Ferroelectricity and Thermochromism in a 2D Dion-Jacobson Organic-Inorganic Hybrid Perovskite.

2D organic-inorganic hybrid perovskites (OIHPs) have become one of the hottest research topics due to their excellent environmental stability and unique optoelectronic properties. Recently, the ferroelectricity and thermochromism of 2D OIHPs have attracted increasing interests. Integrating ferroelectricity and thermochromism into perovskites can significantly promote the development of multichannel intelligent devices. Here, a novel 2D Dion-Jacobson OIHP of the formula (3AMP)PbI4 (where 3AMP is 3-(aminomethyl)pyridinium) is reported, which has a remarkable spontaneous polarization value (Ps) of 15.6 µC cm-2 and interesting thermochromism. As far it is known, such a large Ps value is the highest for 2D OIHPs recorded so far. These findings will inspire further exploration and application of multifunctional perovskites.

Atomic Ruthenium-Promoted Cadmium Sulfide for Photocatalytic Production of Amino Acids from Biomass Derivatives.

Amino acids are the building blocks of proteins and are widely used as important ingredients for other nitrogen-containing molecules. Here, we report the sustainable production of amino acids from biomass-derived hydroxy acids with high activity under visible-light irradiation and mild conditions, using atomic ruthenium-promoted cadmium sulfide (Ru1/CdS). On a metal basis, the optimized Ru1/CdS exhibits a maximal alanine formation rate of 26.0 molAla ⋅ gRu -1 ⋅ h-1, which is 1.7 times and more than two orders of magnitude higher than that of its nanoparticle counterpart and the conventional thermocatalytic process, respectively. Integrated spectroscopic analysis and density functional theory calculations attribute the high performance of Ru1/CdS to the facilitated charge separation and O-H bond dissociation of the α-hydroxy group, here of lactic acid. The operando nuclear magnetic resonance further infers a unique "double activation" mechanism of both the CH-OH and CH3-CH-OH structures in lactic acid, which significantly accelerates its photocatalytic amination toward alanine.

Transfer Hydrogenation with a Carbon-Nitride-Supported Palladium Single-Atom Photocatalyst and Water as a Proton Source.

Solar-driven transfer hydrogenation of unsaturated bonds has received considerable attention in the research area of sustainable organic synthesis; however, water, the ultimate green source of hydrogen, has rarely been investigated due to the high barrier associated with splitting of water molecules. We report a carbon-nitride-supported palladium single-atom heterogeneous catalyst with unparalleled performance in photocatalytic water-donating transfer hydrogenation compared to its nanoparticle counterparts. Isotopic-labeling experiments and operando nuclear magnetic resonance measurements confirm the direct hydrogenation mechanism using in situ-generated protons from water splitting under visible-light irradiation. Density functional theory calculations attribute the high activity to lower barriers for hydrogenation, facilitated desorption of ethylbenzene, and facile hydrogen replenishment from water on the atomic palladium sites.

Highly Ethylene-Selective Electrocatalytic CO2 Reduction Enabled by Isolated Cu-S Motifs in Metal-Organic Framework Based Precatalysts.

Copper-based materials are efficient electrocatalysts for the conversion of CO2 to C2+ products, and most these materials are reconstructed in situ to regenerate active species. It is a challenge to precisely design precatalysts to obtain active sites for the CO2 reduction reaction (CO2 RR). Herein, we develop a strategy based on local sulfur doping of a Cu-based metal-organic framework precatalyst, in which the stable Cu-S motif is dispersed in the framework of HKUST-1 (S-HKUST-1). The precatalyst exhibits a high ethylene selectivity in an H-type cell with a maximum faradaic efficiency (FE) of 60.0 %, and delivers a current density of 400 mA cm-2 with an ethylene FE up to 57.2 % in a flow cell. Operando X-ray absorption results demonstrate that Cuδ+ species stabilized by the Cu-S motif exist in S-HKUST-1 during CO2 RR. Density functional theory calculations indicate the partially oxidized Cuδ+ at the Cu/Cux Sy interface is favorable for coupling of the *CO intermediate due to the modest distance between coupling sites and optimized adsorption energy.

