Abstract
Heterogeneous single-atom catalyst (SAC) opens a unique entry to establishing structure–performance relationship at the molecular level similar to that in homogeneous catalysis. The ...challenge lies in manipulating the coordination chemistry of single atoms without changing single-atom dispersion. Here, we develop an efficient synthetic method for SACs by using ethanediamine to chelate Pt cations and then removing the ethanediamine by a rapid thermal treatment (RTT) in inert atmosphere. The coordination chemistry of Pt single atoms on a Fe
2
O
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support is finely tuned by merely adjusting the RTT temperature. With the decrease in Pt-O coordination number, the oxidation state of Pt decreases, and consequently the hydrogenation activity increases to a record level without loss of chemoselectivity. The tunability of the local coordination chemistry, oxidation states of the metal, and the catalytic performance of single atoms reveals the unique role of SACs as a bridge between heterogeneous and homogeneous catalysis.
To overcome problems associated with loosening of orthopedic implants and surgical site infections, we developed a novel, titanium (Ti)-based material that releases both strontium and silver ions ...(CaSrAg-Ti) based on alkali-and-heat treatment. The results of commercially pure Ti (cp-Ti), Ti that releases Sr ions only (CaSr-Ti), and the novel CaSrAg-Ti material were compared. Mechanical tests were performed to evaluate the in vivo bonding properties of CaSrAg-Ti and the bone-implant contact (BIC) ratio in histological specimens was determined at 4 and 8 weeks after implantation in a rat femur. Also, the in vitro antibacterial activities of this material against methicillin-susceptible Staphylococcus aureus (MSSA) were evaluated after a 24 h incubation period by assaying colony-forming units. In addition, antibacterial activities were evaluated in vivo at 7 days after implantation in a rat subcutaneous pocket model. There was direct contact between the bone and CaSrAg-Ti in histological specimens and no apparent signs of argyrosis in any rat. The bone-bonding strength and the BIC ratio were increased by 2.7- and 2.3-fold for CaSrAg-Ti vs. cp-Ti at 4 weeks and 2.2- and 2.0-fold at 8 weeks, respectively. As compared with cp-Ti, the number of viable MSSA remaining on CaSrAg-Ti was reduced by 100 ± 0% in vitro and 94.2 ± 6.9% in vivo. Ti that releases Sr and Ag ions is a promising material that exhibits both bone-bonding properties and anti-MSSA activities.
ZrC whiskers were prepared on graphite through precursor transformation method. Effects of heat treatment temperature, catalyst concentration and heat treatment time on phase composition and ...microstructure of the ZrC whiskers were investigated. Growth mechanism of the ZrC whisker was analyzed. Results indicated that as heat treatment temperature increasing, catalyst activity increased and energy barrier for the carbothermal reduction reaction reduced, resulting in a gradual increase of both production and diameter of the ZrC whiskers. Catalyst could provide nucleation points for the ZrC whiskers, production and diameter of the ZrC whiskers firstly increased as the catalyst concentration increasing. While, when catalyst concentration was over high, length-diameter ratio of the ZrC whiskers decreased and some whiskers were agglomerated. Heat treatment time affected extent of the carbothermal reduction reaction. Production and length-diameter ratio of the ZrC whiskers increased firstly and then decreased with the increase of heat treatment time. When heat treatment temperature was 1600 °C, catalyst concentration was 0.4 mol/L, heat treatment time was 2 h, the ZrC whiskers with diameter of around 130 nm and length of tens of microns were synthesized. The whiskers were composed of a single-crystal ZrC core and an amorphous ZrO2 shell. Growth of the ZrC whiskers was controlled by solid-liquid-solid (S-L-S) mechanism and the Ostwald ripening mechanism.
Owing to the postharvest mass loss in most tropical and subtropical fruits and vegetables caused by chilling injury (CI), it is necessary to look for effective technologies to alleviate this issue. ...Studies thus far have found that some postharvest technologies could effectively alleviate CI in post-harvest fruits and vegetables.
This review summarizes the temperature and symptoms of CI in common postharvest fruits and vegetables. The postharvest technologies to control CI, which comprised physical (low-temperature conditioning, heat treatment, near-freezing temperature, controlled atmosphere, edible coating and ultraviolet irradiation) and chemical (ethylene and 1-methylcyclopropene, oxalic acid, calcium ions, nitric oxide, melatonin, salicylates and jasmonates, polyamines, and some other chemical substances) treatments, are also detailed. The potential biochemical mechanisms of different postharvest technologies are also proposed and attributed to the following strategies: maintaining membrane structure and sufficient energy supply, enhancing the antioxidant system, promoting the arginine pathway, regulating sugar metabolism, and activating the C-repeat/dehydration response element binding factor (CBF) genes.
