•The effects of PC modified GO on the hydration kinetics, pore structure and C-S-H gels were systematically investigated by a combination of isothermal calorimeter, MIP, nitrogen isotherm adsorption ...analysis, XPS, and NMR.•NMR results showned that the polymerization degree of C-S-H gels was increased with the incorporation of GO.•A 3D network structure of GO modified C-S-H gels was originally proposed that GO intercalated into the interlayer space of C-S-H gels through ionic bonding with Ca2+ and filled in the gel pores.
The effects of graphene oxide (GO) on the hydration kinetics, pore structure, mechanical properties, and the structure of calcium silicate hydrate (C-S-H) gels were systematically investigated by combinatorial techniques. GO can accelerate the cement hydration, refine the pore structure and increase the polymerization degree of C-S-H gels due to the nucleation effects of GO. The specific surface area of cement paste and the number of gel pores were reduced with the addition of GO. A 3D network structure of GO modified C-S-H gels was originally proposed based on the obtained results that GO could intercalate into the interlayer space of C-S-H gels through ionic bonding with Ca2+ and fill in the gel pores. A small fraction of GO (0.022 wt%) increased the 28 d compressive strength by 16.31%–25.60% at a various water to cement ratios, indicating that GO is a potential nano-reinforcing material for cement composites. The results would provide a well understanding of the reinforcing mechanisms of GO in cement composites and pave a pathway for the design of high-performance cement composites.
Molybdenum (Mo)-based compounds with properly engineered nanostructures usually possess improved reversible lithium storage capabilities, which offer great promise to boost the performance of ...lithium-ion batteries (LIBs). Nevertheless, a lack of efficient and high-yield methods for constructing rational nanostructures has largely restricted the application of these potentially important materials. Herein we demonstrate a metal–organic frameworks (MOFs) mediated strategy to successfully synthesize a series of one-dimensional Mo-based/carbon composites with distinct nanostructures. In this process, starting from well-designed MoO3 nanorods, the crystal control growth is first proposed that a layer of MOFs is achieved to be controllably grown on surfaces of MoO3, forming an obvious core–shell structure, and then the adopted precursor can be in situ transformed into MoO2 or Mo2C which are both well confined in conductive porous carbons through direct carbonization at different temperatures, where the MOFs shell serve as both carbon sources and the reactant to react with MoO3 simultaneously. Benefiting from this design, all optimized products exhibit enhanced electrochemical performances when evaluated as anode materials for LIBs, especially the hollow MoO2/C and core–shell Mo2C/C electrodes, show best reversible capacities up to 810 and 530 mAh g–1 even after 600 cycles at a current density of 1 A g–1, respectively. So this work may broaden the application of MOFs as a kind of coating materials and elucidates the attractive lithium storage performances of molybdenum-based compounds.
•Provided opportunities to identify the sole compositional effects on the strengthening of cocrfeni alloy.•Mo provides more pronounced solid solution strengthening than al and Ti.•Al and ti are more ...effective than mo in increasing grain boundary strengthening.•The labusch parameter f was quantified and a close SFE-kHP relation was observed.•Current findings present significant values toward novel alloy design.
