With the recent explosion of scientific data of unprecedented size and complexity, feature ranking and screening are playing an increasingly important role in many scientific studies. In this ...article, we propose a novel feature screening procedure under a unified model framework, which covers a wide variety of commonly used parametric and semiparametric models. The new method does not require imposing a specific model structure on regression functions, and thus is particularly appealing to ultrahigh-dimensional regressions, where there are a huge number of candidate predictors but little information about the actual model forms. We demonstrate that, with the number of predictors growing at an exponential rate of the sample size, the proposed procedure possesses consistency in ranking, which is both useful in its own right and can lead to consistency in selection. The new procedure is computationally efficient and simple, and exhibits a competent empirical performance in our intensive simulations and real data analysis.
Inherent poor stability of perovskite nanocrystals (NCs) is the main impediment preventing broad applications of the materials. Here, TiO2 shell coated CsPbBr3 core/shell NCs are synthesized through ...the encapsulation of colloidal CsPbBr3 NCs with titanium precursor, followed by calcination at 300 °C. The nearly monodispersed CsPbBr3/TiO2 core/shell NCs show excellent water stability for at least three months with the size, structure, morphology, and optical properties remaining identical, which represent the most water‐stable inorganic shell passivated perovskite NCs reported to date. In addition, TiO2 shell coating can effectively suppress anion exchange and photodegradation, therefore dramatically improving the chemical stability and photostability of the core CsPbBr3 NCs. More importantly, photoluminescence and (photo)electrochemical characterizations exhibit increased charge separation efficiency due to the electrical conductivity of the TiO2 shell, hence leading to an improved photoelectric activity in water. This study opens new possibilities for optoelectronic and photocatalytic applications of perovskites‐based NCs in aqueous phase.
TiO2 shell coated CsPbBr3 core/shell nanocrystals are successfully constructed, resulting in excellent water, photo and thermal stability. TiO2 shell coating effectively increases charge separation efficiency, hence leading to an improved photoelectric activity in water.
As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO2) photoreduction into value‐added chemicals and solar fuels (for example, CO, HCOOH, ...CH3OH, CH4) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO2 and H2O to carbohydrates and oxygen (O2) using sunlight, which has inspired the development of low‐cost, stable, and effective artificial photocatalysts for CO2 photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge‐carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems. Recent advances in CO2 photoreduction using semiconductor QDs are highlighted. First, the unique photophysical and structural properties of semiconductor QDs, which enable their versatile applications in solar energy conversion, are analyzed. Recent applications of QDs in photocatalytic CO2 reduction are then introduced in three categories: binary II–VI semiconductor QDs (e.g., CdSe, CdS, and ZnSe), ternary I–III–VI semiconductor QDs (e.g., CuInS2 and CuAlS2), and perovskite‐type QDs (e.g., CsPbBr3, CH3NH3PbBr3, and Cs2AgBiBr6). Finally, the challenges and prospects in solar CO2 reduction with QDs in the future are discussed.
Carbon dioxide (CO2) photoreduction is regarded as an attractive pathway to produce value‐added chemicals and fuels. Recent advances in CO2 photoreduction via semiconductor quantum dots (QDs) in three categories are reviewed: II–VI, I–III–VI, and perovskite‐type QDs. Additionally, current challenges and prospects for QD‐photocatalyzed CO2 reduction are discussed.
Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be ...beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H
, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H
Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis.
Catalytic C1 chemistry based on the activation/conversion of synthesis gas (CO+H2), methane, carbon dioxide, and methanol offers great potential for the sustainable development of hydrocarbon fuels ...to replace oil, coal, and natural gas. Traditional thermal catalytic processes used for C1 transformations require high temperatures and pressures, thereby carrying a significant carbon footprint. In comparison, solar‐driven C1 catalysis offers a greener and more sustainable pathway for manufacturing fuels and other commodity chemicals, although conversion efficiencies are currently too low to justify industry investment. In this Review, we highlight recent advances and milestones in light‐driven C1 chemistry, including solar Fischer–Tropsch synthesis, the water‐gas‐shift reaction, CO2 hydrogenation, as well as methane and methanol conversion reactions. Particular emphasis is placed on the rational design of catalysts, structure–reactivity relationships, as well as reaction mechanisms. Strategies for scaling up solar‐driven C1 processes are also discussed.
Soaking up the sun: This Review highlights recent achievements in solar‐driven C1 chemistry, especially in processes such as solar‐driven Fischer–Tropsch synthesis, the water‐gas‐shift reaction, CO2 hydrogenation, as well as CH4 and CH3OH conversion. Particular emphasis is placed on the rational design of catalysts, structure–reactivity relationships, as well as reaction mechanisms during the solar‐driven processes.
