For the first time, pristine graphene can be controllably crumpled and unfolded. The mechanism for graphene is radically different than that observed for graphene oxide; a multifaced crumpled, ...dimpled particle morphology is seen for pristine graphene in contrast to the wrinkled, compressed surface of graphene oxide particles, showing that surface chemistry dictates nanosheet interactions during the crumpling process. The process demonstrated here utilizes a spray‐drying technique to produce droplets of aqueous graphene dispersions and induce crumpling through rapid droplet evaporation. For the first time, the gradual dimensional transition of 2D graphene nanosheets to a 3D crumpled morphology in droplets is directly observed; this is imaged by a novel sample collection device inside the spray dryer itself. The degree of folding can be tailored by altering the capillary forces on the dispersed sheets during evaporation. It is also shown that the morphology of redispersed crumpled graphene powder can be controlled by solvent selection. This process is scalable, with the ability to rapidly process graphene dispersions into powders suitable for a variety of engineering applications.
The morphological transition of 2D graphene nanosheets to 3D crumpled particles is achieved via a scalable spray‐drying technique. In‐situ microscopy shows that factors such as nanosheet elasticity and surface chemistry affect the crumpling process, such that the crumpling mechanism differs between pristine graphene and graphene oxide. Unfolding of crumpled graphene upon rewetting depends on nanosheet–solvent interactions.
Abstract
Ventilation air methane (VAM) is a potent greenhouse gas source originating from geological wells, current and extinct mineshafts and other terrestrial conduits venting methane to the ...atmosphere, contributing to global methane emissions and disproportionate warming potential. Herein, we introduce the concept of the
methanotrophic material
as an engineering solution. Such materials should be capable of converting methane at ambient temperatures and pressures to a binder product, capturing and permanently sequestering the methane while simultaneously restricting its further emission. While such materials are currently under research development, this goal is supported and facilities by the mathematical framework, introduced and used herein, to evaluate the ability to convert methane, using currently published activity data. We include a case study of the conversion of a characteristic stream of VAM (0.6% methane in air, 1.7 × 10
8
l hr
−1
equivalent to 100 000 standard cubic feet per minute). We show that when appropriately designed, such systems require a surface coverage of less than 1000 m of mine tunnel length (equivalent to 20 000 m
2
areal coverage) in order to reduce the methane emission from this stream by over 99%. Finally, we highlight formaldehyde as a reactive intermediate of methane oxidation which may itself be incorporated into these coating materials. As a component of binders and polymers already used ubiquitously in commercial products, this intermediate ultimately allows these systems to sequester the carbon from methane in a stable and solid form. The results presented here are easily extended to the treatment of other methane streams—either more concentrated or dilute—and the results herein will guide the design and development of a new class of carbon-negative materials.
We demonstrate a simple and effective technique for dispersing pristine (unfunctionalized) graphene at high concentrations in a wide range of organic solvents by use of a stabilizing polymer ...(polyvinylpyrrolidone, PVP). These polymer-stabilized graphene dispersions are shown to be highly stable and readily redispersible even after freeze-drying. This technique yields significantly higher graphene concentrations compared to prior studies. An excellent increase in the thermal conductivity of the fluid by the addition of pristine graphene is also demonstrated. These well-dispersed pristine graphene sheets were then used as a strong and conductive nano-filler for polymer composites. Graphene/PVP composites were produced by the bulk polymerization of
N-vinylpyrrolidone loaded with dispersed graphene, resulting in excellent load transfer and improved mechanical and electrical properties.
