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•Hollow Ni − P amorphous alloy nanospheres were prepared by electroless plating method.•Such hollow catalyst showed a good potential in hydrogenation of sugars to polyols.•Such hollow ...catalyst has the advantages of easy handling and accessibility.•Such hollow catalyst provides more active sites for catalytic reaction.•Such hollow catalyst possesses more electron-enriched inner surface.
In this paper, hollow Ni − P nanospheres (NSs) are prepared through Ni electroless plating on the Au-activated silica NSs externally covered by aminopropyl moieties, followed by removing the silica template with sodium hydroxide. With various characterizations, the resulting hollow Ni − P NSs are identified to be amorphous alloy. During liquid-phase hydrogenation of sugars to sugar alcohols, the hollow Ni − P amorphous alloy NSs delivered much superior catalytic performances to the commercial Raney Ni catalyst, showing a good potential in practical applications. Of particular interest is the unique hollow chamber structure of the hollow Ni − P amorphous alloy NSs, which allows for improving catalytic activity and durability relative to those associated with the dense Ni − P amorphous alloy NSs. This work demonstrated that such hollow Ni materials with nanoporous chamber structure displayed advantages such as easy experimental handling and high accessibility for the reactants in liquid-phase reaction, more Ni active sites, as well as the existence of more electron-enriched inner surface, which is essential to provide highly efficient catalysts for some reactions.
Mesoporous metals have shown significant potential for use in catalysis; however, controllably synthesizing highly ordered mesoporous amorphous alloys is a serious challenge. In this paper, a ...synthesis strategy was developed for generating ordered amorphous alloy nanowire arrays from mesoporous Ni-P by combining mesoporous silica templating with electroless plating. Mesoporous silica is externally grafted with -CH
and internally covered with -NH
acting as an efficient template, ensuring the formation of Ni-P nanowires inside the pore channels and endowing the final product with an ordered mesoporous array structure. The resulting ordered mesoporous Ni-P amorphous alloy nanowire arrays were subjected to a liquid-phase sugar hydrogenation to polyols and exhibited a highly superior catalytic performance (97% glucose conversion and 94% maltose conversion) within 4 h at 4 MPa hydrogen pressure and 373 K relative to those reference catalysts, including conventionally prepared Ni-P amorphous alloy nanoparticles (87% glucose conversion and 86% maltose conversion), ordered mesoporous Ni nanowire arrays (90% glucose conversion and 87% maltose conversion), and the commercial Raney Ni catalyst (76% glucose conversion and 66% maltose conversion). According to a comparative study, the enhanced catalytic efficiencies can be ascribed to the integration of amorphous alloy properties and mesoporous material characteristics. The composition- and morphology-controllable synthesis presented here might supply a general synthetic methodology for rationally designing ordered mesoporous amorphous alloys for a broader range of applications.
Evaluating the delamination process in the synthesis of MXenes (2D transition metal carbides and nitrides) is critical for their development and applications. However, the preparation of large ...defect‐free MXene flakes with high yields is challenging. Here, a power‐focused delamination (PFD) strategy is demonstrated that can enhance both the delamination efficiency and yield of large Ti3C2Tx MXene nanosheets through repetitive precipitation and vortex shaking processes. Following this protocol, a colloidal concentration of 20.4 mg mL–1 of the Ti3C2Tx MXene can be achieved after five PFD cycles, and the yield of the basal‐plane‐defect‐free Ti3C2Tx nanosheets reaches 61.2%, which is 6.4‐fold higher than that obtained using the sonication–exfoliation method. Both nanometer‐thin devices and self‐supporting films exhibit excellent electrical conductivities (≈25 000 and 8260 S cm‐1 for a 1.8 nm thick monolayer and 11 µm thick film, respectively). Hydrodynamic simulations reveal that the PFD method can efficiently concentrate the shear stress on the surface of the unexfoliated material, leading to the exfoliation of the nanosheets. The PFD‐synthesized large MXene nanosheets exhibit superior electrical conductivities and electromagnetic shielding (shielding effectiveness per unit volume: 35 419 dB cm2 g–1). Therefore, the PFD strategy provides an efficient route for the preparation of high‐performance single‐layer MXene nanosheets with large areas and high yields.
A new method for the preparation of large 2D Ti3C2Tx MXene nanosheets is reported. The method is based on conventional etching followed by repetitive precipitation and vortex shaking process, which efficiently transfer the mechanical energy for exfoliation. Consequently, large defect‐free sheets that show an excellent electromagnetic shielding performance are produced with high yields.
The microstructure and mechanical behavior of low-carbon ultrafine grain steel (UFG; 0.165 wt pct carbon) after niobium (Nb) addition were investigated. It was found that the addition of 0.028 wt pct ...of Nb resulted in the optimal tensile strength of 990.8 MPa with an adequate elongation of 15.5 pct. In comparison to the normal UFG steel (without Nb), the strength of Nb-UFG steel was substantially enhanced without any sacrifice of its elongation. The main increased strengthening mechanisms of Nb-UFG steel were precipitation and dislocation strengthening. The improved work hardening and adequate elongation of Nb-UFG steel could be ascribed to geometrically necessary dislocations and heterogeneous ferrite grains. Discontinuous static recrystallization occurred by a small rolling reduction on hardened martensite laths, resulting in the formation of heterogeneous ferrite grains. Ultrafine ferrite grains were surrounded by high-angle grain boundaries, and nanoscale Nb(C, N) carbonitrides providing precipitation strengthening were precipitated mainly in the
α
-phase.
