Stacking Of Nanosheets Research Articles

Scalable Synthesis of Few-Layer MoS2 Incorporated into Hierarchical Porous Carbon Nanosheets for High-Performance Li- and Na-Ion Battery Anodes.

It is still a challenging task to develop a facile and scalable process to synthesize porous hybrid materials with high electrochemical performance. Herein, a scalable strategy is developed for the synthesis of few-layer MoS2 incorporated into hierarchical porous carbon (MHPC) nanosheet composites as anode materials for both Li- (LIB) and Na-ion battery (SIB). An inexpensive oleylamine (OA) is introduced to not only serve as a hinder the stacking of MoS2 nanosheets but also to provide a conductive carbon, allowing large scale production. In addition, a SiO2 template is adopted to direct the growth of both carbon and MoS2 nanosheets, resulting in the formation of hierarchical porous structures with interconnected networks. Due to these unique features, the as-obtained MHPC shows substantial reversible capacity and very long cycling performance when used as an anode material for LIBs and SIBs, even at high current density. Indeed, this material delivers reversible capacities of 732 and 280 mA h g(-1) after 300 cycles at 1 A g(-1) in LIBs and SIBs, respectively. The results suggest that these MHPC composites also have tremendous potential for applications in other fields.

Ultrathin Li4Ti5O12 Nanosheets as Anode Materials for Lithium and Sodium Storage.

Ultrathin Li4Ti5O12 (LTO) nanosheets with ordered microstructures were prepared via a polyether-assisted hydrothermal process. Pluronic P123, a polyether, can impede the growth of Li2TiO3 in the precursor and also act as a structure-directing agent to facilitate the (Li1.81H0.19)Ti2O5·2H2O precursor to form the LTO nanosheets with the ordered microstructure. Moreover, the addition of P123 can suppress the stacking of LTO nanosheets during calcining of the precursor, and the thickness of the nanosheets can be controlled to be about 4 nm. The microstructure of the as-prepared ultrathin and ordered nanosheets is helpful for Li(+) or Na(+) diffusion and charge transfer through the particles. Therefore, the ultrathin P123-assisted LTO (P-LTO) nanosheets show a rate capability much higher than that of the LTO sample without P123 in a Li battery with over 130 mAh g(-1) of capacity remaining at the 64C rate. For intercalation of larger size Na(+) ions, the P-LTO still exhibits a capacity of 115 mAh g(-1) at a current rate of 10 C and a capacity retention of 96% after 400 cycles.

Self-Assembly of Cetyltrimethylammonium Bromide and Lamellar Zeolite Precursor for the Preparation of Hierarchical MWW Zeolite

Construction of hierarchical zeolite catalysts from lamellar zeolite precursor is challenging and promising for industrial catalysis. Although numerous efforts have been dedicated to control the organization of zeolite nanosheets by postsynthetic approaches or employing complex surfactants in hydrothermal synthesis, there is still no successful case that the hierarchical lamellar zeolite is hydrothermally synthesized by the self-assembly of the commercially available simple surfactant cetyltrimethylammonium bromide (CTAB) and inorganic zeolite precursor. In traditional syntheses, the self-assembly of simple surfactants and the growth of microporous framework are hardly compatible from both thermodynamic and kinetic viewpoints, preferring to cause phase separation. Herein, we approach for the first time the hydrothermal synthesis of a mesostructured multilamellar zeolite ECNU-7P, consisting of an alternative stacking of inorganic MWW zeolite nanosheets and organic CTAB layers with large interlayer spacing ...