While facial coverings reduce the spread of SARS‐CoV‐2 by viral filtration, masks capable of viral inactivation by heating can provide a complementary method to limit transmission. Inspired by ...reverse‐flow chemical reactors, we introduce a new virucidal face mask concept driven by the oscillatory flow of human breath. The governing heat and mass transport equations are solved to evaluate virus and CO2 transport. Given limits imposed by the kinetics of SARS‐CoV‐2 thermal inactivation, human breath, safety, and comfort, heated masks may inactivate SARS‐CoV‐2 to medical‐grade sterility. We detail one design, with a volume of 300 ml at 90°C that achieves a 3‐log reduction in viral load with minimal impedance within the mask mesh, with partition coefficient around 2. This is the first quantitative analysis of virucidal thermal inactivation within a protective face mask, and addresses a pressing need for new approaches for personal protective equipment during a global pandemic.
In the last decade, along with the increasing use of graphene oxide (GO) in various applications, there is also considerable interest in understanding its effects on human health. Only a few ...experimental approaches can simulate common routes of exposure, such as ingestion, due to the inherent complexity of the digestive tract. This study presents the synthesis of size‐sorted GO of sub‐micrometer‐ or micrometer‐sized lateral dimensions, its physicochemical transformations across mouth, gastric, and small intestinal simulated digestions, and its toxicological assessment against a physiologically relevant, in vitro cellular model of the human intestinal epithelium. Results from real‐time characterization of the simulated digestas of the gastrointestinal tract using multi‐angle laser diffraction and field‐emission scanning electron microscopy show that GO agglomerates in the gastric and small intestinal phase. Extensive morphological changes, such as folding, are also observed on GO following simulated digestion. Furthermore, X‐ray photoelectron spectroscopy reveals that GO presents covalently bound N‐containing groups on its surface. It is shown that the GO employed in this study undergoes reduction. Toxicological assessment of the GO small intestinal digesta over 24 h does not point to acute cytotoxicity, and examination of the intestinal epithelium under electron microscopy does not reveal histological alterations. Both sub‐micrometer‐ and micrometer‐sized GO variants elicit a 20% statistically significant increase in reactive oxygen species generation compared to the untreated control after a 6 h exposure.
Simulated digestion of graphene oxide promotes its agglomeration in the gastrointestinal tract, allows it to sequester digestive enzymes, and leads to its chemical reduction. Subsequent exposure of a tri‐culture human intestinal epithelium model to small intestinal digesta of graphene oxide shows that the digested material can significantly increase intracellular production of reactive oxygen species at both micrometer‐ and sub‐micrometer lateral sizes.
Colloidal dispersions of nanomaterials are often polydisperse in size, significantly complicating their characterization. This is particularly true for materials early in their historical development ...due to synthetic control, dispersion efficiency, and instability during storage. Because a wide range of system properties and technological applications depend on particle dimensions, it remains an important problem in nanotechnology to identify a method for the routine characterization of polydispersity in nanoparticle samples, especially changes over time. Commonly employed methods such as dynamic light scattering or analytical ultracentrifugation (AUC) accurately estimate only the first moment of the distribution or are not routine. In this work, the use of single‐particle tracking (SPT) to probe size distributions of common nanoparticle dispersions, including polystyrene nanoparticles, single‐walled carbon nanotubes, graphene oxide, chitosan‐tripolyphosphate, acrylate, hexagonal boron nitride, and poly(lactic‐co‐glycolic acid), is proposed and explored. The analysis of particle tracks is conducted using a newly developed Bayesian algorithm that is called Maximum A posteriori Nanoparticle Tracking Analysis. By combining SPT and AUC techniques, it is shown that it is possible to independently estimate the mean aspect ratio of anisotropic particles, an important characterization property. It is concluded that SPT provides a facile, rapid analytical method for routine nanomaterials characterization.
Single‐particle tracking (SPT) is a versatile technique to study the size distributions of nanoparticle dispersions. Combined with a Bayesian method for distribution estimation, SPT is effective at monitoring size distribution changes for common nanoparticle preparations, making it attractive as a technique for routine characterization. Combining with analytical ultracentrifugation, additional particle anisotropy information can be obtained.
