As-prepared Nanosheets Research Articles

Polyallylamine-Rh nanosheet nanoassemblies−carbon nanotubes organic-inorganic nanohybrids: A electrocatalyst superior to Pt for the hydrogen evolution reaction

Rationally tailoring the surface/interface structures of noble metal nanostructures emerges as a highly efficient method for improving their electrocatalytic activity, selectivity, and long-term stability. Recently, hydrogen evolution reaction is attracting more and more attention due to the energy crisis and environment pollution. Herein, we successfully synthesize polyallylamine-functionalized rhodium nanosheet nanoassemblies-carbon nanotube nanohybrids via a facile one-pot hydrothermal method. Three-dimensionally branched rhodium nanosheet nanoassemblies are consisted of two dimensionally atomically thick ultrathin rhodium nanosheets. The as-prepared polyallylamine-functionalized rhodium nanosheet nanoassemblies-carbon nanotube nanohybrids show the excellent electrocatalytic activity for the hydrogen evolution reaction in acidic media, with a low onset reduction potential of −1 mV, a small overpotential of 5 mV at 10 mA cm−2, which is much superior to commercial platinum nanocrystals. Two dimensionally ultrathin morphology of rhodium nanosheet, particular rhodium-polyallylamine interface, and three-dimensionally networks induced by carbon nanotube are the key factors for the excellent hydrogen evolution reaction activity in acidic media.

Impact of key geochemical parameters on the highly efficient sequestration of Pb(II) and Cd(II) in water using g-C3N4 nanosheets

Graphitic-C3N4 (g-C3N4) nanosheets were synthesized successfully and characterized by SEM, TEM, FI-TR, XRD, BET and XPS. A series of experimental results for the removal of Pb(II) and Cd(II) from wastewater were investigated. The g-C3N4 nanosheets exhibited high adsorption capacity towards Pb(II) and Cd(II), which can reach 395.54mg/g and 206.40mg/g at T=333K, pH=6.3, CNaNO3=0.01mol/L. The adsorption kinetics of Pb(II) and Cd(II) complied with the pseudo-second-order model. The Freundlich and Langmuir models were used to simulate the adsorption isotherms of Pb(II) and Cd(II), and the results revealed that the adsorption of Pb(II) on g-C3N4 nanosheets coincided with monolayer adsorption, while the Cd(II) on g-C3N4 nanosheets coincided with multilayer adsorption. The thermodynamic parameters (ΔG0<0, ΔH0>0) revealed that the adsorption process was a spontaneous endothermic process. The experimental results revealed that the as-prepared g-C3N4 nanosheets can be utilized as a friendly, efficient and economical adsorbent for the purification of wastewater.

2D TiO2 nanosheets for ultrasensitive humidity sensing application benefited by abundant surface oxygen vacancy defects

To realize the sensitive and rapid sensing of humidity, 2D as-prepared TiO2 nanosheets (hereafter shorted as TiO2 nanosheets) with characteristics of surface oxygen vacancy defects and large surface area were designed and synthesized. The TiO2 nanosheets-based sensor exhibit superior humidity sensing performance with an ultrahigh sensitivity evidenced by the dramatic impedance variation of more than four orders of magnitude from relative humidity (RH) 11% to 95%, fast response (3 s) and recovery (50 s) process, as well as a small hysteresis (∼4.6%). Additionally, a systematic study of the sensing performances of sensors fabricated from TiO2 nanosheets and two counterparts calcined in N2 and O2 with decreased specific surface area and controlled surface defects, namely TiO2-400 (N2) and TiO2-400 (O2), has been conducted. The results show that at low RH level of 33% and 54%, TiO2-400 (N2) with highest surface oxygen vacancy defects concentration exhibits the highest response of 6.26 and 34, respectively, while at high RH range of 85% to 95%, the TiO2 nanosheets with largest specific surface area shows the highest response which is almost 10 times higher than that of the calcined counterparts. Combining the complex impedance analysis, the overall ultrahigh humidity sensing performance of TiO2 nanosheets-based sensor is attributed to the dissociating promotion by the abundant surface defect and enhanced electrolytic conduction by the large specific surface area.

