ABSTRACT
In order to give full play to the advantages in structure tailoring and quantitative assembly, metal-organic frameworks (MOFs) with different topological structures formed by the self-assembly of inorganic ligands containing sulfur, cobalt ions and large-size ligands were used to prepare electrocatalyst materials for hydrolysis with controllable composition and performance. According to the synthesis proposition, we can not only avoid using additional doped sulfur sources to reduce waste but also make it very convenient for Co and sulfur elements to be uniformly and controllably distributed in the whole material, and enhance the overall synergistic effects. Based on the above considerations, two-dimensional layered and three-dimensional MOFs, Co-MOF-1, and Co-MOF-2, with the same chemical compositions were utilized as the templates, and a series of Co/S-based materials with variable compositions and properties were obtained only by controlling the pyrolysis temperature. For each MOF series, it can be observed that with the increase in the pyrolysis temperature, the derivatives gradually change from Co4S3 to Co9S8 composites, which could be proven by PXRD studies. The electrocatalytic properties of two series of derivatives were also investigated, and the results indicate that the materials containing Co4S3 can indeed show better water-splitting performance than Co9S8 ones. Furthermore, the macroscopic stacking form of the MOF template also plays an important role in determining the electrocatalytic performance of the derived materials. Through an overall comparison, it is found that the electrocatalytic performance of the Co-MOF-1 series is better than that of the Co-MOF-2 series at various temperatures, which should be only caused by the natural packing modes of the pristine MOF template. For Co-MOF-1 derivatives, the retention of the two-dimensional layered structure is favorable to form an electrostatic charge separation layer and electron transport channel, which is beneficial to the intercalation and delamination of hydroxide ions, thus improving the storage capacity of materials, promoting electron transfer, and producing less electron transfer resistance. Therefore, based on the research results, the reasonable design of layered MOF materials containing the specific sulfur-containing linker as water-splitting catalysts is an applicable route for the preparation of economical, environmentally friendly, and low energy consumption electrocatalysts, which should receive increasing attention in the future.
ABSTRACT
Metal-organic frameworks (MOFs) with different topologies formed by the self-assembly of sulfur-containing inorganic ligands, cobalt ions, and large ligands can be used to prepare electrocatalysts for water splitting in order to fully explore the advantages of MOFs in terms of structural tailoring and quantitative assembly. It is possible to avoid using an extradoped sulfur source to reduce waste as well as to disperse Co and sulfur elements evenly and controllably throughout the final material to maximize the overall synergistic effect. In this work, different kinds of bimetallic MOF materials containing sulfur can be synthesized very conveniently by using an economical and practical diffusion method. These materials are directly used as OER electrocatalysts, and the bimetallic MOFs have the best electrocatalytic performance when the ratio of Co to Fe is 6:4. The overpotential at a current density of 10 mA cm-2 was 260 mV, with a Tafel slope of 56 mV dec-1 and good stability. It was assembled with 20% commercial Pt/C material into a two-electrode system for all-water decomposition, and the decomposition voltage at 10 mA cm-2 was 1.81 V. From the electronic configuration microscopic point of view, the introduction of iron ions changed the original synergistic effect for Co-S-Co, which more easily led to the formation of high-valence Co3+ and finally produced highly active electrocatalytic sites. From a macroscopic point of view, the material produced in situ during the electrochemical reaction process not only retains the original 2D layered structure but also utilizes bubbles to produce a loose structure with defective sites. These structural features are advantageous because they provide not only an abundance of active sites and permeable channels but also the necessary interfaces and electron-transport channels for the formation of electrostatic charge-separation layers, making it easier to intercalate and delaminate the hydroxide ions. Furthermore, the changed hydroxyl ions and nitrogen and sulfur atoms on the channel surface may operate as interaction sites, increasing the surface characteristics, facilitating electron transfer, and reducing electron-transfer resistance. To summarize, the rational design of sulfur-containing layered MOF materials directly as water-splitting catalysts is a crucial next step in developing cost-effective, environmentally friendly, and low-energy-consumption electrocatalysts based on the findings of this study.
ABSTRACT
Solvothermal reactions of hexakis(4-carboxyphenoxy)cyclotriphospazene (H6L1) with copper ions in DMF/H2O produced one complex, {[Cu6(L1)2(OH)(H2O)3]·guest} n (1), but with copper ions and auxiliary rigid 4,4-bipyridine (bpy) produced another new complex, namely, {[Cu3(L1)(bpy)(H2O)6]·guest} n (2). These complexes had been characterized by IR spectroscopy, elemental analysis, and X-ray structural determination. 1 exhibits a 3D anionic structure with the binodal 4,8-connected network with Schläfli symbol {46}2{49·618·8}, consisting of Cu6 clusters and L1 ligands. In contrast, complex 2 possesses a different 3D network with trinodal 3,4,6-c topology with Schläfli symbol {4·62}2{42·66·85·102}{64·8·10}. In these two complexes, the semirigid hexacarboxylate ligands adopt distinct conformations to connect metal ions/clusters, which must be ascribed to the addition of the auxiliary rigid ligand in reaction systems. In addition, gas absorption properties of 1 and 2 including CO2 and N2 were further investigated.
ABSTRACT
BACKGROUND: This study explored the effects of physical activity and sedentary behaviour on the decline of cognitive ability among the elderly. To compensate for the limitations of self-reported physical activity, objective measures were used. METHODS: A cross-sectional survey of 308 aged people mean 68.66 ± 5.377 years, in Nanjing, China, was conducted. Physical activity was measured using the ActiGraph GT3X+, and cognitive function was measured using the Montreal Cognitive Assessment. RESULTS: The overall participant model, adjusted for age, BMI, education, and monthly average income, found that light physical activity (ß = 0.006, p < 0.01), moderate-vigorous physical activity (ß = 0.068, p < 0.001), and total physical activity (ß = 0.006, p < 0.01) had a significant linear relationship with cognitive ability, while sedentary time did not (ß = - 0.020, p>0.05). Further, light physical activity only affects the cognitive ability of elderly females (ß = 0.006, p < 0.05). There was an inverted 'U' association between moderate-vigorous physical activity and cognitive ability. The association models found that moderate-vigorous physical activity in the 22.13 min·day- 1~38.79 min·day- 1 range affected cognitive ability most beneficially, with the highest beta coefficient among all groups (ß = 0.091, p < 0.05). CONCLUSIONS: While physical activity can significantly improve cognitive ability among the elderly, sedentary behaviour is associated with decreased cognitive function across genders.
