Robert H. Hurt

Lithium dendrite propagation in solid electrolytes can be mitigated by engineering nanoscale, multifunctional interlayers. This work establishes a general electro–chemo–mechanical design framework for multilayer and composite solid electrolytes.

MoS ₂ nanosheets in metallic 1T-phase enhance the electrical conductivity of fibrin hydrogels and show programmable bioresorption rates and pathways.

Wrinkled graphene coatings are engineered to fulfill multiple functions desired for ultrathin gloves that prevent human exposure to chemical toxicants.

Bacterial growth stage plays an important role in how bacteria interact with nanoparticles, but the effect that two-dimensional nanomaterials may have on this interaction has yet to be rigorously studied. The goal of this study is to explore the role of the growth stage (non-growing, exponential, transitional, and stationary) of Escherichia coli (E. coli) in its response to graphene oxide (GO), MoS₂, and MoSe₂ colloidal nanosheets (ranging 0.00–2.52 μg GO–TOC, MoS₂–Mo, or MoSe₂–Mo mL⁻¹). This study is the first to comprehensively examine the response of E. coli at its various growth stages to two-dimensional nanomaterials. We also examine bacterial response to novel two-dimensional nanomaterials (MoS₂ and MoSe₂) compared to an extensively studied material (GO). The bacterial responses were quantified in terms of respiration and growth rate and membrane permeability. A novel, high throughput technique was applied to rapidly reveal the range of biological responses that occurred. E. coli response to nanosheet exposure was dependent on the concentration and type of nanomaterial, and the bacterial growth stage. GO at 2.27 μg GO–TOC mL⁻¹ led to a 17% reduction in respiration rate. Reductions in growth rate for this condition during the transitional and stationary stages were 9% and 87% respectively, compared to the 0.00 μg GO–TOC mL⁻¹ control condition growth rate. When rapidly growing E. coli in a nutrient-rich environment is exposed to GO, the growth rate increased (up to 22% for the 2.27 μg GO–TOC mL⁻¹ sample). Under these conditions, E. coli can use GO as a scaffold for cellular growth, leading to an increase in growth rate. MoS₂ and MoSe₂ have little impact on the growth and respiration of E. coli regardless of the environment. The membrane permeability assay shows that the Mo nanosheets lead to a greater increase in membrane permeability in E. coli compared to GO. Our characterization of the Mo materials shows that they are smaller and stiffer compared to GO, so they are more likely to puncture the membrane. This study demonstrates that microorganisms have a range of responses to nanosheets and that the physiological condition of the bacteria and the nanosheet type play important roles in their response.

Two-dimensional (2D) materials are a large class of atomically thin, sheet-like solids, whose chemical stability is a critical issue for commercial devices. In addition, the chemical degradation processes that govern stability also determine 2D-material behaviour in biological systems and at the end of life, which have implications for environmental health and safety. There is a significant literature on the degradation of graphene-based materials, but the literature on other 2D materials is fragmentary, often semi-quantitative, and acquired under non-standardized conditions. The present critical review attempts to consolidate this fragmentary data on 2D materials “beyond graphene” in a rational form to allow quantitative meta-analyses and meaningful cross-material comparisons to identify trends and enable modelling. Data mined from 130 publications on 29 distinct chemical compositions were collected in a relational database and converted to 1st-order degradation rate constants. Under typical ambient conditions, either wet or dry, these rate constants vary over five orders of magnitude (1/k from 0.1 to 10 000 h). Through quantitative analysis of variance, 85% of this variation is associated with chemical composition, while other material variables do not show statistical significance in this dataset. The kinetic constants show a very poor correlation with free energy changes for the overall degradation reaction, but there are periodic table trends evident for the transition metal dichalcogenides (K_Te > K_Se > K_S). The atmospheric and aqueous-phase rate constants are cross correlated, allowing aqueous stability to be assessed from the more prevalent atmospheric data as an estimation tool. Introducing high reactivity species found in specialized environments (plasma, ozone, reactive oxygen species, reducing agents, enzymes), enhances degradation rates by 1–3 orders of magnitude, while other solutes or media components do not show large effects across the database. Finally, the results were used to classify 26 materials into three groups (biosoluble, biodegradable, persistent), which together with information on chemical degradation products can be used to accelerate safety assessment and to rationally select 2D materials for biomedical technologies.

