Silk fibroin extracted from the gland of Bombyx mori silkworm is employed as an ideal system to investigate its conformation transition in methanol/D2O solution. The transition process was monitored by Fourier transform infrared (FTIR) spectroscopy coupled with terahertz time domain spectroscopy (THz-TDS). Analysis of FTIR spectra suggests that, with increasing time of treatment, an increasing band at 1634 cm−1 is observed indicating the formation of β-pleated sheets coincident with the loss of intensity of a band at 1673 cm−1 indicating decrease of the random coil structure. In addition, there is a burst phase of 33% occurring during the first 2 minutes when the gland fibroin membranes are immersed into methanol/D2O solution. THz spectra present distinct features for conformations of silk fibroin, in combination with the results obtained from FTIR; the peaks observed at 1.54 THz (51 cm−1), 1.67 THz (55 cm−1), and 1.84 THz (61 cm−1) can be attributed to a β-pleated sheet, α-helix, and random coil, respectively. Intensity change of bands centered at 1.54 THz and 1.84 THz confirms the formation of the β-pleated sheet and the disappearance of the random coil. Kinetic curves obtained from THz spectra indicate that the methanol-induced conformation transition from the random coil to the β-pleated sheet is fitted with an exponential function. The results suggest that THz-TDS presents great potential as a complementary approach in studying the secondary structure of a protein, providing significant insight into the silk-spinning process in vivo.
Three-dimensional (3D) hollow carbon is one of advanced nanomaterials widely applied in oxygen reduction reaction (ORR). Herein, iron niobate (FeNb 2 O 6 ) nanoparticles supported on metal-organic frameworks (MOFs)-derived 3D N -doped interconnected open carbon cages (FeNb 2 O 6 /NICC) were prepared by methanol induced assembly and pyrolysis strategy. During the fabrication process, the evaporation of methanol promoted the assembly and cross linkage of ZIF-8, rather than individual particles. The assembled ZIF-8 particles worked as in-situ sacrificial templates, in turn forming hierarchically interconnected open carbon cages after high-temperature pyrolysis. The as-made FeNb 2 O 6 /NICC showed a positive onset potential of 1.09 V and a half-wave potential of 0.88 V for the ORR , outperforming commercial Pt/C under the identical conditions. Later on, the as-built Zn-air battery with the FeNb 2 O 6 /NICC presented a greater power density of 100.6 mW cm −2 and durable long-cycle stability by operating for 200 h. For preparing 3D hollow carbon materials, this synthesis does not require a tedious removal process of template, which is more convenient than traditional method with silica and polystyrene spheres as templates. This work affords an exceptional example of developing 3D N -doped interconnected hollow carbon composites for energy conversion and storage devices.
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