Search

Background: TiO2 nanoparticles possess adsorption capacity and photocatalytic activity, and are thus fitted for removal of dyes from water. However, TiO2 nanoparticles are difficult to separate from the bulk solution due to high loss. Moreover, TiO2 can only use light with a wavelength of less than 387.5 nm, so the utilization efficiency of solar energy is very low. The present work prepared Fe3O4@C@TiO2-AgBr-Ag composites to overcome the shortcomings of TiO2. Objective: Adsorptive and photocatalytic performance of nano-magnetic materials Fe3O4@C@TiO2- AgBr-Ag. Methods: Fe3O4@C@TiO2 and Fe3O4@C@TiO2-AgBr-Ag magnetic nanocomposites were prepared by the sol-gel method. Their structure was characterized. Performances of Fe3O4@C@TiO2 and Fe3O4@C@TiO2-AgBr-Ag for removing Rh B were thoroughly investigated and compared. Langmuir– Hinshelwood kinetic model was applied to analyze the heterogeneous processes of adsorption and photodegradation. Results: Removal experiments were carried out with Rhodamine B as the subject. The effects of contacting time, pH, subject concentration, and doses of photocatalyst on the removal performance were studied. The removal of Rh B by Fe3O4@C@TiO2 and Fe3O4@C@TiO2-AgBr-Ag involved both adsorption and photodegradation, and the photocatalytic activity of Fe3O4@C@TiO2-AgBr-Ag was much higher than that of Fe3O4@C@TiO2. The optimum removal conditions were determined. Under the optimal conditions, the removal rate of Rhodamine B with Fe3O4@C@TiO2 was 77.8%, and the removal rate of Rhodamine B with Fe3O4@C@TiO2- AgBr-Ag was 87.3%. Conclusion: The coupling of the nanostructured metal Ag to the outer surface of TiO2 could effectively increase photocatalytic efficiency under visible light. The photocatalysts could be separated from bulk solutions by using a magnet and be easily recycled. The removal reaction kinetics fitted with the first-order model.

A new method for fabricating crack is introduced by pressing the wedge on bar. The path of the crack propagation is not regular when the ratio of length and diameter is less than 1.8 on the symmetrical support. The load of the wedge for pressing the notch is given in this paper. The 2-D finite element is applied to simulate the crack propagation by the maximum normal stress theory. The experimental results show that the quality of the fracture section will vary with the span on the three-point bending. In order to control the crack propagation along the desired section regularly, the asymmetrical three-point bending is proposed. The simulation results show that when the difference of the two spans is between 11 and 22 in asymmetrical three-point bending under the parameters condition, the good quality of the section will be obtained, and the experimental results also strong support the conclusion.

Effects of different treatments (solid solution þ cold deformation þ aging condition) on the microstructure of Fe–18Cr–18Mn–0.63N high‐nitrogen austenitic stainless steel and consequently on its mechanical properties were investigated by microscopic observations and mechanical characterizations. For un‐cold‐deformed and 20% cold‐deformed steels, the results show that, all precipitates are Cr2N phase and the granular precipitates transform into cellular precipitates with increasing aging time. However, in 50% cold‐deformed steel only the granular and massive Cr2N precipitates. On the other hand, no cellular Cr2N precipitates are observed, but the precipitation of s phase is induced. In un‐cold‐deformed steel, all tensile properties including the ultimate tensile strength, yield strength, and the elongation decrease with increasing aging time, resulting from the precipitation of the second phase. In the cold‐deformed steels, the tensile and yield strengths decrease while the elongations firstly increase and then decrease with aging time. Actually, in the cold‐ deformed steels, the strain recovery or recrystallization mainly causes the decreases in tensile and yield strength in addition to increase in elongation after aged for 1 h. In contrast, the cellular Cr2N precipitation or granular precipitation mainly results in the continually slow decreases in tensile and yield strengths and the relevant decrease in elongation with aging.

