Covalently Linked 2D-Co3O4/GO Heterostructures: Catalytic and Electrochemical Properties

Covalently cross-linked 2D heterostructures may represent a ground-breaking approach to creating materials with multifunctionalities. To date, however, this field still remains relatively unexplored. In the present work, Co3O4/GO covalently linked heterostructures (Co3O4/GO-CL) were produced using 2D-Co3O4 functionalized with (3-aminopropyl)triethoxysilane (APTES) to react with the carboxyl groups of graphene oxide (GO). The surface and interface properties of the final material were assessed through electrochemical and catalytic studies. We found that the covalent bonds lead to a self-standing and ordered final structure, not observed for the noncovalent material (Co3O4/GO-nCL), also produced for comparison. The catalytic activity of Co3O4/GO-CL over the degradation of Rhodamine 6G showed great performance and the possibility of recycling the catalyst. Electrochemical evaluation stated higher specific capacitance for the covalently bonded material (468 F g-1 against 110 F g-1). Overall, results showed that the covalent bonds may be improving charge-transfer and interfacial area features, thus leading to enhanced catalytic and electrochemical performances.

Structural Modulation of Nitrogen-Rich Covalent Organic Frameworks for Iodine Capture

Developing efficient adsorbent materials for iodine scavenging is essential to mitigate the threat of radioactive iodine causing adverse effects on human health and the environment. In this context, we explored N-rich two-dimensional covalent organic frameworks (COFs) with diverse functionalities for iodine capture. The pyridyl-hydroxyl-functionalized triazine-based novel 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(pyridine-2-amine) (TTPA)-COF possesses high crystallinity (crystalline domain size: 24.4 ± 0.6 nm) and high porosity (specific BET surface area: 1000 ± 90 m2 g-1). TTPA-COF exhibits superior vapor-phase iodine adsorption (4.43 ± 0.01 g g-1) compared to analogous COF devoid of pyridinic moieties, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-COF. The high iodine capture by TTPA-COF is due to the enhanced binding affinity conferred by the extra pyridinic active sites. Furthermore, the crucial role of long-range order in porous adsorbents has been experimentally evidenced by comparing the performance of iodine vapor capture of TTPA-COF with an amorphous network polymer having identical functionalities. We have also demonstrated the high iodine scavenging ability of TTPA-COF from the organic and aqueous phases. The mechanism of iodine adsorption by the heteroatom-rich framework is elucidated through FTIR, XPS, and Raman spectral analyses. The present study highlights the need for structural tweaking of the building blocks toward the rational construction of advanced functional porous materials for a task-specific application.

A critical review on graphene and graphene-based derivatives from natural sources emphasizing on CO2 adsorption potential

Accelerated release of carbon dioxide (CO2) into the atmosphere has become a critical environmental issue, and therefore, efficient methods for capturing CO2 are in high demand. Graphene and graphene-based derivatives have demonstrated promising potential as adsorbents due to their unique properties. This review aims to provide an overview of the latest research on graphene and its derivatives fabricated from natural sources which have been utilized and may be explored for CO2 adsorption. The necessity of this review lies in the need to explore alternative, sustainable sources of graphene that can contribute to the development of viable environmentally benign CO2 capture technologies. The review will aim to highlight graphene as an excellent CO2 adsorbent and the possible avenues, advantages, and limitations of the processes involved in fabricating graphene and its derivatives sourced from both industrial resources and organic waste-based naturally occurring carbon precursors for CO2 adsorption. This review will also highlight the CO2 adsorption mechanisms focusing on density functional theory (DFT) and molecular dynamics (MD)-based studies over the last decade.

Bottom-Up Synthesis of Covalent Organic Frameworks with Quasi-Three-Dimensional Integrated Architecture via Interlayer Cross-Linking

Developing strategies to enhance the structural robustness of covalent organic frameworks (COFs) is of great importance. Here, we rationally design and synthesize a class of cross-linked COFs (^CCOFs), in which the two-dimensional (2D) COF layers are anchored and connected by polyethylene glycol (PEG) or alkyl chains through covalent bonds. The bottom-up fabrication of these ^CCOFs is achieved by the condensation of cross-linked aldehyde monomers and tritopic amino monomers. All the synthesized ^CCOFs possess high crystallinity and porosity, and enhanced structural robustness surpassing the typical 2D COFs, which means that they cannot be exfoliated under ultrasonication and grinding due to the cross-linking effect. Furthermore, the cross-linked patterns of PEG units are uncovered by experimental results and Monte Carlo molecular dynamics simulations. It is found that all ^CCOFs are dominated by vertical cross-layer (interlayer) connections (clearly observed in high-resolution transmission electron microscopy images), allowing them to form quasi-three-dimensional (quasi-3D) structures. This work bridges the gap between 2D COFs and 3D COFs and provides an efficient way to improve the interlayered stability of COFs.

