摘要
纤维素纳米纤丝(CNF)作为一种来源丰富的可再生纳米材料,具有优异的机械性能、高比表面积及化学可修饰性等优点,采用物理或化学交联所制备的CNF基水凝胶具有较好的机械性能和溶胀率等,在工业废水处理领域具有良好的应用前景。本文主要介绍了纯CNF水凝胶和CNF纳米复合水凝胶的相应制备方法及性能,同时也介绍了其在工业废水中对染料或重金属离子吸附方面的应用进展,最后指出了CNF基水凝胶在废水处理应用中存在的问题及未来主要研究方向。
纤维素来源广泛,纳米纤维素是其物理结构最小单元,具有分子链高度有序排列特征,机械性能优异(如高拉伸强度和弹性模量(130~ 150 GPa))、高比表面积、低密度(低至1.6 g/c
造纸、皮革、纺织和食品等工业生产过程大多会产生含有染料和重金属离子的废水,这些污染物以离子或者化合物的形式在生态圈流动分布以及聚集,对人体和其他水生动植物的健康造成了严重的危害。目前,处理含染料、重金属离子废水的方法包括吸附法、生物降解法、絮凝、光催化降解和其他方
与CNC相比,高长径比和半结晶结构的CNF具有明显形成缠结网络的倾向,有利于形成更稳定的水凝胶,且获得的水凝胶弹性更大。基于CNF的优良性能,CNF被广泛用于各种亲水性和疏水性复合基质的增强剂来合成水凝胶,或CNF与聚合物通过物理或化学交联合成纳米复合水凝胶,主要分为纯CNF水凝胶和CNF纳米复合水凝胶。
通常,纯CNF水凝胶中CNF质量分数一般为0.05%~6%,有报道表明CNF水凝胶储能模量(G')值高达100 kP
由于大多数CNF都含有无定形区纤维素和结晶区纤维素,Abe等
CNF水凝胶也非常适用于各种组织工程和生物医学应用。 Bhattacharya等
CNF与诸多亲水性聚合物具有较好的相容性,因此,在CNF中加入其他聚合物可以制成纳米复合水凝胶,常见的聚合物包括聚乙烯醇(PVA)、聚丙烯酰胺(PAM)和聚丙烯酸酯(PAA)、聚乙二醇(PEG)、纤维素衍生物、壳聚糖、胶原蛋白、藻酸盐和明胶
聚乙二醇(PEI),聚氮异丙基丙烯酰胺(PNIPAm),聚甲基乙烯醚(PMVA),马来酸(MA)。
在制备CNF纳米复合水凝胶时可使用较高固含量的CNF分散体形成稳定的结构,并且较高的制备浓度使CNF在均匀化过程中被强制成平行结构,而不是形成随机定向3D网络结构,同时也给脱气和成型带来问题。Benselfelt等
鉴于许多生物组织都表现出机械性各向异性或自愈合性,因此,大多数专家的研究重点也就集中在CNF基水凝胶向异性或自愈合性。叶家婧等

图1 CNF纳米复合水凝胶作为应变传感器的应用探
由于CNF纳米复合水凝胶具有较高的溶胀能力,已有研究将其用作吸收

图2 CNF/CGG复合水凝胶吸附金属离子和染料示意
据国外文献报道,纳米纤维素材料可制备成不同形态的吸附剂,如粉末、凝胶等,可广泛应用于废水中染料和重金属离子的去除。虽然粉末形态的纳米纤维素材料具有比表面积大等优点,但存在易流失、难回收、重复利用率低等缺点。研究者们发现,凝胶状态的纳米纤维素在一定程度上克服了粉末状材料的缺点,并在废水处理领域得到广泛研
高的机械强度、高比表面积和亲水性是功能水凝胶捕捉废水中选择性污染物的特性要求。CNF基水凝胶中的吸附原理包括物理吸附(可逆过程)和化学吸附(不可逆过程),吸附性能很大程度上取决于离子交换和静电相互作用的能

图3 CNF基水凝胶重金属吸附和荧光检测机
合成的荧光CNF基水凝胶放入含有重金属离子的溶液中,荧光CNF基水凝胶表面化学基团诱导溶液中重金属离子初步富集,荧光CNF基水凝胶内部纳米纤维素骨架作为吸附聚集体,加速重金属离子的扩散和聚集;内部三维网络结构提供大量离子传输通道,促进重金属离子从外部扩散到内部。同时,碳量子点被包裹在水凝胶的三维网状结构中,提高荧光信号强度、稳定性。
增加CNF表面负电性基团(如羧基)的含量可以进一步提高其对阳离子的吸附能力,此外,CNF通过表面改性或接枝选择性单体,也可提高CNF对水溶液中重金属的吸附能力。CNF复合壳聚糖的水凝胶都会通过增大比表面积来提高吸附能力,且水凝胶机械性能提高。Zhou等
有研究者使用氧化石墨烯(GO)、CNF和自组装维生素C组合制成了具有蜂窝状结构的多孔混合海绵。将有机染料模型污染物亚甲基蓝和重金属离子C
此外,有研究表
甲基丙烯酸羟乙酯(HEMA)、丙烯酸酯(AA)、石墨烯量子点(GQDs)。
纤维素纳米纤丝(CNF)凭借其来源丰富、可再生、化学反应活性高、比表面积大、密度低等优点,使得CNF基水凝胶具有机械性能高、溶胀率高、生物相容性和刺激响应特性等性能,CNF基水凝胶对工业废水中的重金属离子和染料吸附方面具有巨大的应用潜力。然而,目前关于CNF基水凝胶在工业废水吸附方面的研究主要还是停留在实验室阶段,距离真正应用还有一定的距离,存在的主要挑战包括以下几方面:①为了制备CNF基水凝胶的功能材料,需要寻找更加适合的反应溶剂,提高CNF的分散性,促进反应的进行。②掌握CNF的原料来源和制备技术对CNF基水凝胶性能的影响至关重要。③CNF基水凝胶吸附材料在废水体系中对染料或重金属离子的吸附选择性、再生性、稳定性等均较差,且制备成本高,限制了其在废水处理领域的工业化应用。此外,CNF基水凝胶在废水处理中还需要建立具体的材料吸附性能评价,如吸附量标准、再生次数、力学性能等。总的来说,CNF基水凝胶凭借其优越的机械性能在废水处理、生物医学、环境和生物传感等领域的应用还处于起步阶段,相信通过未来几年的努力克服以上挑战,CNF基水凝胶能够促进社会的进步和改善人们的生活环境。
参考文献
LI Dong, FENG Na, LIU Siyuan, et al. Review on Cellulose Nanocrystal Assembly for Optical Applications[J]. Paper and Biomaterials,2019,4(2):54. [百度学术]
