Gas Exfoliation Research Articles

Gas exfoliation induced N, S-doped porous 2D carbon nanosheets for effective removal of copper ions by capacitive deionization

Using capacitive deionization to remove heavy metal ions from water has received much attention, but the inferior salt adsorption capacity (SAC) of electrode materials has always limited its practical application. Herein, N, S co-doped two-dimensional (2D) porous glucose derived carbon nanosheets (NSPGC) was successfully fabricated, utilizing the gas exfoliation by calcination of thiourea. The NSPGC demonstrates distinct 2D lamellas, high specific surface area (2529 m2 g−1), hierarchical pore structure and high wettability. In electrochemical tests, a high specific capacitance (127 F g−1) and electrons/ions transport performance can be achieved in the NSPGC, moreover it showed a prominent SAC of 206.57 mg g−1 and recoverability in 100 mg L−1 CuSO4 solution. Moreover, the density functional theory (DFT) calculation manifested the intrinsic affinity of Cu2+ improved by N, S co-doping, which played an essential role in enhancing the Cu2+ removal performance of CDI. Our work provided a new insight into the preparation of high-performance CDI electrode materials for Cu2+ removal and promoted the application of CDI in heavy metal wastewater.

Fabrication of tobacco-stem-derived hierarchical porous carbon via synergistic gas exfoliation effect for high-performance supercapacitors

The high-value utilization of agricultural and forestry waste holds the promise of alleviating the issues of energy crisis. Among them, the manufacturing of high-performance supercapacitor electrode materials from tobacco waste biomass is a reliable avenue. In this work, tobacco-stem-derived hierarchical porous carbon (TS-HPC) was prepared by one-pot ball milling and carbonization using calcium carbonate (CaCO3) and potassium oxalate (K2C2O4) as mild activating agents. Due to the synergistic activation of CaCO3 and K2C2O4, the specific surface area of TS-HPC is 2749 m2/g. TS-HPC with the hierarchical porous structure greatly shows an excellent specific capacitance (402 F/g at 0.5 A/g) in the three-electrode configuration. In addition, symmetric supercapacitor based on TS-HPC exhibits 10.2 W h/kg energy density at 150.0 W/kg power density, together with outstanding cycling stability (remains 97.8% after 10,000 cycles). Moreover, we demonstrated that the gas exfoliation of CaCO3 and K2C2O4 could contribute to the formation of hierarchical porous structures with a synergistic activation effect. This work could provide a new perspective on the preparation of biomass-derived carbon as electrode for supercapacitors.

Engineering Nanostructured Interfaces of Hexagonal Boron Nitride-Based Materials for Enhanced Catalysis.

ConspectusHexagonal boron nitrides (h-BNs) are attractive two-dimensional (2D) nanomaterials that consist of alternating B and N atoms and layered honeycomb-like structures similar to graphene. They have exhibited unique properties and promising application potentials in the field of energy storage and transformation. Recent advances in utilizing h-BN as a metal-free catalyst in the oxidative dehydrogenation of propane have triggered broad interests in exploring h-BN in catalysis. However, h-BN-based materials as robust nanocatalysts in heterogeneous catalysis are still underexplored because of the limited methodologies capable of affording h-BN with controllable crystallinity, abundant porosity, high purity, and defect engineering, which played important roles in tuning their catalytic performance. In this Account, our recent progress in addressing the above issues will be highlighted, including the synthesis of high-quality h-BN-based nanomaterials via both bottom-up and top-down pathways and their catalytic utilization as metal-free catalysts or as supports to tune the interfacial electronic properties on the metal nanoparticles (NPs). First, we will focus on the large-scale fabrication of h-BN nanosheets (h-BNNSs) with high crystallinity, improved surface area, satisfactory purity, and tunable defects. h-BN derived from the traditional approaches using boron trioxide and urea as the starting materials generally contains carbon/oxygen impurities and has low crystallinity. Several new strategies were developed to address the issues. Using bulk h-BN as the precursor via gas exfoliation in liquid nitrogen, single- or few-layered h-BNNS with abundant defects could be generated. Amorphous h-BN precursors could be converted to h-BN nanosheets with high crystallinity assisted by a magnesium metallic flux via a successive dissolution/precipitation/crystallization procedure. The as-fabricated h-BNNS featured high crystallinity and purity as well as abundant porosity. An ionothermal metathesis procedure was developed using inorganic molten salts (NaNH2 and NaBH4) as the precursors. The h-BN scaffolds could be produced on a large scale with high yield, and the as-afforded materials possessed high purity and crystallinity. Second, utilization of the as-prepared h-BN library as metal-free catalysts in dehydrogenation and hydrogenation reactions will be summarized, in which they exhibited enhanced catalytic activity over the counterparts from the previous synthesis method. Third, the interface modulation between metal NPs with the as-prepared defects' abundant h-BN support will be highlighted. The h-BN-based strong metal-support interaction (SMSI) nanocatalysts were constructed without involving reducible metal oxides via the ionothermal procedure we developed by deploying specific inorganic metal salts, acting as robust nanocatalysts in CO oxidation. Under conditions simulated for practical exhaust systems, promising catalytic efficiency together with high thermal stability and sintering resistance was achieved. Across all of these examples, unique insights into structures, defects, and interfaces that emerge from in-depth characterization through microscopy, spectroscopy, and diffraction will be highlighted.