Preparation of NiO Nanosheets by Hydrothermal Method and its Electrochemical Capacitive Properties

The precursor Ni (OH)2 was synthesized by a simple hydrothermal method with NiSO4•6H2O and (CH2)6N4 as reactants. Both concentrations of reactants are 0.02 M, 0.04 M, 0.06 M, 0.08 M for experiment contrast, and then NiO was gained after calcination at 400°C. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The electrochemical capacitive characterization was performed using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrical impedance spectroscopy (EIS) measurements in a 6mol/L KOH aqueous solution electrolyte. The result shows that with the increase of concentrations of reactants, nanosheets stack together and turn into thick slices. CV curves have obvious redox peak, the GCD curves are nonlinear and EIS curves of high frequency area are semicircle. From electrochemical analysis, the capacitance type is pseudocapacitance. And a maximal specific capacitance value when two reactants concentration both are 0.08 M which the specific capacitance decreases from 97 F/g (at a current density of 0.3A/g) to 56 F/g (at a current density of 1 A/g).

Flat-on ambipolar triphenylamine/C60 nano-stacks formed from the self-organization of a pyramid-sphere-shaped amphiphile.

A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C60), was synthesized. Structural characterization indicates that this pyramid-sphere-shaped amphiphile (TPA-C60 ) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C60 nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C60-C60 interactions and the ordered phase could not be reformed from the TPA-C60 melt. Oriented crystal arrays of TPA-C60 , which contain flat-on TPA/C60 nano-stacks, can be obtained via a PDMS-assisted crystallization (PAC) technique. The flat-on dual-channel supramolecular structure of TPA-C60 delivered ambipolar and balanced charge-transport characteristics with an average μe of 2.11 × 10-4 cm2 V-1 s-1 and μh of 3.37 × 10-4 cm2 V-1 s-1. The anisotropic charge-transport ability of the pyramid-sphere-shaped amphiphile was further understood based on the lattice structure and the lattice orientation of TPA-C60 revealed from electron diffraction analyses.

Flattening sol–gel nanospheres into a carbon sheet-intercalated cobalt/carbon/cobalt sandwich-nanostructure

Uniform cobalt/carbon/cobalt sandwich-like nanosheet stacks have been constructed by using sol–gel nanospheres covered with CoII–CoIII–LDH as a precursor.

Synergistic Effects in Nanoengineered HNb3O8/Graphene Hybrids with Improved Photocatalytic Conversion Ability of CO2 into Renewable Fuels.

Layered HNb3O8/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores were fabricated via the reorganization of exfoliated HNb3O8 nanosheets with graphene nanosheets (GNs). Numerous interfaces and pores were created by the alternative stacking of HNb3O8 nanosheets with limited size and GNs with a buckling and folding feature. The photocatalytic conversation of CO2 into renewable fuels by optimized HNb3O8/G hybrids yields 8.0-fold improvements in CO evolution amounts than that of commercial P25 and 8.6-fold improvements than that of HNb3O8 bulk powders. The investigation on the relationships between microstructures and improved photocatalytic performance demonstrates that the improved photocatalytic performance is attributed to the exotic synergistic effects via the combination of enhanced specific BET surface area, increased strong acid sites and strong acid amounts, narrowed band gap energy, depressed electron-hole recombination rate, and heterogeneous interfaces.

Few-layer MoS2 nanosheets incorporated into hierarchical porous carbon for lithium-ion batteries

In order to overcome the serious stacking and poor conductivity of graphene-like MoS2 nanosheets, we have developed the synthesis of few-layer MoS2 nanosheets incorporated into biomass-derived hierarchical porous carbon frameworks (labeled as MoS2/C hybrids) utilizing the strong water-absorbing power of auricularia from its inherent rich porous structure. The as-obtained MoS2/C hybrids, when applied as lithium-ion batteries anode materials, show an improved specific capacity of 707.4mAhg−1 compared with the commercial MoS2 nanosheets (580.2mAhg−1) and the corresponding hierarchical porous carbon (215.5mAhg−1). More meaningfully, they possess an impressive cycle life, almost without capacity fading even after 500 cycles at 1600mAg−1. The intriguing performance is mainly attributed to the well-dispersion of few-layer MoS2 nanosheets into hierarchical porous carbon. We believe this work will provide a new insight on the design and synthesis of novel carbon-based electrode materials for potential applications in lithium-ion batteries and other clean energy devices.