刘 慰,司传领,杜海顺,等.纳米纤维素水凝胶的制备及其在生物医学领域的应用进展[J].林业工程学报,2019,4(5):1. [百度学术]
LIU Wei, SI Chuanling, DU Haishun, et al. Advance in preparation of nanocellulose-based hydrogels and their biomedical applications[J]. Journal of Forestry Engineering, 2019,4(5):1. [百度学术]
WANG Mingzheng, CHA Ruitao . Industrialization Progress of Nanocellulose in China[J]. Paper and Biomaterials,2019,4(2):63. [百度学术]
Diego M Nascimento , Yann l Nunes , Maria C B Figueiredo , et al. Nanocellulose nanocomposite hydrogels: technological and environmental issues[J]. Green Chemistry, 2018(3):1. [百度学术]
陈金伟, 商士斌,沈明贵,等.纳米纤维素改性制备重金属离子吸附剂研究进展[J].化工新型材料,2019,47(11):46. [百度学术]
CHEN Jinwei, SHANG Shibin, SHEN Minggui, et al. Research Progress in Preparation of Heavy Metal Ion Adsorbent Modified by Nanocellulose[J].New Chemical Materials, 2019,47(11):46. [百度学术]
覃发梅,邱学青,孙 川,等.纳米纤维素去除水体系重金属离子的研究进展[J]. 化工进展,2019,38(7):3390. [百度学术]
Qin Famei, Qiu Xueqing, Sun Chuan,et al. Research progress in nanocellulose for the removal of heavy metal ions in water[J]. Chemical Industry and Engineering Progress, 2019,38(7):3390. [百度学术]
朱俊芳,杨嵘晟,冯树波.甲基丙烯酸接枝纳米纤维素水凝胶的制备及吸附性能研究[J].化学研究与应用,2019,31(2):325. [百度学术]
Zhu Junfang, Yang Rongsheng, Feng Shubo. Preparation and adsorption properties of methacrylic acid grafted nanocellulose hydrogel[J].Chemical Research and Application,2109,31(2):325. [百度学术]
De France K J, Yager K G, Hoare T, et al.Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field[J]. Langmuir, 2016, 32 (30):7564. [百度学术]
Pääkkö M, Ankerfors M, Kosonen H, et al. Enzymatic Hydrolysis Combined with Mechanical Shearing and High-Pressure Homogenization for Nanoscale Cellulose Fibrils and Strong Gels[J]. Biomacromolecules , 2007, 8 (6):1934. [百度学术]
Fall A B, Lindström S B, Sundman O, et al. Colloidal Stability of Aqueous Nanofibrillated Cellulose Dispersions[J]. Langmuir , 2011, 27 (18):11332. [百度学术]
Lundahl M J, Cunha A G, Rojo E, et al. Strength and Water Interactions of Cellulose I Filaments Wet-Spun from Cellulose Nanofibril Hydrogels[J]. Sci. Rep. , 2016, 6: 30695. [百度学术]
Kevin J, De France, Todd Hoare , et al. Review of hydrogels and aerogels containing nanocelulose[J].Chem. Mater., 2017,29:4609. [百度学术]
Abe K, Yano H. Formation of Hydrogels from Cellulose Nanofibers[J]. Carbohydr. Polym. , 2011, 85 (4):733. [百度学术]
Abe K, Yano H. Cellulose Nanofiber-Based Hydrogels with High Mechanical Strength[J]. Cellulose, 2012, 19 (6):1907. [百度学术]
