ABSTRACT
Searching for efficient and cost-effective electrocatalysts for hydrogen evolution reaction (HER) is significantly desirable and challenging. Herein, N, P co-doped carbon-encapsulated CoP/MoP hybrid (CoP/MoP@NPC) is fabricated using dual-metal-organic-framework (dual-MOF) as precursor by a simple one-step phosphating process. When applied as an electrocatalyst toward the HER, the as-designed CoP/MoP@NPC hybrid shows efficiently catalytic performance with a lower overpotential of 183 mV to deliver a current density of 10 mA cm-2, smaller Tafel slope of 53.3 mV dec-1 as well as long-time stability for 10 h in 0.5 M H2SO4 owing to the distinctive component and structural advantages. Furthermore, the electrode material also displays enhanced electrocatalytic HER activity in alkaline media. Importantly, this work provides an effective and feasible route for the construction of bimetallic phosphide electrocatalysts toward hydrogen production.
ABSTRACT
Exposed surface defect-enriched Co3O4 catalysts derived from metal organic framework (MOF) were fabricated by the promotion of surface Mn species for toluene oxidation. The incorporation of Mn species into Co3O4 surface lattice could give rise to the local lattice distortion in spinel structure, resulting in highly exposed surface defect rather than bulk defect. More Co3+ species were also exposed on the surface of MnOx/Co3O4 samples owing to the electron transfer from Co to Mn species by the occupation of surface Mn in octahedral Co3+ sites. Accordingly, the low-temperature reducibility and high mobility of lattice oxygen were significantly improved in virtue of the highly exposed surface defect and predominately surface Co3+ sites, thus promoting the catalytic activity and stability for toluene oxidation. Moreover, the toluene conversion decreased with the increase of weight hourly space velocity (WHSV). In situ DRIFTS results confirmed the continuous oxidation process for toluene degradation, and the conversion of benzoate into maleic anhydride should be the rate-controlling step.
ABSTRACT
OBJECTIVES: Firstly, according to the characteristics of COVID-19 epidemic and the control measures of the government of Shaanxi Province, a general population epidemic model is established. Then, the control reproduction number of general population epidemic model is obtained. Based on the epidemic model of general population, the epidemic model of general population and college population is further established, and the control reproduction number is also obtained. METHODS: For the established epidemic model, firstly, the expression of the control reproduction number is obtained by using the next generation matrix. Secondly, the real-time reported data of COVID-19 in Shaanxi Province is used to fit the epidemic model, and the parameters in the model are estimated by least square method and MCMC. Thirdly, the Latin hypercube sampling method and partial rank correlation coefficient (PRCC) are adopted to analyze the sensitivity of the model. CONCLUSIONS: The control reproduction number remained at 3 from January 23 to January 31, then gradually decreased from 3 to slightly greater than 0.2 by using the real-time reports on the number of COVID-19 infected cases from Health Committee of Shaanxi Province in China. In order to further control the spread of the epidemic, the following measures can be taken: (i) reducing infection by wearing masks, paying attention to personal hygiene and limiting travel; (ii) improving isolation of suspected patients and treatment of symptomatic individuals. In particular, the epidemic model of the college population and the general population is established, and the control reproduction number is given, which will provide theoretical basis for the prevention and control of the epidemic in the colleges.
ABSTRACT
In situ/operando studies of a heterogeneous catalyst are particularly valuable for achieving a fundamental understanding of catalytic mechanisms at a molecular level by establishing a correlation between the observed catalytic performance and the corresponding surface chemistry during catalysis. Herein, CO oxidation on cobalt oxides was studied via ambient pressure X-ray photoelectron spectroscopy (AP-XPS). During CO oxidation on CoO in the temperature range of 140-180 °C, the active surface phase of CoO progressively transforms to Co3O4. Kinetic studies of CO oxidation on the surface phase CoO at 80-120 °C and on the formed Co3O4 at 160-220 °C show that CoO and Co3O4 exhibit different activation barriers: 49.3 kJ mol-1 for CoO and 36.9 kJ mol-1 for Co3O4. This study demonstrates the transition of the active surface phase of a transition metal oxide-based catalyst under catalytic conditions with no change in the bulk phase of the catalyst.
ABSTRACT
The objective of the present study was to systematically determine the effects of 50 Hertz (Hz) magnetic fields (MFs) on biochemical parameters in rats. Sixty-four adult (5 weeks old, 140-165 g) male Sprague-Dawley rats were randomly divided into four groups: sham, 20 µTesla (µT), 100 µT, and 500 µT 50 Hz MF ( n = 16 in each group). The rats in the MF groups were exposed for 2 h daily for up to 4 weeks. Under these experimental conditions, body weight, organ coefficients, biochemical parameters (blood lipids, myocardial enzymes, liver function, and renal function) were measured. We found that 50 Hz MFs had no significant effects on growth or on the majority of blood biochemical parameters, with the exception of creatinine and cholesterol. However, the changes in creatinine and cholesterol were relatively small and unlikely to be clinically relevant.
