PH-induced structural evolution,photodegradation mechanism and application of bismuth molybdate photocatalyst

In this work, we have elucidated the pH-induced structural evolution of bismuth molybdate photocatalyst based on a hydrothermal synthesis route. With increasing the pH value of precursor solution, pure Bi₂MoO₆ was synthesized at pH 2–5, Bi₂MoO₆-Bi₄MoO₉ mixture was obtained at pH 7–9, pure Bi₄MoO₉ was obtained at pH 11, and pure α-Bi₂O₃ was derived at pH 13. The as-derived samples mainly present particle-like shapes but with different particle sizes (except the observation of Bi₂MoO₆ nanowires in sample S-pH9). The photocatalytic performances between the samples were compared via the degradation of methylene blue (MB) under irradiation of simulated sunlight. The Bi₂MoO₆ sample synthesized at pH 2 exhibited the highest photodegradation performance (η(30 min) = 89.8 %, k_app = 0.05007 min^?1) among the samples. The underlying photocatalytic mechanism and degradation pathways of MB were systematically analyzed. Moreover, the photodegradation performance of the Bi₂MoO₆ photocatalyst was further evaluated at different acidic-alkaline environments as well as in degrading various color and colorless organic pollutants, which provides an important insight into its practical application.     

Tunable microwave absorption properties of nickel-carbon nanofibers prepared by electrospinning

The nickel-carbon nanofibers (Ni-C NFs) were fabricated by the electrospinning of poly(vinyl alcohol) (PVA) and nickel acetate tetrahydrate (NiAc) solution precursor with succedent PVA pyrolyzation and calcination process. The microwave absorption performance and electromagnetic (EM) parameters of the NFs were researched over the frequency range of 2.0–18.0?GHz. Both the impedance matching and EM wave absorption properties of the Ni-C NFs were improved by changing the carbonization temperature. The effect of graphitization degree on reflection loss (RL) and the possible loss mechanisms were directly displayed in the comparative study of each sample. The optimal RL value of ??44.9?dB and an effective frequency bandwidth of 3.0?GHz under a thickness of 3.0?mm can be reached by a sample calcined at 650?°C. These lightweight Ni-C NFs composites can be promising candidates for EM wave absorbers due to the combination of multiple loss mechanisms, nano-size effect and good impedance matching between Ni nanoparticles and CNFs.     

Flexoelectric response of (1-x)BaTiO3-xSrTiO3 ceramics

The measured flexoelectric response of ferroelectric ceramics is usually several orders of magnitude larger than the theoretically calculated response, causing the controversy about the magnitude of the intrinsic response of flexoelectricity in the materials. In order to understand this issue, the temperature-dependent flexoelectric response of (1-x)BaTiO₃-xSrTiO₃ (BST) ceramics were measured. We show that near the Curie temperature (T_c), BST ceramics exhibit the highest flexoelectric response, which is much larger than the intrinsic response calculated theoretically. The response becomes lower at the temperature above or below T_c. The flexoelectric response that is consistent with the theoretical value can only be measured at a temperature much above T_c. Below T_c, the flexoelectric response is also much higher than the theoretical value because of the effect of some extrinsic mechanisms including the surface effect. Our study provides important experimental results to understand the mechanisms of flexoelectric response of ferroelectric ceramics and resolve the controversy about the magnitude of the intrinsic flexoelectric response of the materials.     

桥梁耐候钢Q345qNH在模拟西北大气环境中的腐蚀行为

目的 通过模拟西北大气环境对桥梁耐候钢腐蚀行为的影响,为西北地区桥梁钢耐蚀性能的研究提供理论依据。方法 选取除冰盐介质、NaHSO3介质、混合介质三种腐蚀介质进行干湿交替加速腐蚀实验,并采用扫描电镜+能谱、X射线衍射、电化学测试等方法,分析了Q345qNH钢在三种模拟大气环境中的腐蚀形貌、锈层特征及结构、腐蚀产物及锈层的电化学保护性。结果 Q345qNH钢在三种介质中腐蚀144 h后,腐蚀速率均明显下降,在288~480 h间,NaHSO3介质中的腐蚀速率下降趋势约是混合介质中的1.5倍、除冰盐介质中的3.8倍。三种腐蚀介质中,锈层成分均含有α-FeOOH、γ-FeOOH、Fe3O4,在除冰盐介质和混合介质中还会生成大量的不稳定β-FeOOH和可溶性FeOCl腐蚀产物,锈层疏松不稳定。此外,在NaHSO3介质中,自腐蚀电位Ecorr最高,自腐蚀电流密度Jcorr最低;除冰盐介质和混合介质中,Ecorr差别不大,但混合介质Jcorr<除冰盐介质Jcorr。对比腐蚀480 h的带锈样,稳态腐蚀区的阳极溶解电流密度有：除冰盐介质≈混合介质>NaHSO3介质。结论 Q345qNH钢在除冰盐介质中,各离子之间相互耦合,难以形成致密的保护性锈层,经过长时间的腐蚀过程,危害性最大;在NaHSO3介质中,外锈层元素富集,形成致密、稳定的保护性锈层;在除冰盐+NaHSO3混合介质中生成的锈层,其稳定性、致密性介于前两种介质中的锈层之间。     

Structural,optical and electrical properties of Cu2FeSnSe4 and Cu(In,Al)Se2 thin films