Application of graphene aerogels in oil spill recovery: A review

Oil spills have long been a serious threat to marine environment. Physical recovery is the safest and most efficient method in the emergency disposal of offshore oil spill. Graphene aerogel (GA) has a wide application prospect in offshore oil spill emergency recovery and disposal given its unique structural characteristics. In this article, the preparation methods of GA adsorbent are summarized. On this basis, in the background of the application of offshore oil spill recovery, the related properties and targeted modification schemes of GA, such as adsorption, mechanical, and magnetic properties, as well as photothermal conversion properties for disposal of oil spills with high viscosity, are discussed. The Joule heating/photothermal conversion scheme can improve the recovery efficiency of offshore high viscosity oil spills, and adding metal composite materials can increase the magnetic performance and surface roughness of GA and facilitate positioning and recovery after offshore oil spills disposal. The challenges and prospects of modification research are also highlighted, and guidance for further optimizing the performance of GA in offshore oil spill recovery is provided.

Sorption of Polar Sorbents into GO Powders and Membranes

The comparative study of sorption of polar substances acetonitrile and water into powders and membranes (>10 μm thick) of modified Hummers (HGO) and Brodie (BGO) graphite oxides was performed using isopiestic method (IM) and differential scanning calorimetry (DSC). Additional sorption data were obtained for pyridine and 1-octanol. Sorption measurements were accompanied by conventional XRD and XPS control. Electron paramagnetic resonance (EPR) was additionally used to characterize ordering of the membranes. The impact on sorption of synthetic procedure (Brodie or Hummers), method of making membranes, chemical nature of the sorbent, and method of sorption was systematically examined. It was demonstrated that variations in synthetic procedures within both Hummers and Brodie methods did not lead to changes in the sorption properties of the corresponding powders. Sorption of acetonitrile and pyridine was reduced by approximately half when switching from powders to membranes at ambient temperature. DSC measurements at a lower temperature gave equal sorption of acetonitrile into HGO powder and membranes. Water has demonstrated unique sorption properties. Equal sorption of water was measured for HGO membranes and powders at T = 298 K and at T = 273 K. It was demonstrated that lowering the orientational alignment of the membranes led to the increase of sorption. In practice this could allow one to tune sorption/swelling and transport properties of the GO membranes directly by adjusting their internal ordering without the use of any composite materials.

Quantum chemical simulation of hydrogen adsorption in pores: A study by DFT, SAPT0 and IGM methods

Hydrogen as a versatile energy carrier continues to attract research attention in the field of applied chemistry. One of the fundamental issues on the way to hydrogen economy is the difficulty of hydrogen storage. Physical adsorption of hydrogen in pores is a feasible and effective method of hydrogen storage. Among existing hydrogen-adsorbing materials, carbon nanostructures possess a number of advantages due to their high adsorption capacity, significant strength and low weight. In this work, we use the modern methods of quantum chemistry (DFT, SAPT0 and IGM) to study the adsorption of molecular hydrogen in a series of simulated slit-like carbon micropores with a distance between the walls of d = 4–10 Å, including the introduction of an H2 molecule into a pore, filling pores with these molecules and investigating the interactions between H2 molecules inside the pores. It was found that, depending on the value of parameter d, adsorbed hydrogen molecules form one (d = 6, 7 Å) or two layers (d = 8, 9, 10 Å) inside the pore. At the same time, for pores with small d values, high potential barriers to the introduction of H2 into a pore were observed. The decomposition of the interaction energy into components showed dispersion interactions to make a major contribution to the energy of attraction (72–82%). Moreover, an increase in the number of H2 molecules adsorbed in the pore decreases the significance of dispersion interactions (up to 61%) and increases the contribution of electrostatic and induction interactions to intermolecular attraction. Gravimetric density (GD) values were determined for pores with d = 6, 7, 8, 9, 10 Å, comprising 1.98, 2.30, 2.93, 3.25 and 4.49 wt%, respectively. It is assumed that the revealed peculiarities of hydrogen adsorption in pores will contribute to the use of carbon porous structures as a medium for hydrogen storage.

