Enhanced photocatalytic H2 evolution and phenol degradation over sulfur doped meso/macroporous g-C3N4 spheres with continuous channels

S-doped meso/macroporous g-C₃N₄ spheres (SMCN) were successfully synthesized via an in situ novel method utilizing millimeter-scale porous silica spheres as template and thiourea as precursor and S source. Such SMCN possessed millimeter-scale spherical morphology with continuous channels at 20–80 nm in the interior of the spheres, and exhibited increased H₂ generation rate (15 times) and phenol degradation rate (5 times) under visible light irradiation compared with that over pristine g-C₃N₄, mainly due to the enlarged surface area, enhanced mass transfer and improved efficiency of charges separation all stemming from the synergetic effects of the S doping and pore creating. Notably, density functional theory (DFT) calculations were employed to further understand the mechanism of the photocatalytic enhancement with regard to the optical absorption property at atomic level. Combined with the finite difference time domain (FDTD) simulations aiming at evaluating the effect of the nanoscale pore architecture on the optical absorption ability, it was revealed that not only the S doping but also the meso/macroporous structure resulted in the enhancement of the optical absorption, which was considered to be an essential role for the enhanced photocatalytic performances over SMCN.     

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo₂O₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo₂O₄/Ni@NF) shows the superior specific capacity of 1142 C g⁻¹ at 1 A g⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g⁻¹. These values are about 3.7 times higher than that of the electrode (NiCo₂O₄@NF) without a seed layer, which shows the specific capacity of 305 C g⁻¹@1 A g⁻¹ with cycle stability of 84% even at a lower current density of 1 A g⁻¹. The enhanced performance of the NiCo₂O₄/Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo₂O₄/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe₂O₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo₂O₄/Ni20@NF//rGO-Fe₂O₃@NF asymmetric solid state device delivers an areal capacitance of 446 mF cm⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm⁻² (at 3.58 kW cm⁻²) and power density of 14.88 kW cm⁻² (at 31.41 Wh cm⁻²).     

Transition metal atom doped C2N as catalyst for the oxygen reduction reaction: A density functional theory study

The catalytic mechanism and activity of transition metal atom doped C₂N (M-C₂N, M = Fe, Co, Ni, and Cu) for the oxygen reduction reaction (ORR) are investigated in detail by density functional theory method. All the screened M-C₂N are thermodynamically stable based on the binding energy calculations. The adsorption energy results indicate that the adsorption strength of O₂ and ORR intermediates are decreased in the order of Fe-C₂N ˃ Co-C₂N ˃ Ni-C₂N ˃ Cu-C₂N, in which the adsorption energy values on Cu-C₂N are most close to those on the Pt(111). Based on the relative energy diagram of ORR, the energetically favorable pathway on Fe-C₂N and Co-C₂N is direct 4e⁻ mechanism, in which the O–O bond is directly dissociated after the second electron transfer. While for Ni-C₂N and Cu-C₂N, the most favorable pathway is indirect 4e⁻ mechanism, in which the H₂O₂ is formed as the intermediate product. For all studied M-C₂N, the Ni-C₂N and Cu-C₂N hold better catalytic activity, which could attribute to the contribution of metal atom and part of its activated nitrogen atoms.     

Calculation of phase diagrams for the metastable Al-Fe phases forming in direct-chill (DC)-cast aluminum alloy ingots

In direct-chill (DC)-cast 1xxx-and 5xxx-series Al sheet-ingots, the presence of mainly Fe and some Si, and cooling rates increasing from ≤1 °C/s in the ingot center to ~20 °C/s near the surface cause the formation of metastable intermetallic Al₆Fe and Al_mFe compounds in addition to the stable Al₃Fe, and hence the fir-tree defect. Since the Al-Fe and Al-Fe-Si phase diagrams are not useful in predicting the metastable phase formation, a binary phase diagram study was conducted to calculate the Al-Al₆Fe and Al-Al_mFe metastable phase equilibria using a thermodynamic software and an Al-alloy database. The Al-Al₃Fe phase diagram was calculated using the existing Gibbs energy data which gives the eutectic point at 1.85wt% Fe and the eutectic temperature as 654 °C. The missing Gibbs energy data for the metastable phases were estimated using substitutional and graphical methods and the phase diagrams were calculated. In the Al-Al₆Fe phase diagram, the eutectic temperature is depressed from 654 °C (equilibrium) to 648 °C and the eutectic point is shifted from 1.85wt% Fe to 3.4wt% Fe. In the Al-Al_mFe phase diagram, the eutectic temperature is 643 °C and the eutectic point is at 4.6wt% Fe. The verification of the calculated eutectic temperatures was carried out by DSC measurements which were conducted on samples removed from Al-Fe alloy rods directionally grown in a Bridgman-type solidification furnace. A good agreement is observed between the calculated and measured values.     

