Colloidal quantum dots (QDs) consisting of precious‐metal‐free elements show attractive potentials towards solar‐driven CO2 reduction. However, the inhibition of hydrogen (H2) production in aqueous ...solution remains a challenge. Here, we describe the first example of a carbon–carbon (C−C) coupling reaction to block the competing H2 evolution in photocatalytic CO2 reduction in water. In a specific system taking ZnSe QDs as photocatalysts, the introduction of furfural can significantly suppress H2 evolution leading to CO evolution with a rate of ≈5.3 mmol g−1 h−1 and a turnover number (TON) of >7500 under 24 h visible light. Meanwhile, furfural is upgraded to the self‐coupling product with a yield of 99.8 % based on the consumption of furfural. Mechanistic insights show that the reductive furfural coupling reaction occurs on surface Zn‐sites to consume electrons and protons originally used for H2 production, while the CO formation pathway at surface anion vacancies from CO2 remains.
Reductive carbon–carbon coupling was used to block H2 evolution in CO2 photoreduction in water. Furfural, one of the biomass platform molecules, adsorbs on Zn‐sites consuming electrons and protons originally used for H2 production, but the CO formation pathway at surface anion vacancies remains. Therefore, CO was evolved with a CO/H2 ratio of 265 : 1 in the gas phase and furfural was upgraded to value‐added hydrofuroin.
Inspired by green plants, artificial photosynthesis has become one of the most attractive approaches toward carbon dioxide (CO2) valorization. Semiconductor quantum dots (QDs) or dot‐in‐rod (DIR) ...nano‐heterostructures have gained substantial research interest in multielectron photoredox reactions. However, fast electron–hole recombination or sluggish hole transfer and utilization remains unsatisfactory for their potential applications. Here, the first application of a well‐designed ZnSe/CdS dot‐on‐rods (DORs) nano‐heterostructure for efficient and selective CO2 photoreduction with H2O as an electron donor is presented. In‐depth spectroscopic studies reveal that surface‐anchored ZnSe QDs not only assist ultrafast (≈2 ps) electron and hole separation, but also promote interfacial hole transfer participating in oxidative half‐reactions. Surface photovoltage (SPV) spectroscopy provides a direct image of spatially separated electrons in CdS and holes in ZnSe. Therefore, ZnSe/CdS DORs photocatalyze CO2 to CO with a rate of ≈11.3 µmol g−1 h−1 and ≥85% selectivity, much higher than that of ZnSe/CdS DIRs or pristine CdS nanorods under identical conditions. Obviously, favored energy‐level alignment and unique morphology balance the utilization of electrons and holes in this nano‐heterostructure, thus enhancing the performance of artificial photosynthetic solar‐to‐chemical conversion.
A dot‐on‐rod (DOR) nano‐heterostructure is rationally constructed by anchoring multiple ZnSe QDs on a single CdS nanorod. Due to the favored energy level alignment and the good exposure of ZnSe to the surrounding medium, ultrafast (≈2 ps) charge separation and facile hole utilization are realized, which enable effective and selective CO2‐to‐CO photoreduction taking H2O as an electron donor.
Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs ...was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H2 without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants.
On the dot: A clean and efficient catalytic method for the preparation of disulfides from a variety of thiols in the absence of sacrificial reagents or external oxidants is described. Irradiation of CdSe quantum dots (QDs) with visible light results in good to excellent yields of the disulfides and equivalent amounts of H2. Mechanistic studies provide evidence for the formation of QD‐bound RS. and H. radicals as reaction intermediates.
Semiconducting quantum dots (QDs) have recently triggered a huge interest in constructing efficient hydrogen production systems. It is well established that a large fraction of surface atoms of QDs ...need ligands to stabilize and avoid them from aggregating. However, the influence of the surface property of QDs on photocatalysis is rather elusive. Here, the surface regulation of CdSe QDs is investigated by surface sulfide ions (S2−) for photocatalytic hydrogen evolution. Structural and spectroscopic study shows that with gradual addition of S2−, S2− first grows into the lattice and later works as ligands on the surface of CdSe QDs. In‐depth transient spectroscopy reveals that the initial lattice S2− accelerates electron transfer from QDs to cocatalyst, and the following ligand S2− mainly facilitates hole transfer from QDs to the sacrificial agent. As a result, a turnover frequency (TOF) of 7950 h−1 can be achieved by the S2− modified CdSe QDs, fourfold higher than that of original mercaptopropionic acid (MPA) capped CdSe QDs. Clearly, the simple surface S2− modification of QDs greatly increases the photocatalytic efficiency, which provides subtle methods to design new QD material for advanced photocatalysis.
To unravel how surface sulfide ions (S2−)regulate photocatalytic hydrogen evolution of CdSe quantum dots (QDs), the different roles of introduced S2− on QDs are revealed. The results show that S2− at an earlier stage grows into the lattice and accelerates electron transfer, while afterward the S2− works as ligands and promotes hole transfer, and thus greatly improves the photocatalytic hydrogen evolution efficiency.
