The slow kinetics at the cathode of oxygen reduction reaction (ORR) seriously limits the efficiencies of fuel cells and metal-air batteries. Pt, the state-of-the-art ORR electrocatalyst, suffers from ...high cost, low earth abundance, and poor stability. Here a self-templated strategy based on metal-organic frameworks (MOFs) is proposed for the fabrication of hollow nitrogen-doped carbon spheres that are embedded with cobalt nanoparticles (Co/HNC). The Co/HNC manifests better ORR activities, methanol tolerance, and stability than commercial Pt/C. The high ORR performance of Co/NHC can be attributed to the hollow structure which provides enlarged electrochemically active surface area, the formation of more Co-N species, and the introduction of defects. This work highlights the significance of rational engineering of MOFs for enhanced ORR activity and stability and offers new routes to the design and synthesis of high-performance electrocatalysts.
An efficient and robust in situ surface-confined strategy was demonstrated for the fabrication of single-atom Fe-N4 on N-doped carbon nanoleaves (L-FeNC). Benefiting from abundant Fe-N4 active sites, ...enhanced mass and charge transfer, L-FeNC delivered superior performance for ORR and Zn-air battery to commercial Pt/C.
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•In situ surface-confined strategy was demonstrated to fabricate L-FeNC.•L-FeNC showed an E1/2 of 0.89 V and good stability for ORR in 0.1 M KOH.•High ORR performance is owing to abundant Fe-N4, favored mass and charge transfer.
Controllable fabrication of Fe-N-C based single-atom catalysts (SACs) for enhanced electrocatalytic performance is highly desirable but still challenging. Here, an in situ surface-confined strategy was demonstrated for the synthesis of single atomic Fe-N4 on N-doped carbon nanoleaves (L-FeNC). The in situ generated Zn3Fe(CN)62 could not only serve as a protection layer against collapse of nanoleaves but also provide abundant Fe source for the formation of Fe-N moieties during pyrolysis, leading to high surface area and high graphitization degree of L-FeNC simultaneously. Benefiting from abundant Fe-N4 active sites, enhanced mass and charge transfer, the as-prepared L-FeNC manifested a half-wave potential of 0.89 V for oxygen reduction reaction (ORR) in 0.1 M KOH. A maximum power density of 140 mW cm−2 and stable discharge voltage even after operation for 50,000 s have been demonstrated when the L-FeNC was used as air cathode for Zn-air battery. This work not only provided a unique surface-confined strategy for the synthesis of two-dimensional nanocarbons, but also demonstrated the significant benefit from rational design and engineering of Fe-N-C SACs, thus offering great opportunities for fabrication of efficient energy conversion and storage devices.
Due to the environmental deterioration caused by modern industrialization, the key focus of researchers worldwide is diverted toward clean and sustainable energy sources, such as fuel cells and ...metal-air batteries, where the oxygen reduction reaction (ORR) at the cathode plays a central role. Unfortunately, the sluggish kinetics at the cathode of the ORR, in which the platinum-based (Pt-based) catalyst plays a critical role, is the principal impediment to commercialization. Pt and Pt-based, cutting-edge ORR electrocatalysts suffer from high cost, low methanol tolerance, and poor stability. Researchers have made tremendous efforts towards substitution of Pt-based catalysts, and significant achievements were accomplished in the form of alternatives such as metal oxides, nitrides, chalcogenides, carbides, metal-free nanocarbon, and metal-nitrogen/carbon (M-N/C) nanocomposites. Among these innumerable substitutes of Pt-based catalysts, M-N/C shows great potential because of their high stability, high methanol tolerance, and admirable ORR activities. In this review, we have summarized the principles and factors determining the rate of ORR, which are related to different surface planes of the crystal, surface area, and electronic structure tunability, where the morphology, multiple heteroatom-doping, and controlled particle size play a vital role. Furthermore, we have also discussed the synthetic protocol of different ORR materials such as Pt-based, metal chalcogenides, metal oxides, and M-N/C nanocomposites and the challenges related to these materials. Hopefully, this review will provide a status update as well as new directions to the scientific community engaged in designing novel catalytic materials for energy and environmental applications.
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•Transition metal-N-C electrocatalysts for the oxygen reduction reaction.•A broad perspective on the design and synthesis of the transition metal-N-C electrocatalysts.•Various structural and morphological modifications towards the M-N-C electrocatalysts for efficient ORR reactions.•Electronic structure modulation for ORR explained in detail, based on various experimental work performed.•Future perspectives on the ORR mechanism.
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•Interface α-MnO2/Bi2WO6 heterostructure synthesized with abundant Mn3+/Mn4+ defect.•Boosted visible light by surface oxygen vacancies, defects sites.•O2− and 1O2 were the main ROS ...for TC-HCl degradation, Cr6 reduction.•DFT calculation reveals high charge density at the built-in-interface.•Mechanistic insights into Z-scheme charge transfer.
