High-Efficiency Production of Graphene by Supercritical CO2 Exfoliation with Rapid Expansion

Supercritical CO2 mediated construction of aluminium waste recovered γ-Al2O3 impregnated Dracaena trifasciata biomass-derived carbon composite: A robust electrocatalyst for mutagenic pollutant detection

Inspired by the waste-to-wealth concept, we have recovered the gamma phase aluminium oxide nanoparticles (γ-Al2O3 NPs) from waste aluminium (Al) foils and fabricated a composite with Dracaena trifasciata biomass-derived activated carbon matrix (DT-AC) using supercritical carbon-di-oxide (SC-CO2) pathway. The prepared samples are characterized altogether by various micro- and spectroscopic analyses. Based on the results, the recovered γ-Al2O3 NPs are well impregnated in the DT-AC surface by the action of the microbubble effect from the SC-CO2. The higher D-band and ID/IG value of 1.07 in the Al2O3/DT-AC nanocomposite indicate increased defects and the amorphous nature of the carbon materials. The effect of scan rate (ν) demonstrated greater linearity in ν1/2 vs peak current in the electrochemical detection study of the mutagenic pollutant 4-(methylamino) phenol hemi sulfate, showing a quasi-reversible electron transfer process undergoing diffusion-controlled kinetics. Furthermore, the limit of detection is determined to be 3.2 nM L-1 with an extensive linear range, spanning from 0.05 to 618.25 µM/L. The incredible sensitivity of 2.117 μA μM-1 cm-2, along with excellent selectivity, repeatability, and stability, is observed. Further, the respectable recovery percentage of 98.61 % in the environmental water sample is perceived. The observed outcomes suggest that the prepared Al2O3/DT-AC composite performs as an excellent electrocatalyst material, and the processing techniques used are thought to be sustainable in nature.

Supercritical CO2 Directional-Assisted Synthesis of Low-Dimensional Materials for Functional Applications

Supercritical CO2 (SC CO2 ), as one of the unique fluids that possess fascinating properties of gas and liquid, holds great promise in chemical reactions and fabrication of materials. Building special nanostructures via SC CO2 for functional applications has been the focus of intense research for the past two decades, with facile regulated reaction conditions and a particular reaction field to operate compared to the more widely used solvent systems. In this review, the significance of SC CO2 on fabricating various functional materials including modification of 1D carbon nanotubes, 2D materials, and 2D heterostructures is stated. The fundamental aspects involving building special nanostructures via SC CO2 are explored: how their structure, morphology, and chemical composition be affected by the SC CO2 . Various optimization strategies are outlined to improve their performances, and recent advances are combined to present a coherent understanding of the mechanism of SC CO2 acting on these functional nanostructures. The wide applications of these special nanostructures in catalysis, biosensing, optoelectronics, microelectronics, and energy transformation are discussed. Moreover, the current status of SC CO2 research, the existing scientific issues, and application challenges, as well as the possible future directions to advance this fertile field are proposed in this review.

Appraising the potency of small molecule inhibitors and their graphene surface-mediated organizational attributes on uric acid-melamine clusters

Uric acid (UA) and melamine (MM) crystallization in humans is associated with adverse medical conditions, including the germination of kidney stones, because of their low solubility. The growth of kidney stones, usually formed on renal papillary facades, is accomplished on the matrix-coated surface by the aggregation of preformed crystals or secondary crystal nucleation. Therefore, the effects of inhibitors such as theobromine (TB) and allopurinol (AP) on MM-UA aggregation are investigated by employing classical molecular dynamics simulations on a graphene surface. This impersonates the exact essence of the precipitation of kidney stones. The interaction between MM-UA is very intense and, thus, large clusters are formed on the surface. The presence of TB and AP will, however, substantially inhibit their aggregation. TB and AP significantly impede UA aggregation in particular. Therefore, lower order UA clusters are formed. These smaller UA clusters then pull a lower number of MM towards themselves, resulting in a smaller order UA-MM cluster. MM and UA aggregation on a 2D graphene surface is found to be spontaneous. There is no difference in these molecules' adsorption with a change in the force field parameters (i.e., GAFF and OPLS-AA) for graphene. Moreover, the greater the surface area of graphene, the more molecules are absorbed. The solute-surface van der Waals interaction energy plays a driving force in the adsorption of solute molecules on the surface. In addition, interactions like hydrogen bonding and π-stacking over the graphene surface involve binding all like molecules. These aggregated solute molecules strongly attract more like molecules until all solute molecules are adsorbed on the graphene surface, as estimated by enhanced sampling. The molecular origin of graphene exfoliation by MM is also described here. The present work helps to design novel kidney stone inhibitors.