Solution co-deposition of two-dimensional (2D) nanosheets with chemical solutes yields nanosheet–molecular heterostructures. A feature of these macroscopic layered hybrids is their ability to release the intercalated molecular agent to express chemical functionality on their surfaces or in their near surroundings. Systematic design methods are needed to control this molecular release to match the demand for rate and lifetime in specific applications. We hypothesize that release kinetics are controlled by transport processes within the layered solids, which primarily involve confined molecular diffusion through nanochannels formed by intersheet van der Waals gaps. Here a variety of graphene oxide (GO)/molecular hybrids are fabricated and subject to transient experiments to characterize release kinetics, locations, and mechanisms. The measured release rate profiles can be successfully described by a numerical model of internal transport processes, and the results used to extract effective Z-directional diffusion coefficients for various film types. The diffusion coefficients are found to be 8 orders of magnitude lower than those in free solution due to nanochannel confinement and serpentine path effects, and this retardation underlies the ability of 2D materials to control and extend release over useful time scales. In-plane texturing of the heterostructured films by compressive wrinkling or crumpling is shown to be a useful design tool to control the release rate for a given film type and molecular intercalant. The potential of this approach is demonstrated through case studies on the controlled release of chemical virucidal agents.

Aquatic contamination by per- and polyfluorinated alkyl substances (PFAS) has attracted global attention due to their environmental and health concerns. Current health advisories and surface water regulatory limits require PFAS detection in the parts per trillion (ppt) range. One way to achieve those low detection limits is to use a reliable passive sampling-based monitoring tool for PFAS, as exists for numerous nonpolar persistent organic pollutants. Here we introduce a new graphene-based hydrogel monolith and describe its synthesis, chemical functionalization, property characterization, and testing as a PFAS equilibrium passive sampler. The graphene monoliths were self-assembled by hydrothermal treatment from graphene oxide (GO) aqueous dispersions to produce free standing cylinders of ∼563 mm³ volume consisting of 4 wt% thin-walled porous graphene and ∼96 wt% water. The uptake of 23 PFAS was measured on the as-produced monoliths, and equilibrium partition coefficients (K_SW), were derived for longer chain (C ≥ 8) perfluoroalkyl acids (PFAA) and neutral precursors such as sulfonamides (log K_SW range 1.9–3.6). To increase the K_SW for shorter chain PFAA, the monoliths were chemically modified by a new diazonium-based grafting reaction that introduces positive surface charge without damage to the graphenic backbone. Introduction of benzylamine moieties through the diazonium intermediate switches zeta potential at pH 7 from −45 mV (as-produced graphene) to +5 mV. This modification increased the sorption of short and middle chain PFAA by ten-fold (e.g. log K_SW for PFBA increased from 1.3 to 2.2), thereby improving the functionality of the passive sampler device for a wider range of PFAS. Field deployments demonstrated that the graphene monoliths were capable of detecting key PFAS in the Delaware River.

The development and production of engineered 2D nanomaterials are expanding exponentially, increasing the risk of their release into the aquatic environment. A recent study showed 2D MnO₂ nanosheets, under development for energy and biomedical applications, dissolve upon interaction with biological reducing agents, resulting in depletion of intracellular glutathione levels within fish gill cells. However, little is known concerning their toxicity and interactions with subcellular organelles. To address this gap, we examined cellular uptake, cytotoxicity and mitochondrial effects of 2D MnO₂ nanosheets using an in vitro fish gill cell line to represent a target tissue of rainbow trout, a freshwater indicator species. The data demonstrate cellular uptake of MnO₂ nanosheets into lysosomes and potential mechanisms of dissolution within the lysosomal compartment. MnO₂ nanosheets induced severe mitochondrial dysfunction at sub-cytotoxic doses. Quantitative, single cell fluorescent imaging revealed mitochondrial fission and impaired mitochondrial membrane potential following MnO₂ nanosheet exposure. Seahorse analyses for cellular respiration revealed that MnO₂ nanosheets inhibited basal respiration, maximal respiration and the spare respiratory capacity of gill cells, indicating mitochondrial dysfunction and reduced cellular respiratory activity. MnO₂ nanosheet exposure also inhibited ATP production, further supporting the suppression of mitochondrial function and cellular respiration. Together, these observations indicate that 2D MnO₂ nanosheets impair the ability of gill cells to respond to energy demands or prolonged stress. Finally, our data demonstrate significant differences in the toxicity of the 2D MnO₂ nanosheets and their microparticle counterparts. This exemplifies the importance of considering the unique physical characteristics of 2D nanomaterials when conducting safety assessments.