3D Graphene Hollow Nanospheres@Palladium‐Networks as an Efficient Electrocatalyst for Formic Acid Oxidation

Graphene has served widely as a support material for noble metal nanoparticle electrocatalysts in fuel cells. During the synthesis of electrocatalysts, however, the intense stacking and folding of graphene nanosheets decreases the utilization and activity of electrocatalysts, owing to the following aspects: i) the noble metal wrapped by the winding graphene cannot be fully utilized; ii) the structural destruction of graphene decreases the specific surface area and increases electrical resistance; and iii) the hydrophobicity and wrinkles of graphene greatly increase the mass transfer resistance of fuel molecules and electrolytes. In this work, 3D graphene oxide hollow nanospheres are designed to minimize wrinkles, maximize specific surface area, and realize the regular clipping of 2D graphene oxide. The 3D‐reduced graphene oxide hollow nanosphere supported Pd‐network nanohybrids (3D‐RGO/Pd‐NWs) are then obtained using 3D graphene oxide hollow nanospheres as a reaction precursor. The skeleton of 3D‐RGO not only acts as an exclusive inner conducting shell to promote electron and ion kinetics but is also crucial for enhancing the permeation of fuel molecules and electrolytes. Therefore, 3D‐RGO/Pd‐NWs exhibit enhanced electrocatalytic activity and durability for the formic oxidation reaction in an acidic medium compared to 2D graphene supported Pd nanoparticles and commercial Pd/C electrocatalysts.

Transformation of graphene oxide by ferrous iron: Environmental implications.

Abiotic transformation of graphene oxide (GO) in aquatic environments can markedly affect the fate, transport, and effects of GO. The authors observed that ferrous iron (Fe[II])-an environmentally abundant, mild reductant-can significantly affect the physicochemical properties of GO (examined by treating aqueous GO suspensions with Fe(2+) at room temperature, with doses of 0.032 mM Fe(2+) per mg/L, 0.08 mM Fe(2+) per mg/L, and 0.32 mM Fe(2+) per mg/L GO). Microscopy data showed stacking of GO nanosheets on Fe(2+) treatment. Spectroscopy evidence (X-ray diffraction, Fourier transform infrared transmission, Raman and X-ray photoelectron spectroscopy) showed significant changes in GO surface O-functionalities, in terms of loss of epoxy and carbonyl groups but increase of carboxyl group. The reduction mechanisms were verified by treating model organic molecules (styrene oxide, p-benzoquinone, and benzoic acid) resembling O-containing fragments of GO macromolecules with Fe(2+). With sedimentation and adsorption experiments (using bisphenol A as a model contaminant), the authors demonstrated that Fe(2+) reduced GOs still maintained relatively high colloidal stability, whereas their adsorption affinities were significantly enhanced. Thus, reduction of GO by mild reductants might be of greater environmental concerns than by stronger reducing agents (e.g., N2H4 and S(2-)), because the latter can result in too significant losses of surface O-functionalities and colloidal stability of GO. This interesting aspect should be given consideration in the risk assessment of GO.

Carbon nanofibers synthesized by pyrolysis of chloroform and ethanol mixture

Platelet graphite nanofibers (PGNFs) and turbostratic carbon nanofibers (TSCNFs) were synthesized by the pyrolysis of 3 and 10 vol% chloroform in ethanol, respectively, in the presence of Ni catalyst at 700 °C. Auger electron spectrometry analysis reveals that the participation of chloroform in the synthesis led to Ni–Cl bonding on the surface of the catalysts, resulting in a relatively poor crystalline layer and a coarse surface. Furthermore, the Ni–Cl compound affected the melting point and mobility of Ni, changing the morphology and geometrical shape of Ni particles. A low amount of chlorine in the catalyst led to the formation of smaller catalyst particles with a flat surface, resulting in graphene nanosheets stacked perpendicular to the fiber axis, which became PGNFs. In contrast, a high amount of chlorine in the catalyst led to the aggregation of the catalyst and thus the formation of large catalyst particles with a rough surface, resulting in the random stacking of graphene nanosheets, which became TSCNFs. The participation of chlorine was found to be important in the synthesis of the PGNFs and TSCNFs.