A sensitive electrochemical nonenzymatic biosensor for the detection of H2O2 released from living cells based on ultrathin concave Ag nanosheets

Facile synthesis of ultrathin two-dimensional metallic nanosheets with special physical and chemical properties is still challenging. In this work, ultrathin silver nanosheets were synthesized through the galvanic replacement reaction between silver nitrate and Cu microcages without using any surfactant at room temperature. The as-prepared Ag nanosheets (NSs) were concave and had a thickness of sub-10 nm. And the nanosheets exhibited excellent H2O2 detection property with a high sensitivity of about 320.3 uA mM−1 cm−2 and a low detection limit of 0.17 µM in a wide linear range of 5–6000 μM, and a fast response time (less than 2 s). Besides, the real-time detection of H2O2 induced from living HeLa and SH-SY5Y cells were also achieved, indicating the potential application of as-prepared Ag NSs in monitoring physiological and dynamic in-clinic pathological processes.

A facile synthesis of porous graphene for efficient water and wastewater treatment

The use of two-dimensional graphene-based materials in water treatment has recently gained significant attention due to their unique electronic and thermal mobility, high surface area, high mechanical strength, excellent corrosion resistance and tunable surface chemistry. However, the relatively expensive, poor hydrophobicity, low adsorption capacity and recyclability, and complex post-treatment of the most pristine graphene frameworks limit their practical application. Here, we report a facile scalable method to produce highly porous graphene from reduced graphene oxide via thermal treatment without addition of any catalyst or use of any template. Comparing to conventional graphene counterparts, as-prepared porous graphene nanosheets showed evident improvement in hydrophobicity, adsorption capacity, and recyclability, making them ideal candidate materials for water treatment. Superhydrophobic and superoleophilic porous graphene prepared in this work has been demonstrated as effective absorbents for a broad range of ions, oils and organic solvents, exhibiting high selectivity, good recyclability, and excellent absorption capacities > 90%. The synthesis method of porous graphene reported in this paper is easy to implement, low cost and scalable. These attributes could contribute towards efficient and cost-effective water purification and pollution reduction.

Silver nitrate nanosheet supported on porous carbon three-dimensional substrate as cathode material and its lithium storage mechanism

In this paper, we present the direct application of AgNO3 as a novel host material for lithium storage. Fabricated as cathode material, commercial AgNO3 particles show an initial charge capacity at 157.1 mAh g−1, and retain a capacity of only 11.5 mAh g−1 after 100 cycles. By preparing AgNO3 nanosheets supported on conductive carbon three-dimensional substrate, enhanced lithium storage performance can be achieved. As-prepared AgNO3 nanosheets exhibit the charge capacity at 141.7 mAh g−1 in the first cycle, and maintain at 82.0 mAh g−1 after 100 cycles. The three-dimensional carbon substrate with considerable strength and tenacity supporting AgNO3 nanosheets presents fast electron/ion transport, large electroactive surface area, and excellent structural stability. The reaction mechanism of AgNO3 with Li is also studied by ex situ and in situ techniques during the initial cycle. It can be concluded that lithium storage process of AgNO3 is associated with a quasi-reversible electrochemical conversion reaction. During the discharge process, the electrochemical reaction of AgNO3 with Li results in the formation of Ag and LiNO3. In the reverse charge process, AgNO3 can be re-generated by its conversion reaction. Therefore, it is anticipated that AgNO3 nanosheets can be a probable cathode candidate for lithium-ion batteries.

Ag@AgCl decorated graphene-like TiO2 nanosheets with nearly 100% exposed (0 0 1) facets for efficient solar light photocatalysis

The large scale, ultrathin and (0 0 1) facet exposed anatase two-dimensional (2D) graphene-like TiO2 nanosheets were synthesized by hydrogen-bonding-mediated. The products were employed as scaffolding and deposited Ag@AgCl nanoparticles. The crystalline phase, morphologies and optical properties of as-prepared sample were surveyed. The results indicated that the as-prepared TiO2 nanosheets only have few nanometers thick. The Ag@AgCl nanoparticles were also successfully introduced into the surface of TiO2 nanosheets. By the modified of Ag@AgCl and significant enhanced the absorption spectrum in the visible light region. To assess the photocatalytic activities of as-prepared samples, the methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) were employed to simulate the pollutants. The Ag@AgCl/TiO2 exhibited excellent photocatalysis under solar irradiation. There results suggested that, Ag@AgCl/TiO2-0.6 photocatalyst has suitable size of Ag@AgCl particles, large surface areas, abundant surface active sites and effective photogenerated electron-hole pair's separation, which significant improve the photocatalytic activities.