Cu-based semiconductors Cu₂FeSnSe₄ (CFTSe) and Cu(In, Al)Se₂ (CIAS) have been fabricated using radio-frequency magnetron sputtering combined with rapid thermal selenization processing. For CFTSe, the heating rate ranging from 60 to 150 °C/min results in a difference in structure, morphology and optical properties. Thin film exhibits a pure phase structure, smooth surface and a band gap of 1.19 eV as the heating rate elevated to 90 °C/min. Furthermore, the CFTSe thin film selenized at 90 °C/min own the smallest value of cell volume compared with the others samples, which represents a more stable structure. In terms of the other Cu-based material CIAS, three different selenization pressures, i.e., 1, 5 and 10 Torr, have been employed for CIAS preparation. Thin film transforms into single phase with dense morphology along with the pressure of 1 Torr. The diverse band gap of CIAS thin films from 1.34 to 2.18 eV attribute to two reasons: (i) the various Al content will affect the hybridization degree of Al–Se, and finally tunes the band structure, (ii) amounts of CuSe has a certain degree of effect on the band gap of the CIAS. In addition, the electrical properties of CFTSe and CIAS are also researched with the open circuit voltage (V_oc) of 94 and 365 mV, respectively, signifying potential applications of CFTSe and CIAS for the thin film solar cells.     

Facial synthesis of dandelion-like g-C3N4/Ag with high performance of photocatalytic hydrogen production

Nowadays, energy shortage is one of the major problems in the world. Photocatalytic hydrogen production is a new type of energy technology with good application prospect. As a new type of photocatalytic semiconductor material, g-C₃N₄ has attracted much attention as a photocatalyst. By ultrasonic treatment of a mixed solution of g-C₃N₄ and bovine serum albumin, followed by adding a certain amount of silver nitrate solution and then directly hydrothermal treatment, a special dandelion-like g-C₃N₄/Ag (D-g-C₃N₄/Ag) was prepared. The scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction, Fourier transform infrared, fluorescence and physicochemical adsorption methods were used to characterize the morphology and structure of D-g-C₃N₄/Ag. In addition, the photocatalytic H₂ production of D-g-C₃N₄/Ag with different Ag loadings or in different sacrificial agents and different pH conditions were investigated. The results indicated that when triethanolamine was used as sacrificial agent, photocatalytic hydrogen efficiency was the best, and the rate of photocatalytic hydrogen production reached 862 μmol g⁻¹ h^{− 1} as the Ag loading was 4%.     

Sodium bismuth titanate-based lead-free RAINBOW piezoelectric devices

The piezoelectric properties of lead-free piezoelectric ceramics are normally lower than those of lead oxide-based ceramics. In order to enhance the electromechanical performance of lead-free piezoelectric ceramics, an asymmetric chemical reduction was applied to sodium bismuth titanate (NBT)-based piezoelectric ceramics. Similar to the lead-containing ceramics, a curvature structure can be induced by the reduction in the NBT-based materials and lead-free RAINBOW (reduced and internally biased oxide wafer) devices can be fabricated. A large displacement (approximately 17 μm) under an electric field of 900 V/mm and high piezoelectric sensitivity (>4000 pC/N) under a stress, which are related to the reduction induced curvature, can be measured in the NBT-based devices. The apparent piezoelectric response of the lead-free RAINBOW devices is comparable to that of Pb(Zr,Ti)O₃-based devices. We proposed that apart from the piezoelectric properties, flexoelectric effect could also be a contributing mechanism for the observed apparent piezoelectric response in RAINBOW devices.     

One-step synthesis of Ni3S2 nanowires at low temperature as efficient electrocatalyst for hydrogen evolution reaction

Ni₃S₂ is an emerging cost-effective catalyst for hydrogen generation. However, a large amount of reported Ni₃S₂ was synthesized via multi-step approaches and few were fabricated based on the one-step strategies. Herein, we report a facile one-step low-temperature synthesis of Ni₃S₂ nanowires (NWs). In this strategy, a resin containing sulfur element is recommended as a sulfur resource to form Ni₃S₂ NWs. It presents a plausible explanation on the vapor–solid–solid (VSS) growth mechanism according to the results of this experiment and reported in literature that has been published. The Ni₃S₂ NW exhibits a potential ∼199 mV at 10 mA cm⁻² and the long-term durability over 30 h at 20 mA cm⁻² HER operation, better than other reported Ni₃S₂. More importantly, according to replace transition metal foam as the initial metal, other transition metal sulfide can be readily synthesized via this original approach.     

Synthesis and electrochemical properties of nickel oxide/carbon nanofiber composites

The electrospinning of polyacrylonitrile (PAN) with a polyaniline and graphene sol–gel mixture produced uniform, smooth fibers with an average diameter of 0.3 μm. These electrospun fibers were stabilized for 2 h at 200 °C and then carbonized at 800 °C for 5 h. Composites were prepared by depositing Ni(OH)₂ on the carbon nanofibers (CNFs) and calcining them at different temperatures. The composites were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The effect of the calcination temperatures on the electrochemical properties was studied using cyclic voltammetry and electrochemical impedance spectroscopy. The specific capacitance (SC) was found to be highest (738 F g⁻¹) at a calcination temperature of 400 °C. The charge transfer resistance (R_p) decreased as the calcination temperature was increased. However, the electrical double layer capacitance (EDLC) increased with an increase in the calcination temperature. The EDLC increased from 0.144 F g⁻¹ at a calcination temperature of 100 °C to 485 F g⁻¹ at a calcination temperature of 500 °C.