Macroscopic-Scale Template Synthesis of Robust Carbonaceous Nanofiber Hydrogels and Aerogels and Their Applications
Macroscopic-Scale Template Synthesis of Robust Carbonaceous Nanofiber Hydrogels and Aerogels and Their Applications
复制标题
鲁棒碳质纳米纤维水凝胶和气凝胶的宏观尺度模板合成及其应用
DOI：
10.1002/anie.201200710
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Yu, Shu-Hong
中科院分区：
文献类型：
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作者：
Liang, Hai-Wei;Guan, Qing-Fang;Yu, Shu-Hong
水凝胶和气凝胶是两个典型的凝胶家族，根据它们所包含的介质，即水和空气，分别进行分类。水凝胶不仅以各种形式（例如，果冻、牙膏、隐形眼镜和发胶）渗透到我们的日常生活中，而且还作为功能性软材料被广泛探索用于各种科学领域。[1，2]用空气代替水凝胶或其他湿凝胶中的液体溶剂而不破坏网络结构可以导致新型多孔材料，即气凝胶。[3，4]特别是，凝胶中具有开放孔的3D纳米级网络允许离子和分子进入和快速扩散，因此水凝胶/气凝胶表现出优异的性能，如超级吸附剂，[5，6]电池和超级电容器的电极材料，[7]催化剂载体，[8]以及化学和生物传感器。[9，10]尽管气凝胶具有突出的潜力，但在其广泛的实际应用之前，仍然必须解决气凝胶合成中的几个挑战。与常规气凝胶相关的主要问题是差的机械稳定性。通过在预成型的3D网络上纳米铸造保形聚合物涂层可以提高气凝胶的机械强度，但这伴随着其孔隙率的急剧下降。[11此外，为了防止网络在凝胶中塌陷，超临界干燥是用于溶剂去除的最广泛使用的技术。由于工业超临界干燥的限制，很难大规模制备低成本的气凝胶。虽然最近几种纳米材料包括碳纳米管，[13，14]纤维素纳米纤维[15]和新发现的石墨烯[16]已经被用作构建块并组装成整体凝胶，但缺乏对其物理化学性质的精确控制，特别是结构单元的尺寸、孔隙率和它们的表面化学性质，这在气凝胶的进一步设计和功能化中对于各种应用是至关重要的。在这里，我们报告了一类新的单片水凝胶/气凝胶组成的高度均匀的碳纳米纤维（CNFs），基于最近，发达的模板导向水热碳化（HTC）过程。[17-19]与传统的气凝胶制备工艺相比，我们的合成方法具有一些显著的优点：1）仅使用大型高压釜，无需改变反应物浓度和反应时间，即可从30 mL直接放大到12 L; 2）在宽范围内容易且精确地控制CNF水凝胶/气凝胶的结构参数和机械强度; CNF凝胶具有优异的柔韧性和高的化学反应活性，具有广阔的应用前景。
Hydrogels and aerogels are two typical families of gels, classified according to the medium they encompass, that is, water and air, respectively. Hydrogels have not only pervaded our everyday life in a variety of forms (eg, fruit jellies, toothpaste, contact lenses, and hair gel), but have also been extensively explored as functional soft materials for use in various scientific fields.[1, 2] Replacing the liquid solvent in hydrogels or other wet gels by air without collapsing the network structure can lead to a new type of porous materials, namely, aerogels.[3, 4] Particularly, 3D nanoscale networks with open pores in the gels allow access and fast diffusion of ions and molecules, and thus hydrogels/aerogels have exhibited excellent performance as super adsorbents,[5, 6] electrode materials for batteries and supercapacitors,[7] catalyst supports,[8] and chemical and biological sensors.[9, 10] Despite their outstanding potential, several challenges in aerogel synthesis still must be addressed prior to their extensive practical application. The major problem associated with conventional aerogels is poor mechanical stability. The mechanical strength of aerogels could be enhanced by nanocasting conformal polymer coatings on preformed 3D networks, but this was accompanied by dramatic decreases in their porosity.[11, 12] Furthermore, to prevent the network from collapsing in a gel, supercritical drying is the most widely used technique for solvent removal. It is difficult to prepare low-cost aerogels on a large scale due to the limitations of industrial supercritical drying.Although several nanomaterials including carbon nanotubes,[13, 14] cellulose nanofibers,[15] and the newly discovered graphene [16] have been recently used as building blocks and assembled into monolithic gels, there is a lack of precise control of their physicochemical properties, particularly the size of building blocks, the porosity, and their surface chemistry, which are crucial in the further design and functionalization of aerogels for various applications. Here we report a new class of monolithic hydrogels/aerogels consisting of highly uniform carbonaceous nanofibers (CNFs), based on the recent, well-developed templatedirected hydrothermal carbonization (HTC) process.[17–19] Compared with the conventional process for aerogel preparation, our synthetic method has some significant advantages: 1) Direct scaleup from 30 mL to 12 L just by using a large autoclave and without changing reactant concentrations and reaction time; 2) Easy and precise control of the structural parameters and mechanical strength of the CNF hydrogels/aerogels over a wide range; and 3) Extraordinary flexibility and high chemical reactivity of the CNF gels give them great application potential.