查看更多>>摘要：? 2022 Elsevier B.V.Understanding the role of point defects towards hardening –and influence on secondary phase evolution demands a systematic investigation of defects during aging. In the present work, we investigate defects present/evolved during thermal aging in high Cr content NiCr solid-solution using positron annihilation lifetime and coincidence Doppler broadening spectroscopy. Thermal aging at the studied temperature results in phase transformation of the matrix primarily by discontinuous precipitation leading to Cr precipitation as revealed from field-effect scanning electron microscopy. Positron annihilation results reveal that non-equilibrium thermal (excess) vacancies are predominant defects in the studied alloy. These vacancies are retained in the alloy due to the formation of vacancy-solute complex. During solutionization treatment, the excess vacancies are largely recovered attaining an equilibrium vacancy concentration. On the other hand, excess vacancies are not recovered during thermal aging and stable up to 24 h aging period. In addition to vacancy-solute complex, dislocations are evolved at higher aging times and suggested to be present at the interface of Cr precipitate and matrix. Under the consideration of positron trapping model, the estimated atomic concentration of vacancies (vacancy-solute complex) in the phase transformed NiCr is ~ 10?5 and the dislocation density is ~ 4 × 109 cm?2.
查看更多>>摘要：? 2022 Elsevier B.V.Machine learning based strategies have been increasingly applied in materials science to accelerate the discovery process. Regression algorithm learns the mapping from compositions/features to targeted property and makes prediction for unknown compositions. The quality of features, in some degree, determines the upper limit of the surrogate model performance and the associated search efficiency for desired candidates. We herein propose a data-driven framework combining feature engineering, machine learning, experimental design and synthesis, to optimize the piezoelectric constant of BaTiO3 based ceramics, with the emphasis on feature engineering realized by four strategies. The search for improved piezoelectric constant in the initial data set behaves differently compared to that in the whole unknown space, indicating that the initial data set might be biased to a local scheme. The best composition with a piezoelectric constant of ~ 430 pC/N is synthesized in the second iteration, better than the majority in the initial data set. Insight for the change of piezoelectric constant for the newly synthesized 12 compositions is provided by examining the corresponding evolution of dielectric permittivity within the thermodynamic theory.
查看更多>>摘要：? 2022Defects in grain boundaries and at the surface of perovskite polycrystalline film lead to nonradiative recombination losses and ion migration, which seriously affects the performance and stability of optoelectronic devices. However, the process of passivation by using functional groups in polymers is expected to solve the problem. In this work, a tandem-like perovskite photodetector (PD) is developed, and an improved solution process is proposed to promote perovskite crystal growth and reduce the horizontal grain boundaries by using excess poly(methyl methacrylate) (PMMA) as anti-solvent. In addition, PMMA retained in perovskite grains acts as an interlayer for storing photocarriers, reducing the dark current and enhancing the PD gain. As a result, optimal perovskite PD exhibits a peak specific detectivity of 3.38 × 1012 Jones, a high responsivity of 5.65 A/W, a linear dynamic range of 80 dB, and an external quantum efficiency of 1321% under 532 nm illumination at the small bias of ? 1 V. In addition, the PD has a fast response (5.90 μs rise time, 6.75 μs decay time). These results combine to provide a low-cost method for designing high-performance, ultrafast-response perovskite optoelectronic devices with low power consumption.
