Scalable Synthesis of Crystalline One-Dimensional Carbon Nanothreads through Modest-Pressure Polymerization of Furan

Carbon
nanothreads, which are one-dimensional sp3-rich
polymers, combine high tensile strength with flexibility owing to
subnanometer widths and diamond-like cores. These extended carbon
solids are constructed through pressure-induced polymerization of
sp2 molecules such as benzene. Whereas a few examples of
carbon nanothreads have been reported, the need for high onset pressures
(≥17 GPa) to synthesize them precludes scalability and limits
scope. Herein, we report the scalable synthesis of carbon nanothreads
based on molecular furan, which can be achieved through ambient temperature
pressure-induced polymerization with an onset reaction pressure of
only 10 GPa due to its lessened aromaticity relative to other molecular
precursors. When slowly compressed to 15 GPa and gradually decompressed
to 1.5 GPa, a sharp 6-fold diffraction pattern is observed in situ, indicating a well-ordered crystalline material
formed from liquid furan. Single-crystal X-ray diffraction (XRD) of
the reaction product exhibits three distinct d-spacings
from 4.75 to 4.9 Å, whose size, angular spacing, and degree of
anisotropy are consistent with our atomistic simulations for crystals
of furan nanothreads. Further evidence for polymerization was obtained
by powder XRD, Raman/IR spectroscopy, and mass spectrometry. Comparison
of the IR spectra with computed vibrational modes provides provisional
identification of spectral features characteristic of specific nanothread
structures, namely syn, anti, and syn/anti configurations. Mass spectrometry suggests that
molecular weights of at least 6 kDa are possible. Furan therefore
presents a strategic entry toward scalable carbon nanothreads.