Development of a monitor to simultaneously measure dissolved ozone and organic matter in ozonated water

A method for measuring both dissolved ozone (DO₃) concentration and UV absorbance was developed adopting ultraviolet (UV) absorption method (Japan Water Works Association (JWWA), 1993a, Japan Water Works Association (JWWA), 1993b) using sodium thiosulfate (Na₂S₂O₃) solution for removing residual ozone in ozonated water. A DO₃ monitor based on this method was tested. This method was proven to be effective from experimental results. The performance of the monitor was examined with continuous ozonated water. As a result, the monitor performed stably during about 2 months, so that both DO₃ concentration and UV absorbance in the ozonated water could be accurately measured. Therefore, the authors have proposed the new aquatic control system with this monitor for ozonation.     

Improving the electrochemical properties of carbon anodes in lithium secondary batteries

The electrochemical properties of carbon anodes in lithium secondary batteries are improved by the addition of vanadium as V₂O₅. The action of the added V₂O₅ is different from that obtained by incorporating a nonmetallic element such as nitrogen, boron, phosphorous or silicon. Because it can increase the distance between the 002 planes of the carbon and act as nucleating agent that promotes the formation of a layer-like carbon structure, V₂O₅, not only enlarges the carbon anode's reversible capacity of lithium storage but also improves the cycling behavior.     

A one-pot sealed ammonia self-etching strategy to synthesis of N-defective g-C3N4 for enhanced visible-light photocatalytic hydrogen

Photocatalytic hydrogen (H₂) evolution from water is considered as a prospective approach, which can convert inexhaustible solar energy into chemical energy to alleviate energy crisis and environmental problems. Herein, the N-defective g-C₃N₄ with porous structure was firstly synthesized in a sealed crucible by one-step thermal polymerization method. The experimental data showed that the yield of the catalyst was obviously increased under sealing condition. Moreover, the N-defective g-C₃N₄ prepared from urea precursor under sealed condition reached an optimum photocatalytic H₂ production rate of 597.4 μmol/h and an apparent quantum efficiency of 15.6% at wavelength of 420 nm. This enhanced photocatalytic H₂ production performance is mainly ascribed to the introduction of N-defects, which not only extended of the visible light absorption, but also acted as the electron trap centers to suppress the recombination of the photogenerated electron and hole pairs. This work offers one-step facile strategy for the introduction of N-defects to prepare N-defective g-C₃N₄ with superior photocatalytic activity, which is also a great substitute for the high-energy consuming and complicated synthetic routes.     

Characterization of local texture in a moderately deformed polycrystalline AlSi-alloy

Polycrystalline material of various grain sizes of AlSi-alloy containing second-phase particles have been deformed at room temperature in axisymmetric compression. The variation in crystallographic orientation in the as-deformed material was obtained by the Electron Back Scattered Pattern (EBSP) technique in SEM. “Random” and cumulative long range misorientation gradients have been quantified within the matrix (M) and at heterogeneities such as the grain boundary (GB), the triple line region (TL) and in the vicinity of large second phase particles (P) in material compressed to equivalent plastic strains of 0.2 and 0.4. It is shown that the misorientation gradient increases differently in different regions with increasing strain. Maximum values were found in regions expected to be more strained than average in order to accomodate imposed constraint from neighbouring grains or from the presence of large second phase particles. An important feature of the deformed structure seems to be the cumulative rotation of the lattice about an axis close to the 〈111〉-axis in regions with large misorientations.