查看更多>>摘要：? 2022 The Author(s)Ni-Co bimetallic nanoparticles (NPs) have been synthesized via reduction of Ni and Co hydroxides by hydrazine in water / ethylene glycol solutions. It was found that the particle size and polydispersity of the obtained chemically homogeneous NPs decrease with a decreasing to 50 at.% content of Ni in the reaction mixture. A different trend was observed for Ni25Co75 and was related to the formation of Ni- and Co-rich particles. Ni-Co-NPs were tested as catalysts of hydrolysis of alkaline solutions of NaBH4, with the highest rate of hydrogen generation observed for Ni50Co50. Zero-order kinetics of hydrogen evolution process was observed for all studied systems. Based on the data of the kinetic studies, we conclude that the rate of the hydrolysis process (a) increased with increasing NaBH4 concentration in the range 0.1 – 1 mol/L; (b) decreased by 25% with increasing pH of the solution from 9 to 14. Studies of the temperature dependence of the rates of the hydrolysis process showed that the activation energy of the reaction decreased to 26 kJ/mol with decreasing contents of NaBH4 and catalysts. Based on a comparison of the values of activation energy of hydrolysis reaction and the enthalpy of activation of viscous flow of initial NaBH4 solution and the solution obtained after the hydrolysis, a diffusion-controlled reaction mechanism was proposed.
查看更多>>摘要：? 2022 Elsevier B.V.The design of efficient and stable photocatalysts for the removal of heavy metals in the environment has become a research hotspot. Here, a composite photocatalyst with three-dimensional In2S3 microspheres supported by WO3 nanoparticles was synthesized for the photoreduction of Cr(VI) for the first time. The constructed composite catalyst has a direct Z-scheme electron transport mechanism without any precious metals (Au, Pt, and Ag), quantum dots (TiO2 QDs) or carbon materials (Graphene) as electronic media. Constructing a direct Z-scheme WO3/In2S3 photocatalyst can greatly retain the reduction and oxidation reaction sites on the surface of the heterojunction and accelerate the reduction reaction. Under visible light irradiation, it greatly promotes the photocatalytic reduction of Cr(VI), which is 67.7 times and 3.6 times the reduction rates of WO3 and In2S3, respectively. The favorable photocatalytic performance of WO3/In2S3 should be attributed to the effective interfacial contact between the semiconductors in the Z-scheme system, thereby realizing effective electron transfer and charge separation. In addition, the stability of WO3/In2S3 was studied, and a possible mechanism in the photoreduction process of Cr(VI) was proposed.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, Ti3C2Tx was directly deposited on carbon cloth (CC) to obtain a flexible substrate for NiCo-S. Then, 3D self-supported flexible NiCo-S/Ti3C2Tx/CC composite electrode was prepared by a two-step hydrothermal method. Compared with the NiCo-S/CC electrode, the specific capacity of the NiCo-S/Ti3C2Tx/CC electrode increases from 908 to 1690 C g?1 at 2 A g?1. The rate capability (2–20 A g?1) increases from 42% to 66%, and the cyclic performance (5000 charge-discharge cycles at a current density of 10 A g?1) increases from 50% to 82%. The enhanced electrochemical performance may be attributed to the introduction of Ti3C2Tx, which reduces the resistance of composite and facilitates the electron/ion transport, while the presence of Ti2+ in Ti3C2Tx provides more sites for redox reactions. The assembled flexible all-solid supercapacitor (NiCo-S/Ti3C2Tx/CC//AC) manifests a high energy density of 62 Wh kg?1 at 800 W kg?1 and an excellent cyclic stability with 89% capacity retention after 5000 cycles at 10 A g?1. In addition, the device demonstrates no obvious capacity change at different states and bending angles, showing broad application prospects in high-performance wearable energy-storage devices.
查看更多>>摘要：? 2022 Elsevier B.V.In this contribution, hierarchical copper manganese oxide porous micro/nanospheres have been synthesized through sacrificial manganese carbonate micro/nano spheres precursor. The morphology and structure are examined by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopic (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller adsorption (BET). As electrode of lithium-half cells, the as-synthesized sample demonstrates the remarkably enhanced lithium storage performance compared to those of bulk counterparts and the reported literature, in terms of high first discharge capacity (1191.8 mAh g?1), satisfactory cycle performance (462.7 mAh g?1 at 2 C after 500 cycles), fair rate capability (357.8 mAh g- even at 5 C), quick Li+ diffusion kinetics (1.1 ×10?12 cm2 s?1), as well as low activation energy (13.06 KJ mol?1). Interestingly, the hierarchical micro/nanospheres are well maintained after 500 cycles.