The construction of visible-light-driven hybrid heterostructure photocatalysts is of great significance for environmental remediation, although the utilization of strong visible-light response photocatalysts with high efficiency and stability remains a major challenge. On the other hand, defect engineering is an excellent way to introduce metal cation vacancies in materials, thereby ensuing in highly enhanced catalytic performance. Inspired by this, we effectively constructed a built-in interface α-MnO2/Bi2WO6 heterostructure with abundant intimate interfaces and defective Mn3+/Mn4+ active sites for photocatalytic tetracycline hydrochloride (TC-HCl), hexavalent chromium Cr6+ reduction, and Escherichia coli (E. coli) inactivation. The experimental results, such as the active species test and X-ray photoelectron spectroscopy, indicated that the defective sites Mn3+/Mn4+, surface oxygen vacancies, and Bi(3+x)+ boosted the visible light absorption, and highly enhanced the photoinduced charge separation/transfer. Furthermore, experimental and DFT calculations reveal the high charge density at the built-in interface heterostructure and the Z-scheme charge transfer mechanism during the photocatalytic process. The results further reveal that O2− and 1O2 are the main reactive active species contributing to the photocatalytic reaction. The exceptional TC-HCl decomposition activity of the α-MnO2/Bi2WO6 heterostructure (97.56%, 2.31, and 2.04 times higher than bulk), enhanced reaction kinetics (Kapp = 0.041 min−1, 6.4, and 5.2 times higher than bulk), removal rate of 80.3%, Cr6+ reduction to Cr3+ (98.56%, Kapp = 0.0599 min−1), and almost 100% bacterial inactivation compared to bulk α-MnO2 (42.22%) and Bi2WO6 (47.76%), were mainly due to the enhanced charge separation/transfer at the built-in interface and high charge density. This study opens new horizons for constructing Z-scheme MnO-based interface heterostructures with abundant defect sites for exceptional photocatalytic applications.
•Two novel cobalt (II), I and nickel (II), II complexes with the 4-bromo-3-methyl-1H-pyrazole ligands have been synthesized.•These complexes were characterized FTIR, H-NMR, TGA/DSC and X-ray ...crystallography•The complexes were investigated for electrochemical behaviors and nonlinear optical (NLO) responses.
Two new isostructural cobalt Co(II)(C4H5BrN2)4(Cl)2, I and nickel Ni(II)(C4H5BrN2)4(Cl)2, II complexes were synthesized for linear and nonlinear optical (NLO) responses using the finite field method. The synthesized complexes were characterized using elemental analysis, infrared and H-NMR spectroscopy, TG/DSC analysis, and X-ray crystallography. The crystal analysis indicates that both complexes I and II are mononuclear, and crystallize in the monoclinic space group P21/c. The metal ion in each complex is six coordinated with four nitrogen atoms (from 4-bromo-3-methyl-1H-pyrazole ligand) and two chloride ligands adopting octahedral coordination geometry. Furthermore, the computational predictions for molecular geometries and average third-order nonlinear polarizabilities of I and II are made in current study. The average theoretically predicted third-order nonlinear polarizabilities <γ> of I and II are 95.50 × 10−36 and 91.25 × 10−36 esu, respectively. The <γ> amplitudes values of complexes I and II are ∼5.26 and ∼5.0 times greater than the prototype NLO molecule of para-nitroaniline (p-NA) at same level of theory, which indicates their decent potential as efficient NLO materials.
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The construction of visible-light-driven hybrid heterostructure photocatalysts is of great significance for environmental remediation, although the utilization of strong visible-light response ...photocatalysts with high efficiency and stability remains a major challenge. Defect engineering is an excellent way to introduce metal cation vacancies in materials, thereby ensuing in highly enhanced catalytic performance. Inspired by this, we effectively constructed a built-in interface alpha-MnO2/Bi2WO6 heterostructure with abundant intimate interfaces and defective Mn3+/Mn4+ active sites for photocatalytic tetracycline hydrochloride (TC-HCl), hexavalent chromium Cr6+ reduction, and Escherichia coli (E. coli) inactivation. The experimental results, such as the active species test and X-ray photoelectron spectroscopy, indicated that the defective sites Mn3+/Mn4+, surface oxygen vacancies, and Bi(3+x)+ boosted the visible light absorption, and highly enhanced the photoinduced charge separation/transfer. Furthermore, experimental and DFT calculations reveal the high charge density at the built-in interface heterostructure and the Z-scheme charge transfer mechanism during the photocatalytic process. The results further reveal that O-2(-) and O-1(2) are the main reactive active species contributing to the photocatalytic reaction. The exceptional TC-HCl decomposition activity of the alpha-MnO2/Bi2WO6 heterostructure (97.56%, 2.31, and 2.04 times higher than bulk), enhanced reaction kinetics (K-app = 0.041 min(-1), 6.4, and 5.2 times higher than bulk), removal rate of 80.3%, Cr6+ reduction to Cr3+ (98.56%, K-app = 0.0599 min(-1)), and almost 100% bacterial inactivation compared to bulk alpha-MnO2 (42.22%) and Bi2WO6 (47.76%), were mainly due to the enhanced charge separation/transfer at the built-in interface and high charge density. This study opens new horizons for constructing Z-scheme MnO-based interface heterostructures with abundant defect sites for exceptional photocatalytic applications.