Cooperative Motion in Water-Methanol Clusters Controls the Reaction Rates of Heterogeneous Photocatalytic Reactions.

Detailed information about the influences of the cooperative motion of water and methanol molecules on practical solid-liquid heterogeneous photocatalysis reactions is critical for our understanding of photocatalytic reactions. The present work addresses this issue by applying operando nuclear magnetic resonance (NMR) spectroscopy, in conjunction with density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, to investigate the dynamic behaviors of heterogeneous photocatalytic systems with different molar ratios of water to methanol on rutile-TiO2 photocatalyst. The results demonstrate that methanol and water molecules are involved in the cooperative motions, and the cooperation often takes the form of methanol-water clusters that govern the number of methanol molecules reaching to the active sites of the photocatalyst per unit time, as confirmed by the diffusion coefficients of the methanol molecule calculated in the binary methanol-water solutions. Nuclear Overhauser effect spectroscopy experiments reveal that the clusters are formed by the hydrogen bonding between the -OH groups of CH3OH and H2O. The formation of such methanol-water clusters is likely from an energetic standpoint in low-concentration methanol, which eventually determines the yields of methanol reforming products.

Metallic Ni3 P/Ni Co-Catalyst To Enhance Photocatalytic Hydrogen Evolution.

Metallic Ni3 P/Ni can be used as a co-catalyst to replace noble metal Pt for efficient photocatalytic hydrogen evolution, due to its excellent trapping-electron ability. The applications of metallic Ni3 P/Ni co-catalyst on CdS, Zn0.5 Cd0.5 S, TiO2 (Degussa P25) and g-C3 N4 are further confirmed, indicating its versatile applicability nature like Pt.

Black Tungsten Nitride as a Metallic Photocatalyst for Overall Water Splitting Operable at up to 765†nm.

Semiconductor photocatalysts are hardly employed for overall water splitting beyond 700 nm, which is due to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs; however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Black tungsten nitride is now employed as a metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization.

Fluorine-doped porous single-crystal rutile TiO2 nanorods for enhancing photoelectrochemical water splitting.

Fluorine-doped hierarchical porous single-crystal rutile TiO(2) nanorods have been synthesized through a silica template method, in which F(-) ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at -0.33 V vs. Ag/AgCl) under 100 mW cm(-2) of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO(2) single crystals.

Carbon nitride nanosheet-supported CuO for efficient photocatalytic CO2 reduction with 100% CO selectivity.

The optimal ratio of reaction solutions resulted in excellent performance and product selectivity of CuO/g-C3N4 composites in the photocatalytic CO2 reduction reaction. A pH-dependent chemical exchange saturation transfer (CEST) imaging nuclear magnetic resonance (NMR) method was used to confirm that CuO modification improves the adsorption capacity of CO2.

Scalable synthesis of coordinatively unsaturated metal-nitrogen sites for large-scale CO2 electrolysis.

Practical electrochemical CO2-to-CO conversion requires a non-precious catalyst to react at high selectivity and high rate. Atomically dispersed, coordinatively unsaturated metal-nitrogen sites have shown great performance in CO2 electroreduction; however, their controllable and large-scale fabrication still remains a challenge. Herein, we report a general method to fabricate coordinatively unsaturated metal-nitrogen sites doped within carbon nanotubes, among which cobalt single-atom catalysts can mediate efficient CO2-to-CO formation in a membrane flow configuration, achieving a current density of 200 mA cm-2 with CO selectivity of 95.4% and high full-cell energy efficiency of 54.1%, outperforming most of CO2-to-CO conversion electrolyzers. By expanding the cell area to 100 cm2, this catalyst sustains a high-current electrolysis at 10 A with 86.8% CO selectivity and the single-pass conversion can reach 40.4% at a high CO2 flow rate of 150 sccm. This fabrication method can be scaled up with negligible decay in CO2-to-CO activity. In situ spectroscopy and theoretical results reveal the crucial role of coordinatively unsaturated metal-nitrogen sites, which facilitate CO2 adsorption and key *COOH intermediate formation.