The catalytic nature of semiconducting quantum dots (QDs) for photocatalytic hydrogen (H2) evolution can be thoroughly aroused, not because of coupling with external cocatalysts, but through ...partially covering controlled amount of ZnS shell on the surface. Specifically, CdSe QDs, with an optimal coverage of ZnS (≈46%), can produce H2 gas with a constant rate of ≈306.3 ± 21.1 µmol mg−1 h−1 during 40 h, thereby giving a turnover number of ≈(4.4 ± 0.3) × 105, which is ≈110‐fold to that of unmodified CdSe QDs under identical conditions. The performance of H2 evolution is comparable to or even better than the commonly used external cocatalysts, e.g., metal complexes, noble metals assisted photosystems. Mechanistic insights indicate that the dramatically enhanced activity and stability of bare QDs for photocatalytic H2 production are derived from (i) inhibiting exciton annihilation at trap states, (ii) preventing the photo‐oxidation of core frameworks, and (iii) retaining tunneling efficiencies of photogenerated electrons and holes to reactive sites with partial ZnS coverage.
The self‐catalytic nature of semiconducting quantum dots (QDs) for photocatalytic H2
evolution can be thoroughly aroused by a simple surface engineering method, which not only eliminates the reliance on external cocatalysts in designing artificial photocatalysts, but also provides privileges in making QD‐based devices practically viable.
Unlike their bulk counterpart, CuxInyS quantum dots (QDs) prepared by an aqueous synthetic approach, show promising activity for photocatalytic hydrogen evolution, which is competitive with the ...state‐of‐the‐art Cd chalcogen QDs. Moreover, the as‐prepared CuxInyS QDs with In‐rich composition show much better efficiency than the stoichiometric ones (Cu/In=1:1).
Indium summer: CuxInyS quantum dots (QDs) prepared by an aqueous synthetic approach are demonstrated to be promising candidates for photocatalytic H2 evolution. The In‐rich CuxInyS QDs show much better activity than stoichiometric CuInS2 QDs (Cu/In=1:1) and are comparable to the state‐of‐the‐art Cd chalcogen (CdS, CdSe, and CdTe) QDs for H2 generation under visible‐light irradiation.
SUMMARY
Two factors are proposed to account for the unusual features of organellar genomes: the disruptions of organelle‐targeted DNA replication, repair, and recombination (DNA‐RRR) systems in the ...nuclear genome and repetitive elements in organellar genomes. Little is known about how these factors affect organellar genome evolution. The deep‐branching vascular plant family Selaginellaceae is known to have a deficient DNA‐RRR system and convergently evolved organellar genomes. However, we found that the plastid genome (plastome) of Selaginella sinensis has extremely accelerated substitution rates, a low GC content, pervasive repeat elements, a dynamic network structure, and it lacks direct or inverted repeats. Unexpectedly, its organelle DNA‐RRR system is short of a plastid‐targeted Recombinase A1 (RecA1) and a mitochondrion‐targeted RecA3, in line with other explored Selaginella species. The plastome contains a large collection of short‐ and medium‐sized repeats. Given the absence of RecA1 surveillance, we propose that these repeats trigger illegitimate recombination, accelerated mutation rates, and structural instability. The correlations between repeat quantity and architectural complexity in the Selaginella plastomes support these conclusions. We, therefore, hypothesize that the interplay of the deficient DNA‐RRR system and the high repeat content has led to the extraordinary divergence of the S. sinensis plastome. Our study not only sheds new light on the mechanism of plastome divergence by emphasizing the power of cytonuclear integration, but it also reconciles the longstanding contradiction on the effects of DNA‐RRR system disruption on genome structure evolution.
Significance Statement
We hypothesize that the interplay of the deficient DNA replication, repair, and recombination system and the high repeat content has led to the extraordinary divergence of the Selaginella sinensis plastome. Our study not only sheds new light on the mechanism of plastome divergence by emphasizing the power of cytonuclear integration, but it also reconciles the longstanding contradiction on the effects of DNA replication, repair, and recombination system disruption on genome structure evolution.
Solar H2 evolution of CdSe QDs can be significantly enhanced simply by introducing a suitable hole‐accepting‐ligand for achieving efficient hole extraction and transfer at the nanoscale interfaces, ...which opens an effective pathway for dissociation of excitons to generate long‐lived charge separation, thus improving the solar‐to‐fuel conversion efficiency.
Cold stress profoundly affects plant growth and development and is a key factor affecting the geographic distribution and evolution of plants. Plants have evolved adaptive mechanisms to cope with ...cold stress. Here, through the genomic analysis of Arabidopsis, three
species and 17 other representative species, we found that both cold-related genes (
) and their collinearity were preferentially retained after polyploidization followed by genome instability, while genome-wide gene sets exhibited a variety of other expansion mechanisms. The cold-related regulatory network was increased in
genomes, which were recursively affected by polyploidization. By combining our findings regarding the selective retention of
from this ecological genomics study with the available knowledge of cold-induced chromosome doubling, we hypothesize that cold stress may have contributed to the success of polyploid plants through both increasing polyploidization and selectively maintaining
during evolution. This hypothesis requires further biological and ecological exploration to obtain solid supporting evidence, which will potentially contribute to understanding the generation of polyploids and to the field of ecological genomics.
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