RESUMEN
Nafion membranes are widely used as proton exchange membranes, but their proton conductivity deteriorates in high-temperature environments due to the loss of water molecules. To address this challenge, we propose the utilization of porous aromatic frameworks (PAFs) as a potential solution. PAFs exhibit remarkable characteristics, such as a high specific surface area and porosity, and their porous channels can be post-synthesized. Here, a novel approach was employed to synthesize a PAF material, designated as PAF-45D, which exhibits a specific surface area of 1571.9 m2·g-1 and possesses the added benefits of facile synthesis and a low cost. Subsequently, sulfonation treatment was applied to PAF-45D in order to introduce sulfonic acid groups into its pores, resulting in the formation of PAF-45DS. The successful incorporation of sulfonic groups was confirmed through TG, IR, and EDS analyses. Furthermore, a novel Nafion composite membrane was prepared by incorporating PAF-45DS. The Nyquist plot of the composite membranes demonstrates that the sulfonated PAF-45DS material can enhance the proton conductivity of Nafion membranes at high temperatures. Specifically, under identical film formation conditions, doping with a 4% mass fraction of PAF-45DS, the conductivity of the Nafion composite membrane increased remarkably from 2.25 × 10-3 S·cm-1 to 5.67 × 10-3 S·cm-1, nearly 2.5 times higher. Such promising and cost-effective materials could be envisioned for application in the field of Nafion composite membranes.
RESUMEN
Yttrium borides have attracted much attention for their superconducting and high chemical stability. However, the fundamental knowledge of the mechanical properties and hardness of yttrium borides is rather lack. Here, we performed a systematic investigation on yttrium borides with various stoichiometries based on an unbiased CALYPSO structure search method and first-principles calculations. A new YB6 compound with R3m hexagonal structure is observed, which is more stable than the experimental synthesized Pm3Ì m phase. The calculated formation enthalpy, elastic constants, and phonon dispersions distinctly show that the R3m-YB6 is energetically, mechanically, and dynamically stable. The density of states and electronic band structure reveal that all the stable yttrium borides are metallic. Based on a semiempirical method, the Vicker hardness of R3m-YB6 is expectant to be 37.0 GPa, indicating it is a potential ultrahard metal. Our results provide insights for future synthesis and design of new type functional materials.
RESUMEN
The provirus DNA sequence of porcine endogenous retrovirus (PERV) distributed in the pig genome is the major obstacle that restricts the swine as the organ donors in xenotransplantation, and the copy number of PERV varies greatly among different breeds and individuals. In the experiment, 67 healthy, female Chinese Experimental Mini-Pigs (CEMPs) aged at 3-6 months were selected from the Animal Husbandry Station of China Agricultural University, the copy number of PERV and types of envelope protein gene (env) were then investigated by means of PCR analysis and Southern blotting. It is showed that the distribution of types of envelope protein gene in Landrace and CEMPs makes little difference, but the proportion of individuals carrying two types of envelope protein gene (env-A and env-B, which is denoted as env-AB) is much larger than those which carry only one type of envelope protein gene (env-A or env-B). Meanwhile, two endogenous retrovirus free pigs were found for the first time during our research, and the copy number of others is relatively low, which is about 10 to 20. All the results illuminate the genetic diversity of indigenous pig breeds in China and the potential of CEMPs to serve as organ donors in xenotransplantation.