Conspectus Lead halide perovskite nanocrystals (NCs) have been widely studied for application in optoelectronic devices due to their excellent optical properties and low-cost synthesis. However, the ...toxicity of lead and the poor stability of the NCs hindered their practical applications. Sn2+-based perovskite with low toxicity was first developed; however, the Sn2+-based perovskite NCs are unstable in air and oxidize easily. Recently, air-stable lead-free perovskite NCs have been developed and received increasing attention. Unfortunately, the optical and optoelectronic properties of these lead-free halide perovskite NCs are generally far worse than those of lead-perovskite NCs. Understanding the charge-carrier dynamics of semiconductors is crucial to improve their optical properties. In this Account, we mainly review our recent research progress on the study of charge-carrier dynamics in air-stable lead-free perovskite NCs. The exciton trapping followed by nonradiative recombination was the major carrier relaxation pathway and resulted in a low photoluminescence quantum efficiency (PLQE). A feasible route for passivating surface traps and tuning the self-trapped excitons from “dark” (nonradiative) to “bright” (radiative) was proposed. Through this strategy, the PLQE could be increased over 100-fold. In addition, we have compared several photophysical properties of lead-free perovskite NCs with that of lead perovskite NCs, such as charge-carrier relaxation, exciton–phonon coupling, and hot-carrier cooling. In 2017, we reported the synthesis, optical properties, and charge-carrier dynamics of Cs3Bi2X9 (X: Cl, Br, I) NCs. The Cs3Bi2Br9 NCs exhibited clear exciton trapping processes with time scales in the range of 2–20 ps. The fast trapping processes could be passivated via the use of surfactants (such as oleic acid), and the PLQE increased over 20-fold (from 0.2% to 4.5%). The low PLQE may be due to the reduced dimensionality of Cs3Bi2Br9 (2D) compared with the 3D cubic perovskite structure of CsPbBr3. We next reported double perovskite Cs2AgSb1–y Bi y X6 (X: Br, Cl; 0 ≤ y ≤ 1) NCs, which exhibited a similar 3D cubic perovskite structure to that of the lead-perovskite NCs. The charge-carrier dynamics indicated that the sub-band-gap exciton trapping processes were dominated by ultrafast (∼1–2 ps) intrinsic self-trapping and trapping at surface defects (∼50–100 ps). While trapping at surface defects can be passivated using surfactants, the self-trapping processes is due to the giant carrier–phonon coupling effect. By designing direct band gap double perovskite NCs to tune the sub-band-gap trapping processes, bright dual-color emission was achieved. Furthermore, the violet PLQE could be improved to 36.6%, which is comparable to that in lead halide perovskite NCs. We hope this Account will deepen the understanding of the charge-carrier dynamics in lead-free perovskite NCs and guide the design of high-performance lead-free perovskites.
Abstract
While inheriting the exceptional merits of single atom catalysts, diatomic site catalysts (DASCs) utilize two adjacent atomic metal species for their complementary functionalities and ...synergistic actions. Herein, a DASC consisting of nickel-iron hetero-diatomic pairs anchored on nitrogen-doped graphene is synthesized. It exhibits extraordinary electrocatalytic activities and stability for both CO
2
reduction reaction (CO
2
RR) and oxygen evolution reaction (OER). Furthermore, the rechargeable Zn-CO
2
battery equipped with such bifunctional catalyst shows high Faradaic efficiency and outstanding rechargeability. The in-depth experimental and theoretical analyses reveal the orbital coupling between the catalytic iron center and the adjacent nickel atom, which leads to alteration in orbital energy level, unique electronic states, higher oxidation state of iron, and weakened binding strength to the reaction intermediates, thus boosted CO
2
RR and OER performance. This work provides critical insights to rational design, working mechanism, and application of hetero-DASCs.
Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pH-universal ...electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm
with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur.