Pd-Pd/PdO as active sites on intercalated graphene oxide modified by diaminobenzene: fabrication, catalysis properties, synergistic effects, and catalytic mechanism

Pd-Pd/PdO nanoclusters well dispersed on intercalated graphene oxide (GO) (denoted as GO@PPD-Pd) were prepared and characterized. GO@PPD-Pd exhibited high catalytic activity (a TOF value of 60 705 h-1) during the Suzuki coupling reaction, and it could be reused at least 6 times. The real active centre was Pd(200)-Pd(200)/PdO(110, 102). A change in the Pd facets on the surface of PdO was a key factor leading to deactivation, and the aggregation and loss of active centres was also another important reason. The catalytic mechanism involved heterogeneous catalysis, showing that the catalytic processes occurred at the interface, including substrate adsorption, intermediate formation, and product desorption. The real active centres showed enhanced negative charge due to the transfer of electrons from the carrier and ligands, which could effectively promote the oxidative addition reaction, and Pd(200) and the heteroconjugated Pd/PdO interface generated in situ also participated in the coupling process, synergistically boosting activity. Developed GO@PPD-Pd was a viable heterogeneous catalyst that may have practical applications owing to its easy synthesis and stability, and this synergistic approach can be utilized to develop other transition-metal catalysts.

Theoretical Investigation of Carbon Dioxide Adsorption on Li+-Decorated Nanoflakes

Recently, the capture of carbon dioxide, the primary greenhouse gas, has attracted particular interest from researchers worldwide. In the present work, several theoretical methods have been used to study adsorption of CO2 molecules on Li+-decorated coronene (Li+@coronene). It has been established that Li+ can be strongly anchored on coronene, and then a physical adsorption of CO2 will occur in the vicinity of this cation. Moreover, such a decoration has substantially improved interaction energy (Eint) between CO2 molecules and the adsorbent. One to twelve CO2 molecules per one Li+ have been considered, and their Eint values are in the range from -5.55 to -16.87 kcal/mol. Symmetry-adapted perturbation theory (SAPT0) calculations have shown that, depending on the quantity of adsorbed CO2 molecules, different energy components act as the main reason for attraction. AIMD simulations allow estimating gravimetric densities (GD, wt.%) at various temperatures, and the maximal GDs have been calculated to be 9.3, 6.0, and 4.9% at T = 77, 300, and 400 K, respectively. Besides this, AIMD calculations validate stability of Li+@coronene complexes during simulation time at the maximum CO2 loading. Bader's atoms-in-molecules (QTAIM) and independent gradient model (IGM) techniques have been implemented to unveil the features of interactions between CO2 and Li+@coronene. These methods have proved that there exists a non-covalent bonding between the cation center and CO2. We suppose that findings, derived in this theoretical work, may also benefit the design of novel nanosystems for gas storage and delivery.

Interface chemistry of two-dimensional heterostructures - fundamentals to applications

Two-dimensional heterostructures (2D HSs) have emerged as a new class of materials where dissimilar 2D materials are combined to synergise their advantages and alleviate shortcomings. Such a combination of dissimilar components into 2D HSs offers fascinating properties and intriguing functionalities attributed to the newly formed heterointerface of constituent components. Understanding the nature of the surface and the complex heterointerface of HSs at the atomic level is crucial for realising the desired properties, designing innovative 2D HSs, and ultimately unlocking their full potential for practical applications. Therefore, this review provides the recent progress in the field of 2D HSs with a focus on the discussion of the fundamentals and the chemistry of heterointerfaces based on van der Waals (vdW) and covalent interactions. It also explains the challenges associated with the scalable synthesis and introduces possible methodologies to produce large quantities with good control over the heterointerface. Subsequently, it highlights the specialised characterisation techniques to reveal the heterointerface formation, chemistry and nature. Afterwards, we give an overview of the role of 2D HSs in various emerging applications, particularly in high-power batteries, bifunctional catalysts, electronics, and sensors. In the end, we present conclusions with the possible solutions to the associated challenges with the heterointerfaces and potential opportunities that can be adopted for innovative applications.

Covalent Cross-Linking of 2H-MoS2 Nanosheets

The combination of 2D materials opens a wide range of possibilities to create new-generation structures with multiple applications. Covalently cross-linked approaches are a ground-breaking strategy for the formation of homo or heterostructures made by design. However, the covalent assembly of transition metal dichalcogenides flakes is relatively underexplored. Here, a simple covalent cross-linking method to build 2H-MoS₂ -MoS₂ homostructures is described, using commercially available bismaleimides. These assemblies are mainly connected vertically, basal plane to basal plane, creating specific molecular sized spaces between MoS₂ sheets. Therefore, this straightforward approach gives access to the controlled connection of sulfide-based 2D materials.