A-Site Mixing to Adjust the Photovoltaic Performance of a Double-Cation Perovskite: It Is Not Always the Simple Way.

Considerable progress has been made in improving the performance of optoelectronic devices based on hybrid organic-inorganic perovskites of the form ABX3. However, the influences of A-site doping on the structure and dynamics of the inorganic perovskite crystal lattice and, in turn, on the optoelectronic performance of the resulting devices remain poorly understood at an atomic level. This work addresses this issue by combining the results of several experimental characterization methods for three-dimensional MA1-xDMAxPbBr3 perovskite single crystals (MA, methylammonium; DMA, dimethylammonium). The results reveal a two-stage change in lattice with an increase in DMA content, which has completely opposite effects on the optoelectronic performance of the double-cation perovskite. At low DMA concentrations, fast reorientation of incorporated DMA cations strengthens the interaction between MA cations and the lattice without significant lattice distortion, which could suppress lattice fluctuation and thus improve the photovoltaic performance. At high DMA concentrations, the lattice get a severe distortion, leading to poorer photovoltaic performance.

Rapid Identification of Adulteration in Edible Vegetable Oils Based on Low-Field Nuclear Magnetic Resonance Relaxation Fingerprints.

Most current approaches applied for the essential identification of adulteration in edible vegetable oils are of limited practical benefit because they require long analysis times, professional training, and costly instrumentation. The present work addresses this issue by developing a novel simple, accurate, and rapid identification approach based on the magnetic resonance relaxation fingerprints obtained from low-field nuclear magnetic resonance spectroscopy measurements of edible vegetable oils. The relaxation fingerprints obtained for six types of edible vegetable oil, including flaxseed oil, olive oil, soybean oil, corn oil, peanut oil, and sunflower oil, are demonstrated to have sufficiently unique characteristics to enable the identification of the individual types of oil in a sample. By using principal component analysis, three characteristic regions in the fingerprints were screened out to create a novel three-dimensional characteristic coordination system for oil discrimination and adulteration identification. Univariate analysis and partial least squares regression were used to successfully quantify the oil adulteration in adulterated binary oil samples, indicating the great potential of the present approach on both identification and quantification of edible oil adulteration.

Graphite carbon nitride doped with a benzene ring for enhanced photocatalytic H2 evolution.

Graphitic carbon nitride (g-C3N4) has been identified as a promising material for photocatalytic hydrogen (H2) production, but it shows a low activity. Herein, g-C3N4 doped with a benzene ring (B-CNx) was synthesized via a simple thermal polycondensation method, exhibits 5.4 times higher H2 evolution rate than the pristine one, and achieves a high apparent quantum yield of 4.11% at 420 nm.

Solvent Water Controls Photocatalytic Methanol Reforming.

Understanding the role of different solvent molecules for practical solid-liquid heterogeneous photocatalytic reactions is critical for determining the pathway of the reaction. In this study, the operando nuclear magnetic resonance (NMR) method, combined with density functional theory (DFT) calculations, was employed to evaluate the control effect of solvent water in the photocatalytic reforming mechanism of methanol with a Pt-TiO2 catalyst. Results indicate that the presence of water effectively promotes the formation of the HCHO intermediate but inhibits the H2 evolution originating from the switch of the hydrogen source of the H2 formation from CH3OH to H2O. More interestingly, as detected directly in the ab initio molecular dynamics simulation, a small amount of H2O can dissociate, and the evolved -OH species at Ti5c site can greatly reduce the C-H activation barrier of -CH3O, contributing to the formation of oxidation products (e.g., HOCH2OH and CH3OCH2OH) on the Pt-TiO2 surface.