In the context of standardized training for general practitioners, the emphasis is still primarily on clinical skills, which does not fully encompass the overall development of general practitioners. ...This study implemented a practice-based learning and improvement (PBLI) project among students and evaluated its effectiveness based on indicators such as learning outcomes, students' subjective experiences, and annual grades. This study offers recommendations for optimizing general practitioners' teaching and residential training programs.
60 residents who participated in the regular training of general practitioners at the First Clinical College of Tongji Medical College of Huazhong University of Science and Technology from January 2019 to January 2022 were selected for this study. They were randomly divided into two groups, the PBLI group, and the control group, using a random number table method. Out of the 60 residents, 31 were assigned to the control group and 29 were assigned to the PBLI group. The participants in the PBLI group received additional PBLI training along with their daily residential training, while the participants in the control group only took part in the latter. The effectiveness of the PBLI program was analyzed by conducting a baseline survey, administering questionnaires, and evaluating examination results.
After implementing the program, the PBLI group scored significantly higher than the control group (p < 0.05). Throughout the implementation process, students in the PBLI group expressed high satisfaction with the learning project, particularly with its content and alignment with the training objective. The teacher's evaluation of the PBLI group students surpassed that of the control group in various areas, including literature retrieval, self-study, courseware development, speech ability, and clinical thinking.
The PBLI program aims to encourage resident-centered study in standardized residency training. This approach is beneficial because it motivates students to engage in active learning and self-reflection, ultimately enhancing the effectiveness of standardized residency training.
Two‐electron oxygen photoreduction to hydrogen peroxide (H2O2) is seriously inhibited by its sluggish charge kinetics. Herein, a polarization engineering strategy is demonstrated by grafting ...(thio)urea functional groups onto covalent triazine frameworks (CTFs), giving rise to significantly promoted charge separation/transport and obviously enhanced proton transfer. The thiourea‐functionalized CTF (Bpt‐CTF) presents a substantial improvement in the photocatalytic H2O2 production rate to 3268.1 µmol h−1 g−1 with no sacrificial agents or cocatalysts that is over an order of magnitude higher than unfunctionalized CTF (Dc‐CTF), and a remarkable quantum efficiency of 8.6% at 400 nm. Mechanistic studies reveal the photocatalytic performance is attributed to the prominently enhanced two‐electron oxygen reduction reaction by forming endoperoxide at the triazine unit and highly concentrated holes at the thiourea site. The generated O2 from water oxidation is subsequently consumed by the oxygen reduction reaction (ORR), thereby boosting overall reaction kinetics. The findings suggest a powerful functional‐groups‐mediated polarization engineering method for the development of highly efficient metal‐free polymer‐based photocatalysts.
(Thio)urea‐functionalized covalent triazine frameworks (CTFs) are rationally designed, showing an outstanding photocatalytic activity toward production of H2O2 in water (3268.1 μmol h−1 g−1 with a quantum yield of 8.6% at 400 nm for the thiourea‐functionalized CTF) via reducing molecular oxygen (O2). This is much higher than most of the reported metal‐free polymer‐based photocatalysts in nonsacrificial systems.
NiFe‐based layered double hydroxides (LDHs) are among the most efficient oxygen evolution reaction (OER) catalysts in alkaline medium, but their long‐term OER stabilities are questionable. In this ...work, it is demonstrated that the layered structure makes bulk NiFe LDH intrinsically not stable in OER and the deactivation mechanism of NiFe LDH in OER is further revealed. Both operando electrochemical and structural characterizations show that the interlayer basal plane in bulk NiFe LDH contributes to the OER activity, and the slow diffusion of proton acceptors (e.g., OH−) within the NiFe LDH interlayers during OER causes dissolution of NiFe LDH and therefore decrease in OER activity with time. To improve diffusion of proton acceptors, it is proposed to delaminate NiFe LDH into atomically thin nanosheets, which is able to effectively improve OER stability of NiFe LDH especially at industrial operating conditions such as elevated operating temperatures (e.g., at 80 °C) and large current densities (e.g., at 500 mA cm−2).
