Self-assembled
lignin nanospheres (LNS) have attracted much attention
due to the new opportunities provided for the preparation of value-added
products derived from lignin. However, the internal connections of
the LNS generally depend on weak intermolecular forces, leading to
low solubility resistance and thermostability. In this study, we present
a simple method for the fabrication of covalent–noncovalent
forces stabilizing lignin nanospheres (HT-LNS) through utilizing the
natural characteristic that lignin molecules undergo irreversible
condensation under high-temperature stimulation. Experiments demonstrated
that the action of temperature resulted in the fracture of β-O-4
ether and Cα–Cβ bonds, as
well as hydroxyl and −OCH3 lignin molecule groups,
leading to the formation of free radicals in the LNS. In addition,
a large number of adjacent intramolecular and intermolecular radicals
almost simultaneously generated chemical cross-linking via α-5,
β-5, β–β′ bonds, and so forth. The
amount of lignin molecules participating in the cross-linking reaction
increased with temperature, which gradually reduced the HT-LNS diameter
from 597 to 477 nm and enhanced the maximum decomposition peak from
367.7 to 395.1 °C. The solubility of nanospheres in ethanol and
tetrahydrofuran (THF) decreased from 93.92 to 10.39% and from 98.09
to 22.45% with increasing treatment temperature, respectively. The
HT-LNS can be employed in the preparation of superhydrophobic coatings,
replacing non-environmentally friendly silica nanoparticles. The water
contact and slide angles were determined as 151.9 ± 1.4 and 9.4
± 0.5°, respectively. Moreover, the application of HT-LNS
for the preparation of lignin-based carbon nanospheres maintained
a perfect spherical structure with tiny graphitic area and the content
of carbon atoms reached up to 94.99%. This study provides a simple
and effective technology platform for the development of green materials.
Blend films with long nanowires of zinc octaethylporphyrin (ZnOEP) embedded in an insulating polymer of poly(methyl methacrylate) (PMMA) have been successfully fabricated by a one-step spin-coating process. Concerning photoactive blends based on small-molecule semiconductors, this is quite a novel strategy and allows us to greatly reduce the issues related to low device performance, such as phase-separation, poor connectivity of the semiconducting layer, and higher densities of interfacial defects. Intensive studies on the correlation between the film morphology and device performance have revealed that excellent photodetector performance is derived from efficient charge transport and good connectivity observed in highly crystalline, interconnected ZnOEP nanowires embedded in an insulating PMMA matrix. To the best of our knowledge, this is the first demonstration of a blend-film-based organic photodetector, which exhibits high sensitivity, high stability, high I(on)/I(off) ratio, excellent mechanical flexibility, and a broadband responsivity region extending up to 1050 nm. The unique characteristics of facile fabrication, high sensitivity, excellent mechanical stability, and broadband responsivity can make the blend film of ZnOEP and PMMA promising in large-area flexible photodetectors.
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