•Role of magnetic moment in catalytic activity.•Effect on the magnetic moment on the d-band center.•Effect of bimetallic on the stability of single-atom catalyst on adjacent position.•Evaluating of ...z-directed orbital for catalytic activity.•Tuning of electronic structure for oxidative and reductive species.
Numerous articles on M-N-C-based materials have been extensively studied for their catalytic activity in various reaction perspectives, such as CO oxidation, CO2 reduction, oxygen reduction, and oxygen/hydrogen evaluation. However, the understanding of the involvement of d-orbitals of transition metal atoms and the tunability of their electronic structure for different catalytic species is under observation. Herein we have suggested bimetallic iron-doped nitrogen-based graphene FeN4-MN4/Gr (M= Co, Ni, Cu, Zn) and single-atom iron-doped nitrogen-based graphene for comparative study. The effect of bimetallic atoms on iron on the adjacent position was studied by Bader charge, adsorption energy for different species, and the strengthening of iron nitrogen codoped graphene Fe-N4/Gr. Moving from Co to Zn, the number of outermost electrons is increasing, creating steric hindrances effect and torsional strain, affecting Bader charge and formation energy and changing the bond length between nitrogen and iron. Similarly, steric hindrance also has a prominent effect on the d-orbital, as moving from Co to Zn, the availability of finding of d-orbital on z-direction are increasing which is confirmed by adsorption energy of different species like Co, O2, and H+ + e−. Our finding reveals that not only d-orbitals along the z-direction can play a vital role in catalytic activity, but the d-band center and magnetic moment also have a projecting role in boosting catalytic activity.
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Background: Intraocular pressure measurement (IOP) is of pivotal importance for the diagnosis and management of glaucoma. The objective of this study was to compare intraocular pressure measurement ...with Goldmann Applanation tonometer (GAT) and non-contact Air-Puff tonometer (APT). Material & Methods: This comparative cross-sectional study was conducted at outpatient Department of Ophthalmology, District Headquarters Teaching Hospital, Bannu, Pakistan, from October 2015 to February 2016. The IOP was measured first with APT (Canon Full Auto Tonometer TX-F, Japan) followed by its measurement with GAT (HAAG-STRIET AT 900, Koeniz Switzerland) Results: This study included 200 eyes of 100 patients. Among 100 patients, 57(57%) were males and 43(43%) were females. Age range was from 16 to 78 years with a mean of 42.5 years. The IOP measured with APT ranged from 10 mmHg to 47mmHg with a mean of 18.17+8.25 mmHg, while IOP recorded with GAT ranged from 10 mmHg to 41mmHg with a mean of 15.59+7.75 mmHg. There was a significant difference in the mean IOP measured with APT and GAT, with APT recording a mean IOP of 2.58 mmHg higher than GAT (p=0.003). Conclusion: Both APT and GAT are commonly used for IOP measurement. There is a reasonably good agreement between the two tonometers at IOP within the normal range. However GAT is more accurate and reliable. APT overestimates IOP, particularly in cases above the upper limit of normal IOP. The results of APT should be confirmed with GAT, particularly when the IOP exceeds the normal range for the diagnosis and treatment of glaucoma.
Background: Refractive errors are one of the commonest causes of visual impairment and disability. The aim of this study was to evaluate the distribution of different types of refractive errors. ...Material & Methods: This descriptive prospective study including one thousand and eighty seven patients was conducted at outpatient department of Ophthalmology, DHQ Teaching Hospital, Bannu, from October 2014 to March 2015. Refraction was done with Neitz streak retinoscope and Topcon auto-refractometer. Results: Among 1087 patients studied, 739(67.98%) were males and 348(32.02%) females. Age range was 25 to 80 years with a mean of 45.1. Refractive errors ranged from -14D to +10D. Myopia was the commonest refractive error found in 479(44.06%) patients, hyperopia in 286 (26.31%) and astigmatism in 307(28.20%) patients. Conclusion: Refractive errors are among the major causes of visual impairment, disability and blindness. However refractive errors are easily correctable. Effective measures should be taken for screening and refraction to combat the avoidable visual impairment and disability due to refractive errors.
