Abstract
New approaches for the engineering of the 3D microstructure, pore modality, and chemical functionality of hierarchically porous nanocarbon assemblies are key to develop the next generation of functional aerogel and membrane materials. Here, interfacially driven assembly of carbon nanotubes (CNT) is exploited to fabricate structurally directed aerogels with highly controlled internal architectures, composed of pseudo-monolayer, CNT microcages. CNT Pickering emulsions enable engineering at fundamentally different length scales, whereby the microporosity, mesoporosity, and macroporosity are decoupled and individually controlled through CNT type, CNT number density, and process energy, respectively. In addition, metal nanocatalysts (Cu, Pd, and Ru) are embedded within the architectures through an elegant sublimation and shock-decomposition approach; introducing the first approach that enables through-volume functionalization of intricate, pre-designed aerogels without microstructural degradation. Catalytic structure-function relationships are explored in a pharma-important amidation reaction; providing insights on how the engineered frameworks enhance catalyst activity. A sophisticated array of advanced tomographic, spectroscopic, and microscopic techniques reveal an intricate 3D assembly of CNT building-blocks and their influence on the functional properties of the enhanced nanocatalysts. These advances set a basis to modulate structure and chemistry of functional aerogel materials independently in a controlled fashion for a variety of applications, including energy conversion and storage, smart electronics, and (electro)catalysis.
Highlights
The discovery of atomically thin carbon nanostructures, such as carbon nanotubes (CNTs) and graphene, with an array of impressive and unique physiochemical properties[1,2,3,4] has led to intensive research efforts into the development of a diverse range of new nanocarbon-based applications and technologies, including energy storage,[5] water treatment,[6] sensing,[7] structural composites,[8] actuators,[9] neural cell growth frameworks,[10] and many more.[11]
To investigate aerogel-induced impact on NP functionality, Cu–CuOdecorated double-wall CNT (DWCNT) and multiwall CNT (MWCNT) aerogels are assessed for their catalytic activity in a heterogeneous oxidative amidation reaction and compared with their equivalent unassembled powder analogues.[41]
Crosslinked CNT aerogels exhibit decoupled multimodal porosity controlled by the selection of CNT inner cavity, CNT number density, and droplet size
Summary
The discovery of atomically thin carbon nanostructures, such as carbon nanotubes (CNTs) and graphene, with an array of impressive and unique physiochemical properties[1,2,3,4] has led to intensive research efforts into the development of a diverse range of new nanocarbon-based applications and technologies, including energy storage,[5] water treatment,[6] sensing,[7] structural composites,[8] actuators,[9] neural cell growth frameworks,[10] and many more.[11]. Emulsion-templating has been successfully exploited to produce GO aerogels with defined, monomodal macroporous closed-cell internal architectures.[26] An interesting feature of emulsiontemplated aerogel synthesis is its scalability, as demonstrated by the fabrication of large scale, free-standing GO aerogel sheets (1 m2), based on significant inhibition of crack formation and propagation due to the disrupted alignment of GO liquid crystals in the presence of a discontinuous oil-phase.[27] Another advantage is the compatibility of emulsion-templated aerogel synthesis with continuous processing microfluidic techniques to generate superelastic reduced-GO aerogels.[28] The utilization of advanced microfluidic techniques highlights the wide ranging scope of emulsion-templating synthetic approaches, including their great potential for highly engineered aerogel microstructures Despite this potential, there are no examples which explore interfacial nanocarbon chemistry for the engineering and modulation of aerogel porosities at different length scales or to achieve this through decoupled, independent processes. To investigate aerogel-induced impact on NP functionality, Cu–CuOdecorated DWCNT and MWCNT aerogels are assessed for their catalytic activity in a heterogeneous oxidative amidation reaction and compared with their equivalent unassembled powder analogues.[41]
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