Rhodium Dopants on Zn2 GeO4 Surfaces as Active Sites for Photocatalytic Water Splitting.

Doping has been widely used to engineer efficient photocatalysts for the water-splitting process in energy conversion and storage systems. Although composition tuning through heteroatom doping is one of the strategies to enhance photoactivity, the origin of the increased activity by doping remains unclear and most illustrations of its role fall in the band engineering area. Herein, it is reported that the rhodium dopants on the surface of Zn2 GeO4 , which affect the band structure negligibly, can act as active sites for water splitting. As a result, the Rhδ+ /Zn2 GeO4 photocatalyst demonstrates excellent stability for up to 460 days and significant enhancement of the photocatalytic activity to that of the undoped photocatalyst. The findings in this work may open the door for a rethink of the detailed principles of dopants in photocatalysis, and highlight a feasible route to fabricating efficient photocatalysts.

Isolation of single Pt atoms in a silver cluster: forming highly efficient silver-based cocatalysts for photocatalytic hydrogen evolution.

The atomically controlled transition of nanohybrids and their effects on charge-carrier dynamics are highly desirable for fundamental studies in photocatalysis. Herein, for the first time, a method combining atomic monodispersity and single-atom alloy was used to prepare a new form of highly efficient silver-based cocatalysts (Ag25 & Pt1Ag24) on graphitic carbon nitride, representing a novel photocatalytic system for hydrogen evolution.

Controllable Synthesis of Hexagonal WO3 Nanoplates for Efficient Visible-Light-Driven Photocatalytic Oxygen Production.

Facilitating charge-carrier separation and transfer is fundamentally important to improve the photocatalytic performance of semiconductor materials. Herein, two-dimensional hexagonal WO3 nanoplates were synthesized by a two-step route: rapid evaporation and solid-phase sintering. The as-prepared WO3 exhibits an enhanced activity of photocatalytic water oxidation compared to bulk monoclinic WO3 . The electron dynamics analysis reveals that a more efficient charge-carrier separation in the former can be obtained, the origin of which can be attributed to an increased number of surface defects in hexagonal WO3 nanoplates. This work not only presents a novel and simple method to produce two-dimensional hexagonal WO3 nanoplates, but also demonstrates that surface defects and two-dimensional geometric structures can promote the charge separation, which may be extended to the design of other efficient photocatalysts.

One-step fabrication of porous oxygen-doped g-C3N4 with feeble nitrogen vacancies for enhanced photocatalytic performance.

Porous oxygen-doped graphitic carbon nitride (g-C3N4) with feeble nitrogen vacancies was fabricated through thermal polycondensation of melamine with an appropriate amount of polyvinylpyrrolidone. After optimization, the bandgap of g-C3N4 can be narrowed by 0.2 eV and the specific surface area expanded, which contribute to increasing the utilization of solar energy. Consequently, the optimized g-C3N4 exhibits impressive enhancement in photocatalytic hydrogen evolution performance, by nearly 5 times compared with the pristine one under the irradiation of visible light.

Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions.

Proton transfer (PT) processes in solid-liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid-liquid phases.

The mechanisms of brassinosteroids' action: from signal transduction to plant development.

Brassinosteroids play diverse roles in plant growth and development. Plants deficient in brassinosteroid (BR) biosynthesis or defective in signal transduction show many abnormal developmental phenotypes, indicating the importance of both BR biosynthesis and the signaling pathway in regulating these biological processes. Recently, using genetics, proteomics, genomics, cell biology, and many other approaches, more components involved in the BR signaling pathway were identified. Furthermore, the physiological, cellular, and molecular mechanisms by which BRs regulate various aspects of plant development, are being discovered. These include root development, anther and pollen development and formation, stem elongation, vasculature differentiation, and cellulose biosynthesis, suggesting that the biological functions of BRs are far beyond promoting cell elongation. This review will focus on the up-to-date progresses about regulatory mechanisms of the BR signaling pathway and the physiological and molecular mechanisms whereby BRs regulate plant growth and development.