In the current work, a parallel comparison of the influence of Al, Mo and Ti, on the microstructure and strengthening of the CoCrFeNi alloy was conducted. To achieve this, inconsistencies on variables including the extent of alloying, thermomechanical processing and property-evaluation method were avoided. Microstructurally, following cold-rolling, annealing of the 4 at.% Al-doped alloys at 800–1000 °C did not result in phase separation; nevertheless, that of the 4 at.% Mo- and Ti-doped alloys led to the respective formation of σ and η phase and, consequently, caused extra strengthening through the Orowan dislocation bypassing mechanism. Our systematic qualitative analysis and DFT calculations showed that Al and Ti are more effective than Mo in reducing the stacking fault energy (SFE) of the CoCrFeNi alloy, because they can induce more considerable deformation of electronic density, making the gliding of atomic layers easier. Following identical thermomechnical processing, Al-, Mo-, and Ti-doping causes different extent of solid solution strengthening and grain boundary strengthening. Mo causes the most pronounced solid solution strengthening but does not benefit the grain boundary strengthening; in contrast, the effectiveness of grain boundary strengthening is boosted by the doping Al and Ti. Current analyses support that Labusch instead of Fleischer mechanism is applicable to explain the differences in solid solution strengthening, and the observed differences in grain boundary strengthening arise from the different tendency of Al, Mo and Ti to reduce the SFE of CoCrFeNi. In addition, we determined the value of the dimensionless parameter f in the Labusch model for CoCrFeNi-based alloys and observed a close relation between Hall-Petch slope and SFE. Although more in-depth studies are needed to provide full and mechanistic understandings, both these findings in fact presents significant values toward designing novel single-phase high-strength CoCrFeNi-based alloys through manipulating the solid solution and grain boundary strengthening by compositional tuning.
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The microstructure and a few mechanical-related properties of a series of multi-equiatomic-cation (NbTaZr)C-based carbides, namely (NbTaZr)C, (NbTaZrW)C, (ZrNbTaHf)C and (NbTaZrHfW)C, were assessed ...to shed light into understanding the role of composition. Dense, pure and homogeneous rock-salt structured ceramics are achievable for all four compositions through spark plasma sinntering at 2200 °C for 10 min. Neither the hardness nor the fracture toughness is determined solely by the number of cations; among the four high entropy ceramics, (NbTaZrW)C exhibits the best combination of hardness and fracture toughness. Electronic structure and lattice distortion differences can explain part of the property differences, such as the lowered Young's modulus of (NbTaZrW)C and (NbTaZrHfW)C compared to (NbTaZr)C; but certainly, more in-depth theoretical investigations are needed to provide a full understanding of the effects of W and/or Hf addition on the hardness and fracture toughness of (NbTaZr)C.
•Microstructure and properties of a series of (NbTaZr)C-based ceramics were assessed and compared.•Dense, pure and homogeneous rock-salt structured HECs are achievable for all four investigated HECs.•The number of cations alone cannot determine the properties of HECs.•(NbTaZrW)C exhibits the best promising combination of hardness and fracture toughness.•This series of HECs, especially (NbTaZrW)C, can serve as the starting materials for future UHTC design.
Graphitic carbon nitride (g-C3N4, CN) has attracted increasing interests in the field of photocatalysis due to its high visible-light-response. However, its photocatalytic activity is still lower for ...degradation of refractory contaminants such as Cr(VI) and Rhodamine B (RhB) etc. Herein, we report a facile method to synthesize a novel sulfur(S)-doped CN/reduced graphene oxide (rGO) porous nanosheet (S-CN/rGO PNs) via a supramolecular self-assembling followed by a solvothermal treatment. The as-prepared porous S-CN/rGO PNs are stable with high specific surface area ∼188.5 m2g-1 and exhibit a significantly enhanced photocatalytic activity of ∼17-fold and 15-fold higher than that of bulk CN for the degradation of RhB and Cr(VI) under visible light irradiation, respectively. Typically, 50 mL of 15 mg/mL RhB can be degraded within 20 min by 10 mg S-CN/rGO PNs. The mechanism can be explained by the synergistic effect of S doping and porous structure which can effectively reduce the band gap of CN and increase the specific surface area to promote the separation and transfer of photo-generated charge carriers. The results have provided a new way to significantly enhance the photocatalytic activity of g-C3N4 for degradation of refractory contaminants.
