Bioenergy crops are an attractive option for use in energy production. A good plant candidate for bioenergy applications should produce a high amount of biomass and resist harsh environmental ...conditions. Carbon-based nanomaterials (CBNs) have been described as promising seed germination and plant growth regulators. In this paper, we tested the impact of two CBNs: graphene and multi-walled carbon nanotubes (CNTs) on germination and biomass production of two major bioenergy crops (sorghum and switchgrass). The application of graphene and CNTs increased the germination rate of switchgrass seeds and led to an early germination of sorghum seeds. The exposure of switchgrass to graphene (200 mg/l) resulted in a 28% increase of total biomass produced compared to untreated plants. We tested the impact of CBNs on bioenergy crops under salt stress conditions and discovered that CBNs can significantly reduce symptoms of salt stress imposed by the addition of NaCl into the growth medium. Using an ion selective electrode, we demonstrated that the concentration of Na+ ions in NaCl solution can be significantly decreased by the addition of CNTs to the salt solution. Our data confirmed the potential of CBNs as plant growth regulators for non-food crops and demonstrated the role of CBNs in the protection of plants against salt stress by desalination of saline growth medium.
Dispersion of carbon nanotubes (CNTs) into liquids typically requires ultrasonication to exfoliate individuals CNTs from bundles. Experiments show that CNT length drops with sonication time (or ...energy) as a power law t ⁻ᵐ. Yet the breakage mechanism is not well understood, and the experimentally reported power law exponent m ranges from approximately 0.2 to 0.5. Here we simulate the motion of CNTs around cavitating bubbles by coupling Brownian dynamics with the Rayleigh–Plesset equation. We observe that, during bubble growth, CNTs align tangentially to the bubble surface. Surprisingly, we find two dynamical regimes during the collapse: shorter CNTs align radially, longer ones buckle. We compute the phase diagram for CNT collapse dynamics as a function of CNT length, stiffness, and initial distance from the bubble nuclei and determine the transition from aligning to buckling. We conclude that, depending on their length, CNTs can break due to either buckling or stretching. These two mechanisms yield different power laws for the length decay (0.25 and 0.5, respectively), reconciling the apparent discrepancy in the experimental data.
Electrochemical exfoliation is a promising bulk method for producing graphene from graphite; in this method, an applied voltage drives ionic species to intercalate into graphite where they form ...gaseous species that expand and exfoliate individual graphene sheets. However, a number of obstacles have prevented this approach from becoming a feasible production route; the disintegration of the graphite electrode as the method progresses is the chief difficulty. Here we show that if graphite powders are contained and compressed within a permeable and expandable containment system, the graphite powders can be continuously intercalated, expanded, and exfoliated to produce graphene. Our data indicate both high yield (65%) and extraordinarily large lateral size (>30 μm) in the as-produced graphene. We also show that this process is scalable and that graphene yield efficiency depends solely on reactor geometry, graphite compression, and electrolyte transport.
Abstract
Ti
3
C
2
T
x
belongs to the family of MXenes, 2D materials with an attractive combination of functional properties suitable for applications such as batteries, supercapacitors, and strain ...sensors. However, the fabrication of devices and functional coatings based on Ti
3
C
2
T
x
remains challenging as they are prone to chemical degradation by their oxidation to TiO
2
. In this paper, we examine the oxidation of Ti
3
C
2
T
x
in air, liquid, and solid media via conductivity measurements to assess the shelf life of Ti
3
C
2
T
x
MXenes. The oxidation of Ti
3
C
2
T
x
was observed in all the media used in this study, but it is fastest in liquid media and slowest in solid media (including polymer matrices). We also show that the conventional indicators of MXene oxidation, such as changes in color and colloidal stability, are not always reliable. Finally, we demonstrate the acceleration of oxidation under exposure to UV light.
Stretchable, bendable, and foldable conductive coatings are crucial for wearable electronics and biometric sensors. These coatings should maintain functionality while simultaneously interfacing with ...different types of surfaces undergoing mechanical deformation. MXene sheets as conductive two-dimensional nanomaterials are promising for this purpose, but it is still extremely difficult to form surface-agnostic MXene coatings that can withstand extreme mechanical deformation. We report on conductive and conformal MXene multilayer coatings that can undergo large-scale mechanical deformation while maintaining a conductivity as high as 2000 S/m. MXene multilayers are successfully deposited onto flexible polymer sheets, stretchable poly(dimethylsiloxane), nylon fiber, glass, and silicon. The coating shows a recoverable resistance response to bending (up to 2.5-mm bending radius) and stretching (up to 40% tensile strain), which was leveraged for detecting human motion and topographical scanning. We anticipate that this discovery will allow for the implementation of MXene-based coatings onto mechanically deformable objects.
The isothermal curing kinetics of carbon nanotube loaded epoxy was investigated using rheometry and differential scanning calorimetry (DSC) at a range of temperatures. Rheo-kinetics was used to ...observe time-dependent rheological changes in elastic (G′) and viscous (G″) moduli, and complex viscosities of epoxy-CNT samples during isothermal curing. DSC measurements were also performed to monitor the curing reaction, in order to compare against the rheo-kinetic parameters. The Kamal-Sourour kinetic model describes the curing of the epoxy-CNT system for rheo-kinetics and DSC well. The activation energies of the curing reaction were found to be ∼36 kJ/mol and ∼33 kJ/mol using rheo-kinetics analysis and DSC, respectively. In addition, radio-frequency (RF) electromagnetic fields were used to heat and cure the epoxy-CNT sample; such heating techniques are valuable in a number of epoxy processing technologies. G′, G″, and complex viscosities of RF heated samples were measured to monitor RF-aided curing. This allows us to monitor the curing kinetics inside samples being heated by RF fields; the data indicate that RF-aiding curing is faster than curing rates for samples undergoing curing inside a measurement device such as a rheometer or DSC, because the heat generated is immediate and volumetric.