Examining slit pore widths within plasma-exfoliated graphitic material utilising Barrett–Joyner–Halenda analysis

BJH analysis is shown to be a highly useful method to estimate the distance between stacks within plasma-exfoliated graphitic material, and is shown to coincide with data obtained from SEM, AFM and XRD analysis.

From 2D Graphene Nanosheets to 3D Graphene-based Macrostructures

The combination of exceptional functionalities offered by 3D graphene-based macrostructures (GBMs) has attracted tremendous interest. 2D graphene nanosheets have a high chemical stability, high surface area and customizable porosity, which was extensively researched for a variety of applications including CO₂ adsorption, water treatment, batteries, sensors, catalysis, etc. Recently, 3D GBMs have been successfully achieved through few approaches, including direct and non-direct self-assembly methods. In this review, the possible routes used to prepare both 2D graphene and interconnected 3D GBMs are described and analyzed regarding the involved chemistry of each 2D/3D graphene system. Improvement of the accessible surface of 3D GBMs where the interface exchanges are occurring is of great importance. A better control of the chemical mechanisms involved in the self-assembly mechanism itself at the nanometer scale is certainly the key for a future research breakthrough regarding 3D GBMs.

Acetylation of graphite oxide

Unlike many methods of chemical modification of Graphite Oxide (GO) reported during 1930-1960 and re-studied in much detail over the last decade, acetylation somehow escaped attention and remained almost completely unexplored. Acetylated Graphite Oxide (AcGO) was prepared using a reaction with acetic anhydride. Successful acetylation is evidenced by an increase in the average interlayer distance from d(001) = 7.8 Å in the precursor GO to 10 Å in AcGO. The amount of oxygen in AcGO significantly decreased compared to the precursor GO (C/O = 2.2), reflecting partial reduction of GO in the process of acetylation and resulting in a scarcely functionalized material with C/O = 6.2. A theoretical model of the complete acetylation of GO results in a non-porous close packed molecular structure with an interlayer distance of ∼10 Å, in good agreement with experiment. Remarkably, AcGO shows significant swelling despite the oxidation degree being comparable to that of reduced GO, which does not swell in polar solvents. Moreover, AcGO shows swelling in acetonitrile similar to that of the precursor GO but not in water, thus providing an example of selectivity in the sorption of common polar solvents. The low oxidation degree combined with selective swelling properties makes AcGO a promising material for membrane applications.

Fullerene-intercalated graphene nanocontainers for gas storage and sustained release

Molecular dynamics simulations are performed to investigate the storage capacity and sustained release of nitrogen (N₂) in the graphene-based nanocontainers. Sandwiched graphene-fullerene composites (SGFC) composed of two parallel graphene sheets and intercalated fullerenes are constructed. The simulation results show that the mass density of N₂ at the first layer is extremely high, due to the strong adsorption ability of graphene sheets. And N₂ molecules at this adsorbed layer are thermodynamically stable. Furthermore, we analyze the storage efficiency of SGFC. In general, the gravimetric and volumetric capacities decrease with the increasing number of intercalated fullerenes. On the contrary, the stability of SGFC is enhanced by more intercalated fullerenes. We therefore make a compromise and propose that 1 fullerene per 5 nm² graphene to build a SGFC, which is much effective to storage N₂. We also verify the reversibility that N₂ can sustainably release from the SGFC. Our results may provide insights into the design of graphene-based nanocomposites for gas storage and sustained release with excellent structural stability and high storage capacity. Graphical abstract.

Thermally reduced pillared GO with precisely defined slit pore size

Graphene oxide (GO) pillared with tetrakis(4-aminophenyl)methane (TKAM) molecules shows a narrow distribution of pore size, relatively high specific surface area, but it is hydrophilic and electrically not conductive. Analysis of XRD, N₂ sorption, XPS, TGA and FTIR data proved that the pillared structure and relatively high surface area (∼350 m² g⁻¹) are preserved even after thermal reduction of GO pillared with TKAM molecules. Unlike many other organic pillaring molecules, TKAM is stable at temperatures above the point of GO thermal reduction, as demonstrated by TGA. Therefore, gentle annealing results in the formation of reduced graphene oxide (rGO) pillared with TKAM molecules. The TKAM pillared reduced graphene oxide (PrGO/TKAM) is less hydrophilic as found using dynamic vapor sorption (DVS) and more electrically conductive compared to pillared GO, but preserves an increased interlayer-distance of about 12 Å (compared to ∼7.5 Å in pristine GO). Thus we provide one of the first examples of porous rGO pillared with organic molecules and well-defined size of hydrophobic slit pores. Analysis of pore size distribution using nitrogen sorption isotherms demonstrates a single peak for pore size of ∼7 Å, which makes PrGO/TKAM rather promising for membrane and molecular sieve applications.

