Nanostructured transition metal dichalcogenides (TMDs) are proven to be efficient and robust earth‐abundant electrocatalysts to potentially replace precious platinum‐based catalysts for the hydrogen ...evolution reaction (HER). However, the catalytic efficiency of reported TMD catalysts is still limited by their low‐density active sites, low conductivity, and/or uncleaned surface. Herein, a general and facile method is reported for high‐yield, large‐scale production of water‐dispersed, ultrasmall‐sized, high‐percentage 1T‐phase, single‐layer TMD nanodots with high‐density active edge sites and clean surface, including MoS2, WS2, MoSe2, Mo0.5W0.5S2, and MoSSe, which exhibit much enhanced electrochemical HER performances as compared to their corresponding nanosheets. Impressively, the obtained MoSSe nanodots achieve a low overpotential of −140 mV at current density of 10 mA cm−2, a Tafel slope of 40 mV dec−1, and excellent long‐term durability. The experimental and theoretical results suggest that the excellent catalytic activity of MoSSe nanodots is attributed to the high‐density active edge sites, high‐percentage metallic 1T phase, alloying effect and basal‐plane Se‐vacancy. This work provides a universal and effective way toward the synthesis of TMD nanostructures with abundant active sites for electrocatalysis, which can also be used for other applications such as batteries, sensors, and bioimaging.
A general and facile method is developed for high‐yield, large‐scale production of water‐dispersed, ultrasmall, high‐percentage 1T‐phase, single‐layer transition metal dichalcogenide nanodots with high‐density active edge sites and clean surface, including MoS2, WS2, MoSe2, Mo0.5W0.5S2, and MoSSe, which exhibit much enhanced electrochemical hydrogen evolution reaction performances as compared to their corresponding nanosheets.
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•Proposed rotating-vibrating magnetic abrasive polishing method for double-layered internal surface finishing.•Modelled material removal process and revealed surface evolution ...mechanism.•Evaluated effects of process parameters on material removal and surface/subsurface quality.•Achieved uniform material removal on both polished surfaces and obtained damage-free surface.
Components with complex internal surfaces are increasingly important for gas and fluid flow applications in aerospace and automotive industries. Recently, as an emerging manufacturing technology, three-dimensional (3D) additive manufacturing (AM) technology enables one-step fabrication of these complex internal surfaces. Although 3D AM technology eliminates the need for complex assembly process, due to the poor surface and sub-surface integrity, achieving a favourable surface condition is challenging. Therefore, a post-polishing process is essential for these 3D AM complex internal surfaces. This paper presents a novel rotating-vibrating magnetic abrasive polishing method to finish a kind of complex internal surface which has a double-layered tube structure made by selective laser melting (SLM) of Inconel 718. The principle of the method was illustrated and the material removal process was modelled. The feasibility of the method was verified and the surface evolution mechanism under different motions was revealed. The effects of process parameters on material removal and surface quality were evaluated quantitatively. The results showed that material was uniformly removed from both of the external surface of inner tube and internal surface of outer tube. The uneven surface caused by partially melt powders during SLM process was smoothed and the surface roughness was reduced from about 7 μm Ra to less than 1 μm Ra. Relatively higher material removal efficiency and lower surface roughness were obtained through combining rotation and vibration motions. The surface quality was improved representing by the increase of surface nanohardness and release of residual stress after polishing. There was no subsurface deformation and damage observed so that a damage-free surface was obtained.
Several metallurgical issues arise during melting and solidification-based additive manufacturing (AM) methods which limit their use to only a few alloys. This study shows how capillarity-driven ...bridging can serve as a new and rapid tool of assembling powder particles into 3D structures providing the least metallurgical complexity. According to the established conceptual framework, in-situ binding agent can be derived autogenously from selective interactions of a liquid solvent with superficial layer of powder particles to form in-situ solid interparticle bridges which enables AM at ambient conditions. Magnesium (Mg) is the most difficult engineering metal to handle in all 3D AM processes in view of its intrinsic properties. Supported by transmission and scanning electron microscopies together with Fourier transform infrared and Raman spectroscopy, the introduced 3D printing concept is readily accomplished for Mg alloys by conversion of MgO film, inevitably existing on the outermost layer of Mg powder, into interparticle bridges. In the absence of pyrolysis-adapted sintering profile, these bridges fully decompose during the following sintering step which result in functional Mg parts with chemical composition same as the starting Mg powder with zero contamination, according to chemical and thermal analysis results. The introduced capillary-mediated binding of particles is simple and generic that could be extended to additively manufacture other metals, ceramics and found applications in other traditional ex-situ binder-based processes.
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The crystal phase-based heterostructures of noble metal nanomaterials are of great research interest for various applications, such as plasmonics and catalysis. However, the synthesis of unusual ...crystal phases of noble metals still remains a great challenge, making the construction of heterophase noble metal nanostructures difficult. Here, we report a one-pot wet-chemical synthesis of well-defined heterophase fcc-2H-fcc gold nanorods (fcc: face-centred cubic; 2H: hexagonal close-packed with stacking sequence of "AB") at mild conditions. Single particle-level experiments and theoretical investigations reveal that the heterophase gold nanorods demonstrate a distinct optical property compared to that of the conventional fcc gold nanorods. Moreover, the heterophase gold nanorods possess superior electrocatalytic activity for the carbon dioxide reduction reaction over their fcc counterparts under ambient conditions. First-principles calculations suggest that the boosted catalytic performance stems from the energetically favourable adsorption of reaction intermediates, endowed by the unique heterophase characteristic of gold nanorods.
