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Química

纤维素纳米纤维生物模板复合气凝胶的合成方法

Published: May 09, 2019
doi:
10.3791/59176
, , , , , ,
1Department of Chemistry and Life Science,United States Military Academy, 2Department of Mathematical Sciences,United States Military Academy, 3Armament Research, Development and Engineering Center,U.S. Army RDECOM-ARDEC

Summary

提出了纤维素纳米纤维生物模板复合气凝胶的合成方法。由此产生的复合气凝胶材料为催化、传感和氢气储存应用提供了潜力。

Abstract

本文提出了一种合成纤维素纳米纤维生物模板化复合气凝胶的方法。惰性金属气凝胶合成方法往往导致脆弱的气凝胶形状控制不良。使用Carboxy甲基化纤维素纳米纤维(CNFs)形成共价粘结水凝胶,可减少金属离子,如在CNF上,在上临界后控制纳米结构和宏观气凝胶单体形状干燥。在存在乙烯二胺的情况下,使用1-乙基-3-(3-二甲基氨基丙基)盐酸甲酰胺(EDC)实现碳甲基化纤维化纳米纤维的交联。CNF 水凝胶在整个合成步骤中保持其形状,包括共价交联、与前体离子的平衡、高浓度还原剂的金属还原、水中的沉淀、乙醇溶剂交换和 CO2超临界干燥。改变前体钚的电浓度,可以通过直接的电子化学还原来控制最终气凝胶复合材料中的金属含量,而不是依赖于其他预成型纳米粒子的相对缓慢的凝聚溶胶技术。该方法以扩散为基础,将化学物种引入和去除水凝胶,适用于较小的散装几何形状和薄膜。纤维素纳米纤维-铂复合气凝胶的特征,带扫描电子显微镜、X 射线衍射学、热重力分析、氮气吸附、电化学阻抗光谱和循环伏特测量表示具有高表面积、金属化的多孔结构。

Introduction

基斯特勒首先报道的气凝胶,提供比散装材料1、2、3密度低的多孔结构。贵金属气凝胶因其在功率和能源、催化和传感器应用方面的潜力而引起了科学界的兴趣。贵金属气凝胶最近通过两种基本策略合成。一种策略是诱导预先形成的纳米粒子4、5、6、7的凝聚。纳米粒子的溶胶凝聚可以由链接分子驱动,溶液离子强度的变化,或简单的纳米粒子表面自由能量最小化7,8,9。另一个策略是从金属前体溶液9、10、11、12、13的单一还原步骤中形成气凝胶。这种方法还用于形成双金属和合金贵金属气凝胶。第一种策略通常很慢,可能需要长达数周的纳米粒子凝聚14。直接还原方法虽然通常比较快,但宏观气凝胶单体的形状控制较差。

一种可能的综合方法,以解决挑战与控制惰性金属气凝胶宏观形状和纳米结构是采用生物温度15。生物模板利用从胶原蛋白、明胶、DNA、病毒到纤维素等生物分子,为纳米结构的合成提供一个形状导向模板,由此产生的金属纳米结构具有生物模板分子16,17。纤维素纳米纤维作为生物模板很有吸引力,因为纤维素材料具有高天然丰度,其高纵横比线性几何形状,以及化学功能化其葡萄糖单体的能力 18,19 20,21,22,23.纤维素纳米纤维 (CNF) 已用于合成用于光阳极24的三维 TiO2纳米线、用于透明纸电子25的银纳米线 25 和用于催化的铂气凝胶复合材料26.此外,TEMPO氧化纤维素纳米纤维已被用作生物模板和还原剂在制备铂装饰CNF气凝胶27。

这里提出了一种合成纤维素纳米纤维生物模板复合气凝胶的方法。形状控制较差的易碎气凝胶适用于一系列贵金属气凝胶合成方法。用于形成共价水凝胶的Carboxy甲基化纤维素纳米纤维(CNFs)允许减少CNF上的金属离子,如金晶,从而在超临界干燥后控制纳米结构和宏观气凝胶单片形状。Carboxy甲基化纤维素纳米纤维交联是使用1-乙基-3-(3-二甲基氨基丙基)盐酸甲二酰胺(EDC)在乙烯二胺作为CNF之间的链接分子的情况下实现的。CNF 水凝胶在整个合成步骤中保持其形状,包括共价交联、与前体离子的平衡、高浓度还原剂的金属还原、水中的沉淀、乙醇溶剂交换和 CO2超临界干燥。前体子浓度变化允许通过直接减少的气凝胶金属含量来控制最终气凝胶的金属含量,而不是依赖于在溶胶方法中使用的预成型纳米粒子的相对缓慢的凝聚。该方法以扩散为基础,将化学物种引入和去除水凝胶,适用于较小的散装几何形状和薄膜。纤维素纳米纤维-铂复合气凝胶的特征,带扫描电子显微镜、X 射线衍射学、热重力分析、氮气吸附、电化学阻抗光谱和循环伏特测量表示高表面积,金属化的多孔结构。

