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• The effective engineering constants of hexagonal monolayers are evaluated. • The elastic modulus of graphene-like structures is investigated in thermal environments. • The effects of force constant and temperature-dependent CTE are examined. • This efficient analytical model is introduced instead of computationally intensive methods. • The proposed method can be applied to other quasi-cellular multilayer structures. In this paper, the effective elastic properties of hexagonal monolayers such as graphene, boron nitride, silicon carbide, and aluminum nitride are evaluated using the asymptotic homogenization method taking into account temperature changes. The effective properties are determined analytically by considering temperature, force constants, bond lengths, and thickness, using atomic interactions within the context of the unit cell problem. The relationship between environmental temperature and the coefficient of thermal expansion is established by considering changes in the values ​​of bond stretching, bond angle bending, and torsion resistance constants at different temperatures from 0 to 1800 K. The results provided by the proposed homogeneous model are consistent with the valid findings of other researchers in the literature. It is found that these different hexagonal nanosheets exhibit isotropic temperature-dependent properties and their Young's and shear modulus decrease almost linearly as the temperature rises, considering a constant coefficient of thermal expansion. However, Poisson's ratio is found to be independent of temperature. Furthermore, the temperature-dependent elastic properties of these nanosheets become nonlinear when the variation of the coefficient of thermal expansion with temperature is taken into account. The Young and shear moduli of the nanosheets increase as the coefficient of thermal expansion decreases and vice versa. The highest elastic modulus values are obtained when the thermal expansion is close to its minimum threshold. However, it is recognized that the elastic modulus of graphene and boron nitride nanosheets is higher than that of silicon carbide and aluminum nitride at any temperature. As an alternative to lengthy computer modeling or rigorous testing, the homogeneous models provided can be used to simulate nanosheets. [ABSTRACT FROM AUTHOR]

In most cases, to obtain high‐performance electrode materials for lithium‐ion batteries (LIBs), it is necessary to optimize both their molecular structure and morphology. Normally, the molecular structure of covalent organic frameworks (COFs) can be well engineered by chemical design, while their morphology is mainly optimized by post‐processing. Herein, by introducing a flexible building unit containing sp3 N redox‐active centers, a bipolar‐type TP‐TA COF assembled by uniform 2D hexagonal nanosheets is synthesized in a one‐step reaction without any post‐processing, achieving the highly challenging simultaneous optimization of both molecular structure and morphology required for high‐performance electrode materials. Thus, when used as cathode material for LIBs, its combined optimized chemical structure and favorable morphology of TP‐TA COF synergistically render a high capacity (207 mA h g−1 at 200 mA g−1), excellent rate performance (129 mA h g−1 at 5.0 A g−1), and cycling stability (93% capacity retention after 1500 cycles at 5.0 A g−1). [ABSTRACT FROM AUTHOR]

Antimonene (Sb) has been widely studied owing to its high carrier mobility, high thermal conductivity, and tunable electronic properties. Conventional synthetic methods for antimonene nanosheets (Sb-NSs) are more complex and multi-step reactions, mainly including the epitaxial growth method, mechanical peeling method, electrochemical separation method, and liquid-phase separation method. Here, we report a simple method for the synthesis of Sb-NSs on Ni foam from two-dimensional (2D) nanosheets to one-dimensional (1D) nanowires via hydrothermal method. The fabricated hexagonal Sb-NSs exhibit a transverse scale of 400 nm and a thickness of approximately 50 nm. When evaluated as anode materials for lithium storage, hexagonal Sb-NSs deliver a high reversible capacity of 870.3 mAh g ^−1 at 0.2 A g ^−1 and a reversible capacity of 375 mAh g ^−1 at 0.2 A g ^−1 after 60 cycles. As a result, the successful preparation of dimensional-switching Sb-NMs provides a new class of 2D materials for LIBs.

