[en] Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo₂N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo₂N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo₂N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (|Δ G_H*|), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo₂N to form stable structures of Co doped Mo₂N (Co-Mo₂N) and Cu doped Mo₂N (Cu-Mo₂N). Compared with pristine Mo₂N, both Cu-Mo₂N and Co-Mo₂N demonstrated a much improved cocatalytic effect over g-C₃N₄ in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co-Mo₂N with the highest conductivity and lowest |Δ G_H*| illustrated the best cocatalytic effect, and the H-2 production performance (367.8 μ mol g^-1 h^-1) of Co-Mo₂N/g-C₃N₄ achieved was 10 and 5 times higher than those of Mo₂N/g-C₃N₄ and Cu-Mo₂N/g-C₃N₄. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application. (authors)

[en] A kind of dielectric barrier discharge (DBD) device composed of water electrodes with 3 × 3 forms can produce large-area low-temperature plasmas at atmospheric pressure. To reflect the discharge characteristics of DBD better, a dynamic simulation model, which is based on the voltage controlled current source (CCS), is established, then the established model in Matlab/Simulink is used to simulate the DBD in air. The voltage–current waves and Lissajous at a voltage of 10 kV, 11 kV and 12 kV peak value with a frequency of 15 kHz are studied. The change of the discharge power of DBD with a different amplitude and frequency of applied voltage is also analyzed. The result shows the voltage–current waves, Lissajous and discharge power of DBD under different conditions from the simulation agree well with those of the experiment. In addition, we propose a method to calculate the dielectric barrier capacitance $C_{\mathrm{d}}$ and the gap capacitance $C_{\mathrm{g}},$ which is valid through analyzing the variation of capacitance at different voltage amplitudes. (paper)

[en] Magnetic graphene oxide /chitosan (MCGO) nanocomposite was prepared by ultrasonic method using graphene oxide and chitosan as raw materials and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxy succinimide (NHS) as activators, and the adsorption performance of UO₂²⁺ on MCGO was investigated. The results of SEM, FT-IR and XRD show that MCGO is successfully achieved, and the size of Fe₃O₄ is nanoscale. It is found that the MCGO has equilibrium adsorption capacity of 266.67 mg/g at pH = 5.5, initial UO₂²⁺ concentration of 160 mg/L, adsorption time of 1.5 h and adsorption temperature of 288 K. The experimental equilibrium data were fitted with thermodynamics and kinetics models. The results show that MCGO conforms to Langmuir isotherm model and pseudo-second order kinetic model as well as the adsorption of endothermic spontaneous process. The first re-utilization rate of MCGO is up to 98.47%, and reaches 74.43% after repeatedly adsorbing and desorbing for 6 cycles, which shows that MCGO has a good reusability. (authors)

[en] Highlights: • A look-up table was built for wall temperatures of supercritical pressure water. • The best heat transfer correlation was selected to supplement wall temperatures. • Four-dimensional linear interpolation was adopted to calculate wall temperatures. • 81.33% of the predicted wall temperatures fall into the ±1% error band. Wall temperature of heat transfer tubes is one of the most important parameters indicating the operation safety of various heat transfer facilities, and as a result, estimation of the wall temperature becomes one of the main tasks in the design of heat transfer facilities. The wall temperature look-up table (Tw-LUT) can be established directly from experimental data and can be then used to estimate the wall temperature of the heat transfer tubes, avoiding the approximation or extrapolation of fluid properties that inevitably exists in the heat transfer correlations. In view of the problems existing in applications with wall temperature estimations of the heat transfer tube, such as limited data points and the limited application scopes of parameters, a look-up table is built in this paper for wall temperatures of vertically-upward round tubes of 10 mm tube diameter with heat transfer to supercritical water (SCW), under conditions with pressure in the range from 22.5 to 31 MPa, the mass velocity in the range from 200 to 3000 kg·m⁻²·s⁻¹, the heat flux in the range from 200 to 1800 kW·m⁻², and the bulk fluid enthalpy in the range from 1000 to 3000 kJ·kg⁻¹. In order to cover the gaps between the experimental data points, and to improve the prediction accuracy of the Tw-LUT, the best heat transfer correlation is selected for each local area of interest in the LUT based on its prediction accuracy in the corresponding local area, and then the best heat transfer correlation is adopted to supplement wall temperature results to fill up the Tw-LUT. The comparison between the wall temperatures by the Tw-LUT and the experimental wall temperatures is carried out to verify the accuracy of the Tw-LUT, and it is shown that the mean absolute deviation of the results is 0.87%, and 87.81% of the results fall into the $\pm$3% error band, indicating that the Tw-LUT has a good accuracy for wall temperature prediction and the establishment method is reliable and can be used to build other look-up tables. The Tw-LUT can be applied not only to normal heat transfer conditions but also to deteriorated heat transfer conditions and enhanced heat transfer conditions with a satisfactory accuracy.

