Designing non‐precious electrocatalysts to synergistically achieve a facilitated mass/electron transfer and exposure of abundant active sites is highly desired but remains a significant challenge. ...Herein, a composite electrocatalyst consisting of highly dispersed Co/CoP heterojunction embedded within a hierarchically ordered macroporous‐mesoporous‐microporous carbon matrix (Co/CoP@HOMC) is rationally designed through the pyrolysis of polystyrene sphere‐templated zeolite imidazolate framework‐67 (ZIF‐67) assemblies. The combined experimental and theoretical calculations reveal that Co/CoP interfaces not only provide richly exposed active sites but also optimize hydrogen/water absorption free energy via electronic coupling, while the interconnected macroporous structure enables a superior mass transfer to all accessible active sites. As a result, the as‐developed Co/CoP@HOMC composites exhibit outstanding catalytic activity with overpotentials of only 120 and 260 mV at 10 mA cm−2 for the hydrogen evolution reaction and oxygen evolution reaction in 1.0 m KOH, respectively. Moreover, an alkaline electrolyzer constructed by Co/CoP@HOMC requires an ultralow cell voltage of 1.54 V to achieve 10 mA cm−2, outperforming that of the Pt@C||IrO2@C couple (1.64 V).
Hierarchically ordered porous carbon‐supported heterostructured Co/CoP nanoparticles (Co/CoP@HOMC) are rationally designed. Owing to the synergistic coupling effect, highly exposed active sites, and enhanced mass transfer, the Co/CoP@HOMC exhibits an exceptional catalytic activity for both the hydrogen evolution reaction and the oxygen evolution reaction.
The rational design of an efficient and inexpensive electrocatalyst based on earth‐abundant 3d transition metals (TMs) for the hydrogen evolution reaction still remains a significant challenge in the ...renewable energy area. Herein, a novel and effective approach is developed for synthesizing ultrafine Co nanoparticles encapsulated in nitrogen‐doped carbon nanotubes (N‐CNTs) grafted onto both sides of reduced graphene oxide (rGO) (Co@N‐CNTs@rGO) by direct annealing of GO‐wrapped core–shell bimetallic zeolite imidazolate frameworks. Benefiting from the uniform distribution of Co nanoparticles, the in‐situ‐formed highly graphitic N‐CNTs@rGO, the large surface area, and the abundant porosity, the as‐fabricated Co@N‐CNTs@rGO composites exhibit excellent electrocatalytic hydrogen evolution reaction (HER) activity. As demonstrated in electrochemical measurements, the composites can achieve 10 mA cm−2 at low overpotential with only 108 and 87 mV in 1 m KOH and 0.5 m H2SO4, respectively, much better than most of the reported Co‐based electrocatalysts over a wide pH range. More importantly, the synthetic strategy is versatile and can be extended to prepare other binary or even ternary TMs@N‐CNTs@rGO (e.g., Co–Fe@N‐CNTs@rGO and Co–Ni–Cu@N‐CNTs@rGO). The strategy developed here may open a new avenue toward the development of nonprecious high‐performance HER catalysts.
3D hierarchical structures consisting of ultrafine Co nanoparticles embedded in in situ formed N‐doped carbon‐nanotube‐grafted graphene sheets are fabricated by a novel and universal strategy. These structures exhibit excellent hydrogen evolution reaction (HER) activity and durability in both alkaline and acidic solution.
In this paper, the direct acyloxylation of the α-C(sp2)–H bond in tertiary β-enaminones is accomplished under catalyst-free conditions and ambient temperature by using aroyl peroxides as coupling ...partners. By means of a thermoinduced free-radical pathway, the present method enables facile and efficient synthesis of both acyloxylated chromones and enaminones.
In order to explore the evolution mechanism of water and mud inrush, based on the fluid-solid coupling similarity theory and a large number of matching tests, fault similar materials with mountain ...sand, gravel, and red clay as raw materials and surrounding similar rock materials with mountain sand, red clay, cement, and water as raw materials are developed. Similar materials’ physical and mechanical properties and hydraulic properties with different ratios are tested and analyzed. The results show that the red clay content influences the mechanical properties of similar materials and their hydraulic properties, and the gravel substrate mainly influences the fault permeability coefficient. Similar material can be adjusted within a certain range of mechanical parameters. The material is simple and suitable for developing similar materials for different low and medium strength rock masses. Finally, a similar material was used in a model test of the tunnel fault fracture zone to reveal the mechanism of water and mud bursts in the tunnel. The study results can be used as a reference for the development of similar materials for tunnel fracture zone surrounding rocks.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The cascade reactions between NH 2-functionalized enaminones and sulfonyl hydrazines have been developed for the synthesis of fully substituted pyrazoles. By making use of the hydrophilic primary ...amino group in the enaminones, the reactions proceed well in the medium of pure water in the presence of molecular iodine, TBHP, and NaHCO3 via cascade C-H sulfonylation and pyrazole annulation. The cleavage of the C–N bond in enaminones is confirmed by the experiment using 15 N-labeled enaminone.