Nanodiamond/nitrogen-doped graphene (core/shell) as an effective and stable metal-free electrocatalyst for oxygen reduction reaction

Nitrogen-doped graphene (N-G) covering a nanodiamond (ND) was prepared via the thermal conversion of ND followed by a new post-doping treatment. Compared with conventional N-G, the core-shell structure of ND/N-G weakened the stacking of graphene nanosheets. Meanwhile the prepared ND/N-G showed a high level of electrocatalytic activity for oxygen reduction reaction (ORR) and a high electrochemical stability. No metal impurities are expected to be introduced into the N-G through this treatment. There is strong support for N-doped as an important factor to enhance the ORR electrocatalytic activity of carbon materials.

Rate and mechanism of the photoreduction of birnessite (MnO2) nanosheets

The photoreductive dissolution of Mn(IV) oxide minerals in sunlit aquatic environments couples the Mn cycle to the oxidation of organic matter and fate of trace elements associated with Mn oxides, but the intrinsic rate and mechanism of mineral dissolution in the absence of organic electron donors is unknown. We investigated the photoreduction of δ-MnO2 nanosheets at pH 6.5 with Na or Ca as the interlayer cation under 400-nm light irradiation and quantified the yield and timescales of Mn(III) production. Our study of transient intermediate states using time-resolved optical and X-ray absorption spectroscopy showed key roles for chemically distinct Mn(III) species. The reaction pathway involves (i) formation of Jahn-Teller distorted Mn(III) sites in the octahedral sheet within 0.6 ps of photoexcitation; (ii) Mn(III) migration into the interlayer within 600 ps; and (iii) increased nanosheet stacking. We propose that irreversible Mn reduction is coupled to hole-scavenging by surface water molecules or hydroxyl groups, with associated radical formation. This work demonstrates the importance of direct MnO2 photoreduction in environmental processes and provides a framework to test new hypotheses regarding the role of organic molecules and metal species in photochemical reactions with Mn oxide phases. The timescales for the production and evolution of Mn(III) species and a catalytic role for interlayer Ca(2+) identified here from spectroscopic measurements can also guide the design of efficient Mn-based catalysts for water oxidation.

Bottom-Up Synthesis of Titanate Nanosheets in Aqueous Sols and Their Morphology Change by the Addition of Organic Ligands and Dialysis

The size, shape, and stacking of titanate nanosheets synthesized by heating aqueous mixtures of titanium complexes and tetrabutylammonium hydroxide were dependent on the type and amount of organic ligands and the amount of tetrabutylammonium ion (TBA+). When titanium isopropoxide was used as the titanium source, most titanate crystals were smaller than 10 nm in lateral size. However, the use of titanium complexes provided a lateral size of about 100 nm. The titanate crystals were synthesized by the acid–base reaction of titanic acid and TBAOH. The decrease in titanic acid concentration by titanium complex formation led to larger titanate crystals by the inhibition of crystal nucleation. Moreover, the use of triethanolamine and lactic acid as an organic ligand provided round and hexagonal titanate crystals, respectively. However, when the concentration of organic ligands was decreased by the dialysis of the titanate sols, the form of titanate crystals was changed to a rhombic shape. Thus, the adsorption of...

Self-Assembly Influenced by Geometrical Orientation of Nanosheet in Layered Nanoparticles

An influence of geometrical orientation of two-dimensional (2D) nanosheets on long-term rheological self-assembly with the aid of H 2 O molecules is investigated by positronium lifetime spectroscopy. It is found that self-assembly is accelerated for the well self-assembled sample due to in-plane ordering of 2D nanosheets. The acceleration of self-assembly is further enhanced for the sample prepared by uniaxial pressure compaction owing to stacking of 2D nanosheets with a highly ordered state. The present results evidence that self-assembly is significantly influenced by local geometrical orientation of 2D nanosheets in layered nanoparticles.