Graphdiyne (GDY) with a direct band gap, excellent carrier mobility and uniform pores, is regarded as a promising photocatalytic material for solar energy conversion, while the research on GDY in ...photocatalysis is a less developed field. Herein, the distinctive structure, adjustable band gap, and electronic properties of GDY for photocatalysis is firstly summarized. The construction and progress of GDY‐based photocatalysts for solar energy conversion, including H2 evolution reaction (HER), CO2 reduction reaction (CO2RR) and N2 reduction reaction (NRR) are then elaborated. At last, the challenges and perspectives in developing GDY‐based photocatalysts for solar fuel production are discussed. It is anticipated that a timely Minireview will be helpful for rapid progress of GDY in solar energy conversion.
Because of their large specific surface area, adjustable band gap, and uniformly pore structure, graphdiyne (GDY) materials have become a rising star for photocatalytic energy conversion. This Minireview summarizes the unique physicochemical properties of GDY as well as the construction and progress of GDY‐based photocatalysts for hydrogen evolution, CO2 reduction and nitrogen reduction.
Photo/electrocatalytic ammonia synthesis has recently developed fast while the ammonia yields over state‐of‐the‐art photo/electrocatalysts are still very moderate. Such low concentration of ...synthesized NH3 brings about a challenge to the reliable quantification of the product in photo/electrocatalysis. Notably, we found that the quantitative detection of ammonia concentration below 0.2 ppm is error‐prone, which is likely the case happening in the majority of photo/electrocatalytic NH3 synthesis, thus arising concerns about the rationality and accuracy for low‐concentration ammonia quantification in these processes. Herein, we discuss the methodology used and analyze the reliability of various detection methods for the detection of trace ammonia in aqueous media. The challenges facing the detection of low concentration of ammonia in photo/electrocatalysis can be overcome by integration with multiple detection methods. According to the data presented, we also propose an effective criterion for precise quantification of ammonia, avoiding the unreasonable comparisons in photo/electrocatalytic ammonia synthesis.
The analytical methods for the detection of ammonia concentration below 0.2 ppm in photo/electrocatalytic N2 fixation are evaluated rigorously, reliably, and insightfully. The low‐concentration ammonia quantification minefield was indicated and a rigorous ammonia detection flowchart as well as another reference standard to achieve a more accurate and responsible ammonia detection in photo/electrocatalysis was concluded.
Over the past decades, N‐heterocyclic carbene (NHC) organocatalysis has undergone a flourish of development on the basis of closed‐shell reaction paths. By contrast, the emerging area of ...single‐electron transfer (SET) reactions enabled by NHC catalysis still remain underdeveloped, but offer plenty of opportunities to develop new catalytic modes and useful synthetic methods. A number of interesting transformations were triggered by the SET process from the electron‐rich Breslow intermediates to various single‐electron acceptors. In additions, recent studies revealed that the Breslow radical cations could also be generated by single‐electron reduction of the electron‐deficient acyl azolium intermediates. These discoveries open a new avenue for NHC organocatalysis to harness radical reactions. The present review will focus on the exciting advancements in the dynamic area of radical NHC organocatalysis.
NHC organocatalysis: The development of N‐heterocyclic carbene (NHC) organocatalysis presents new opportunities in radical reactions. The Breslow intermediate‐based radical cations, which could be generated through single‐electron oxidation or reduction, enabled a series of novel radical transformations. These advancements greatly extend the synthetic potential of N‐heterocyclic carbene catalysis.
► Volatile–char interactions are a common phenomenon in gasification. ► Volatile–char interactions affect almost every aspect of low-rank-fuel gasification. ► This paper provides an overview of the ...progress in this area.
Volatile–char interactions are an important phenomenon in almost all existing gasification processes. The volatile–char interactions can very significantly affect almost every aspect of low-rank fuel gasification, including the volatilisation of alkali and alkaline earth metallic species that are inherent catalysts for gasification, the evolution of char structure, the dispersion of inherent catalysts and thus the reactivity of char. The volatile–char interactions can also influence the formation of pollutant-forming species such as NH3. This paper provides an overview of our recent work in this area. The essence of volatile–char interactions appears to be the interactions between radicals, especially H radicals, and the char during pyrolysis and gasification. The volatile–char interactions must be an important consideration in the development of new gasification technologies for low-rank fuels such as brown coal and biomass to minimise the adverse effects and maximise the positive effects of volatile–char interactions during the gasification of low-rank fuels.
In recent years, visible-light-driven organic reactions have been experiencing a significant renaissance in response to topical interest in environmentally friendly green chemical synthesis. The ...transformations using inexpensive, readily available visible-light sources have come to the forefront in organic chemistry as a powerful strategy for the activation of small molecules. In this review, we focus on recent advances in the development of visible-light-driven organic reactions, including aerobic oxidation, hydrogen-evolution reactions, energy-transfer reactions and asymmetric reactions. These key research topics represent a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.
PDF