Breast cancer is the second leading cause of death for women all over the world. Since the cause of the disease remains unknown, early detection and diagnosis is the key for breast cancer control, ...and it can increase the success of treatment, save lives and reduce cost. Ultrasound imaging is one of the most frequently used diagnosis tools to detect and classify abnormalities of the breast. In order to eliminate the operator dependency and improve the diagnostic accuracy, computer-aided diagnosis (CAD) system is a valuable and beneficial means for breast cancer detection and classification. Generally, a CAD system consists of four stages: preprocessing, segmentation, feature extraction and selection, and classification. In this paper, the approaches used in these stages are summarized and their advantages and disadvantages are discussed. The performance evaluation of CAD system is investigated as well.
Azo dyes are recalcitrant and refractory pollutants that constitute a significant burden on the environment. The report here is focused on the decolorization treatment of water soluble azo dye methyl ...orange (MO) by chemically synthesized nanoscale zerovalent iron (NZVI) particles. Experimental variables such as initial dye concentration, iron dosage, solution pH and temperature were studied systematically. Batch experiments suggest that the decolorization efficiency was enhanced with the increase of NZVI dosage and reaction temperature, but decreased with increasing initial dye concentration and initial solution pH. Further studies indicated that existence of inorganic salt (Na
2SO
4) could inhibit the decolorization of MO. Kinetic analyses based on the experimental data elucidated that the decolorization process followed a first order exponential decay kinetics model. The activation energy was determined to be 35.9
kJ/mol.
•Aim of this survey is to provide an overview of the available MRI denoising methods.•Help the researchers to develop a new denoising method for MR images.•Helps to choose the best denoising method ...for further image processing methods.•Like segmentation, registration, classification used in computer aided diagnosis.
Over the past several years, although the resolution, signal-to-noise ratio and acquisition speed of magnetic resonance imaging (MRI) technology have been increased, MR images are still affected by artifacts and noise. A tradeoff between noise reduction and the preservation of actual detail features has to be made in the way that enhances the diagnostically relevant image content. Therefore, noise reduction is still a difficult task. A variety of techniques have been presented in the literature on denoising MR images and each technique has its own assumptions, advantages and limitations. The purpose of this paper is to present a survey of the published literature in dealing with denoising methods in MR images. After a brief introduction about magnetic resonance imaging and the characteristics of noise in MRI, the popular approaches are classified into different groups and an overview of various methods is provided. The denoising method's advantages and limitations are also discussed.
Neutrosophic set (NS), a part of neutrosophy theory, studies the origin, nature and scope of neutralities, as well as their interactions with different ideational spectra. NS is a formal framework ...that has been recently proposed. However, NS needs to be specified from a technical point of view for a given application or field. We apply NS, after defining some concepts and operations, for image segmentation.
The image is transformed into the NS domain, which is described using three membership sets:
T,
I and
F. The entropy in NS is defined and employed to evaluate the indeterminacy. Two operations,
α-mean and
β-enhancement operations are proposed to reduce the set indeterminacy. Finally, the proposed method is employed to perform image segmentation using a
γ-means clustering. We have conducted experiments on a variety of images. The experimental results demonstrate that the proposed approach can segment the images automatically and effectively. Especially, it can segment the “clean” images and the images having noise with different noise levels.
Engineering photosensitizers into stimuli-responsive supramolecular nanodrugs allows enhanced spatiotemporal delivery and controllable release of photosensitizers, which is promising for dedicated ...and precise tumor photodynamic therapy. Complicated fabrication for nanodrugs with good tumor accumulation capability and the undesirable side-effects caused by the drug components retards the application of PDT in vivo. The fact that extracellular adenosine triphosphate (ATP) is overexpressed in tumor tissue has been overlooked in fabricating nanomedicines for tumor-targeting delivery. Hence, herein we present metal-free helical nanofibers formed in aqueous solution from the coassembly of a cationic porphyrin and ATP as a nanodrug for PDT. The easily accessible and compatible materials and simple preparation enable the nanodrugs with potential in PDT for cancer. Compared to the cationic porphyrin alone, the porphyrin–ATP nanofibers exhibited enhanced tumor-site photosensitizer delivery through whole-body blood circulation. Overexpressed extracellular ATP stabilizes the porphyrin–ATP nanodrug within tumor tissue, giving rise to enhanced uptake of the nanodrug by cancer cells. The enzyme-triggered release of photosensitizers from the nanodrugs upon biodegradation of ATP by intracellular phosphatases results in good tumor therapeutic efficacy. This study demonstrates the potential for employing the tumor microenvironment to aid the accumulation of nanodrugs in tumors, inspiring the fabrication of smart nanomedicines.
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