Nanoporous photocatalysts developed through heat-driven stacking of graphitic carbon nitride nanosheets

Nanostructured g-C3N4 with high surface area from heat treatment of guanidinium cyanurate exhibits better optical properties and enhanced photocatalytic activity.

Synthesis of inter-crystalline mesoporous ZSM-5 generated by self-interlocked MFI nanosheet stacks

ZSM-5 products with inter-crystalline mesopores originating from the SI-ONSs can be produced in the ternary composition domain established.

Fluidized‐bed CVD of unstacked double‐layer templated graphene and its application in supercapacitors

Graphene is inclined to stack with each other that greatly hinders the full utilization of its intrinsic extraordinary properties. Introducing protuberant spacers is a straightforward strategy to avoid the stacking of graphene nanosheets, resulting in a novel unstacked double‐layer templated graphene (DTG) structure. Herein, a family of layered double hydroxides were used for the bulk chemical vapor deposition (CVD) of DTG in a fluidized‐bed reactor. A high specific surface area of 1554.2 m2 g−1 and a large pore volume of 1.70 cm3 g−1 were achieved. When used as the electrode material for supercapacitors, the DTG afforded a specific capacitance of 65.5 F g−1 at a sweep rate of 5.0 mV s−1 and a capacitance retention of 77% when the sweep rate was increased to 500 mV s−1. Therefore, the DTG obtained via fluidized bed CVD is a promising electrode material for supercapacitor applications. © 2014 American Institute of Chemical Engineers AIChE J, 61: 747–755, 2015

Highly Textured Tin(II) Sulfide Thin Films Formed from Sheetlike Nanocrystal Inks

Highly textured tin(II) sulfide thin films are prepared from a nanocrystal ink comprised of high-aspect-ratio nanosheets. The orthorhombic nanosheets are synthesized colloidally to isolate lateral growth and minimize the presence of alternate crystal phases. The tin sulfide films deposited from the nanosheets exhibit pure elemental composition, micrometer-sized grains, and a remarkable degree of texturing. The films consist of lamellar stacking of nanosheets with some intercalation, and the average sheet thickness is ∼30 nm. The SnS films have an indirect band gap of 1.23 eV, and density functional theory calculations indicate minimal quantum confinement contributions. The anisotropic electronic properties of tin sulfide are greatly intensified in films formed by this process, yielding an in-plane mobility of 5.7 cm2/(V s) but an out-of-plane resistivity as high as 30 kΩ cm. This work represents a new strategy for nanocrystal inks in which the nanocrystal morphology is tailored to direct film orientation, grain size, and transport properties. The method provides a route for the deposition of high-quality, layered semiconductor thin films with applications in photovoltaics and two-dimensional (2-D) electronics.

Nanoindentation measurements of Teflon‐AF nanosheets

ABSTRACTWe report the formation of cohesive, mechanically robust thin films of Teflon‐AF formed via self‐assembly of nanoparticles at both air/water and oil/water interfaces of micro‐emulsion droplets. We also present results of morphological and mechanical investigations of thin films formed at these oil/water interfaces. Scanning electron microscope and low angle X‐ray diffraction characterization of drop cast thin films from the micro‐emulsions showed the presence of stacks of nanosheets with an average thickness of 6 nm. Atomic force microscopy (AFM) characterization put the thickness at a much lower value of around 2 nm implying that these sheets are comprised of molecular sheets of Teflon‐AF. AFM characterization also indicated that these sheets are stretched molecular films comprising inter‐diffused molecular chains, arranged in a regular fashion. Nanoindentation studies of these films unambiguously demonstrated the “tablet sliding” mechanism, similar to nacre, for dissipating applied stress. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41360.