2D nickel oxide nanosheets with highly porous structure for high performance capacitive energy storage

Developing advanced electrochemical electrode materials with excellent performance is critical to their future energy storage devices. Herein, we design and synthesize two-dimensional (2D) porous structure nickel oxide (NiO) nanosheets via a facile and scalable hydrothermal approach, and further heating. The effects of heating time on the electrochemical performances are investigated. The results indicate that the maximum specific capacitance is achieved for NiO nanosheets when heating temperature and time are 300 °C and 3 h, respectively (namely NiO-3). The as-prepared NiO-3 nanosheet are grown uniform on the skeleton of reduced graphene oxide (rGO). The optimum NiO/rGO displays a reversible discharge capacity of 781.7 F g−1 at 1 A g−1, and shows an ultra-long life-span with over 94% capacitance retention after 4000 cycles. The enhanced electrochemical properties for NiO/rGO can be ascribed to a collaborative effect between NiO and rGO, which possess high capacitance storage ability and excellent conductivity, respectively.

Superstructure Ta2O5 mesocrystals derived from (NH4)2Ta2O3F6 mesocrystals with efficient photocatalytic activity.

Superstructured mesocrystalline Ta2O5 nanosheets were successfully prepared from mesocrystalline (NH4)2Ta2O3F6 nanorods by the annealing method for the first time. The as-prepared mesocrystalline Ta2O5 nanosheets in this work showed remarkable visible light absorption, mainly due to the formation of oxygen vacancy defects in the mesocrystalline Ta2O5 nanosheets, which was also confirmed by XPS spectra, Raman spectra and EPR spectra. Besides, the mesocrystalline Ta2O5 nanosheets showed a highly enhanced photocatalytic activity of 11 268.24 μmol g-1 h-1, about 3.95 times that of commercial Ta2O5. Moreover, the specific surface area of the mesocrystalline Ta2O5-800 nanosheets was 16.34 m2 g-1, about 5.32 times that of the commercial Ta2O5 (3.072 m2 g-1). The valence band XPS spectra indicated a strong oxidizing ability of the mesocrystalline Ta2O5 nanosheets in comparison to that of commercial Ta2O5. The formation of superstructured Ta2O5 mesocrystals generated long lifetime carriers and effective conduction pathways, which greatly enhanced the photocatalytic activity for hydrogen production.

MoS2 Nanosheets Vertically Aligned on Hierarchically Porous Graphitic Carbon for High-Performance Lithium Storage

Molybdenum disulfide (MoS2) is considered as a promising anode for next-generation Lithium-ion batteries (LIBs) due to its high theoretical capacity (∼ 670 mAh g−1). However, its low conductivity and enormous volume expansion during charge/discharge processes lead to a poor cycling stability and inferior rate performance. To address these issues, MoS2 nanosheets @ hierarchically porous graphitic carbon composite is designed and prepared by a metal compound-assisted chemical vapor deposition method combined with the hydrothermal method. The as-prepared MoS2 nanosheets @ hierarchically porous graphitic carbon composite exhibits a high reversible capacity of 1027 mAh g−1 at 0.1 A g−1, a good rate capability of 857 mAh g−1 at 1 A g−1, and an excellent cycling stability (792 mAh g−1 after 500 cycles at 1 A g−1). The outstanding performance can be attributed to the unique 3D structure of the MoS2 nanosheets @ hierarchically porous graphitic carbon composite, which not only provide more active sites and facilitate the access of ions, but also improve the conductivity and effectively suppress the volume change during the charge/discharge process.

A rechargeable aluminum-ion battery based on a VS2 nanosheet cathode.

As a typical member of transition-metal dichalcogenides (TMDs), VS2 has been evaluated as the aluminum-ion battery cathode for the first time. To further improve their stability and conductivity, the as-prepared VS2 nanosheets are modified with graphene (denoted as G-VS2). And the G-VS2 electrode delivers a high initial discharge capacity of 186 mA h g-1 at 100 mA g-1 with almost 100% coulombic efficiency after 50 cycles. Furthermore, an explicit intercalation mechanism of Al into G-VS2 has been investigated by in/ex situ XRD, ex situ Raman and TEM spectroscopy. And the G-VS2 composite proves to be an impressive cathode material for aluminum-ion batteries (AIBs). This work might put forward the application of TMDs in AIBs.

Shape-controlled synthesis of porous carbons for flexible asymmetric supercapacitors.

N-Doped carbon nanomaterials have gained tremendous research interest in energy storage because of their high capacitance and chemical stability. Here, N-doped porous carbons (NPCs) with multiple shape-controlled and tunable morphologies are developed through a direct one-step pyrolysis/activation method. Typically, NPC-700-1, which is 5 nm thick and 6 μm wide, shows a high surface area (1591.5 m2 g-1) and hierarchical micro-, meso-, and macroporous architecture. The maximum specific capacitance of the as-prepared carbon nanosheets is 406 F g-1 at 1 A g-1 in KOH electrolyte. Moreover, flexible all-solid-state asymmetric supercapacitor devices assembled from NPCs and NiCo2O4 deliver a superior energy density of 42.7 W h kg-1 at 794.6 W kg-1, and good cycling ability (94% after 10 000 cycles). All the results suggest that NPCs have great potential for high performance wearable electronics and energy storage devices.

