Heterojunction of MXenes and MN4-graphene: Machine learning to accelerate the design of bifunctional oxygen electrocatalysts.

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the development of excellent bifunctional electrocatalysts, which are key functions in clean energy production. The emphasis of this study lies in the rapid design and investigation of 153 MN4-graphene (Gra)/ MXene (M2NO) electrocatalysts for ORR/OER catalytic activity using machine learning (ML) and density functional theory (DFT). The DFT results indicated that CoN4-Gra/Ti2NO had both good ORR (0.37 V) and OER (0.30 V) overpotentials, while TiN4-Gra/M2NO and MN4-Gra/Cr2NO had high overpotentials. Our research further indicated orbital spin polarization and d-band centers far from the Fermi energy level, affecting the adsorption energy of oxygen-containing intermediates and thus reducing the catalytic activity. The ML results showed that the gradient boosting regression (GBR) model successfully predicted the overpotentials of the monofunctional catalysts RhN4-Gra/Ti2NO (ORR, 0.39 V) and RuN4-Gra/W2NO (OER, 0.45 V) as well as the overpotentials of the bifunctional catalyst RuN4-Gra/W2NO (ORR, 0.39 V; OER, 0.45 V). The symbolic regression (SR) algorithm was used to construct the overpotential descriptors without environmental variable features to accelerate the catalyst screening and shorten the trial-and-error costs from the source, providing a reliable theoretical basis for the experimental synthesis of MXene heterostructures.

Effects of different strains fermentation on nutritional functional components and flavor compounds of sweet potato slurry.

In this paper, we study the effect of microbial fermentation on the nutrient composition and flavor of sweet potato slurry, different strains of Aspergillus niger, Saccharomyces cerevisiae, Lactobacillus plantarum, Bacillus coagulans, Bacillus subtilis, Lactobacillus acidophilus, and Bifidobacterium brevis were employed to ferment sweet potato slurry. After 48 h of fermentation with different strains (10% inoculation amount), we compared the effects of several strains on the nutritional and functional constituents (protein, soluble dietary fiber, organic acid, soluble sugar, total polyphenol, free amino acid, and sensory characteristics). The results demonstrated that the total sugar level of sweet potato slurry fell significantly after fermentation by various strains, indicating that these strains can utilize the nutritious components of sweet potato slurry for fermentation. The slurry's total protein and phenol concentrations increased significantly, and many strains demonstrated excellent fermentation performance. The pH of the slurry dropped from 6.78 to 3.28 to 5.95 after fermentation. The fermentation broth contained 17 free amino acids, and the change in free amino acid content is closely correlated with the flavor of the sweet potato fermentation slurry. The gas chromatography-mass spectrometry results reveal that microbial fermentation can effectively increase the kinds and concentration of flavor components in sweet potato slurry, enhancing its flavor and flavor profile. The results demonstrated that Aspergillus niger fermentation of sweet potato slurry might greatly enhance protein and total phenolic content, which is crucial in enhancing nutrition. However, Bacillus coagulans fermentation can enhance the concentration of free amino acids in sweet potato slurry by 64.83%, with a significant rise in fresh and sweet amino acids. After fermentation by Bacillus coagulans, the concentration of lactic acid and volatile flavor substances also achieved its highest level, which can considerably enhance its flavor. The above results showed that Aspergillus niger and Bacillus coagulans could be the ideal strains for sweet potato slurry fermentation.

A study on hydrogen storage performance of Ti decorated vacancies graphene structure on the first principle.

The structural properties, formation energy, adsorption energy, and electronic properties of vacancy graphene are studied by first-principles analysis. We found that the formation energy and adsorption energy of double vacancy graphene (DVG-4) are the largest. A single defect in DVG-4 can adsorb at least nine hydrogen molecules, and compared with Ti modified single vacancy graphene (SVG-Ti), the adsorption capacity is increased by 80%. When DVG-4 adsorbs the second, third, and fourth hydrogen molecules, the adsorption energy is greater than 0.7 eV, which is not conducive to the release. Density of state (DOS) and electron density difference (EDIFF) results reveal that charge transfer occurs among hydrogen molecules, Ti atoms, and DVG-4, decreasing the hydrogen adsorption capacity of DVG-4 by 33%. DVG - 4 has the potential to become an excellent hydrogen storage material.

Mechanism for hydrogen evolution from water splitting based on a MoS2/WSe2 heterojunction photocatalyst: a first-principle study.

In this study, density functional theory and hybrid functional theory are used to calculate the work function and energy band structure of MoS2 and WSe2, as well as the binding energy, work function, energy band structure, density of states, charge density difference, energy band alignment, Bader charge, and H adsorption free energy of MoS2/WSe2. The difference in work function led to the formation of a built-in electric field from WSe2 to MoS2, and the energy band alignment indicated that the redox reactions were located on the MoS2 and WSe2 semiconductors, respectively. The binding energy of MoS2 and WSe2 indicated that the thermodynamic properties of the heterogeneous structure were stable. MoS2 and WSe2 gathered electrons and holes, respectively, and redistributed them under the action of the built-in electric field. The photogenerated electrons and holes were enriched on the surface of WSe2 and MoS2, which greatly improved the efficiency of hydrogen production by photocatalytic water splitting.

Study on bubble detectors used as personal neutron dosimeters.

Neutron bubble detector is so far the only personal neutron dosimeter satisfying the energy response criteria of the International Committee of Radiation Protection 60 (ICRP 60). This paper presents our studies on neutron bubble detectors including the manufacture, the relevant equipments, the basic calibrations and on-site tests for monitoring personal neutron dose. The results of calibrations show that the highest sensitivity so far manufactured by the authors reaches about 4bubbles/µSv, the correlation coefficient of dose response is 0.99, and the in-batch consistency and reproducibility are up to the ISO standards. The results of on-site test show that the in-batch consistency and between-batch consistency are within 15% relative standard uncertainty. The results are directly readable. The detectors are portable, especially suitable for on-site neutron dose monitoring in n-γ mixed radiation fields.

Study on anti-reflection of CR-39 by the nuclear track technique.

Nuclear tracks can be etched into pores in which the refractive indexes gradually increase, so that the sample surface reflects very few lights back. CR-39 samples were bombarded with sulfur ions from the Tandem Accelerator HI-13 of CIAE. Three kinds of procedures were performed in the following treatments. The reflectivity was measured for all samples, untreated and treated, within the wavelengths of visible light. The results indicated that the reflectivity of the CR-39 samples modified with the track technique and multilayer coating can be as low as 0.1%.

Radiochemical neutron-activation analysis of uncertified ultra-trace rare earth elements in two biological certified reference materials.

Radiochemical neutron activation analysis (RNAA) has been used for the determination of eight rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu) in two Chinese certified reference materials (CRM), GBW 08503 (wheat powder) and GBW 09101 (human hair). These determinations are important for possible certification of the above mentioned ultra-trace elements, so far not certified. A simple one-step (REE)F3 precipitation was used. Chemical yields were determined for all relevant elements by means of tracer experiments. The two CRM were also analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) to compare the merits and draw-backs of these two major trace analytical techniques for these particular elements. RNAA was proven to be a reliable technique for ultra-trace analysis, especially in the certification of some ultra-trace elements.