The porous structure of tetrakis(4-aminophenyl)methane (TKAM)-pillared graphene oxide preserves after thermal reduction providing rare example of true pillared reduced GO material with precise slit pore size and sizable surface area.

Adsorption-Induced Expansion of Graphene Oxide Frameworks: Observation by in Situ Neutron Diffraction

We have investigated adsorption-induced deformation in graphene oxide framework materials (GOFs) using neutron diffraction at sample pressures up to 140 bar. GOFs, made by the solvothermal reaction of graphite oxide and benzene-1,4-diboronic acid, are a suitable candidate for deformation studies due to their narrow (∼1 nm), monodispersed, slit-shaped pores whose width can be measured by diffraction techniques. We have observed, in situ, a monotonic expansion of the slit width with increasing pressure upon adsorption of xenon, methane, and hydrogen under supercritical conditions. The expansion of ∼4% observed for xenon at a pressure of 48 bar is the largest deformation yet reported for supercritical adsorption on a carbonaceous material. We find that the expansion of the three gases can be mapped onto a common curve based solely on their Lennard-Jones parameters, in a manner similar to a law of corresponding states.

Dependence of the Properties of 2D Nanocomposites Generated by Covalent Crosslinking of Nanosheets on the Interlayer Separation: A Combined Experimental and Theoretical Study

Covalently cross-linked heterostructures of 2D materials are a new class of materials which possess electrochemical and photochemical hydrogen evolution properties. It was of considerable interest to investigate the role of interlayer spacing in the nanocomposites involving MoS₂ and graphene sheets and its control over electronic structures and catalytic properties. We have investigated this problem with emphasis on the hydrogen evolution properties of these structures by a combined experimental and theoretical study. We have linked MoS₂ based nanocomposites with other 2D materials with varying interlayer spacing by changing the linker and studied their hydrogen evolution properties. The hydrogen evolution activity for these composites decreases with increasing linker length, which we can link to a decrease in magnitude of charge transfer across the layers with increasing interlayer spacing. Factors such as the nature of the sheets, interlayer distance as well as the nature of the linker provide pathways to tune the properties of covalently cross-linked 2D material rendering this new class of materials highly interesting.

Intercalation of Layered Materials from Bulk to 2D

Intercalation in few-layer (2D) materials is a rapidly growing area of research to develop next-generation energy-storage and optoelectronic devices, including batteries, sensors, transistors, and electrically tunable displays. Identifying fundamental differences between intercalation in bulk and 2D materials will play a key role in developing functional devices. Herein, advances in few-layer intercalation are addressed in the historical context of bulk intercalation. First, synthesis methods and structural properties are discussed, emphasizing electrochemical techniques, the mechanism of intercalation, and the formation of a solid-electrolyte interphase. To address fundamental differences between bulk and 2D materials, scaling relationships describe how intercalation kinetics, structure, and electronic and optical properties depend on material thickness and lateral dimension. Here, diffusion rates, pseudocapacity, limits of staging, and electronic structure are compared for bulk and 2D materials. Next, the optoelectronic properties are summarized, focusing on charge transfer, conductivity, and electronic structure. For energy devices, opportunities also emerge to design van der Waals heterostructures with high capacities and excellent cycling performance. Initial studies of heterostructured electrodes are compared to state-of-the-art battery materials. Finally, challenges and opportunities are presented for 2D materials in energy and optoelectronic applications, along with promising research directions in synthesis and characterization to engineer 2D materials for superior devices.

Constructing a three-dimensional graphene structure via bonding layers by ion beam irradiation

In recent years, the use of the multilayer graphene sheets has been considered more than the single-layer due to the cost-effectiveness and the possibility of mass production. But this type of graphene has some kind of structural weakness due to the weak physical link between its layers. Then, in order to strengthen, many structural modifications are proposed by various techniques to manage the mechanisms at interlayer distances. In this study, the focused ion beam irradiation method has been examined to cross-link and strengthen multi-layer graphene sheets with the help of the molecular dynamics simulation technique. Then, uniaxial and transverse tensile tests were performed to check the mechanical properties of obtained cross-linked multilayer graphene sheets. The results of this research can be considered for the creation of a new class of graphene structures. Such structures could be implemented as a membrane in water desalination or as a storage foam in hydrogen or carbon dioxide storage.

Alkynylation of graphene via the Sonogashira C-C cross-coupling reaction on fluorographene

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes.

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes. Theoretical calculations revealed that fluorographene can efficiently bind and oxidize the palladium catalyst on electrophilic sites activated by fluorine atoms. This paves the way towards conductive and mechanically robust 3D covalent networks.