The effects of niobium (Nb) on the thermal stability and mechanical properties of a low-carbon ultrafine grain steel (UFG) were investigated. Results indicate that compared to the Nb-free UFG steel, ...the dissolved Nb in the Nb-UFG steel before annealing was beneficial to improve the thermal stability and strength but harmful to plasticity. The grain boundaries movement was inhibited by numerous Nb(C, N) particles re-precipitated during annealing, leading to the refined ferrite grains, subsequently the higher thermal stability and strength of the Nb-UFG steel. The decreased elongation was attributed to the finer ferrite grains and coarse Fe
3
C particles. However, the thermal stability and strength of the Nb-UFG steel were also enhanced without any elongation sacrifice when Nb was partially dissolved in matrix before annealing. The superior balance between strength and ductility is ascribed to the precipitation strengthening of fine Nb(C, N) particles, appropriate ferrite grain size and finer Fe
3
C particles. In addition, although the thermal stability of the steel with completely solute Nb before annealing was better than that with partially solute Nb, the strength and elongation of the former decreased due to the inferior work hardening ability caused by finer ferrite grains and larger Fe
3
C particles.
Graphical Abstract
The heat treatments with different quenching and tempering temperatures were conducted to clarify the effects of Q&T (quenching and tempering) parameters on phase transformation, microstructure, ...precipitation, mechanical properties in an oil casing steel. Results reveal that the optimum property of tensile strength of 1071 MPa and elongation of 16.62% was obtained at quenching temperature of 920°C and tempering temperature of 715°C. The volume fraction of carbides decreased with quenching temperature and increased with the tempering temperature. The increased volume fraction of carbides at a higher tempering temperature contributes to the higher strength by precipitation strengthening. The decreased strength at a higher quenching tempering temperature originates from the larger prior austenite grains and concomitantly decreased volume fraction of carbides. Moreover, with the increase of tempering temperature, the carbides transformed from needle or rod-like shapes to almost spherical. And the apparent yield point appeared in the specimen quenched at 920°C and tempered at 715°C due to interaction between dislocations and carbide particles during deformation.
The work hardening behavior of α + θ UFG steel related to α + θ two phase microstructure is more complicated than that of single-phase materials. Very few studies have been conducted on the work ...hardening of α + θ UFG steels. Therefore, it is necessary to study the correlation between the work hardening and α + θ microstructure. In this study, the work hardening behavior of low-carbon ultrafine grain (UFG) steels with different grain size of ferrite and cementite particles, fabricated by rolling and annealing process, was studied. The α grain size was decreased to 132 ± 11 and 200 ± 19 nm in specimens cryorolled and annealed at 450 and 550 °C, which were smaller than that in specimen cold-rolled and annealed at 550 °C. However, the specimen cryorolled and annealed at 550 °C had a tensile strength of 740.3 MPa, which was lower than that in the other specimens. Results indicate that the work hardening is affected by ferrite and cementite in the UFG steels. The relatively coarse ferrite phase and the large number of fine intragranular cementite particles contribute to better work hardening. The intragranular cementite particles play a significant role in the improvement of work hardening, because the geometrically necessary dislocations are apt to form and store around intragranular cementite particles, while the intergranular cementite particles result in the decreased dislocation accumulation ability of ferrite and impair the strength of grain boundaries and work hardening of ferrite + cementite ultrafine grain steels.
A facile in situ one-step route for the preparation of platinum nanoparticles supported on metal–organic frameworks (MOFs) without adding stabilizing agents was developed. The obtained 10% Pt@MOF-T3 ...material possessed a large surface area and high crystallinity. Meanwhile, uniform and well-dispersed platinum nanoparticles were formed inside the cavities of MOFs, which could be attributed to the efficient complexation and stabilization effect derived from the dipyridyl groups. The as-synthesized 10% Pt@MOF-T3 sample showed high activity and selectivity in the hydrogenation of 5-hydroxymethylfurfural (HMF). This excellent catalytic performance could be attributed to the synergistic effects of well-dispersed platinum nanoparticles and electron donation offered by MOFs. Meanwhile, the presence of bipyridine ligands in the MOF framework avoided the irreversible adsorption of the hydrocarbon compounds, leading to the enhanced catalytic efficiency. Besides, it was easily recycled and reused at least five times, showing good recyclability.
A novel bifunctional ordered phenolic resin with Brønsted acid and Lewis acid sites (Yb(OTf)2/PhSO3H-MPR) was prepared for the first time by a two-step sulfonation and postgrafting protocol. The ...Brønsted acids (benzenesulfonic acids) were transformed from the phenyl groups that existed in the skeleton of ordered mesoporous phenolic resin. Meanwhile, the benzenesulfonic acids can coordinate with Yb(OTf)3 compound, resulting in the generation of Lewis acids in the pore channels of ordered phenolic resin. Yb(OTf)2/PhSO3H-MPR sample retained large specific surface and well-ordered hexagonal mesopores. As expected, it can promote one-pot cascade reaction by using glucose as the reactant to produce 5-hydroxymethylfurfural with good conversion and moderate selectivity. This synergistic catalytic performance could be attributed to its uniformly distributed Brønsted–Lewis acids. Meanwhile, the intrinsic hydrophobic pore surface can decrease the interference of water solvent, leading to enhanced catalytic efficiency. Besides, it was reused more than five times, showing good stability in water.
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