[en] Single-walled carbon nanotubes (SWCNTs), due to their outstanding electrical and optical properties, are expected to have extensive applications, such as in transparent conductive films and ultra-small field-effect transistors (FETs). However, those applications can only be best realized with pure metallic or pure semiconducting SWCNTs. Hence, identifying and separating metallic from semiconducting SWCNTs in as-grown samples are crucial. In addition, knowledge of the type of an SWCNT is also important for further exploring its new properties in fundamental science. Here we report employing scanning near-field optical microscopy (SNOM) as a direct and simple method to identify metallic and semiconducting SWCNTs on SiO ₂ /Si substrates. Metallic and semiconducting SWCNTs show distinct near-field optical responses because the metallic tubes support plasmons whereas the semiconducting tubes do not. The reliability of this method is verified using FET testing and Rayleigh scattering spectroscopy. Our result demonstrates that the SNOM technique provides a reliable, simple, noninvasive and in situ method to distinguish between metallic and semiconducting SWCNTs. (paper)

[en] Highlights: • The Allam cycle with liquefied natural gas cold energy utilization is analyzed. • Exergoeconomic analysis and multi-objective optimization are conducted. • The electrical efficiency of the optimized system is up to 65.7%. • The optimal total product unit cost of 16.654 $/GJ is obtained. • The introduction of bypass stream compression heat improves the system performance. The Allam cycle is a promising oxy-fuel combustion power cycle with high electrical efficiency and near-zero carbon dioxide emissions. In this paper, the thermodynamic and exergoeconomic analyses are performed for a novel combined power and cooling oxy-fuel power cycle, which combines the Allam cycle with liquefied natural gas regasification process. Parametric study is conducted to investigate the effects of key cycle variables on the electrical and exergy efficiencies and total product unit cost of the proposed cycle. Multi-objective optimization is carried out to maximize the exergy efficiency and minimize the total product unit cost. The results show that Condenser 2 has the highest exergy destruction of 22.81 MW, followed by the combustor (22.72 MW). The combustor, Condenser 2 and gas turbine are the three most important components from exergoeconomic aspects. The introduction of adiabatic compression heat of the bypass stream has a positive impact on the system performance, especially when the outlet temperature of the combustor is low. The optimization results indicate that the exergy efficiency and the total product unit cost cannot reach the optimal values at the same time. The highest exergy efficiency of 50.31% and the lowest total product unit cost of 16.654 $/GJ are obtained respectively with different sets of cycle variables. In addition, the electrical efficiency of the optimized proposed cycle is up to around 65.7%, about 11 percentage points higher than that of the Allam cycle.

