Publications by authors named "James William Klett"

2 Publications

  • Page 1 of 1

Graphene reinforced carbon fibers.

Sci Adv 2020 Apr 24;6(17):eaaz4191. Epub 2020 Apr 24.

Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer's Way, Charlottesville, VA 22904, USA.

The superlative strength-to-weight ratio of carbon fibers (CFs) can substantially reduce vehicle weight and improve energy efficiency. However, most CFs are derived from costly polyacrylonitrile (PAN), which limits their widespread adoption in the automotive industry. Extensive efforts to produce CFs from low cost, alternative precursor materials have failed to yield a commercially viable product. Here, we revisit PAN to study its conversion chemistry and microstructure evolution, which might provide clues for the design of low-cost CFs. We demonstrate that a small amount of graphene can minimize porosity/defects and reinforce PAN-based CFs. Our experimental results show that 0.075 weight % graphene-reinforced PAN/graphene composite CFs exhibits 225% increase in strength and 184% enhancement in Young's modulus compared to PAN CFs. Atomistic ReaxFF and large-scale molecular dynamics simulations jointly elucidate the ability of graphene to modify the microstructure by promoting favorable edge chemistry and polymer chain alignment.
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http://dx.doi.org/10.1126/sciadv.aaz4191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182419PMC
April 2020

Efficient Solar-Thermal Distillation Desalination Device by Light Absorptive Carbon Composite Porous Foam.

Glob Chall 2019 Aug 8;3(8):1900003. Epub 2019 Apr 8.

Energy and Transportation Science Division Oak Ridge National Laboratory Oak Ridge TN 37831 USA.

Solar-thermal driven desalination based on porous carbon materials has promise for fresh water production. Exploration of high-efficiency solar desalination devices has not solved issues for practical application, namely complicated fabrication, cost-effectiveness, and scalability. Here, direct solar-thermal carbon distillation (DS-CD) tubular devices are introduced that have a facile fabrication process, are scalable, and use an inexpensive but efficient microporous graphite foam coated with carbon nanoparticle and superhydrophobic materials. The "black" composite foam serving as a solar light absorber heats up salt water effectively to produce fresh water vapor, and the superhydrophobic surface of the foam traps the liquid feed in the device. Two proof-of-principle distillation systems are adopted, i.e., solar still and membrane distillation and the fabricated devices are evaluated for direct solar desalination efficiency. For the solar still, nanoparticle and fluorosilane coatings on the porous surface increase the solar energy absorbance, resulting in a solar-steam generation efficiency of 64% from simulated seawater at 1 sun. The membrane distillation demonstrates excellent vapor production (≈6.6 kg m h) with >99.5% salt rejection under simulated 3 sun solar-thermal irradiation. Unlike traditional solar desalination, the adaptable DS-CD can easily be scaled up to larger systems such as high-temperature tubular modules, presenting a promising solution for solar-energy-driven desalination.
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http://dx.doi.org/10.1002/gch2.201900003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6686170PMC
August 2019