The development of low-price and highly efficient catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has always been challenging with regard to water splitting. Pyrrhotite Fe 7 S 8 has become a research hotspot due to its abundant reserves, high electrical conductivity and excellent catalytic activity. In general, introducing metal heteroatoms into transition metal sulfides (TMSs) can effectively enhance the activity and stability of TMSs. Herein, Co-doped pyrrhotite Fe 7 S 8 nanosheets were obtained by a straightforward two-step method consisting of hydrothermal treatment followed by subsequent heat treatment. Results from XPS analysis and contact angle measurements showed that doping optimized the chemical environment around iron atoms and enhanced the adsorption of water molecules on the surface of Fe 7 S 8 , thereby greatly improving the electrocatalytic efficiency of water electrolysis. Compared with other counterparts, Co 0 · 95 Fe 6 · 05 S 8 exhibited superior OER activity with an overpotential of 311 mV at a current density of 10 mA cm−2, and higher performance towards HER with an overpotential of 284 mV at 10 mA cm−2 in alkaline solution. In sum, Co 0 · 95 Fe 6 · 05 S 8 is promising as a bifunctional catalyst for water splitting under alkaline conditions. [ABSTRACT FROM AUTHOR]

Abstract We reported a new layered ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O which crystallizes in two-dimensional (2D) nanosheets morphology in our previous work. Herein, two-dimensional hexagonal ZnCo 2 O 4 nanosheets were synthesized by the thermal transformation of the ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O precursor. Benefiting from this special hexagonal nanosheet morphology, the as-prepared ZnCo 2 O 4 electrode has induced a pseudo-capacitance contribution, leading to a stable discharge capacity of 688 mAh g−1 (at 5.0 A g−1) over 1000 cycles. To the best of our knowledge, the rate performance of ZnCo 2 O 4 for lithium ion batteries (LIBs) is superior to those of previously reported ZnCo 2 O 4 electrodes. Further applied to sodium ion batteries, ZnCo 2 O 4 electrode show fascinating performance with the specific capacity of 463 mAh g−1 after 60 cycles. This study provides a promising strategy for developing high-quality ZnCo 2 O 4 nanosheet electrodes for long-cycle-life and high-power LIBs and sodium ion batteries (SIBs). Graphical abstract Image 1 Highlights • Hexagonal ZnCo 2 O 4 nanosheet has been synthesized from the hydroxide precursor. • Our ZnCo 2 O 4 electrode exhibits high-rate performance for lithium ion battery. • Our ZnCo 2 O 4 electrode show fascinating performance in sodium ion storage. [ABSTRACT FROM AUTHOR]

In this work, a novel two-dimensional hexagonal mesoporous nickel oxide (2D-HM NiO) and titanium substituted NiO (Ti (1, 3, 5, 7 and 9 mol%)-NiO) nanosheets (NSs) are synthesized via a one-step hydrothermal method. The as-prepared 2D-HM NiO and Ti (1–9%)-NiO NSs are used to fabricate cost-effective counter electrodes (CEs) for DSSCs. The DSSCs device made with NiO and 1% of Ti-substituted NiO (1-TNO) CEs show excellent electrochemical properties and photovoltaic performance. The 100 consecutive cycles of cyclic voltammetry (CV) shows that NiO and 1-TNO CEs have high chemical stability towards I − /I 3 − redox mediator as compared with Pt CE. For the first time, the power conversion efficiency (PCE) of DSSCs with NiO-based CE reached up to 4.08% whereas 1-TNO CE a PCE slightly increased up to 4.12% which is relatively closer to Pt-based CE (5.34%) under identical working conditions. The high performance of NiO and 1-TNO CEs can be attributed to the large number of electrocatalytic active sites and fast ion diffusion, which is due to the high specific surface area of the 2D nanosheet structure with mesoporous nature. [Display omitted] • A novel NiO and Ti (1-9%) substituted NiO nanosheets were synthesized by the one-step hydrothermal method. • The NiO and Ti (1-9%)-NiO CEs exhibit high chemical stability. • NiO and 1% of Ti- NiO counter electrodes act as the efficient electrocatalyst for species reduction. • The new record PCE of 4.08% was achieved for DSSCs fabricated with NiO CE and the PCE of 4.12% was obtained with 1-TNO CE. [ABSTRACT FROM AUTHOR]

