Migration Of Reactants Research Articles

Highly-sensitive and anti-interferential electrochemical determination of hazardous metronidazole using w-NiSO4·NiS2 coated ZIF-67-derived cobalt/nitrogen-doped carbon

Metronidazole (MNZ) is non-biodegradable and highly soluble in water, it is easy to accumulate in the aquatic environment, which has toxic effects in clinical applications such as causing peripheral neuritis, cardiogenic shock and pseudomembranous colitis. In this paper, Co/NC@w-NiSO4·NiS2 nanospheres were successfully constructed by coating w-NiSO4·NiS2 on the surface of ZIF-67 as the growth substrate via hydrothermal method and subsequent calcination for electrochemical detection of metronidazole (MNZ). The nanostructure and composition of the materials were confirmed by SEM, TEM, FT-IR and XPS. The sensitivity of Co/NC@w-NiSO4·NiS2 sensor for MNZ detection is 1977.14 μA/(mM·cm2); the limit of detection (LOD) is as low as 0.009 μM and the linear range is 1 ∼ 200 and 200 ∼ 1000 μM. Moreover, the modified sensor can resist the interference from many traditional living substances, and has good reproducibility and stability. High catalytic activity requires effective molecular transport and exposure of active sites. The successful construction of Co/NC@w-NiSO4·NiS2 nanostructure promotes the dispersion of materials and the migration of reactants on the electrode surface, and the w-NiSO4·NiS2 coating on the irregular particles of ZIF-67-derived cobalt/nitrogen-doped carbon suppressed the stacking of the w-NiSO4·NiS2 nanosheets to expose more catalytic sites. These factors are conducive to increasing the catalytic activity of the modified sensor for highly sensitive MNZ detection and ensuring the activity of catalyst in multiple catalytic cycles.

In Situ Sulfidation for Controllable Heterointerface of Cobalt Oxides–Cobalt Sulfides on 3D Porous Carbon Realizing Efficient Rechargeable Liquid-/Solid-State Zn–Air Batteries

Designing and constructing highly efficient bifunctional electrocatalysts for oxygen reduction (ORR) and oxygen evolution (OER) is critical to the development of rechargeable Zn–air batteries. Taking into account the multistep electron-transfer process of oxygen electrocatalytic reactions, it is very desirable to design a suitable construction for electrocatalysts with fantastic electronic transport properties and structural advantages. Herein, we highlight in situ heterointerface engineering and a three-dimensional (3D) porous network structure in preparing the electrocatalysts of N,S-codoped 3D carbon matrix with Co₉S₈/CoO heterojunction (Co–S–O/NSCN). Systematic characterization and electrochemical experiments confirm that the destabilized charge distribution induced by the Co₉S₈/CoO heterojunction promotes the fast transfer of electrons during the electrocatalytic process. The well-designed 3D-interconnected network structure composed of 2D nanosheets and in situ-generated 1D carbon nanotubes facilitates the multidimensional electron delivery and reactant migration, along with other additional structural advantages of high surface area and enhanced electronic conductivity. Benefiting from these significant advantages, Co–S–O/NSCN exhibits outstanding oxygen electrocatalytic performance with the ORR half-wave potential of 0.865 V, the OER potential of 1.665 V at 10 mA cm–² (ORR-OER potential gap of 0.80 V), and extraordinary durability in 0.1 M KOH, outperforming the noble-metal Pt/C catalyst and most of the reported Co-based electrocatalysts. Impressively, both the rechargeable Zn–air batteries using liquid and solid electrolytes, assembled by Co-S-O/NSCN catalysts, show satisfactory performance with low charge–discharge gap and long cycling life. This work highlights the superiority of the heterointerface and advanced structural configuration in oxygen electrochemistry, thus giving some inspiration for the fabrication of significant metal–air cathode electrocatalysts.