To evaluate specimen size dependence on the tensile properties of additively manufactured (AM) components, various rectangular specimens, ranging from miniaturised to ASTM standard specimens, are ...machined from electron beam melted Ti-6Al-4V and used for the tensile testing. It is found that the elongation is strongly related to the sample size while the yield and ultimate tensile strengths exhibit an independent feature. Three major aspects, (i) presented location of lack of fusion, (ii) size and segregation of pores, and (iii) slimness ratio, have a synergic influence on the elongation of different specimen sizes with various cross-section area. Our findings suggest that microscale tests arise uncertainties in measurement, which must be considered in order to provide quantifiable levels of confidence when applying such tests to discriminate a material's behaviour. The experimental results and analyses provide a guideline for the design and testing of non-standard specimens for AM components.
Although two‐dimensional (2D) metal oxide/sulfide hybrid nanostructures have been synthesized, the facile preparation of ultrathin 2D nanosheets in high yield still remains a challenge. Herein, we ...report the first high‐yield preparation of solution‐processed ultrathin 2D metal oxide/sulfide hybrid nanosheets, that is, TixTa1−xSyOz (x=0.71, 0.49, and 0.30), from TixTa1−xS2 precursors. The nanosheet exhibits strong absorbance in the near‐infrared region, giving a large extinction coefficient of 54.1 L g−1 cm−1 at 808 nm, and a high photothermal conversion efficiency of 39.2 %. After modification with lipoic acid‐conjugated polyethylene glycol, the nanosheet is a suitable photothermal agent for treatment of cancer cells under 808 nm laser irradiation. This work provides a facile and general method for the preparation of 2D metal oxide/sulfide hybrid nanosheets.
Turn up the heat: Ultrathin 2D metal oxide/sulfide hybrid nanosheets in the general form TixTa1−xSyOz were prepared from TixTa1−xS2 layered bulk crystals using an electrochemical Li‐intercalation method. The nanosheets exhibit strong absorbance in the near‐infrared region, and as such are suitable for photothermal treatment of cancer cells following their modification with lipoic acid‐conjugated polyethylene glycol.
ABSTRACT
Phase engineering is arising as an attractive strategy to tune the properties and functionalities of nanomaterials. In particular, amorphous/crystalline heterophase nanostructures have ...exhibited some intriguing properties. Herein, the one-pot wet-chemical synthesis of two types of amorphous/crystalline heterophase PdCu nanosheets is reported, in which one is amorphous phase-dominant and the other one is crystalline phase-dominant. Then the aging process of the synthesized PdCu nanosheets is studied, during which their crystallinity increases, accompanied by changes in some physicochemical properties. As a proof-of-concept application, their aging effect on catalytic hydrogenation of 4-nitrostyrene is investigated. As a result, the amorphous phase-dominant nanosheets initially show excellent chemoselectivity. After aging for 14 days, their catalytic activity is higher than that of crystalline phase-dominant nanosheets. This work demonstrates the intriguing properties of heterophase nanostructures, providing a new platform for future studies on the regulation of functionalities and applications of nanomaterials by phase engineering.
RSA 905, a rapidly solidified aluminum alloy, has been widely utilized in optical, automotive, and aerospace industries owing to its superior mechanical properties such as hardness and strength ...compared to conventional aluminum alloys. However, the surface finishing of RSA 905 to achieve submicron surface roughness is quite challenging and was rarely addressed. This paper presents an experimental and analytical study on magnetic field-assisted finishing (MFAF) of RSA 905 through a systematic investigation on surface integrity in relation to the MFAF process parameters. The effect of abrasive and polishing speed conditions on material removal and surface roughness was quantitatively investigated. The surface and subsurface quality were evaluated by optical microscope and scanning electron microscope (SEM) observations, residual stress measurement, surface microhardness and tribology test. The results show that relatively high material removal and low surface roughness were obtained under conditions using the SiC abrasive with a grit size of 12 µm at polishing speed of 400 rpm or using the Al₂O₃ abrasive with a grit size of 5 µm at polishing speed of 800 rpm. Heat melt layer caused by wire electrical discharge machining (EDM) during the sample preparation was removed by MFAF without inducing new subsurface damage. The MFAF process also helps release the surface residual stress and improve the tribological performance although the surface microhardness was slightly reduced.
Subwavelength gratings have been of great interest recently due to their ability to eliminate multiple orders. However, high index contrast ( Δ n ∼ 3 ) is typically achieved using metals or ...high-index dielectrics surrounded by vacuum in order to maintain good optical selectivity. Here, we theoretically propose and experimentally realize a selective subwavelength grating using an index contrast of Δ n ∼ 1.2 without vacuum. Despite its low index contrast, our simulation and experiments show that good optical selectivity is achieved using the same physics as subwavelength gratings made of high-index contrast. Such polymer-based encapsulated gratings are easier to scale up for use in large-area applications such as photovoltaics and lighting.
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