The strong excitonic effects widely exist in polymer-semiconductors and the large exciton binding energy (E
) seriously limits their photocatalysis. Herein, density functional theory (DFT) ...calculations are conducted to assess band alignment and charge transfer feature of potential donor-acceptor (D-A) covalent organic frameworks (COFs), using 1,3,5-tris(4-aminophenyl)triazine (TAPT) or 1,3,5-tris(4-aminophenyl)benzene (TAPB) as acceptors and tereph-thaldehydes functionalized diverse groups as donors. Given the discernable D-A interaction strengths in the D-A pairs, their E
can be systematically regulated with minimum E
in TAPT-OMe. Guided by these results, the corresponding D-A COFs are synthesized, where TAPT-OMe-COF possesses the best activity in photocatalytic H
production and the activity trend of other COFs is associated with that of calculated E
for the D-A pairs. In addition, further alkyne cycloaddition for the imine linkage in the COFs greatly improves the stability and the resulting TAPT-OMe-alkyne-COF with a substantially smaller E
exhibits ~20 times higher activity than the parent COF.
Unravelling the intrinsic mechanism of electrocatalytic oxygen evolution reaction (OER) by use of heterogeneous catalysts is highly desirable to develop related energy conversion technologies. Albeit ...dynamic self‐reconstruction of the catalysts during OER is extensively observed, it is still highly challenging to operando probe the reconstruction and precisely identify the true catalytically active components. Here, a new class of OER precatalyst, cobalt oxychloride (Co2(OH)3Cl) with unique features that allow a gradual phase reconstruction during OER due to the etching of lattice anion is demonstrated. The reconstruction continuously boosts OER activities. The reconstruction‐derived component delivers remarkable performance in both alkaline and neutral electrolytes. Operando synchrotron radiation‐based X‐ray spectroscopic characterization together with density functional theory calculations discloses that the etching of lattice Cl− serves as the key to trigger the reconstruction and the boosted catalytic performance roots in the atomic‐level coordinatively unsaturated sites (CUS). This work establishes fundamental understanding on the OER mechanism associated with self‐reconstruction of heterogeneous catalysts.
A new class of precatalyst for the oxygen evolution reaction (OER), cobalt oxychloride (Co2(OH)3Cl), displays unique features that allow a gradual phase reconstruction due to electrochemistry‐induced etching. The reconstruction continuously boosts the OER activity. Operando synchrotronradiation‐based X‐ray spectroscopic characterizations together with density functional theory calculations provide atomic‐level insight that the boosted catalytic performance results from coordinatively unsaturated sites of the cobalt.
Harvesting solar energy for catalytic conversion of CO2 into valuable chemical fuels/feedstocks is an attractive yet challenging strategy to realize a sustainable carbon-cycle utilization. ...Homogeneous catalysts typically exhibit higher activity and selectivity as compared with heterogeneous counterparts, benefiting from their atomically dispersed catalytic sites and versatile coordination structures. However, it is still a “black box” how the coordination and electronic structures of catalysts dynamically evolve during the reaction, forming the bottleneck for understanding their reaction pathways. Herein, we demonstrate to track the mechanistic pathway of photocatalytic CO2 reduction using a terpyridine nickel(II) complex as a catalyst model. Integrated with a typical homogeneous photosensitizer, the catalytic system offers a high selectivity of 99% for CO2-to-CO conversion with turnover number and turnover frequency as high as 2.36 × 107 and 385.6 s–1, respectively. We employ operando and time-resolved X-ray absorption spectroscopy, in combination with other in situ spectroscopic techniques and theoretical computations, to track the intermediate species of Ni catalyst in the photocatalytic CO2 reduction reaction for the first time. Taken together with the charge dynamics resolved by optical transient absorption spectroscopy, the investigation elucidates the full mechanistic reaction pathway including some key factors that have been often overlooked. This work opens the “black box” for CO2 reduction in the system of homogeneous catalysts and provides key information for developing efficient catalysts toward artificial photosynthesis.
Surface-enhanced Raman spectroscopy (SERS) is a powerful technique that can capture the electronic–vibrational “fingerprint” of molecules on surfaces. Ab initio prediction of Raman response is a ...long-standing challenge because of the diversified interfacial structures. Here we show that a cost-effective machine learning (ML) random forest method can predict SERS signals of a trans-1,2-bis (4-pyridyl) ethylene (BPE) molecule adsorbed on a gold substrate. Using geometric descriptors extracted from quantum chemistry simulations of thousands of ab initio molecular dynamics conformations, the ML protocol predicts vibrational frequencies and Raman intensities. The resulting spectra agree with density functional theory calculations and experiment. Predicted SERS responses of the molecule on different surfaces, or under external fields of electric fields and solvent environment, demonstrate the good transferability of the protocol.
The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting ...to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization.
