MXenes with applications in supercapacitors and secondary batteries:A comprehensive review

Two-dimensional(2D)materials have received tremendous attention because they possess a set of merits not available in bulk materials,such as large specific surface area,low energy barrier for electron transportation and short ion diffusion path.These advantages are desirable especially for the electrodes in electrochemical energy storage devices.MXenes,first synthesized in 2011 by etching their MAX phase precursors,have plural reasons to represent a new family of 2D materials.Their rich diversity in structure and composition together with the uncommon combination of good electrical conductivity and hydrophilicity makes themselves outstand in the whole 2D materials world.Based on these advantages,MXenes hold great promise for various technologically important applications,particularly in developing new energy storage techniques for advanced smart systems,such as portable and flexible electronics.There have been remarkable research achievements in the synthesis and application of MXene-based materials.While new synthesis routes being continuously reported,MXenes with new composition and novel structure have also been routinely discovered,which will undoubtedly help understand the fundamental properties and expand the application scope of MXenes.As for their energy storage-related applications,to cope with the intrinsic weakness of MXenes,many endeavors have been made by doping,structure-tuning and compositing with hybrid ingredients.In this review,the current status of MXenes synthesis and up-to-date progress of their applications in supercapacitors,metal-ion batteries and lithium sulfur batteries are summarized and discussed,and the typical work on the application of MXenes for the aforementioned three categories is respectively tabulated for reference and comparison.

Regression Analysis of Nutrient Elements between Soil and Tobacco Leaves and Their Influences on Aroma Quality of Flue-cured Tobacco

This study aimed to analyze the relationship between nutrient elements K, Ca, Mg, Cu, Mn, Zn and Fe in tobacco-planting soils and tobacco leaves from six main tobacco-producing areas, and to investigate the influences of these elements on chemical composition and aroma components in tobacco leaves. Results showed that there were certain relationship between contents of nutrient elements in tobacco-planting soils and contents of corresponding elements in tobacco leaves; various elements exhibited different influences on the aroma quality of flue-cured tobacco. Based on the actual situation of nutrient contents in soils from different tobaccoproducing areas, contents of various elements in tobacco leaves should be regulated by soil fertilization and foliar spraying, thereby improving the aroma quality of flue-cured tobacco.

Extracellular magnetic labeling of biomimetic hydrogel-induced human mesenchymal stem cell spheroids with ferumoxytol for MRI tracking

Labeling of mesenchymal stem cells(MSCs)with superparamagnetic iron oxide nanoparticles(SPIONs)has emerged as a potential method for magnetic resonance imaging(MRI)tracking of transplanted cells in tissue repair studies and clinical trials.Labeling of MSCs using clinically approved SPIONs(ferumoxytol)requires the use of transfection reagents or magnetic field,which largely limits their clinical application.To overcome this obstacle,we established a novel and highly effective method for magnetic labeling of MSC spheroids using ferumoxytol.Unlike conventional methods,ferumoxytol labeling was done in the formation of a mechanically tunable biomimetic hydrogel-induced MSC spheroids.Moreover,the labeled MSC spheroids exhibited strong MRI T2 signals and good biosafety.Strikingly,the encapsulated ferumoxytol was localized in the extracellular matrix(ECM)of the spheroids instead of the cytoplasm,minimizing the cytotoxicity of ferumoxytol and maintaining the viability and stemness properties of biomimetic hydrogel-induced MSC spheroids.This demonstrates the potential of this method for post-transplantation MRI tracking in the clinic.

MORPHOLOGY OF BLACK CARBON AEROSOLS AND UBIQUITY OF 50-NANOMETER BLACK CARBON AEROSOLS IN THE ATMOSPHERE

Different-sized aerosols were collected by an Andersen air sampler to observe the detailed morphology of the black carbon （BC） aerosols which were separated chemically from the other accompanying aerosols, using a Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer （SEM-EDX）. The results indicate that most BC aerosols are spherical particles of about 50 nm in diameter and with a homogeneous surface. Results also show that these particles aggregate with other aerosols or with themselves to form larger agglomerates in the micrometer range. The shape of these 50-nm BC spherical particles was found to be very similar to that of BC particles released from petroleum-powered vehicular internal combustion engines. These spherical BC particles were shown to be different from the previously reported fullerenes found using Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry （MALDI-TOF-MS）.

Difference between low-volume and high-volume Andersen samplers in measuring atmospheric aerosols

The mass concentration and size distribution of aerosols in Tokaimura were investigated using a high-volume and a low-volume Andersen sampler. A difference was found using the two samplers： the concentration of total aerosols determined with the high-volume sampler is smaller than that of the low-volume sampler by 70-90% throughout the year. Compared to the high-volume sampler, low-volume sampler gave lower concentration for aerosols 〉7 μm, higher concentration for aerosols of 3.3-7.0 μm and 〈 1.1 μm, though similar results for aerosols of 1.1-3.3 μm. The low-volume sampler was found to have better separation efficiency and higher accuracy.