Effective in silico methods to predict protein corona compositions on engineered nanomaterials (ENMs) could help elucidate the biological outcomes of ENMs in biosystems without the need for ...conducting lengthy experiments for corona characterization. However, the physicochemical properties of ENMs, used as the descriptors in current modeling methods, are insufficient to represent the complex interactions between ENMs and proteins. Herein, we utilized the fluorescence change (FC) from fluorescamine labeling on a protein, with or without the presence of the ENM, as a novel descriptor of the ENM to build machine learning models for corona formation. FCs were significantly correlated with the abundance of the corresponding proteins in the corona on diverse classes of ENMs, including metal and metal oxides, nanocellulose, and 2D ENMs. Prediction models established by the random forest algorithm using FCs as the ENM descriptors showed better performance than the conventional descriptors, such as ENM size and surface charge, in the prediction of corona formation. Moreover, they were able to predict protein corona formation on ENMs with very heterogeneous properties. We believe this novel descriptor can improve in silico studies of corona formation, leading to a better understanding on the protein adsorption behaviors of diverse ENMs in different biological matrices. Such information is essential for gaining a comprehensive view of how ENMs interact with biological systems in ENM safety and sustainability assessments.
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•A set of novel descriptors for engineered nanomaterials was obtained by the screening method of fluorescamine labeling.•This set of descriptors helped build machine learning models to predict the composition of protein corona.•The modeling approach with the new descriptors can predict corona formation on heterogenous nanomaterials.
In this paper, we demonstrate a facile technique to disperse pristine few-layer graphene (FLG) in water utilizing a triphenylene based stabilizer (C10) that non-covalently functionalizes the surface ...without micelle formation. The yield of FLG in the final dispersion (0.2 mg FLG/mg C10) is much higher than comparable surfactants and polymers stabilizers. This dispersion is reversible in response to pH changes unlike conventional stabilizers. The C10-stabilized FLG dispersion is also stable against heat and lyophilization. This non-covalent functionalization does not disrupt the pristine structure of the graphene sheets; instead, these coatings allow for stable, aggregation-resistant FLG dispersion, as characterized through TEM. To demonstrate the utility of such dispersions, we prepared pristine FLG-loaded poly (vinyl alcohol) (PVA) composites by a simple solution casting process. This is the first example of PVA composites based on pristine graphene. These composites have enhanced electrical properties at relatively low filler fraction (0.26 vol% FLG). Moreover, these composites exhibit improved mechanical properties established by tensile and hardness tests results; these data suggest anisotropic reinforcement caused by graphene alignment.
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Abstract
Ventilation air methane (VAM) is a potent greenhouse gas source originating from geological wells, current and extinct mineshafts and other terrestrial conduits venting methane to the ...atmosphere, contributing to global methane emissions and disproportionate warming potential. Herein, we introduce the concept of the
methanotrophic material
as an engineering solution. Such materials should be capable of converting methane at ambient temperatures and pressures to a binder product, capturing and permanently sequestering the methane while simultaneously restricting its further emission. While such materials are currently under research development, this goal is supported and facilities by the mathematical framework, introduced and used herein, to evaluate the ability to convert methane, using currently published activity data. We include a case study of the conversion of a characteristic stream of VAM (0.6% methane in air, 1.7 × 10
8
l hr
−1
equivalent to 100 000 standard cubic feet per minute). We show that when appropriately designed, such systems require a surface coverage of less than 1000 m of mine tunnel length (equivalent to 20 000 m
2
areal coverage) in order to reduce the methane emission from this stream by over 99%. Finally, we highlight formaldehyde as a reactive intermediate of methane oxidation which may itself be incorporated into these coating materials. As a component of binders and polymers already used ubiquitously in commercial products, this intermediate ultimately allows these systems to sequester the carbon from methane in a stable and solid form. The results presented here are easily extended to the treatment of other methane streams—either more concentrated or dilute—and the results herein will guide the design and development of a new class of carbon-negative materials.
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