Pyrolytic gas exfoliation and template mediation inducing defective mesoporous carbon network from industrial lignin for advanced lithium-ion storage

Enzymatic hydrolysis lignin (EHL) from the biorefinery industry has been considered an ideal carbon source to prepare high-performance carbonaceous electrodes due to its high aromaticity and abundance. However, the severe agglomeration of the directly carbonized EHL results in insufficient lithium storage sites and inferior transfer kinetics. Herein, a delicate strategy of pyrolytic gas exfoliation and template mediation through ZnCO3 and ZnC2O4 decomposition was developed to engineer the microstructure of EHL-derived carbonaceous material (ECM) at 650 °C for robust lithium storage. The mesoporous ECM with an interconnected grape-like (200 nm) network is prepared by single CO2 exfoliation and ZnO templating. Surface micropores are engineered by temporary ZnO activation at 500–650 °C. The blocky ECM with coexisting micro/mesopores is prepared by dual CO/CO2 exfoliation and ZnO templating. The tempestuous release of CO2 produces deep micropores. The developed mesoporous structure boosts fast Li-ion transportation and accessibility for defects. In addition, the nanostructured grape-like (200 nm) network exposes active surface defects and shortens the charge-diffusion distance. Thus, the mesoporous ECM displays a robust capacity (534.1 mAh·g−1 at 0.2 A·g−1), superior rate capability (323.4 mAh·g−1 at 1 A·g−1) and excellent cycling stability. The blocky ECM with coexisting micro/mesopores shows better lithium storage performance than the microporous blocky ECM prepared by ZnCl2 activation.

Gas exfoliation mechanisms of graphitic carbon nitride into few-layered nanosheets

Gas exfoliation mechanisms of graphitic carbon nitride into few-layered nanosheets

Designing the effective microstructure of lignin-based porous carbon substrate to inhibit the capacity decline for SnO2 anode

As the traditional anode material of lithium-ion batteries, tin dioxide (SnO2) has the characteristics of a high theoretical capacity and stable crystal structure. However, the alloying/de-alloying reaction between tin and lithium ions causes volume expansion and continuously generates an SEI film, which causes the electrode to fall off the current collector and the capacity fade rapidly. Generally, a composite of carbon materials and SnO2 can alleviate the expansion and pulverization phenomena. However, the microstructure of carbon materials is complex and changeable, which makes it difficult to definitively state the influence mechanism of the microstructure on the lithium storage performance of composite materials. Here, three kinds of lignin-based porous carbons (LPCs) with different microstructural characteristics, along with a high graphitization, high specific surface area and hierarchical porosity, are obtained by regulating the process of gas exfoliation and in situ activation. Furthermore, a series of LPC/SnO2 composites are obtained by an ultrasonic dispersion and ball milling method. Electrochemical property results show that the hierarchical porous LPCs are more conducive to the dispersion/coating of SnO2 nanoparticles and that the reversible specific capacity of the electrode material increases from 64 to 620 mA h g−1, effectively mitigating the expansion and pulverization of SnO2 during the lithium storage process.

The Preparation of Black Phosphorus Quantum Dots by Gas Exfoliation with the Assistance of Liquid N₂.