[en] Transferring high-quality exfoliated graphene flakes onto different substrates while keeping the graphene free of polymer residues is of great importance, but at the same time very challenging. Currently, the only feasible way is the so-called all-dry “pick-and-lift” method, in which a hexagonal boron nitride (hBN) flake is employed to serve as a stamp to pick up graphene from one substrate and to lift it down onto another substrate. The transferred graphene samples, however, are always covered or encapsulated by hBN flakes, which leads to difficulties in further characterizations. Here, we report an improved “pick-and-lift” method, which allows ultra-clean graphene flakes to be transferred onto a variety of substrates without hBN coverage. Basically, by exploiting the superlubricity at the graphene/hBN stack interface, we are able to remove the top-layer hBN stamp by applying a tangential force and expose the underneath graphene. (paper)

[en] Highlights: • A competitive colorimetric aptasensor was developed for saxitoxin detection. • HCR products was used to facilitate the colorimetric transduction by AuNPs nanozyme. • Magnetic separation contributed to reduce the background signals. • The aptasensor provided high sensitivity towards saxitoxin determination. • The innovation can be referred for other small molecules and toxins. Saxitoxin (STX) is a small molecule toxin (Mw. ca. 299 g/mol) with high acute toxicity, and it has urgent need of facile analytical methods. Herein, a competitive colorimetric aptasensor was developed for highly sensitive detection of STX. An anti-STX aptamer was hybridized with a complementary strand on the magnetic beads and was competitively bound by STX. The supernatant containing the aptamer binding to STX was obtained by magnetic separation, which could trigger hybridization chain reaction (HCR) to generate rigid double stranded DNAs (dsDNAs) with sticky end and variable length. These HCR-dsDNAs were found to be able to facilitate significant enhancement on the peroxidase-like catalytic capability of AuNPs nanozyme towards 3,3,5,5-tetramethylbenzidine (TMB). The concentration of STX was responded in a “turn on” mode, based on the amplified colorimetric transduction thereof. The aptasensor realized high sensitivity, with a limit of detection (LOD) as low as 42.46 pM. Moreover, a wide linear detection range of 78.13–2500 pM, good selectivity, as well as good recovery rates of 106.2–113.5% when analyzing STX in real shellfish samples were obtained. This strategy could be referred to develop robust aptasensors for simple and highly sensitive detection of other small molecules and toxins.

[en] The phase transition of nuclei with increasing angular momentum (or spin) and excitation energy is one of the most fundamental topics of nuclear structure research. The odd-N nuclei with A ≈ 160 are widely considered belonging to the well-deformed region, and their excitation spectra are energetically favored to exhibit the rotational characteristics. In this work, however, the evidence suggesting that the nuclei changes from rotation to vibration along the yrast lines as a function of spin was found. The simple method, named as E-Gamma Over Spin (E-GOS) curves, would be used to discern the evolution from rotational to vibrational structure in nuclei for various spin ranges. Meanwhile, in order to understand the band structure properties of nuclei, theoretical calculations have been performed for the yrast bands of the odd-A rare-earth nuclei within the framework of the total routhian surface (TRS) model. The TRS plots predict that the ¹⁶⁵Yb and ¹⁵⁷Dy isotopes have large quadrupole shapes at low spin states. At higher rotational frequency (ħω > 0.50 MeV), a clear reduction of the quadrupole deformation is indicated by the present results, and the isotopes become rigid in the γ deformation. (authors)

[en] A functionalized nanocrystal cellulose bearing amino and sulfonic acid groups (Am-sNCC) is prepared through a two-step chemical modification of microcrystal cellulose powders, first by sulfonic acid and then by a 3-trimethoxysilyl propyl ethylenediamine. The structure of Am-sNCC is characterized by Fourier Transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). A sulfonated poly(ether ether ketone ketone) (Ph-SPEEKK) is synthesized via the direct sulfonation of a high-molecular-weight phenylated polymeric precursor under a mild reaction condition. The nanocomposite membranes composed of the Ph-SPEEKK matrix and the Am-NCC additive are successfully prepared by a solution casting method. The properties related to their application for proton exchange membranes are carefully evaluated. The nanocomposite membranes containing Am-sNCC, which served as a performance-enhancing component to form hydrogen bonding networks with the Ph-SPEEKK matrix, exhibited much improved dimensional stability, higher water absorption capacities, higher proton conductivity, better mechanical and fuel cell properties than the Ph-SPEEKK membrane.