Pure organic phosphorescent molecules are promising compounds for applications of phosphorescence, yet their utilization is restricted because of inefficient intersystem crossing (ISC) between ...singlet and triplet states. Molecular aggregation has been deemed a viable strategy to modulate molecular luminescence in solution, yet its impact on the phosphorescence is rarely investigated. In this work, we carried out first-principle studies to elucidate how aggregation of selected phosphorescent molecules will affect their phosphorescence behavior. Our calculations show that the overall ISC rate is appreciably enhanced, thanks to a decrease of energy gaps (ΔE) and an increase in the number of ISC channels between singlet and triplet states as the degree of aggregation develops. This facilitates singlet-to-triplet conversion. More importantly, the phosphorescence lifetime increases with the increase of the degree of molecular aggregation. The long-lived phosphorescence associated with aggregation benefits from multiple factors, including small singlet–triplet gaps, enhanced overall ISC rates, and suppression of fluorescence. We believe this aggregation-induced ISC mechanism may be employed as an alternative approach for realizing persistent phosphorescence.
Chiral chromophores and their ordered assemblies are intriguing for yielding circularly polarized luminescence (CPL) and exploring intrinsic structure–light emission relationships. With the ...extensively studied chiral organic molecules and inorganic nanoparticle assemblies for the amplified CPL, the assemblies of copper halide hybrid clusters have attracted intensive attention due to their potential efficient CPL. Here, we report robust chiral phosphine–copper iodide hybrid clusters and their layered assemblies in crystalline states for amplified CPL. We reveal that the intermolecular interactions endow the clusters with the capability of assembling into chiral crystalline CPL materials, including hexagonal platelet-shaped microcrystals (g lum ≈ 9.5 × 10–3) and highly oriented crystalline films (g lum ≈ 5 × 10–3). Owing to the high crystalline feature of the thin film, we demonstrate an electroluminescent device with bright electroluminescence (1200 cd m–2).
To explore the CT characteristics of small lung nodules and improve the diagnosis of pulmonary ground-glass nodules less than 10 mm in size.
We retrospectively analyzed CT images of 161 pulmonary ...nodules (less than 10 mm in size) with spiculation, lobulation, vacuoles, and pleural indentation and compared these images with pathological results or follow-up CT images. The relationships between the ground-glass nodules (GGNs) and blood vessels were observed. The GGN-vessel relationship was divided into four types, Type I (pass-by), Type II (pass-through), Type III (distorted/dilated), Type IV (complicated). The vessels traveling through a GGN were divided into three categories, category A (arteries), category B (veins), category C (arteries and veins).
161 GGNs were divided into three groups (benign group, pre-invasive group, and adenocarcinoma group) according to their pathological diagnosis. Significant differences in density of nodules were observed among the three different groups (p < 0.05). Significant differences in the shape (round/round-like or not) of the nodules were observed between the benign group and the pre-invasive group and between the pre-invasive group and the adenocarcinoma group (p < 0.05). No significant differences in the presence of vacuoles were observed between the benign group and the pre-invasive group or between the pre-invasive group and the adenocarcinoma group (p ＞0.05), but a significant difference was observed between the benign group and the adenocarcinoma group (p < 0.05). The differences in the vascularization of the lesions among the three groups were statistically significant (p < 0.05). No significant differences or correlations were observed between vascular categories and GGN groups (p > 0.05).
For subcentimeter nodules, mixed GGNs with vacuoles, well-defined border, combined with Type III or Type IV GGN-vessel relationship may strongly suggest malignant.
Previous studies mainly focused on CT diagnosis of pulmonary nodules (≤ 3 cm in diameter), but this study focused on ground-glass nodules less than 10 mm in diameter, which had not been fully studied. For subcentimeter nodules, mixed GGNs with vacuoles, well-defined border, especially the GGN-vessel relationship manifest as Type III (distorted/dilated) or Type IV (complicated) may strongly suggest malignant.
Strawberry anthracnose caused by
species is an important disease that may cause significant economic losses. Based on multilocus sequence analyses and morphological characteristics, 64 isolates from ...strawberry anthracnose samples collected from nine Chinese provinces and municipalities were identified as three species:
(29 isolates),
(23 isolates), and
(12 isolates). Isolates of
.
showed strong aggressiveness to fruit and leaves. Isolates of
.
showed strong aggressiveness to crowns. Isolates of
.
were weakly or not pathogenic to fruit, leaves, or crowns. Sensitivity to carbendazim was determined for a total of 75 isolates, including 11 previously preserved. Two isolates of
.
were highly resistant (HR) and 21 were moderately resistant (MR). Nine isolates of
.
were sensitive (S), 24 were HR, and four were MR. All 15 isolates of
.
were insensitive, and their mycelial growth was not completely inhibited on potato dextrose agar amended with 500 μg/ml carbendazim. Beta-tubulin (
) of representative isolates was amplified and sequenced, revealing a glutamic acid substituted by alanine at codon 198 in HR isolates of
.
and
.
. MR isolates of
.
and
.
had a point mutation at codon 200, causing a replacement of phenylalanine acid by tyrosine. No point mutation was detected at codons 50, 167, 198, 200, or 240 in TUB2 of
.
insensitive isolates. Overall, this study revealed that
.
was the dominant species causing anthracnose on strawberry and could improve the understanding of the management of fungicide resistance in
species on strawberry in China.
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