Bhattacharya M, Malinen M M, Lauren P, et al. Nanofibrillar Cellulose Hydrogel Promotes Three-Dimensional Liver Cell Culture[J]. Controlled Release, 2012, 164 (3):291. [百度学术]
Zander N E, Dong H, Steele J, et al. Metal Cation Cross-Linked Nanocellulose Hydrogels as Tissue Engineering Substrates[J]. ACS Appl. Mater. Interfaces, 2014, 6 (21): 18502. [百度学术]
Masruchin N, Park B D, Causin V, et al. Characteristics of TEMPO-Oxidized Cellulose Fibril-Based Hydrogels Induced by Cationic Ions and Their Properties[J]. Cellulose, 2015, 22 (3):1993. [百度学术]
Dong H, Snyder J F, Tran D T, et al. Hydrogel, Aerogel and Film of Cellulose Nanofibrils Functionalized with Silver Nanoparticles[j]. Carbohydr. Polym. ,2013, 95 (2): 760. [百度学术]
Yang J, Xu F, Han C R. Metal Ion Mediated Cellulose Nanofibrils Transient Network in Covalently Cross-Linked Hydrogels: Mechanistic Insight into Morphology and Dynamics[J]. Biomacromolecules ,2017, 18:1019. [百度学术]
Benselfelt T, Lars Wagberg . Unidirectional swelling of dynamic cellulose nanofibril networks;A platform for tunable hydrogels and aerogels with 3D shaperbility[J]. Biomacromolecules, 2019,20(6):401. [百度学术]
叶家婧,陈 鑫,鄢雨欣,等. 纳米纤维素自愈合水凝胶的构筑[J]. 广州化工,2019,47(4):39. [百度学术]
YE Jiaqian, CHEN Xin, YAN Yuxin, et al.Preparation of self-healing hydrogels based on cellulose nanofibrils[J].Guangzhou Chemical Industry,2019,47(4):39. [百度学术]
SHAO Changyou, WANG Meng, MENG Lei, et al. Mussel-inspried cellulose nanocomposite tough hydrogels with synergistic self-healing, adhesive, and strain-sensitive properties[J].Chemistry of Materials,2018,30(9):3110. [百度学术]
Chinga-Carrasco G, Syverud K. Pretreatment-Dependent Surface Chemistry of Wood Nanocellulose for pH-Sensitive Hydrogels[J]. Biomater. Appl., 2014, 29 (7491):423. [百度学术]
Yue Y, Han J, Han G, et al. Cellulose Nanofibers Reinforced Sodium Alginate-Polyvinyl Alcohol Hydrogels: Core-Shell Structure Formation and Property Characterization[J].Carbohydr. Polym, 2016, 147: 155. [百度学术]
Dai Lei, Cheng Ting, Xi Xiangju, et al. A versatile TONC/CGG self-assembling hydrogel for integrated wastewater treatment[J].Cellulose, 2019:doi.org/10.1007/s10570-019-02834-x. [百度学术]
殷晓春,思广慧,师玉卓,等.纳米纤维素的改性及其吸附重金属离子的应用研究[J].高分子通报,2019(11):15. [百度学术]
YIN Xiaochun, SI Guanghui, SHI Yuzhou,et al. A review on adsorption of heavy metal ions by modified nanocellulose-based materials[J].Polymer Bulletin,2019(11):15. [百度学术]
Zhou J,Butchosa N, Jayawardena H S N, et al.Synthesis of multifunctional cellulose nanocrystals for lectin recognition and bacterial imaging[J].Biomacromolecules.2015,16:1426. [百度学术]