Crystal transformation of 2D tungstic acid H2WO4 to WO3 for enhanced photocatalytic water oxidation

New photocatalytic materials for stable reduction and/or oxidization of water by harvesting a wider range of visible light are indispensable to achieve high practical efficiency in artificial photosynthesis. In this work, we prepared 2D WO3·H2O and WO3 nanosheets by a one-pot hydrothermal method and sequent calcination, focusing on the effects of crystal transformation on band structure and photocatalytic performance for photocatalytic water oxidation in the presence of electron acceptors (Ag+) under simulated solar light irradiation. The as-prepared WO3 nanosheets exhibit enhanced rate of photocatalytic water oxidation, which is 6.3 and 3.6 times higher than that of WO3·H2O nanosheets and commercial WO3, respectively. It is demonstrated that the releasing of water molecules in the crystal phase of tungstic acid results in transformation of the crystal phase from orthorhombic WO3·H2O to monoclinic WO3, significantly improving the activity of photocatalytic water oxidation in the presence of Ag+ because the shift-up of conduction band of WO3 matches well with the electrode potential of Ag+/Ag(s), leading to efficient separation of photoinduced electrons and holes in pure WO3 nanosheets.

Facile One-Pot Two-Step Synthesis of Novel in Situ Selenium-Doped Carbon Nitride Nanosheet Photocatalysts for Highly Enhanced Solar Fuel Production from CO2

Novel in situ Se-doped carbon nitride (C3N4) nanosheets are synthesized for the first time by a facile one-pot two-step strategy. The as-prepared Se-doped C3N4 nanosheets show a high visible light driven formic acid production rate of 1.001 × 105 μmol gcat–1 h–1. It represents the highest value reported in literature for formic acid production from CO2 by visible light harvesting C3N4 photocatalysts. The exceptional photocatalytic activity is largely attributed to selenium-doped conjugated system besides porous nanosheet morphology of the photocatalyst. The presence of midgap state in carbon nitride (−0.35 V vs standard hydrogen electrode) due to Se doping is found to significantly extend the light absorption up to 570 nm thereby further enhancing light harvesting ability of the photocatalyst. The current work not only provides a facile and scalable route to synthesize highly efficient Se-doped carbon nitride (C3N4) nanosheet photocatalysts but also sheds light on devising new avenues for rational design ...

The ultra-high NO2 response of ultra-thin WS2 nanosheets synthesized by hydrothermal and calcination processes

Ultra-thin WS2 nanosheets with a thickness of about 5 nm were synthesized by an economical hydrothermal method and the following calcination process. A three dimensional wall-like structure was formed by the interconnecting WS2 nanosheets. The growth mechanism of as-prepared WS2 nanosheets was discussed, and it was deduced that mesolamellar tungsten sulfide (WS-L) with intercalated CTA+ cations was formed by co-condensation reaction of WS42− and CTAB in the hydrothermal process. The resistive gas sensors based on as-prepared WS2 nanosheets showed a p-type character, achieved a superior response of 9.3% to 0.1 ppm NO2 gas at room temperature (25 °C) and a good stability in low and moderate humidity. The excellent NO2 sensing properties can be attributed to the ultra-thin nanostructure of the WS2 nanosheets.

General Facet-Controlled Synthesis of Single-Crystalline {010}-Oriented LiMPO4 (M = Mn, Fe, Co) Nanosheets

Facet-controlled synthesis of phospho-olivine (LiMPO4, M = Mn, Fe, Co) cathode materials is of particular interest to manipulate their electrochemical properties because of their anisotropic ionic transport behavior. This study provides a general facet-controlled synthesis of single-crystalline LiMPO4 (M = Mn, Fe, Co) nanosheets with significantly large exposure of (010)-facets, which has not been readily achieved by conventional solution-based coprecipitation or solid-reaction methods. The as-obtained nanosheets show controllable thickness with the thinnest thickness down to 15–20 nm and lateral dimension up to ∼5 μm. Due to the shortened lithium ion diffusion pathway and high ratio of active surface enabled by the thin thickness, the as-prepared LiFePO4 nanosheets, as a model material, demonstrate greatly improved rate capability and cycling stability, with a reversible capacity of ∼80 mA h g–1 at a current rate of 30 C and a stable capacity retention of ∼93% after 500 cycles at a current rate of 5 C. F...