This review found that a variety of postharvest treatments have been developed to control CI in postharvest fruits and vegetables. The key findings were that the effects of some postharvest treatments—such as ethylene and 1-methylcyclopropene—on fruit and vegetable CI are contradictory. Some key factors, such as the time and temperature of heat treatment and the dose of ultraviolet radiation, need to be regarded when applying postharvest technologies. Some small-molecule signal substances that from natural plant and the combination of different treatments are potential future research directions for controlling CI in postharvest fruits and vegetables.
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•The temperature and symptom of chilling injury (CI) of common product are summarized.•The technologies and biochemical mechanism to control the CI are summarized.•The effect of some technologies on CI of fruits and vegetables are contradictory.•There are some key factors when some technologies applied for alleviating CI.
In this work, nanostructured Yb2SiO5/mullite-SiC/Si environmental barrier coatings (EBCs) were prepared to investigate the effect of heat treatment on the microstructure and phase transition of ...nanostructured Yb2SiO5/mullite-SiC/Si coatings. The Yb2SiO5 content and microstructure evolution in the coatings were thoroughly analyzed before and after heat treatment. The results demonstrate a slight decrease in the porosities of nanostructured Yb2SiO5 and mullite-SiC coatings, accompanied by a gradual growth in grain sizes with increasing heat treatment time, indicating the nanostructured EBCs show good resistance to sintering. Moreover, the thickness of thermal growth oxidation layer is only 200 nm at 1250 °C for 500 h of heat treatment. In particular, the presence of the Yb2O3 phase has been observed to exert a favorable influence on the thermal stability of nanostructured EBCs. This work provides an innovative strategy for designing advanced EBCs with excellent high-temperature thermal stability.
Due to easy re-stacking, low yield of few-layered MXenes (f-MXenes), the applications of MXenes are mainly restricted in multi-layered MXenes (m-MXenes) state. Although f-MXenes can be prepared from ...m-MXenes, after exfoliation process, a mass of sediments which are still essentially compact MXenes are usually directly discarded, leading to low utilization of raw m-MXenes. Herein, a classified preparation strategy is adopted to exploit the raw m-MXenes and traditional MXenes sediments, taking multi-layered Ti
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C
2
T
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MXene as an example. Via rational delamination and subsequent treatment to Ti
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C
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T
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sediments, we succeed in achieving classified and large-scale preparation of various Ti
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C
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MXene derivatives, including few-layered Ti
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C
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T
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(f-Ti
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C
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T
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) powders, f-Ti
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C
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T
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films, and Ti
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C
2
T
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MXene-derived nanowires with heterostructure of potassium titanate and Ti
3
C
2
T
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. We demonstrate the necessity of “step-by-step delamination” towards traditional Ti
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C
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T
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sediments to improve the yield of f-Ti
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C
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T
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from 15% to 72%; the feasibility of “solution-phase flocculation (SPF)” to fundamentally solve the re-stacking phenomenon, and oxidation degradation issues of f-Ti
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C
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T
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during storage; as well as the convenience of SPF to deal with time-consuming issues of fabricating Ti
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C
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T
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films. What’s more, alkali-heat treatment of final Ti
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C
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T
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sediments turns waste into treasure of Ti
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C
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T
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-derived nanowires, leading to 100% utilization of raw Ti
3
C
2
T
x
. The content of one-dimensional (1D) nanowires in the hybrids can be adjusted by controlling alkalization time. The 3D architecture heterostructure composed of 1D nanowires and 2D nanosheets exhibits gorgeous application potential. This work can expand preparation and application of various MXenes derivatives, promoting process of various MXenes.
Electron Beam Melting (EBM), a powder bed additive layer manufacturing process, was used to produce Ti–6Al–4V specimens, whose microstructure, texture, and tensile properties were fully ...characterized. The microstructure, analyzed by optical microscopy, SEM/EBSD and X-ray diffraction, consists in fine α lamellae. Numerical reconstruction of the parent β phase highlighted the columnar morphology of the prior β grains, growing along the build direction upon solidification of the melt pool. The presence of grain boundary αGB along the boundaries of these prior β grains is indicative of the diffusive nature of the β→α phase transformation. Texture analysis of the reconstructed high temperature β phase revealed a strong pole in the build direction. For mechanical characterization, tensile specimens were produced using two different build themes and along several build orientations, revealing that vertically built specimens exhibit a lower yield strength than those built horizontally. The effect of post processing, either mechanical or thermal, was extensively investigated. The influence of surface finish on tensile properties was clearly highlighted. Indeed, mechanical polishing induced an increase in ductility – due to the removal of critical surface defects – as well as a significant increase of the apparent yield strength – caused by the removal of a ~150µm rough surface layer that can be considered as mechanically inefficient and not supporting any tensile load. Thermal post-treatments were performed on electron beam melted specimens, revealing that subtransus treatments induce very moderate microstructural changes, whereas supertransus treatments generate a considerably different type of microstructure, due to the fast β grain growth occurring above the transus. The heat treatments investigated in this work had a relatively moderate impact on the mechanical properties of the parts.