张 蝶,蔡 杰,徐 威,等. 纤维素纳米纤维水凝胶的构筑与吸附性能研究[J]. 材料工程学报,2019,4(2):92. [百度学术]
ZHANG Die, CAI Jie, XU Wei, et al. Synthesis, characterization and adsorption property of cellulose nanofiber-based hydrogels[J].Journal of Forestry Engineering,2019,4(2):92. [百度学术]
Yu Z, Liu J, Tan C S, et al. Supramolecular Nested Microbeads as Building Blocks for Macroscopic Self-healing Scaffolds[J].Angewandte Chemie International Edition,2018,57(12):3079. [百度学术]
Van Tran, V Park D, Lee Y C. Hydrogel Applications of Contaminants in Water and Wastewater Treatment[J]. Environmental Science and Pollution Research,2018,http://doi.org/10.1007/s11356-018-2605-y. [百度学术]
Abdelwahab H E, Hassan S Y, Mostafa M A, et al. Synthesis and Characterization of Glutamic-chitosan Hydrogel for Copper and Nickel Removal from Wastewater[J].Molecules,2016,21(6):684. [百度学术]
Guo Xin, Xu Dong, Yan Hanmeng,et al. A novel fluorescent nanocellulosic hydrogel based on carbon dots for efficient adsorption and sensitive sensing in heavy metals[J].Journal of Materials Chemistry A,2019,47:27081. [百度学术]
Zhou Y, Fu S, Zhang L, et al. Use of Carboxylated Cellulose Nanofibrils-Filled Magnetic Chitosan Hydrogel Beads as Adsorbents for Pb(II)[J]. Carbohydr Polym., 2014, 101:75. [百度学术]
Youselfi N, Wong K K, Hosseinidoust Z, et al. Hierarchically porous, ultra strong reduced grapheme oxide-cellulose nanocrystal sponges for exceptional adsorption of water contaminants[J].Nanocale,2018,10(15):7171. [百度学术]
Mohammed N,Grishkewich N,Waeijen H A,et al. Continuous Flow Adsorption of Methylene Blue by Cellulose Nanocrystals-Alginate Hydrogel Beads in Packed Columns[J].Carbohydr. Polym., 2016, 136: 1194. [百度学术]
Ren J, Dai Q, Zhong H, et al. Quaternized xylan/cellulose nanocrystal reinforced magnetic hydrogels with high strength[J]. Cellulose,2018,25(8):4537. [百度学术]
Chau M,Sriskandha S E,Pichugin D,et al. Ion-mediated gelation of aqueous suspensions of cellulose nanocrystals[J]. Biomacromolecules,2015,16: 2455. [百度学术]
Jamileh Shojaeiarani , Dilpreet bajwa , Alimohammad Shirzadifar . A review on cellulose nanocrystals as promising biocompounds for the synthsis of nanocomposite hydrogels[J]. Carbohydrate Polymers, 2019,216:247. [百度学术]
Jamileh Shojaeiarani, Dilpreet Bajwa, Alimohammad Shirzadifar. A review on cellulose nanocrystals as promising biocompounds for the synthesis of nanocomposite hydrogels[J].Carbohydrate Polymers, 2019,216:247. CPP [百度学术]