The interlayer basal plane in bulk NiFe layered double hydroxide (LDH) contributes to the oxygen evolution reaction (OER) activity. Restricted diffusion of proton acceptors within the interlayers of bulk NiFe LDH causes catalyst dissolution. Exfoliating multilayered NiFe LDH into single‐layered nanosheets greatly improves the catalytic stability of NiFe LDH in alkaline OER.
We present herein a highly efficient atroposelective synthesis of axially chiral 1,1′‐bipyrroles bearing an N−N linkage from simple hydrazine and 1,4‐diones. Further product derivatizations led to ...axially chiral bifunctional compounds with high potential in asymmetric catalysis. For this chrial phosphoric acid (CPA)‐catalyzed double Paal–Knorr reaction, an intriguing Fe(OTf)3‐induced enantiodivergence was also observed.
A highly efficient atroposelective synthesis of axially chiral 1,1′‐bipyrroles bearing an N−N linkage from simple hydrazine and 1,4‐diones is presented. Further product derivatizations led to axially chiral bifunctional compounds with high potential in asymmetric catalysis. For this chiral phosphoric acid (CPA)‐catalyzed double Paal–Knorr reaction, an intriguing Fe(OTf)3‐induced enantiodivergence was also observed.
An iron‐catalyzed coupling reaction of O‐acyloximes and O‐benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6‐ketonitriles, pyrrolines ...and imidazolines via carbon‐centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring‐opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3‐hydrogen transfer, providing insights into iron‐catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen‐containing products.
Functionalized heterocycles and ketonitriles were synthesized by coupling O‐acyloximes and O‐benzoyl amidoximes with silyl enol ethers using an iron catalyst. The three reaction pathways of the iminyl radical to carbon‐centered radicals gave rise to the diversity of products (see scheme).
In recent years, asymmetric catalysis of ynamides has attracted much attention, but these reactions mostly constructed central chirality, except for a few examples on the synthesis of axially chiral ...compounds which exclusively relied on noble‐metal catalysis. Herein, a facile access to axially chiral N‐heterocycles enabled by chiral Brønsted acid‐catalyzed 5‐endo‐dig cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method allows the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities. Moreover, organocatalysts and ligands based on such axially chiral N‐arylindole skeletons are demonstrated to be applicable to asymmetric catalysis.
A chiral Brønsted acid‐catalyzed atroposelective cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method enables the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities.
From typical electrical appliances to thriving intelligent robots, the exchange of information between humans and machines has mainly relied on the contact sensor medium. However, this kind of ...contact interaction can cause severe problems, such as inevitable mechanical wear and cross‐infection of bacteria or viruses between the users, especially during the COVID‐19 pandemic. Therefore, revolutionary noncontact human–machine interaction (HMI) is highly desired in remote online detection and noncontact control systems. In this study, a flexible high‐sensitivity humidity sensor and array are presented, fabricated by anchoring multilayer graphene (MG) into electrospun polyamide (PA) 66. The sensor works in noncontact mode for asthma detection, via monitoring the respiration rate in real time, and remote alarm systems and provides touchless interfaces in medicine delivery for bedridden patients. The physical structure of the large specific surface area and the chemical structure of the abundant water‐absorbing functional groups of the PA66 nanofiber networks contribute to the high performance synergistically. This work can lead to a new era of noncontact HMI without the risk of contagiousness and provide a general and effective strategy for the development of smart electronics that require noncontact interaction.
Flexible noncontact sensing based on a high‐sensitivity humidity sensor is realized by anchoring multilayer graphene (MG) into electrospun polyamide (PA) 66 for human–machine interaction systems, which can achieve not only asthma detection, via monitoring the respiration rate in real time, and remote alarm systems, but also touchless interfaces in medicine delivery for bedridden patients.
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