Carbon dioxide adsorption and cycloaddition reaction of epoxides using chitosan-graphene oxide nanocomposite as a catalyst

One of today's major challenges is to provide green materials for a cleaner environment. We have conducted studies on carbon dioxide (CO₂) adsorption and conversion to valuable products by an ecofriendly approach based in chitosan/graphene oxide (CSGO) nanocomposite film. Rheological behavior indicates that the CSGO has a better solvation property than the pure chitosan. An adsorption capacity of 1.0152mmolCO₂/g of CSGO nanocomposite at 4.6bar was observed. The catalytic behavior of the CSGO nanocomposite in the presence of tetra-n-butylammonium iodide (n-Bu₄NI) as co-catalyst was evaluated for the cycloaddition of CO₂ to epoxides, to give cyclic carbonates, in the absence of any solvent. These results strongly suggest that the CSGO nanocomposite may open new vistas towards the development of ecofriendly material for catalytic conversion and adsorption of CO₂ on industrial scale.

Facile synthesis and color-tunable properties of monodisperse β-NaYF4:Ln3+ (Ln = Eu, Tb, Tm, Sm, Ho) microtubes

In this study, monodisperse and uniform β-NaYF₄ hexagonal microtubes were successfully synthesized via a simple hydrothermal method without any organic surfactants, employing Y(OH)CO₃ colloid spheres as precursors.

2D Material Armors Showing Superior Impact Strength of Few Layers

We study the ballistic properties of two-dimensional (2D) materials upon the hypervelocity impacts of C₆₀ fullerene molecules combining ab initio density functional tight binding and finite element simulations. The critical penetration energy of monolayer membranes is determined using graphene and the 2D allotrope of boron nitride as case studies. Furthermore, the energy absorption scaling laws with a variable number of layers and interlayer spacing are investigated, for homogeneous or hybrid configurations (alternated stacking of graphene and boron nitride). At the nanolevel, a synergistic interaction between the layers emerges, not observed at the micro- and macro-scale for graphene armors. This size-scale transition in the impact behavior toward higher dimensional scales is rationalized in terms of scaling of the damaged volume and material strength. An optimal number of layers, between 5 and 10, emerges demonstrating that few-layered 2D material armors possess impact strength even higher than their monolayer counterparts. These results provide fundamental understanding for the design of ultralightweight multilayer armors using enhanced 2D material-based nanocomposites.

Atomistic simulations of graphite etching at realistic time scales

Hydrogen-graphite interactions are relevant to a wide variety of applications, ranging from astrophysics to fusion devices and nano-electronics. In order to shed light on these interactions, atomistic simulation using Molecular Dynamics (MD) has been shown to be an invaluable tool. It suffers, however, from severe time-scale limitations. In this work we apply the recently developed Collective Variable-Driven Hyperdynamics (CVHD) method to hydrogen etching of graphite for varying inter-impact times up to a realistic value of 1 ms, which corresponds to a flux of ∼1020 m-2 s-1. The results show that the erosion yield, hydrogen surface coverage and species distribution are significantly affected by the time between impacts. This can be explained by the higher probability of C-C bond breaking due to the prolonged exposure to thermal stress and the subsequent transition from ion- to thermal-induced etching. This latter regime of thermal-induced etching - chemical erosion - is here accessed for the first time using atomistic simulations. In conclusion, this study demonstrates that accounting for long time-scales significantly affects ion bombardment simulations and should not be neglected in a wide range of conditions, in contrast to what is typically assumed.

Multilayered intercalation of 1-octanol into Brodie graphite oxide

Multilayered intercalation of 1-octanol into the structure of Brodie graphite oxide (B-GO) was studied as a function of temperature and pressure. Reversible phase transition with the addition/removal of one layer of 1-octanol was found at 265 K by means of X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The same transition was observed at ambient temperature upon a pressure increase above 0.6 GPa. This transition was interpreted as an incongruent melting of the low temperature/high pressure B-GO intercalated structure with five layers of 1-octanol parallel to GO sheets (L-solvate), resulting in the formation of a four-layered structure that is stable under ambient conditions (A-solvate). Vacuum heating allows the removal of 1-octanol from the A-solvate layer by layer, while distinct sets of (00l) reflections are observed for three-, two-, and one-layered solvate phases. Step by step removal of the 1-octanol layers results in changes of distance between graphene oxide planes by ∼4.5 Å. This experiment proved that both L- and A-solvates are structures with layers of 1-octanol parallel to GO planes. Unusual intercalation with up to five distinct layers of 1-octanol is remarkably different from the behaviour of small alcohol molecules (methanol and ethanol), which intercalate B-GO structure with only one layer under ambient conditions and a maximum of two layers at lower temperatures or higher pressures. The data presented in this study make it possible to rule out a change in the orientation of alcohol molecules from parallel to perpendicular to the GO planes, as suggested in the 1960s to explain larger expansion of the GO lattice due to swelling with larger alcohols.