查看更多>>摘要：? 2022 Elsevier B.V.g-C3N4 powders with different morphology and surface charged property were obtained by acidification, oxidation and exfoliation treatment of melamine. Acid treatment converts -NH2 group in melamine into -NH3NO3 group, and further oxidation reduces the existing C[sbnd]N[sbnd]H bond, promotes the formation of C[sbnd]N[sbnd]C and N[sbnd](C)3 bond in g[sbnd]C3N4, and ensures the formation of layered g-C3N4 structure; acid treatment and exfoliation were beneficial to increase the pore volume of g-C3N4 and enhance the redox ability of g-C3N4. The degradation rate of acid treated g-C3N4 to Rhodamine B in visible light was 3.13 times that of untreated g-C3N4, and the degradation rate of acid treated g-C3N4 to ciprofloxacin was 5.04 times that of untreated g-C3N4, further indicating that acid treated-oxidation-exfoliated treatment can improve the photocatalytic degradation effect of g-C3N4 and expand the application range of g-C3N4. The layered g-C3N4 with different surface charges can be selectively loaded onto the semiconductor materials with exposed active crystal surfaces, providing conditions for controllable preparation of Z-type heterojunction with enhanced redox ability.
查看更多>>摘要：? 2022 Elsevier B.V.The shift of martensite transformation temperatures with magnetic field is an essential parameter for magnetic shape memory effect as well as for magnetocalorics. We compare the dependence of martensite transformation temperature on magnetic field in Ni2MnGa and Ni2MnGa0.95In0.05 single crystals. Choosing the stoichiometric and isoelectronic compound enables to observe the effect of In alloying free from the influence of off-stoichiometry. The martensite start temperature, Ms, decreases several kelvins in low magnetic fields (< 1 T). In high field (> 2 T), Ms increases with the magnetic field and the Ms(H) dependence is about linear with the slope of 0.26 K/T (Ni2MnGa) and 0.36 K/T (Ni2MnGa0.95In0.05). Modest 1.25 at% indium alloying decreases not only transformation temperature Ms by about 100 K but also considerably decreases the latent heat of martensite transformation from 1.99 kJ/kg (Ni2MnGa) to 0.29 kJ/kg (Ni2MnGa0.95In0.05) determined from Clausius-Clapeyron equation. The latent heat of premartensitic transformation also decreases, approximately five times.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, green emission fluorescence carbon dots (G-CDs) were prepared using chitosan and p-phenylenediamine as precursors. Furthermore, the fluorescence of the prepared G-CDs was quenched by Nitrite (NO2-) with excellent selectivity and sensitivity due to internal filtration effect (IFE) Therefore, G-CDs was applied to monitor NO2- as an “on-off” fluorescence probe and obtained a wide linear range (1–300 μM) with limit of detection (LOD) 1.00 μM. Another hand, the fluorescence of G-CDs was also quenched by Au3+ due to fluorescence resonance energy transfer (FRET) effect caused by the in-situ formed Au nanoparticles (AuNPs). Interestingly, the addition of enrofloxacin (Enr) to G-CDs/AuNPs system led to the aggregation of AuNPs with partly lager size G-CDs, and the quenched fluorescence of the G-CDs/AuNPs system was restored, accompanying with visible fluorescence color change from green to blue. The “on-off-on” detection method through the constructed G-CDs/AuNPs system to Enr obtained good effects, such as high selectivity, sensitivity, visibility, relatively wide linear range (1–50 mg/L) and low LOD (0.04 mg/L). Additionally, the prepared G-CDs could be used for the detection of NO2- and Enr in actual water samples, proving it is an excellent candidate for environmental detection of NO2- and Enr.
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