Novel multifunctional construction materials are needed to promote resilient infrastructure in the face of climate change and extreme weather. Nanostructured materials such as geopolymer reinforced with carbon-based nanomaterials are a promising way to reach that goal. In recent years, several studies have investigated the influence of nanomaterials on the physical properties of geopolymer composites such as compressive strength and fracture toughness. Yet, a fundamental understanding of the influence of nanomaterials on the nanoscale and micron-scale structure has been elusive so far. Our research objective is to understand how multiwalled carbon nanotubes (MWCNT) can help tailor the microstructure of geopolymers to yield architected multifunctional nanocomposites. We synthesized geopolymer nanocomposites reinforced with 50-nm thick multiwalled carbon nanotubes with mass fractions in the range of 0.1 wt%, 0.2 wt%, and 0.5 wt%. Our major finding is that MWCNTs act as hard templates that promote geopolymer formation via self-assembly. Geopolymer nanoparticle growth is observed along the walls of MWCNTs. A refinement in grain size is observed: increasing the fraction of MWCNTs by 0.5 wt% leads to a reduction in grain size by 54%. Similarly, increasing the mass fraction of MWCNTs leads to a densification of the geopolymer matrix as demonstrated by the Fourier transform infrared spectroscopy results and the statistical deconvolution analysis. Mercury intrusion porosimetry shows a nanoscale tailoring of the pore size distribution: a 26% decrease in porosity is observed as the fraction of MWCNTs is increased to 0.5 wt%. As a result of these nanoscale structural changes, a greater resistance to long-term deformation is observed for MWCNT-reinforced geopolymers, as the creep modulus increases both locally and macroscopically. At the macroscopic level, a 42% increase in the macroscopic logarithmic creep modulus is observed as the fraction of MWCNTs is increased to 0.5 wt%. These findings and the supporting methodology are important to understand how to manipulate matter below 100 nm. This research also paves the way for the design of resilient infrastructure materials with tailored microstructure and mechanical properties.
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Metal-catalyst-free access to multiwalled carbon nanotubes/silica nanocomposites (MWCNT/SiO 2 ) from a single-source precursor
The present study introduces a facile single-source precursor preparative access to bamboo-like multiwalled carbon nanotubes (MWCNTs) highly dispersed within a mesoporous silica-rich matrix. The metal-free single-source precursor was synthesized via a one-pot sol–gel process using tetramethyl orthosilicate (TMOS) and 4,4′-dihydroxybiphenyl (DHBP) and converted subsequently via pyrolysis under an argon atmosphere into MWCNT/silica nanocomposites. The in situ segregation of the highly defective bamboo-like MWCNTs was carefully investigated and has been shown to occur within the mesopores of the silica-rich matrix at relatively low temperatures and without the use of a metal catalyst. The experimental results have been supported by extensive computational simulations, which correlate the molecular architecture of the single-source precursor with the structural features of the carbon phase segregating from the silica matrix. Furthermore, the role of hydrogen in the stability of the prepared nanocomposites as well as in the high-temperature evolution and morphology of the segregated MWCNTs has been discussed based on vibrational spectroscopy, calorimetric studies and empirical potential calculations. The results obtained within the present study may allow for designing highly-defined nanocarbon-containing composites with tailored structural features and property profiles.
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- Award ID(s):
- 1634448
- NSF-PAR ID:
- 10105092
- Date Published:
- Journal Name:
- Dalton Transactions
- ISSN:
- 1477-9226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The structural characteristics of polymer nanocomposites with functionalized multiwall carbon nanotubes (MWCNTs) in poly(methyl methacrylate) matrix have been studied in relation to nanofiller loading and surface functionality. Different functional groups have been covalently attached on the MWCNTs sidewalls in order to induce interfacial interactions at nanofiller/polymer interface, which resulted in an improved nanomechanical features. Structural properties of nanocomposites, studied with XRD and Raman analysis, indicated the most pronounced decrease in a degree of amorphousness for samples containing 0.5 and 1 wt% of MWCNTs functionalized with dapsone (dapson‐MWCNT) and diethyl malonate (dem‐MWCNT). SEM and TEM micrographs confirmed improved dispersibility of the MWCNTs modified with aromatic structure of dapsone inside PMMA matrix. A significant increase in a glass transition temperature of over 60°C has been found for the 1 wt% dapson‐MWCNT nanocomposite. Additional modification of dapson‐MWCNT by further increasing aromaticity and voluminosity of attached moiety (fid‐MWCNT), showed 30°C increases in a glass transition temperature at 4 wt% of nanofiller loading, which is similar to shift of 37°C with loading of MWCNTs modified with ester terminal group. A maximum increase of 56% of reduced modulus and 86% of hardness was obtained for 1 wt% loading of dapson‐MWCNT nanofiller. POLYM. COMPOS., 38:E472–E489, 2017. © 2016 Society of Plastics Engineers
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null (Ed.)Carbon-based catalysts have been attracting extensive attention as viable candidates to replace platinum towards oxygen reduction reaction, a critical process at fuel cell cathode. An advancement has been the development of carbon-supported iron carbide (Fe3C/C) catalysts derived from the pyrolysis of metal organic frameworks (MOFs). In the present study, a series of Fe3C/C nanocomposites were prepared by controlled pyrolysis of FeMOF-NH2 with a systemic variation of the iron and zinc compositions in the MOF precursor. Scanning/transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopic measurements were carried out to examine the morphologies, structures, and elemental composition of the nanocomposites, while nitrogen adsorption/desorption and Raman studies were used to characterize the surface area and porosity. It was found that an optimal zinc to iron feeding ratio was required to produce a catalyst with a preferential pore size distribution. Electrochemical measurements revealed that the sample derived from 20% zinc replacement in the FeMOF-NH2 precursor exhibited the best electrocatalytic activity in alkaline media among the series, with the most positive onset potential and highest limiting current, which coincided with the highest surface area and porosity. The results suggest that deliberate structural engineering is critical in manipulating and optimizing the electrocatalytic activity of metal,nitrogen-codoped carbon nanocomposites.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9DT01783F