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In recent years, reports of plastic debris in the gastrointestinal (GI) tract of fish have been well documented in the scientific literature. This, in turn, increased concerns regarding human health ...exposure to microplastics through the consumption of contaminated fish. Most of the available research regarding microplastic toxicity has focused on marine organisms through direct feeding or waterborne exposures at the individual level. However, little is known about the trophic transfer of microplastics through the aquatic food chain. Freshwater zooplankton Daphnia magna (hereafter Daphnia), and the fathead minnow Pimephales promelas (FHM), are well-known model species used in standard toxicological studies and ecological risk assessments that provide a simple model for trophic transfer. The aim of this study was to assess the tissue translocation, trophic transfer, and depuration of two concentrations (20 and 2000-part ml−1) of 6 μm polystyrene (PS) microplastics particles between Daphnia and FHM. Bioconcentration factors (BCF) and bioaccumulation factors (BAF) were determined. Fluorescent microscopy was used to determine the number of particles in the water media and within the organs of both species. Throughout the five days of exposure, PS particles were only found within the GI tract of both species. The BCF for Daphnia was 0.034 ± 0.005 for the low concentration and 0.026 ± 0.006 for the high concentration. The BAF for FHM was 0.094 ± 0.037 for the low concentration and 0.205 ± 0.051 for the high concentration. Between 72 and 96 h after exposure all microplastic particles were depurated from both species. The presence of food had a significant effect on the depuration of microplastic particles from Daphnia but not for FHM. Based on the low BCF and BAF values for both species, rapid depuration rates, and null translocation of microplastic particles to organs and tissues from the GI tract, there is a low probability that microplastics will bioconcentrate and bioaccumulate under environmental conditions.
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•There was minimal uptake (<1%) of PS microplastics by Daphnia and fathead minnow.•Microplastics were quantified in the gut and did not translocate to other organs.•Microplastics had short retention times and were fully depurated within 72–96 h.•Low BCF and BAF values were found for Daphnia and fathead minnow, respectively.•Food presence significantly increased depuration of microplastics in Daphnia.
Low uptake, null translocation, and short retention time, indicate a low probability that 6 μm PS microplastics will bioconcentrate and bioaccumulate under environmentally relevant conditions.
We demonstrate that functionalized pyrene derivatives effectively stabilize single- and few-layer graphene flakes in aqueous dispersions. The graphene/stabilizer yield obtained by this method is ...exceptionally high relative to conventional nanomaterial stabilizers such as surfactants or polymers. The mechanism of stabilization by pyrene derivatives is investigated by studying the effects of various parameters on dispersed graphene concentration and stability; these parameters include stabilizer concentration, initial graphite concentration, solution pH, and type and number of functional groups and counterions. The effectiveness of the pyrene derivatives is pH-tunable, as measured by zeta potential, and is also a function of the number of functional groups, the electronegativity of the functional group, the counterion, the relative polarity between stabilizer and solvent, and the distance from the functional group to the basal plane. Even if the dispersion is destabilized by extreme pH or lyophilization, the graphene does not aggregate because the stabilizer remains adsorbed on the surface. These dispersions also show promise for applications in graphene/polymer nanocomposites (examined in this paper), organic solar cells, conductive films, and inkjet-printed electronic devices.
High disposability, high durability, and indiscriminate use have led to the accumulation of plastics at uncontrolled rates in the environment. However, plastics are not the only source of water ...pollution in the environment. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a group of pharmaceuticals widely and highly consumed in the market due to a low price and over-the-counter accessibility. NSAIDs are frequently detected in surface water environments at μg L−1 concentrations. In the present study, the sorption behavior of three NSAIDs (ibuprofen, naproxen, diclofenac) was examined with four types of microplastics (polystyrene (PS), ultra-high molecular weight polyethylene (UHMWPE), average molecular weight medium density polyethylene (AMWPE), and polypropylene (PP)), under varying water conditions. Low sorption occurred between NSAIDs and microplastics under environmentally relevant conditions. The sorption process exhibited a pronounced pH dependency due to the effect of pH on the speciation of the compounds and the surface charge of the particles. Only under acidic conditions (pH: 2), NSAIDs were highly sorbed onto microplastics mainly ruled by hydrophobic interactions. Among NSAIDs tested, diclofenac exhibited the highest sorption coefficients to microplastics. Polyethylene particles exhibited the highest affinity for NSAIDs.
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•Low sorption occurred with NSAIDs and MPs under environmentally relevant conditions.•NSAID sorption onto microplastics was highly dependent on pH.•Diclofenac exhibited the highest sorption coefficients.•Polyethylene microplastics exhibited the highest sorption capacity for NSAIDs.•Microplastics are not substantial vectors for NSAIDs in the environment.
Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non‐oxidized graphene) are described. General metrics are outlined that can be used to assess the ...quality and processability of various “graphene” products, as well as metrics that determine the potential for industrial scale‐up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large‐scale production.
Recent developments in the exfoliation, dispersion, and processing of pristine graphene are described. Quantitative metrics are outlined to describe both graphene quality and graphene‐processing techniques. Finally, the major challenges are detailed regarding industrial scale‐up of pristine graphene production and processing into multifunctional materials, as well as the associated quality/quantity tradeoffs.
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