Graphene Synthesis: Method, Exfoliation Mechanism and Large-Scale Production

Graphene is a unique attractive material owing to its characteristic structure and excellent properties. To improve the preparation efficiency of graphene, reduce defects and costs, and meet the growing market demand, it is crucial to explore the improved and innovative production methods and process for graphene. This review summarizes recent advanced graphene synthesis methods including “bottom-up” and “top-down” processes, and their influence on the structure, cost, and preparation efficiency of graphene, as well as its peeling mechanism. The viability and practicality of preparing graphene using polymers peeling flake graphite or graphite filling polymer was discussed. Based on the comparative study, it is potential to mass produce graphene with large size and high quality using the viscoelasticity of polymers and their affinity to the graphite surface.

Dispersed graphene materials of biomedical interest and their toxicological consequences

Graphene is one-atom thick nanocarbon displaying a unique honeycomb structure and extensive conjugation. In addition to high surface area to mass ratio, it displays unique optical, thermal, electronic and mechanical properties. Atomic scale tunability of graphene has attracted immense research interest with a prospective utility in electronics, desalination, energy sectors, and beyond. Its intrinsic opto-thermal properties are appealing from the standpoint of multimodal drug delivery, imaging and biosensing applications. Hydrophobic basal plane of sheets can be efficiently loaded with aromatic molecules via non-specific forces. With intense biomedical interest, methods are evolving to produce defect-free and dispersion stable sheets. This review summarizes advancements in synthetic approaches and strategies of stabilizing graphene derivatives in aqueous medium. We have described the interaction of colloidal graphene with cellular and sub-cellular components, and subsequent physiological signaling. Finally, a systematic discussion is provided covering toxicological challenges and possible solutions on utilizing graphene formulations for high-end biomedical applications.

Supercritical Fluid-Facilitated Exfoliation and Processing of 2D Materials

Since the first intercalation of layered silicates by using supercritical CO2 as a processing medium, considerable efforts have been dedicated to intercalating and exfoliating layered two-dimensional (2D) materials in various supercritical fluids (SCFs) to yield single- and few-layer nanosheets. Here, recent work in this area is highlighted. Motivating factors for enhancing exfoliation efficiency and product quality in SCFs, mechanisms for exfoliation and dispersion in SCFs, as well as general metrics applied to assess quality and processability of exfoliated 2D materials are critically discussed. Further, advances in formation and application of 2D material-based composites with assistance from SCFs are presented. These discussions address chemical transformations accompanying SCF processing such as doping, covalent surface modification, and heterostructure formation. Promising features, challenges, and routes to expanding SCF processing techniques are described.

Effect of silane functionalized graphene prepared by a supercritical carbon dioxide process on the barrier properties of polyethylene terephthalate composite films

In this work, a simple and eco-friendly strategy to modify graphene nanoplatelets (GNs) with different silane coupling agents using a supercritical carbon dioxide (Sc-CO₂) process has been presented, and effect of the modified GNs on the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of GN/PET composite films was studied. FT-IR, SEM, EDX and TG results indicated that Sc-CO₂ process was an effective strategy to modify GNs with silane coupling agents. Addition of the modified GNs into PET matrix could greatly decrease the OTR and WVTR values of the GNs/PET composite films, and the WVTR of GNs560/PET composite film and OTR of GNs550/PET composite film were respectively decreased about 90.08% and 58.04%, as compared to those of GNs/PET composite film. It is found that the gas barrier property of GN/PET composites was attributed to not only the tortuous path effect caused by GNs themselves and the interfacial interaction, but also the affinity of binding bonds between GNs and the polymer to the gas molecules. It is believed that this work provided a strategy to design and prepare CN/polymer composites with high barrier properties.

Adding silane modified GNs prepared by a Sc-CO₂ process into a PET matrix could greatly enhance the barrier properties of the GNs/PET composites.The barrier performance of GNs/PET composites was greatly enhanced by modifying GNs with silane coupling agents via Sc-CO₂ process.