Sensitization
of a wide-gap oxide semiconductor with a visible-light-absorbing
dye has been studied for decades as a means of producing H2 from water. However, efficient overall water splitting using a dye-sensitized
oxide photocatalyst has remained an unmet challenge. Here we demonstrate
visible-light-driven overall water splitting into H2 and
O2 using HCa2Nb3O10 nanosheets
sensitized by a Ru(II) tris-diimine type photosensitizer, in combination
with a WO3-based water oxidation photocatalyst and a triiodide/iodide
redox couple. With the use of Pt-intercalated HCa2Nb3O10 nanosheets further modified with amorphous
Al2O3 clusters as the H2 evolution
component, the dye-based turnover number and frequency for H2 evolution reached 4580 and 1960 h–1, respectively.
The apparent quantum yield for overall water splitting using 420 nm
light was 2.4%, by far the highest among dye-sensitized overall water
splitting systems reported to date. The present work clearly shows
that a carefully designed dye/oxide hybrid has great potential for
photocatalytic H2 production, and represents a significant
leap forward in the development of solar-driven water splitting systems.
Regenerated silk fibroin fibers from the cocoons of silkworm, Bombyx mori, were prepared with hexafluoro solvents, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) or hexafluoroacetone-trihydrate (HFA), as dope solvents and methanol as coagulation solvent. The regenerated fiber prepared from the HFIP solution showed slightly larger tensile strength when the draw ratio is 1:3 than that of native silk fiber, but the strength of the regenerated fiber with draw ratio 1:3 from the HFA solution is much lower than that of native silk fiber. This difference in the tensile strength of the regenerated silk fibers between two dope solvents comes from the difference in the long-range orientation of the crystalline region rather than that of short-range structural environment such as the fraction of beta-sheet structure. The increase in the biodegradation was observed for the regenerated silk fiber compared with native silk fiber. Preparations of regenerated silk fibroin fibers containing spider silk sequences were obtained by mixing silk fibroins and silk-like proteins with characteristic sequences from a spider, Naphila clavipes, to produce drag-line silk in E. coli in the fluoro solvents. A small increase in the tensile strength was obtained by adding 5% (w/w) of the silk-like protein to the silk fibroin. The production of silk fibroin fibers with these spider silk sequences was also performed with transgenic silkworms. Small increase in the tensile strength of the fibers was obtained without significant change in the elongation-at-break.
Peptides with a combination of hydrophilic and hydrophobic sequences mimicking the primary structure of Bombyx mori silk fibroin were synthesized and studied in the solid state by NMR using 13C selective labeling coupled with 13C conformation-dependent chemical shifts and 2D solid-state spin-diffusion NMR. The hydrophilic sequence was poly(l-glutamic acid) (E)
n
, and the hydrophobic one was the consensus sequence of the crystalline fraction of B. mori silk fibroin, (AGSGAG)4. The balance of hydrophilic and hydrophobic characters of the peptide was controlled by changing the relative length, n, of (E)
n
from 4 to 8. When n = 4 and 5, the structure of the hydrophobic sequence is basically Silk I (the structure of B. mori silk fibroin before spinning in the solid state), and the polyglutamate sequences are random coil. On the other hand, when n = 6−8, the structure of the polyglutamate sequence changes gradually from random coil to β-sheet, and the hydrophobic sequence adopts a mixture of β-sheet and random coil/distorted β-turn forms, although the fraction of the latter form decreases gradually by increasing the number n from 6 to 8. Molecular dynamics and molecular mechanics calculations were also performed to examine the stability of the aggregated domains of the peptides in the solid state. The conformational change of (E)4(AGSGAG)4 was monitored in the solid state by decreasing the pH of the aqueous solution during the sample preparation.
[reaction: see text] The 9,10-dicyanoanthracene-sensitized photoreaction of 1-methyl- and 1,1'-dimethyl-2,2',3,3'-tetraphenylbicyclopropenyl gives the corresponding benzene and Dewar benzene derivatives, indicating that their photoinduced electron-transfer bicyclopropenyl-benzene rearrangements proceed via Dewar benzenes.
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