Graphene oxide (GO) is an attractive candidate for use as a nano-reinforcement in cement composites. However, a prerequisite for GO to fulfill its function is the uniform dispersion of GO throughout ...the cement matrix. In this paper, the dispersion behavior of GO modified by lignosulfonate (LS), polycondensate of β-naphthalene sulfonate formaldehyde (PNS), and polycarboxylate superplasticizer (PC) in cement pore solution was investigated by a combination of visual observation, optical microscopy and transmission electron microscopy (TEM). Results show that GO modified by PC exhibited better dispersion in cement pore solution than LS and PNS. Zeta potential analysis demonstrated that LS and PNS failed to adsorb onto the GO surface when pH > 11, while successful attachment of PC to GO was achieved even in the alkaline environment. The dispersion mechanisms of PC modified GO were thought to be a combination of covering the surface of GO, lowering the free Ca2+ concentration and impeding the cross-linking of Ca2+ due to steric hindrance effect of PC. With the addition of PC modified GO, the fluidity and mechanical strength of cement composites were improved significantly, indicating that this dispersion route can be successfully used for the preparation of GO reinforced cement composites.
A schematic diagram of the dispersion mechanisms of PC@GO in cement pore solution is shown in this figure.
In Stage I, the strong complexation between COO− on the main chain of PC and Ca2+ in cement pore solution was responsible for the sharp increase in zeta potential (Fig. a). This interaction resulted in lowering the Ca2+ concentration in the system and reduced the probability of cross-linking GO sheets by free Ca2+. In addition, the steric hindrance effect provided by PEO side chains could prevent Ca2+ from approaching GO sheets. For these reasons, the stability of GO in cement pore solution was significantly improved.
After adsorption saturation of Ca2+ on the main chain of PC (Fig. b), free Ca2+ ions gradually overcame the steric hindrance effect of PEO side chains and reached the surface of GO, which could be linked to the gradual increase of the zeta potential in Stage II (Fig. c). Unfortunately, the adsorbed Ca2+ cross-linked the adjacent GO sheets to form agglomerates (Fig. d).
The decline of zeta potential in Stage III was believed to be attributed to the desorption of PC from the GO surface, as shown in Fig. e. The specific surface area of GO dramatically decreased with the formation of agglomerates, leading to a reduction in the number of active sites for PC adsorption. Afterwards, severe GO agglomerates were found since the steric hindrance effects provided by PC became dissipated, as shown in Fig. f.
According to the above analysis, the dispersion mechanisms of PC@GO were considered to be a combination of lowered free Ca2+ concentration due to the strong complexation between PC and Ca2+ and steric hindrance effect provided by PEO side chains. Display omitted
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•Graphene oxide induces synthesis of button-shaped amorphous Fe2O3/rGO/CNFs films.•The am-Fe2O3/rGO/CNFs shows a capacity of 584 mA h g−1 at 2 A g−1 after 400 cycles.•The film ...exhibits good flexibility and can be utilized as flexible anodes for LIBs.•The hierarchical structure accounts for the excellent electrochemical performance.
Constructing high-performance flexible lithium-ion batteries (LIBs) is imperative to satisfy the rapid demand of flexible and wearable electronics. Herein, we demonstrate a novel strategy to fabricate button-shaped amorphous Fe2O3/rGO/carbon nanofibers (am-Fe2O3/rGO/CNFs) films as freestanding flexible anodes for LIBs through in-situ electrospinning and subsequent one-step carbonization. Intercalating highly oxidized GO into the electrospun precursor not only induces tight growth of button-shaped amorphous Fe2O3 nanoparticles onto rimous CNFs matrix, but also substantially enhances the mechanical flexibility of the resulting films. Owing to the distinctive hierarchical structure, especially amorphous nature of Fe2O3 and intimate connection between am-Fe2O3 and the conductive substrate, the am-Fe2O3/rGO/CNFs-20 film delivers an excellent reversible capacity of 811 mA h g−1 at 0.1 A g−1, as well as remarkable rate performance and cycling stability (584 mA h g−1 over 400 cycles at a high current density of 2 A g−1). The electrode also exhibits impressive flexibility, which can power an array of light-emitting diodes, even bended and folded, demonstrating great potential for flexible LIBs. The facile synthesis strategy and excellent electrochemical performance endow it with great potential for application in flexible energy storage.