Reduction of Oxidized Pd/Ag(111) Surfaces by H2: Sensitivity to PdO Island Size and Dispersion

Understanding the migration of species across interfaces in bimetallic systems is key to exploiting their bifunctionality for chemical reactivity and heterogeneous catalysis. The present study demonstrates that the sizes and dispersion of oxidized Pd islands present on oxidized Ag(111) in addition to the concentration of active Pd sites have a significant influence on the rate of surface reduction by H2. Two distinct types of Pd oxide islands were generated for this investigation and characterized using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy. Small, uniformly dispersed PdOx islands (1–5 nm diameter) were created by depositing Pd onto AgOx surfaces, while larger, non-uniformly dispersed PdOx agglomerates (30–50 nm) were produced by depositing Pd on Ag(111) prior to oxidizing. Based on XPS, the small PdOx islands have a higher concentration of undercoordinated Pd atoms than the large agglomerates. Both types of PdOx are found to dramatically enhance the reduction of AgOx by H2 at 300 K due to the ability of PdOx to dissociate H2; the pure AgOx surfaces are unreactive toward H2. The rate of reduction at 300 K is found to be 2–4 times larger for the AgOx surface covered by small, uniformly dispersed PdOx islands. The higher reactivity of this surface is attributed to enhanced migration of oxygen and hydrogen atoms between the PdOx and AgOx phases due to the sizes and high dispersion of the small PdO islands as well as the higher concentration of active Pd sites on the PdOx domains. This study demonstrates that reactant migration between co-existing surface phases is highly sensitive to both the intrinsic chemical activity and morphological properties of the active phase (PdOx) and reveals that these properties can be significantly influenced by the method of synthesizing the oxidized bimetallic surfaces.

Deoxygenation of octanoic acid catalyzed by hollow spherical Ni/ZrO2

A series of Ni located on hollow spherical ZrO2 catalysts was prepared, and their catalytic performances for octanoic acid deoxygenation were investigated. The ZrO2 hollow spheres saturated by the water phase served as a nanoreactor that captured octanoic acid to react with Ni located inside a hollow spherical ZrO2. The complete conversion of octanoic acid deoxygenation could be achieved by migration of reactants and products in the water-oil biphasic phase. Oxygen vacancies on ZrO2 that resulted from calcination temperature improved the catalytic activity of deoxygenation. Propionic acid was taken as a model compound instead of octanoic acid in view of their same functional group (carboxyl), to study the mechanisms of hydrodeoxygenation, decarbonylation, and decarboxylation through density functional theory of calculations. The main reaction route was decarboxylation which was consistent with the experimental results.

Comment on “Effect of Al2O3 and Bi2O3 on the Formation Mechanism of Sn‐Doped Ba2Ti9O20”

in a recent article of the Journal, Yu et al.1 reported their experimental results on the effect of Al2O3 and Bi2O3 on the formation mechanism of Sn‐doped Ba2Ti9O20. They claimed that both Al2O3 and Bi2O3 can dramatically assist the formation of Sn‐doped Ba2Ti9O20 but are based on different mechanisms. They concluded that first, Bi2O3 melts above 830°C and accelerates the migration of the involved reactants to form Ba2Ti9O20; second, Al2O3 can reduce the height of the potential energy barrier of the formation of Ba2Ti9O20 due to the intergrowth of BaAl2Ti6O16 phase. They explained their results from a point of view that the formation of Ba2Ti9O20 is controlled by (1) the migration of reactants to the interfaces and (2) the height of the potential‐energy barrier of the reaction at the interfaces. However, based on their results, we feel their conclusions are incautious and may be misleading, as will be discussed later.

A Comparison of Pad-Dry-Cure and Low Add-On Reactant Application on Cotton Fabrics

The unfavorable effect of reactant migration in padded cotton fabrics during.drying on the balance of crease recovery and abrasion weight loss was confirmed once more. The influence of fabric type and pretreatments such as scouring and bleaching was studied. With the aid of a low add-on method making use of an engraved roller it can be shown that if the add-on is kept under a level of 30-40%, migration is largely prevented. Consequently, the balance of properties approaches that of a fabric with a uniform reactant distribution. The effect of the surface-active agents in low add-on methods was studied. The interaction between pretreatment and amount of surface active agent applied is clearly illustrated.