Due to the diversified atomic structures and electronic properties, two-dimensional monolayer nanocarbon materials (graphyne or graphdiyne) composed of sp and sp2 hybridization C atoms have received the widespread attention in recent years. The fundamental questions include how the sp orbital hybridization affects the electronic structure of graphyne. In order to investigate the structure dependent electronic structures of graphyne, the energetic stabilities and electronic structures of -graphyne and its derivatives (-N) with N carbon atoms on each edge of the hexagons are investigated by density functional theory (DFT) calculations in this work. In our DFT calculations we adopt generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) using the CASTEP module implemented in Materials Studio. The studied -Ns consist of hexagon carbon rings connected by vertexes whose edges have various numbers of carbon atoms N= 1-10. The structure and energy analyses show that -Ns with even-numbered carbon chains have alternating single and triple C-C bonds, energetically more stable than those with odd-numbered carbon chains possessing continuous C-C double bonds. The calculated electronic structures indicate that -Ns can be either metallic (odd N) or semiconductive (even N), depending on the parity of number of hexagon edge atoms regardless of the edge length due to Jahn-Teller distortion effect. Some semiconducting -graphyne derivatives (-N, N= 2, 6, 10) are found to possess Dirac cones (DC) with small direct band gaps 10 meV and large electron velocities 0.255106-0.414106 m/s, ～30%-50% of that of graphene. We find that Dirac cones also appear in -3 and -4 when we shorten the double bonds and elongate the triple bonds in -3 and -4 respectively. These results show that the bond length change will affect the characteristics of band structure and suggests that the band structure characteristics may be influenced by Peierls distortion in a two-dimensional system. Our DFT studies indicate that introducing sp carbon atoms into the hexagon edges of graphene opens the way to switching between metallic and semiconductor/DC electronic structures via tuning the parity of the number of hexagon edge atoms without doping and defects in nanocarbon materials and nanoelectronic devices.

Although comprehensive research findings of the cyclic deformation and dislocation structures of Cu single crystals with various orientations have been well established over the four decades,studies on the thermal stability of dislocation structures in fatigued Cu single crystals are still rarely reported.In the present work,[233]Cu single crystals oriented for coplanar double slip were firstly cyclically deformed at different plastic strain amplitudesγ_(p1) up to saturation,and then annealed at different temperatures for 30 min.The dislocation structures induced by cyclic deformation as well as the microstructural changes resulting from subsequent annealing treatments were detected by using the electron channeling contrast(ECC) technique in SEM and TEM.It was found that the dislocation structures have undergone an obvious process of recovery at 300°C,and the recrystallization even partially takes place in the sample fatigued at highγ_(p1) However,at 500 and 800°C,the violent recrystallization takes place in all crystals and a large number of annealing twins have appeared.As the plastic strain amplitude and accumulated plastic strain increase,the degree of strain concentration would be significantly aggravated,providing a higher local strain energy for the occurrence of recrystallization and the initiation of twins,so that the recrystallization takes place more noticeably,and annealing twins become coarser and the number of them increases notably.The formation of annealing twins is closely related to the appearance of stacking faults.The DSC measurements demonstrated that the recrystallization process and the formation process of twins should be a gradually-developing process,instead of a suddenly-forming process.

The fatigue dislocation structures in cyclically saturated [4 18 41] single-slip-oriented Cu single crystal at different values of plastic strain amplitude pl, as well as their thermal stabilities under annealing at different temperatures for 30 min are studied using the electron channeling contrast (ECC) technique in scanning electron microscopy (SEM). It is found that the dislocation structures, such as veins, PSB ladders, PSB cells, Labyrinths, etc. undergo an obvious process of recovery after annealing at 300 ℃. However, when the annealing temperature is higher than 500℃, those dislocation structures basically disappear, and the recrystallization takes place in all specimens, meanwhile, annealing twins form in most cases. The occurrence of the recrystallization and the formation of annealing twins are related not only to the annealing temperature and applied pl, but also closely to the accumulative cyclic plastic strain.