and nanochitin, the two nanofibers can be 'self-assembled' in an aqueous dispersion to form a composite hydrogel. After freeze-drying, cellulose and chitin composite aerogels can be obtained. Due to the presence of multiple functional groups on the surface, the composite aerogels exhibit good adsorption effects and can be used as a green and efficient adsorbent for water purification.

The advantages of this method include: 1. Simple and convenient. Due to the electrostatic force between the nanofibers, the hydrogel can be formed in one minute by 'self-assembly' after mixing the two dispersions; This method avoids the use of dangerous chemical cross-linking agents; 3. Universal adaptability, this method of electrostatic force induced 'self-assembly' is also applicable to the production of other biomass macromolecules hydrogels.

(cd) 局部脱乙酰基反应获得表面带正电荷的纳米甲壳素; (e)静电力诱导'自组装'形成复合水凝胶; (fg)冷冻干燥后获得轻质(f)、多孔(g)复合气凝胶。 Figure 1. (ab) TEMPO oxidation reaction to obtain negatively charged nanocellulose on the surface; (cd) Local deacetylation reaction to obtain positively charged nanochitin on the surface; (e) Electrostatic force induced 'self-assembly' to form a composite Hydrogel; (fg) A lightweight (f), porous (g) composite aerogel was obtained after freeze-drying.

(fg) 纳米纤维分散液初始浓度对水凝胶产率的影响; (hi) 纳米纤维素与纳米甲壳素质量配比对水凝胶产率的影响。 Figure 2. (ae) Manufacturing process of composite hydrogel; (fg) Effect of initial concentration of nanofiber dispersion on hydrogel yield; (hi) Mass ratio of nanocellulose and nanochitin on hydrogel yield Impact.

(b) 不同pH环境下纳米纤维素与纳米甲壳素之间的离子键和氢键连接。 Figure 3. (a) XPS spectra of composite aerogels at different solution pH; (b) Ionic and hydrogen bonding between nanocellulose and nanochitin at different pH environments.

(bc) 不同pH条件下,气凝胶对亚甲基蓝(b)和三价砷(c)的吸附。 Figure 4. (a) Composite hydrogel and aerogel adsorb methylene blue; (bc) Adsorption of methylene blue (b) and trivalent arsenic (c) by aerogel at different pH conditions.  

. (df) 复合气凝胶对三价砷的吸附动力学(a),等温线(b),及与其它材料吸附效果的对比图(c)。 Figure 5. (ac) Adsorption kinetics of methylene blue on composite aerogel (a), isotherm (b), and comparison with other materials (c); (df) Trivalent aerogel on trivalent Adsorption kinetics of arsenic (a), isotherm (b), and comparison of adsorption effects with other materials (c).

Figure 6. Multiple adsorption of methylene blue by composite aerogels.

Recently, the achievement was published in ACS Applied Materials & Interfaces (DOI: 10.1021 / acsami.9b15139) under the title of Biohybrid Hydrogel and Aerogel from Self-Assembled Nanocellulose and Nanochitin as a High-Efficiency Adsorbent for Water Purification. Zhang Xuefeng , Mississippi State University The assistant professor is the corresponding author and first author of the paper, and Associate Professor EI Barbary Hassan is the co-corresponding author of the paper. This project was supported by the USDA National Forest Products Laboratory Fund (G00002749).

Paper link:

X. Zhang, I. Elsayed, C. Navarathna, GT Schueneman, EB Hassan, Biohybrid Hydrogel and Aerogel from Self-Assembled Nanocellulose and Nanochitin as a High-Efficiency Adsorbent for Water Purification, ACS Appl. Mater. Interfaces. 11 (2019) 46714--46725.

http://pubs.acs.org/doi/10.1021/acsami.9b15139

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