[Display omitted] • A NaCl-assisted pyrolysis strategy is proposed for synthesizing FeNC catalysts. • 2D hexagonal N -doped carbon nanosheets supported FeN x sites was prepared. • The FeNC-NaCl-900 has a high specific surface area and micropore-hosted FeNx sites. • The FeNC-NaCl-900 achieves a high half-wave potential (0.90 V) for ORR. • The Zn/Al-air batteries equipped with FeNC-NaCl-900 exhibit excellent performances. Iron coordinated with nitrogen (FeN x) sites hosted in the micropores of carbon substrate offer excellent performance for the oxygen reduction reaction (ORR). Achieving a highly exposed and dispersed FeN x sites accessible for ORR is still challenging to date. In this work, two-dimensional hexagonal carbon nanosheets supported FeN x moieties (FeNC-NaCl- T) were synthesized via a molten NaCl-assisted pyrolysis strategy. Benefit from the high specific surface area (1371.635 m3·g−1) and highly dispersed FeN x sites, the optimized FeNC-NaCl-900 exhibits superior ORR activity with a high half-wave potential of 0.90 V in alkaline electrolyte. Impressively, with FeNC-NaCl-900 as the cathode catalyst in aqueous zinc–air battery, achieving a remarkable performance with a high peak power density of 177 mW·cm−2 and competitive durability (200 h). Furthermore, the Al-air battery equipped with FeNC-NaCl-900 attained an ultrahigh specific capacity of 2257.48 mAh·g−1 at a large discharge current of 100 mA cm−2. These findings provide guidance for the development of high performance FeNC catalysts and their applications in metal-air batteries. [ABSTRACT FROM AUTHOR]

Sheet-like precursors of Co 3O 4 and Ag/Co 3O 4 composites with different Ag contents were synthesized with assistance of triethylamine via a hydrothermal process. The final samples were fabricated by calcing each precursor at 400 °C. The as-prepared samples were identified and characterized by thermogravimetric analysis and differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy, respectively. The Co 3O 4 and Ag/Co 3O 4 composite samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The electrocatalytic results indicated that all the samples showed enhanced electrocatalytic performance for p-nitrophenol by comparing a bare glass carbon electrode, and p-nitrophenol could be reduced by Co 3O 4 at a high peak current but a rather higher peak potential but be reduced effectively by Ag/Co 3O 4 composites at lower potential. Ag/Co 3O 4 composites with 4 % Ag displayed the highest electrocatalytic activity. [ABSTRACT FROM AUTHOR]

The present work studies the mechanical properties of epoxy-based composites which are reinforced by hexagonal monolayer nanosheets such as graphene, boron nitride, silicon carbide and aluminum nitride, based on the Kalamkarov's general asymptotic homogenization composite shell model. This parametric study on total atomic interactions in the unit cell with the asymptotic homogenization method allows clearly establishing effective Young's modulus, shear modulus, Poisson's ratios and stiffness coefficients of hexagonal nanosheets and epoxy-based composites reinforced with them as functions of the force constants, bond length, thickness and volume fractions. The present homogenized sandwich-like model has simplified rules which consider interfacial forces and clears the behavior of the matrix-reinforcement interface. The results from the present homogenized model show good agreement with the trustworthy results of other researchers which are available in the literature. Moreover, the present model is useful for modeling nanostructures instead of heavy computational modeling or difficult experiments. [ABSTRACT FROM AUTHOR]

Novel single-crystal hexagonal MnTiO 3 nanosheets with exposed {0001} facets have been synthesized via a simple one-pot hydrothermal method using NaOH as a mineralizer and tetraethylammonium hydroxide (TEAH) as a morphology controller. The intermediate morphologies of MnTiO 3 nanostructures such as nanoparticles, nanowires, nanorods, and nanodiscs are trapped kinetically by adjusting the synthesis conditions. This approach enables us to elucidate the growth mechanisms of MnTiO 3 nanosheets based on the tetraethylammonium cation adsorption abilities on different MnTiO 3 crystal facets combined with density functional theory calculations. Dissolution and recrystallization processes are involved during the MnTiO 3 crystallization. The surface-controlled MnTiO 3 has been found to be effective as a catalyst for ozonation in the degradation of 4-chlorophenol (4-CP). Within typical experimental conditions (catalyst dosage = 0.3 g L -1 , [4-CP] 0 = 50 mg L -1 , [O 3 ] = 20 mg L -1 , gas flow = 0.1 L min -1 , pH 6.8, and T = 293 K), the total organic carbon (TOC) removal efficiency of 4-CP in catalytic ozonation with well-structured MnTiO 3 (MnTiO 3 -180-10 sample) was 76.3% after 60 min, compared with only 22.1 and 38.5% TOC removal in the absence of catalyst and with uncontrolled MnTiO 3 (MnTiO 3 -no TEAH sample), respectively. Benefiting from the high exposure percentage of {0001} facet, mixed-valences of manganese, surface hydroxyl groups, and the enrichment Lewis acid sites provided by Mn and Ti, the morphology-controlled MnTiO 3 nanosheets can be applied as heterogeneous catalytic ozonation catalysts which exhibit excellent pollutant degradation. We anticipate that MnTiO 3 can be a promising candidate material for the application in remediation of organic pollutants in water.