Selenium Nanosheets: 2D Nonlayered Selenium Nanosheets: Facile Synthesis, Photoluminescence, and Ultrafast Photonics (Advanced Optical Materials 24/2017)

In article number 1700884, Han Zhang and co-workers show that non-layered materials can be exfoliated into 2D nanosheets by a liquid phase exfoliation method. Importantly, the as-prepared 2D Se nanosheets exhibit excellent ultrashort pulse generation of an optical communication band. The cartoon rabbit on the cover has firm front teeth, which enables the foods with strong anisotropy between length and thickness directions to be thinned. The bread and carrot denote layered materials (such as graphite) and non-layered materials (such as bulk Se crystal), respectively. The rabbit's front teeth denote probe sonication in the liquid phase exfoliation process that is believed to be oriented in the vertical direction.

Highly sensitive nonenzymetic glucose sensing platform based on MOF-derived NiCo LDH nanosheets/graphene nanoribbons composite

Herein, a novel sensing platform based on NiCo layered double hydroxide (LDH) nanosheets/graphene nanoribbons (GNRs) modified glassy carbon electrode is presented for sensitive non-enzymetic determination of glucose. In the first step, nanoflower-like NiCo LDH nanosheets were grown on the surface of ZIF-67 dodecahedron nanocrystals which used as sacrificial template and were further characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and FTIR. In the next step, in order to fabricate a mechanically stable modified electrode, the as-prepared nanosheets were mixed with narrow graphene nanoribbons synthesized through longitudinal unzipping of MWCNTs as an effective binder which in one hand increase the mechanical stability of the composite film and on the other hand, enhance the electrical conductivity of the final modified electrode. The catalytic behavior of the NiCo NSs/GNR modified electrode toward the electro-oxidation of glucose was investigated in NaOH alkaline solution by using cyclic voltammetry (CV) and amperometry techniques. As an enzymeless glucose sensor, the proposed sensing platform exhibited fast amperometric responses with high sensitivity (344μAmM−1cm−2) and low detection limit of 0.6μM within a wide dynamic linear range from 5μM to 0.8mM. Moreover, the electrode also demonstrated excellent selectivity toward glucose in the presence of common interfering species such as AA, DA and UA as well as good long-term stability which makes it an appropriate candidate for further practical applications.

Porous CoP nanosheet arrays grown on nickel foam as an excellent and stable catalyst for hydrogen evolution reaction

Three dimensional porous CoP nanosheet arrays grown on nickel foam composite were designed and constructed through a combination of electrodeposition and phosphatization. Nanosheet arrays of cobalt (II) hydroxide were firstly formed on nickel foam via electrodeposition which is further phosphatized to form defect-rich porous CoP nanosheets. The as-prepared CoP nanosheets exhibit high activity as a catalyst for the hydrogen evolution reaction, and the overpotentials of generating a current density of 10 mA cm−2 are 79.5 mV and 86.6 mV in acidic and basic electrolytes, respectively. In addition, the as-prepared CoP nanosheet catalyst shows excellent stability in acidic electrolyte, and no obvious degradation was observed at 10 mA cm−2 for 50 h. The high activity is attributed to the unique three dimensional structure of the material as well as the metalloid characteristics of CoP.

Two-dimensional metal phosphorus trisulfide nanosheet with solar hydrogen-evolving activity

The development and utilization of photocatalysts to realize water-splitting without any external bias or sacrificial agents has received the limelight. As a novel two-dimensional layered material, metal phosphorus trichalcogenides (MPTs) cause wide research interest, presently. However, the growth of ultrathin two-dimensional MPT crystals is a great challenge to hinder their application. Here, we initially grow few-atomic layered nickel phosphorus trisulfide (NiPS3) as promising photocatalyst for hydrogen evolution. The as-prepared NiPS3 hexagonal nanosheet, as thin as few atomic layers (≤ 3.5nm), has lateral size of larger than 15µm. These ultrathin NiPS3 crystals can directly generate hydrogen gas from pure water without any sacrificial agents under sunlight. With ultraviolet photoelectron spectrometer and electrochemical impedance spectroscopy, we show that the attractive photocatalytic activity of the ultrathin NiPS3 crystals arise from their appropriate positions of the band edges. This discovery is expected to make a contribution to develop next generation solar-fuel conversion catalysts for H2 production.