Protocol

注意:使用前请查阅所有相关的安全数据表 (SDS)。执行化学反应时,请使用适当的安全实践,包括使用烟罩和个人防护设备 (PPE)。氢气的快速演化会导致反应管中的高压,导致瓶盖爆裂,溶液喷出。确保反应管保持打开状态,并指向远离实验者,如协议中规定的那样。 1. 纤维素纳米纤维水凝胶制备 纤维素纳米纤维溶液的制备:通过将1.5克的Carboxy甲基纤维化纳米纤维与50 mL的去离?…

Representative Results

图1描述了在乙烯二胺存在的情况下将纤维素纳米纤维与EDC共价交联的方案。EDC 交联导致卡博基和原胺功能组之间的酰胺键。鉴于Carboxy甲基纤维素纳米纤维仅具有用于交联的甲酰基组,因此,存在二胺链接分子(如乙烯二胺)对于通过两个酰胺键将两个相邻的CNF共价连接至关重要。为了确认交联,图2显示了与CNF水凝胶相比,在存在乙烯…

Discussion

这里介绍的贵金属纤维素纳米纤维生物模板气凝胶合成方法,使气凝胶复合材料具有稳定的金属成分。离心后压实纤维纳米纤维的共价交联导致水凝胶在随后的氧化铝在氧化铝的合成步骤中具有机械的持久性,即钠的电平衡、电化学还原、喷皮、溶剂交换,和超临界干燥。水凝胶稳定性在电化学还原步骤中至关重要,因为还原剂溶液的浓度高(2MNaBH 4),并因此产生猛烈的氢进化。本研究中使用的?…

Declarações

The authors have nothing to disclose.

Acknowledgements

作者感谢美国陆军贝内特实验室的斯蒂芬·巴托卢奇博士和约书亚·莫雷尔博士使用他们的扫描电子显微镜。这项工作得到了美国西点军校的教师发展研究基金赠款的支持。

Materials

0.5 mm platinum wire electrode BASi MW-4130 Used for auxillery electrode and separately for lacquer coating and use as a working electrode
1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) Sigma-Aldrich  1892-57-5
2-(N-morpholino)ethanesulfonic acid (MES) Sigma-Aldrich 117961-21-4 
Ag/AgCl (3M NaCl) Reference Electrode BASi MF-2052
Carboxymethyl cellulose, TEMPO Cellulose Nanofibrils, Dry Powder University of Maine Process Development Center No 8
Ethanol, 200 proof PHARMCO-AAPER 241000200
Ethylenediamine Sigma-Aldrich  107-15-3
Fourier-Transform Infrared (FTIR) Spectrometer, Frontier Perkin Elmer L1280044
Hydrochloric Acid CORCO 7647-01-0
Na2PdCl4 Sigma-Aldrich 13820-40-1
NaBH4 Sigma-Aldrich 16940-66-2
Pd(NH3)4Cl2 Sigma-Aldrich 13933-31-8
Potentiostat Biologic-USA VMP-3 Electrochemical analysis-EIS, CV
Scanning Electron Mciroscope (SEM) Helios 600 Nanolab ThermoFisher Scientific
Supercritical Dryer Leica EM CPD300 Aerogel supercritical drying with CO2
Surface and Pore Analyzer Quantachrome NOVA 4000e Nitrogen gas adsorption
Thermal Gravimetric Analysis TA instruments TGA Q500
Ultrasonic Cleaner MTI EQ-VGT-1860QTD
XRD PanAlytical Empyrean X-ray diffractometry
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Tags

Cellulose NanofiberBiotemplatePalladiumAerogelCompositeSynthesis MethodCrosslinkingHydrogelFTIR
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Burpo, F. J., Palmer, J. L., Mitropoulos, A. N., Nagelli, E. A., Morris, L. A., Ryu, M. Y., Wickiser, J. K. Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels. J. Vis. Exp. (147), e59176, doi:10.3791/59176 (2019).
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