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•A method of removing microplastics by magnetic carbon nanotubes was proposed.•Excellent performance of 100% removal was achieved for microplastics.•The mechanism of magnetic carbon ...nanotubes adsorption had been deeply discussed.•The recovering of magnetic carbon nanotubes and reusability were also investigated.
Microplastics (MPs), as reservoirs of cocktail of contaminants, impose severe impacts on human and ambient water environment. Therefore, efficient and eco-friendly MPs removal techniques are urgently needed. In this study, for the first time, magnetic carbon nanotubes (M−CNTs) have been synthesized as adsorbates to remove MPs. M−CNTs were effectively adsorbed on polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA) and all the MPs/M−CNTs composites were readily separated from aqueous solutions by magnetic force. When the 5 g⋅L−1 of M−CNTs was added, target MPs (5 g⋅L−1) were completely removed within 300 min. The maximum adsorption capacities of PE, PET and PA were 1650, 1400 and 1100 mg-M−CNTs⋅g−1, respectively. This process was hardly affected by the COD, NH3-N, and PO43− substance and all MPs were completely removed from the wastewater discharged from a kitchen waste treatment plant. Furthermore, the adsorbed M−CNTs can be recycled via thermal treatment (600 °C) and these M−CNTs were featured with the same magnetic properties and comparable MPs removal capacity to the original ones. After being used for four times, M−CNTs were still able to remove ~80% of total MPs in the testing solution. The observed effectual removal of MPs from prepared solutions and wastewater highlights M−CNTs as promising techniques for the control of MPs pollution.
This paper presents the results from a recent investigation into the impact of thermal etching and oxidation on grain growth across the surface and bulk of carbon steel during heat treatment. The ...study used in situ high temperature Scanning Electron Microscopy imaging, facilitated by a novel heat stage, to capture microstructural changes during heat treatments between 800 and 920 °C. The key observations made using this surface imaging included oxidation, the formation and development of thermal etching, and grain boundary movement. In situ data were further supported by ex situ compositional and optical microstructural data obtained by first sectioning the bulk material. Comparison between the results highlighted a significant discrepancy between the surface and bulk grain growth of the specimens during heat treatment at all temperatures. Further investigation concluded that the combination of thermal etching and oxidation lead to the retardation of grain growth on the surface of the carbon steel, but that grain growth in the bulk specimen appeared to be unaffected. The mechanism that causes the grain retardation is not dissimilar to that of Zenner pinning, where in this case oxide particles pin the newly exposed etched grain boundaries. Hence, oxidation formation within the boundaries decreases the energy of the overall system resulting in movement of the grain boundary becoming less energetically favourable. It is anticipated that these findings will be used to improve understanding of the surface effects that occur during the heat treatment of carbon steel in a vacuum environment.
In order to improve the tensile properties of additively manufactured Ti-6Al-4V parts, specific heat treatments have been developed. Previous work demonstrated that a sub-transus thermal treatment at ...920 °C followed by water quenching generates a dual-phase α+α′ microstructure with a high work-hardening capacity inducing a desirable increase in both strength and ductility. The present study investigates the micromechanical behavior of this α+α′ material as well as the thermal stability of the metastable α’ martensite. To that end, annealing of the α+α′ microstructure is performed and the resulting microstructural evolution is analyzed, along with its impact on the tensile properties. A deeper understanding of the micromechanics of the multiphase microstructure both before and after annealing is achieved by performing in-situ tensile testing within a SEM, together with digital image correlation for full-field local strain measurements. This approach allows the strain partitioning to be quantified at a microscale and highlights a significant mechanical contrast between the two phases. In the α+α′ microstructure, the α′ phase is softer than the α phase, which is confirmed by nanoindentation measurements. Partial decomposition of the martensite during annealing induces a substantial hardening of the α′ phase, which is attributed to fine-scale precipitation and solution strengthening. A scale transition model based on the iso-work assumption and describing the macroscopic tensile behavior of the material depending on the individual mechanical behavior of each phase is also proposed. This model enables to provide insights into the underlying deformation and work-hardening mechanisms.
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