Black phosphorus quantum dots (BPQDs), a type of nanoscale black phosphorus (BP), have fantastic application prospects in various fields. However, the premise of the application of BPQDs depends on its effective preparation. At present, most of preparation processes of BPQDs involve in organic solvents which may be harmful to humans and the environment. Furthermore, some chemical impurities may inevitably be introduced into the final product. In addition, all the preparation processes need to be carried out under an inert gas due to the instability of BPQDs, which makes the reaction conditions more harsh and complicated. Therefore, an efficient and simple method for the preparation of BPQDs by gas exfoliation with the assistance of liquid N₂ (l-N₂) was developed for the first time in this study. This method is environmentally friendly and impurity-free because l-N₂ is a nontoxic liquid that can be gasified to form N₂. The obtained BPQDs were characterized by XRD, Raman, SEM, TEM and UV-Vis techniques and they had a lateral size of 9±3 nm.

Gas exfoliation of graphitic carbon nitride to improve the photocatalytic hydrogen evolution of metal-free 2D/2D g-C3N4/graphdiyne heterojunction

Abstract Metal-free photocatalysts have received increasing attention as nonmetal elements are abundant in the earth and friendly to the environment. Graphitic carbon nitride (g-C3N4) as a typical two-dimensional (2D) metal-free photocatalysts for water splitting has attracted increasing interest due to its economic production and environmentally friend features. However, the high photocarriers recombination rate constraint its catalytic activity. Combining the single- or few-layered g-C3N4 nanosheets with other 2D functional materials to form efficient metal-free heterojunction photocatalysts is one of the effective strategies to improve the photocarriers separation. Herein, we introduce a simple and efficient method to scalable preparation few-layered g-C3N4 nanosheets using gas exfoliation of bulk g-C3N4 in liquid nitrogen. Then we introduce the g-C3N4 nanosheets into construct a 2D/2D heterojunction of g-C3N4/graphdiyne by π-π interaction, where graphdiyne (GDY) as a new 2D carbon allotrope, has excellent holes transfer nature. We find that the 2D/2D g-C3N4/GDY photocatalyst with 1% GDY is the optimum condition, with the highest H2 evolution rate of 454.28 μmol h−1. The superior photocatalytic performance may be attributed to the excellent photocarriers separation in g-C3N4 under the built-in field, where GDY can rapid transport holes from g-C3N4 to the sacrificial agents.

Gas-assisted exfoliation of boron nitride nanosheets enhancing adsorption performance

Abstract A gas exfoliation strategy for controllable preparation of boron nitride (BN) nanosheets with few-layered structure were reported. The green exfoliation process provides the BN nanosheets remarkable increment of adsorption capacities to organic contaminants, which is ascribed to better exposure of active sites originating from the larger surface area and thinner layer. Moreover, the prepared BN also exhibits outstanding recyclability.

Restriction of Molecular Rotors in Ultrathin Two-Dimensional Covalent Organic Framework Nanosheets for Sensing Signal Amplification

Covalent organic frameworks (COFs) have emerged as promising crystalline porous materials with well-defined structures, high porosity, tunable topology, and functionalities suitable for various applications. However, studies of few-layered ultrathin two-dimensional (2D) COF nanosheets, which may lead to unprecedented properties and applications, are still limited. Herein, we report the targeted synthesis of three azine-linked and imine-linked 2D COFs named NUS 30–32 using monomers containing aggregation-induced emission (AIE) rotor-active tetraphenylethylene (TPE) moieties, affording micro- and meso-dual pores in NUS-30 and NUS-32 and triple pores in NUS-31. For the first time, we demonstrate that these isostructural bulk COF powders can be exfoliated into ultrathin 2D nanosheets (2–4 nm thickness) by a temperature-swing gas exfoliation approach. Compared with TPE monomers and COF model compounds, the AIE characteristic of NUS 30–32 nanosheets is distinctly suppressed because of the covalent restriction o...