A series of macrocyclic multinucleating phenoxyimine ligands and the corresponding neutral binuclear (2-Ni 2 ) and trinuclear (3-Ni 3 ) nickel catalysts have been efficiently synthesized. The ...trinuclear nickel complex 3-Ni 3 showed high activity, high thermal stability, and slow chain transfer in ethylene polymerization, thus producing polyethylene with high molecular weight and low branch density. Highly regiospecific and isospecific polymerization of propylene was also achieved with 3-Ni 3 , generating regioregular and highly isotactic propylene with high T m and crystallinity. This is the first example of regio- and stereocontrolled propylene polymerization promoted by nickel phenoxyimine catalysts. Statistical analysis suggested selective 1,2-insertion and enantiomorphic site control mechanism in the chain propagation step, likely caused by the unique steric effect of macrocyclic ligands and the potential cooperative effect.
Effects of Al addition (0.0, 0.5, 3.0, 7.2 wt%) on microstructure, texture and mechanical properties of Mg-3.5Ca based alloys were investigated. Our results revealed that the addition of Al to the ...as-cast Mg-3.5Ca alloy resulted in the transformation of precipitated secondary phase from Mg2Ca to (Mg, Al)2Ca, Al2Ca and even Mg17Al12 phase. Moreover, the as-cast microstructure evolution influenced dynamic recrystallization and texture formation in the subsequent extrusion process. As Al content increased from 0.0 to 7.2 wt%, the elongation to fracture (EL) of as-extruded Mg-3.5Ca alloy was monotonously increased from 1.9% to 9.8% in tension, while counterparts were changeless in compression. As-extruded Mg-3.5Ca-3.0Al alloy showed higher yield and ultimate strength increased by about 42.2 MPa and 71.4 MPa than those of extruded Mg-3.5Ca alloy in tension, respectively. Moreover, when Al addition was up to 7.2 wt%, both tensile yield strength and ultimate tensile strength were in steep decline. The effects of Al addition on compressive mechanical properties (compressive yield strength and ultimate compressive strength) were similar to that in tension. Especially, significantly deteriorated tension-compression asymmetry (TCA) of Mg-3.5Ca-7.2Al alloy was ascribed to grain coarsening and secondary phase transformation. Besides, Al addition also had a significant impact on the hardening capacity (Hc) and strain hardening behavior of Mg-3.5Ca alloy. In particular, as 7.2 wt% Al was added, the hardening capacity of the Mg-3.5Ca alloy was significantly increased from 0.09 to 0.56 in tension. As a result, proper Al addition to Mg-3.5Ca alloy could improve the comprehensive mechanical performance, whereas excessive Al addition not only significantly decreased the strength, but also deteriorated the TCA performance.
Molecules with luminescence have been extensively investigated, but the luminescence of a stable molecule with a triplet ground state has not been observed. Synthesis of boron-containing radicals has ...attracted lots of interest because of their unique electronic structures and potential applications in organic semiconductors. Though some boron-based diradicals have been reported, neutral boron-containing diradicals with triplet ground states are rare. Herein two borocyclic diradicals with different substituents (
3
and
4
) have been isolated. Their electronic structures were investigated by EPR and UV spectroscopy, and SQUID magnetometry, in conjunction with DFT calculations. Both experiment and calculation suggest that
3
is an open shell singlet diradical while
4
is a triplet ground state diradical with a large singlet-triplet gap (0.25 kcal mol
−1
). Both diradicals show multi fluorescence peaks (
3
: 414, 431, and 470 nm;
4
: 420, 433, and 495 nm).
3
displays multiple redox steps and is a potential material towards the design of high-density memory devices.
4
represents the first example of a neutral triplet boron-containing diradical with a strong ferromagnetic interaction, and also is the first stable triplet diradical emitter.
Stable borocyclic diradical emitters with a tunable ground state.
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