Abstract Carbon materials with unique sp 2 ‐hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom‐up” strategy by pyrolysis of graphitic carbon nitride (g‐C 3 N 4 ) (or other carbon/nitrogen (C, N)‐enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon‐based catalysts with tunable morphologies, including carbon nano‐balls, carbon nanotubes, nitrogen/sulfur (S, N) doped‐carbon nanosheets, and single‐atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric‐gas chromatography‐mass spectrometry measurements indicates that the release of C─N‐related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g‐C 3 N 4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon‐based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses.
New nanostructures often reflect new and exciting properties. Here, we present an two-dimensional, hitherto unreported PdO square network with lateral dimensions up to hundreds of nanometers growing on reduced graphene oxide (rGO), forming a hybrid nanofilm. An intermediate state of dissolved Pd(0) in the bacterium S. oneidensis MR-1 is pivotal in the biosynthesis and inspires an abiotic synthesis. The PdO network shows a lattice spacing of 0.5 nm and a thickness of 1.8 nm on both sides of an rGO layer and is proposed to be cubic or tetragonal crystal, as confirmed by structural simulations. A 2D silver oxide analog with a similar structure is also obtained using an analogous abiotic synthesis. Our study thus opens a simple route to a whole new class of 2D metal oxides on rGO as promising candidates for graphene superlattices with unexplored properties and potential applications for example in electronics, sensing, and energy conversion.
Abstract Directly converting methane to methanol with solar light and eco‐friendly oxidants is challenging due to single‐step conversion process where the designed active sites commonly cleave C─H bonds in both methane and methanol. Herein, a novel method is proposed to break activity‐selectivity trade‐off in methane conversion to methanol through interface engineering. Taking BiOI/BN as a proof‐of‐concept model, it's discovered that engineered interface provides distinct active sites for methane activation and overoxidation products photoreduction. Based on in situ infrared spectroscopy, ultrafast laser spectroscopy, and theoretical calculations, it is unlocked that the engineered interface induces the passivation of original trap states in BiOI component, greatly hindering ultrafast trap‐mediated recombination of photo‐induced carriers (≈39.7 ps). Benefiting from it, long‐lived electrons could directly participate in active radicals generation, ensuring effective methane activation. Subsequently, overoxidation carbon intermediates and protons are captured by active sites from the BN component and rapidly accumulated on the surface. This enables effective injection of electrons into bonding orbitals of C─H bonds in methanol, accelerating the occurrence of C─H re‐bonding process. Ultrafast photo‐induced charge and carbon intermediates transfer at interfaces results in high methane conversion rate of 15.5% under atmospheric pressure and maintains methanol selectivity of 86.4% for 24 h long‐time reaction process.
Oxyfluoride glass and glass ceramics codoped with Er3+/Yb3+ ions of the same composition were prepared. Nanocrystals in the glass ceramics were formed,characterized by xray diffraction and fluorescence spectra. The measurements by using the differential thermal analysis and the crystal parameter calculation by JuddOfelt theory indicated that the rareearth ions have entered the nanocrystals. At the same time, the ratio of the nanocrystalline phases in glass and glass ceramics before and after annealing was calculated respectively.
The effect of seed soaking with zinc sulfate on growth and physiological characteristics of rice seedlings was studied using seeds of IR8192 and BY typed rice as subjects treated with different concentrations of zinc sulfate(0,0.0005%,0.001%,0.005%,0.01%,0.05%,0.10%,0.15%,0.25%).The results showed that rice seeds treated with seed soaking in appropriate zinc concentration promoted plant growth and accumulation of dry matter,increased the amount of chlorophyll a,b and a+b in leaves,enhanced the superoxide dismutase(SOD),peroxidase(POD),catalase(CAT) activity,reduced malondialdehyde(MDA) content and increased soluble protein and soluble sugar content.However,the optimal zinc concentrations of seed soaking were different as to different types of rice.IR8192 typed rice treated with 0.001% concentration of zinc sulfate had the best treatment effect,while the optimal concentration of BY typed rice was 0.005% which resulted in toxic effect on IR8192.With the zinc concentration of seed soaking going on increasing until it exceeded plant tolerance,growth of rice seedlings would begin to be inhibited.This experiment indicates that seed soaking in appropriate concentration of zinc sulfate can promote growth of rice seedlings,enhance the level of antioxidant enzyme in the course of growth,slow down the role of lipid peroxidation and enhance the level of material metabolism,yet zinc concentration exceeding plant tolerance will result in toxic effect on rice seedlings.
Axial resolution is a key factor in optical coherence tomography (OCT). Biomedical applications will benefit from improved resolution and quality that ultrahigh resolution OCT can provide. Existing approaches to improve axial resolution of OCT mostly depend on new broadband light sources, which are always costly and inconvenient in instrumentation. In this paper we adopt an alternative method to enhance the axial resolution of OCT by combining coherence gate with optical superresolution. A three-zone phase pupil filter is designed and inserted into the sample arm of OCT. The depth responses measured demonstrate that an improvement of more than 15% in axial resolution is achieved in the proposed OCT system.
Abstract Based on the density functional theory, the stereoselectivity of the asymmetric synthesis of tetrahydroisoquinolinopyrazole derivatives by the cycloaddition reaction of C, N ‐cyclic azomethine imines with allyl alkyl ketones which was catalyzed using a chiral primary amine is studied theoretically. The results demonstrate that the four chiral transition states ( TS‐1R2R , TS‐1R2S , TS‐1S2R and TS‐1S2S ) are formed by the reaction of dienamine intermediate with C, N ‐cyclic azomethine imine, and the reaction barrier of TS‐1R2S is in the lowest level (ΔG=6.98 kcal/mol). The consequence reveal that the 1R2S configuration product is formed by TS‐1R2S transition state. Non‐covalent interaction and electron density topology analysis show that the stereoselectivity of the chiral product is determined through van der Waals forces and hydrogen bond interaction of the transition state molecules.
The phonon-assisted quantum cutting (PQC) model is presumed to clarify the red up-conversion luminescence process in Er3+/Yb3+ co-doped glass ceramics by the excitation and emission spectra. The red up-conversion luminescence of Er3+ ions mainly comes from three-photon absorption by the PQC process when the rare earth ions are doped in the glass ceramics and excited by 980 nm pumped-laser. Er3+ ions absorb three-photons and relax to the 4G11/2 state and then emit red up-conversion luminescence by the PQC process. The factor coefficient for the relation of pump-laser power and up-conversion intensity (P-I) is found by the analysis of excitation spectra of the red luminescence, which plays a major role to understand the true red up-conversion luminescence process. The new P-I relation is explained by the model of PQC.
Abstract On the basis of the density functional theory (DFT), the process of cycloaddition reaction of diazocarbonyl compounds with enones without leaving groups to obtain pyrazoles was proposed. First, the diazocarbonyl compounds reacted with enones to offer the intermediates by cycloaddition reaction, which was captured of hydrogen of the intermediate by the base to offer the nonaromatic pyrazole intermediate, which then give the final product by oxidation and isomerization in the air. This protocol corrected the reaction mechanism that was proposed in the experimental section. The negative correlation between the yields of products with the charges of ADCH at the C1 position of enones was also founded, which was consistent with the experimental results. The protocol could provide theoretical guidance for designing more efficient cycloaddition reaction.
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