Gas adsorption properties of graphene-based materials

Clean energy sources and global warming are among the major challenges of the 21st century. One of the possible actions toward finding alternative energy sources and reducing global warming are storage of H₂ and CH₄, and capture of CO₂ by using highly efficient and low-cost adsorbents. Graphene and graphene-based materials attracted a great attention around the world because of their potential for a variety applications ranging from electronics, gas sensing, energy storage and CO₂ capture. Large specific surface area of these materials up to ~3000m²/g and versatile modification make them excellent adsorbents for diverse applications. Here, graphene-based adsorbents are reviewed with special emphasis on their adsorption affinity toward CO₂, H₂ and CH₄. This review shows that graphene derivatives obtained mainly via "chemical exfoliation" of graphite and further modification with polymers and/or metal species can be very effective sorbents for CO₂ and other gases and can compete with the currently used carbonaceous or non-carbonaceous adsorbents. The high adsorption capacities of graphene-based materials are mainly determined by their unique nanostructures, high specific surface areas and tailorable surface properties, which make them suitable for storage or capture of various molecules relevant for environmental and energy-related applications.

Covalent cross-linking as a strategy to generate novel materials based on layered (2D) and other low D structures

Covalent linking of 2D structures such as graphene, MoS₂and C₃N₄by employing coupling reactions provides a strategy to generate a variety of materials with new or improved properties.

Graphene-based porous materials with tunable surface area and CO2 adsorption properties synthesized by fluorine displacement reaction with various diamines

A mild, operationally simple and controllable protocol for preparing graphene-based porous materials is essential to achieve a good pore-design development. In this paper, graphene-based porous materials with tunable surface area were constructed by the intercalation of fluorinated graphene (FG) based on the reaction of reactive CF bonds attached to graphene sheets with various amine-terminated molecules. In the porous materials, graphene sheets are like building blocks, and the diamines covalently grafted onto graphene framework act as pillars. Various diamines are successfully grafted onto graphene sheets, but the grafting ratio of diamines and reduction degree of FG differ greatly and depend on the chemical reactivity of diamines. Pillared diamine molecules chemically anchor at one end and are capable of undergoing a different reaction on the other end, resulting in three different conformations of graphene derivatives. Nitrogen sorption isotherms revealed that the surface area and pore distribution of the obtained porous materials depend heavily on the size and structure of diamine pillars. CO2 uptake capacity characterization showed that ethylenediamine intercalated FG achieved a high CO2 uptake density of 18.0 CO2 molecules per nm(2) at 0°C and 1.1bars, and high adsorption heat, up to 46.1kJmol(-1) at zero coverage.

Holey graphene frameworks for highly selective post-combustion carbon capture

Atmospheric CO₂ concentrations continue to rise rapidly in response to increased combustion of fossil fuels, contributing to global climate change. In order to mitigate the effects of global warming, development of new materials for cost-effective and energy-efficient CO₂ capture is critically important. Graphene-based porous materials are an emerging class of solid adsorbents for selectively removing CO₂ from flue gases. Herein, we report a simple and scalable approach to produce three-dimensional holey graphene frameworks with tunable porosity and pore geometry, and demonstrate their application as high-performance CO₂ adsorbents. These holey graphene macrostructures exhibit a significantly improved specific surface area and pore volume compared to their pristine counterparts, and can be effectively used in post-combustion CO₂ adsorption systems because of their intrinsic hydrophobicity together with good gravimetric storage capacities, rapid removal capabilities, superior cycling stabilities, and moderate initial isosteric heats. In addition, an exceptionally high CO₂ over N₂ selectivity can be achieved under conditions relevant to capture from the dry exhaust gas stream of a coal burning power plant, suggesting the possibility of recovering highly pure CO₂ for long-term sequestration and/or utilization for downstream applications.