Gas-exfoliated porous monolayer boron nitride for enhanced aerobic oxidative desulfurization performance

Hexagonal boron nitride has been regarded to be an efficient catalyst in aerobic oxidation fields, but limited by the less-exposed active sites. In this contribution, we proposed a simple green liquid nitrogen gas exfoliation strategy for preparation of porous monolayer nanosheets (BN-1). Owing to the reduced layer numbers, decreased lateral sizes and artificially-constructed pores, increased exposure of active sites was expected, further contributed to an enhanced aerobic oxidative desulfurization (ODS) performance up to ∼98% of sulfur removal, achieving ultra-deep desulfurization. This work not only introduced an excellent catalyst for aerobic ODS, but also provided a strategy for construction of some other highly-efficient monolayer two-dimensional materials for enhanced catalytic performance.

Few-layered graphene via gas-driven exfoliation for enhanced supercapacitive performance

High-quality graphene flakes have long been desirable for numerous applications including energy storage, printable electronics, and catalysis. In this contribution, we report a green, efficient, facile gas-driven exfoliation process for the preparation of high-quality graphene in large scale. The gas exfoliation process was realized by the interplay between the expansion of interlayer at high temperature and the gasification of liquid nitrogen within the interlayer. Detailed experiments demonstrated that the higher temperature was critical to the formation of fewer layers. The exfoliated graphene was proved to be of high quality. We further investigated the electrochemical behavior of this exfoliated graphene. As a result, this few-layered graphene demonstrated an enhanced capability as a supercapacitor, much higher than its counterpart parent material.

Highly sensitive airflow sensors with an ultrathin reduced graphene oxide film inspired by gas exfoliation of graphite oxide

A highly-sensitive, novel airflow sensor is demonstrated with an ultrathin reduced graphene oxide film with tunable interlayer gaps.

Controlled Gas Exfoliation of Boron Nitride into Few‐Layered Nanosheets

AbstractThe controlled exfoliation of hexagonal boron nitride (h‐BN) into single‐ or few‐layered nanosheets remains a grand challenge and becomes the bottleneck to essential studies and applications of h‐BN. Here, we present an efficient strategy for the scalable synthesis of few‐layered h‐BN nanosheets (BNNS) using a novel gas exfoliation of bulk h‐BN in liquid N2 (L‐N2). The essence of this strategy lies in the combination of a high temperature triggered expansion of bulk h‐BN and the cryogenic L‐N2 gasification to exfoliate the h‐BN. The produced BNNS after ten cycles (BNNS‐10) consisted primarily of fewer than five atomic layers with a high mass yield of 16–20 %. N2 sorption and desorption isotherms show that the BNNS‐10 exhibited a much higher specific surface area of 278 m2 g−1 than that of bulk BN (10 m2 g−1). Through the investigation of the exfoliated intermediates combined with a theoretical calculation, we found that the huge temperature variation initiates the expansion and curling of the bulk h‐BN. Subseqently, the L‐N2 penetrates into the interlayers of h‐BN along the curling edge, followed by an immediate drastic gasification of L‐N2, further peeling off h‐BN. This novel gas exfoliation of high surface area BNNS not only opens up potential opportunities for wide applications, but also can be extended to produce other layered materials in high yields.

Controlled Gas Exfoliation of Boron Nitride into Few-Layered Nanosheets.

The controlled exfoliation of hexagonal boron nitride (h-BN) into single- or few-layered nanosheets remains a grand challenge and becomes the bottleneck to essential studies and applications of h-BN. Here, we present an efficient strategy for the scalable synthesis of few-layered h-BN nanosheets (BNNS) using a novel gas exfoliation of bulk h-BN in liquid N2 (L-N2 ). The essence of this strategy lies in the combination of a high temperature triggered expansion of bulk h-BN and the cryogenic L-N2 gasification to exfoliate the h-BN. The produced BNNS after ten cycles (BNNS-10) consisted primarily of fewer than five atomic layers with a high mass yield of 16-20 %. N2 sorption and desorption isotherms show that the BNNS-10 exhibited a much higher specific surface area of 278 m(2) g(-1) than that of bulk BN (10 m(2) g(-1) ). Through the investigation of the exfoliated intermediates combined with a theoretical calculation, we found that the huge temperature variation initiates the expansion and curling of the bulk h-BN. Subseqently, the L-N2 penetrates into the interlayers of h-BN along the curling edge, followed by an immediate drastic gasification of L-N2 , further peeling off h-BN. This novel gas exfoliation of high surface area BNNS not only opens up potential opportunities for wide applications, but also can be extended to produce other layered materials in high yields.