Rational synthesis of Pd nanoparticle-embedded reduced graphene oxide frameworks with enhanced selective catalysis in water

A three-dimensional (3D) Pd-reduced graphene oxide framework (Pd-rGOF) with hierarchical macro- and mesoporous structures has been developed via covalence- and coordination-assisted self-assembly approach. In this facile fabrication process, GO was first cross-linked with triethylene tetramine (TETA) to form 3D GOF, in which well-dispersed and ultrasmall Pd nanoparticles (NPs) in situ grew and embedded the framework. The obtained nanopores, 3D Pd-rGOF, can act as nanoreactors to help the reaction substrates thoroughly contact with the surface of Pd NPs, thereby exhibiting high activity and selectivity toward the Tsuji-Trost reaction in water, with 99% conversion and selectivity for most substrates. Moreover, the 3D Pd-rGOF catalyst can be reused more than ten times without significant loss of activity, rendering this catalyst long-term stability. The abovementioned observations make the rGOF a universal platform to coordinate other noble metal ions (NM) to construct desired NM-rGOF nanocatalysts with improved activity, selectivity, and durability that can be used in a broad range of practical applications.

Straightforward Generation of Pillared, Microporous Graphene Frameworks for Use in Supercapacitors

Microporous, pillared graphene-based frameworks are generated in a simple functionalization/coupling procedure starting from reduced graphene oxide. They are used for the fabrication of high-performance supercapacitor devices.

The improved electrochemical performance of cross-linked 3D graphene nanoribbon monolith electrodes

Technical advancement in the field of ultra-small sensors and devices demands the development of novel micro- or nano-based architectures. Here we report the design and assembly of cross-linked three dimensional graphene nanoribbons (3D GNRs) using solution based covalent binding of individual 2D GNRs and demonstrate its electrochemical application as a 3D electrode. The enhanced performance of 3D GNRs over individual 2D GNRs is established using standard redox probes--[Ru(NH3)6](3+/2+), [Fe(CN)6](3-/4-) and important bio-analytes--dopamine and ascorbic acid. 3D GNRs are found to have high double layer capacitance (2482 μF cm(-2)) and faster electron transfer kinetics; their exceptional electrocatalytic activity towards the oxygen reduction reaction is indicative of their potential over a wide range of electrochemical applications. Moreover, this study opens a new platform for the design of novel point-of-care devices and electrodes for energy devices.

3D polyaniline porous layer anchored pillared graphene sheets: enhanced interface joined with high conductivity for better charge storage applications

Here, we report synthesis of a 3-dimensional (3D) porous polyaniline (PANI) anchored on pillared graphene (G-PANI-PA) as an efficient charge storage material for supercapacitor applications. Benzoic acid (BA) anchored graphene, having spatially separated graphene layers (G-Bz-COOH), was used as a structure controlling support whereas 3D PANI growth has been achieved by a simple chemical oxidation of aniline in the presence of phytic acid (PA). The BA groups on G-Bz-COOH play a critical role in preventing the restacking of graphene to achieve a high surface area of 472 m(2)/g compared to reduced graphene oxide (RGO, 290 m(2)/g). The carboxylic acid (-COOH) group controls the rate of polymerization to achieve a compact polymer structure with micropores whereas the chelating nature of PA plays a crucial role to achieve the 3D growth pattern of PANI. This type of controlled interplay helps G-PANI-PA to achieve a high conductivity of 3.74 S/cm all the while maintaining a high surface area of 330 m(2)/g compared to PANI-PA (0.4 S/cm and 60 m(2)/g). G-PANI-PA thus conceives the characteristics required for facile charge mobility during fast charge-discharge cycles, which results in a high specific capacitance of 652 F/g for the composite. Owing to the high surface area along with high conductivity, G-PANI-PA displays a stable specific capacitance of 547 F/g even with a high mass loading of 3 mg/cm(2), an enhanced areal capacitance of 1.52 F/cm(2), and a volumetric capacitance of 122 F/cm(3). The reduced charge-transfer resistance (RCT) of 0.67 Ω displayed by G-PANI-PA compared to pure PANI (0.79 Ω) stands out as valid evidence of the improved charge mobility achieved by the system by growing the 3D PANI layer along the spatially separated layers of the graphene sheets. The low RCT helps the system to display capacitance retention as high as 65% even under a high current dragging condition of 10 A/g. High charge/discharge rates and good cycling stability are the other highlights of the supercapacitor system derived from this composite material.

Fluorosurfactants-Directed Preparation of Homogeneous and Hierarchical-Porosity CMP Aerogels for Gas Sorption and Oil Cleanup

Homogeneous, hierarchical-porosity and highly hydrophobic conjugated microporous polymer (CMP) aerogels are facilely prepared assisted by fluorosurfactants. The fluorosurfactants show several roles in controlling the gelation process, modulating pore structures, and raising the hydrophobicity of materials, thus giving rise to aerogels with exceptional gas sorption and oil cleanup performance.