Evaluating the Use of Alternatives Assessment To Compare Bulk Organic Chemical and Nanomaterial Alternatives to Brominated Flame Retardants

Alternatives assessment (AA) provides a framework for selection of safer substitutes for problematic chemicals. This study assesses alternatives for flame retardants (FR) in electrical and electronic equipment (EEE), including two common brominated FR, decabromodiphenyl ether (deca-BDE) and tetrabromobisphenol A (TBBPA). Although deca-BDE is restricted in the EU and undergoing phase-out in the US, TBBPA is still widely used. However, concerns about potential hazards are driving a search for halogen-free alternatives. Nonhalogenated organic chemical alternatives (e.g., phosphorus-based FRs) as well as minerals (e.g., montmorillonite) and nanomaterials (e.g., carbon nanotubes) have been proposed, yet it is unclear whether current frameworks can be used to systematically compare such heterogeneous alternatives. This study aims to (i) identify technologically and economically viable alternative FRs and (ii) evaluate each under the current AA frameworks, to (iii) elucidate challenges and shortcomings to adopting proposed alternatives. Uncertainties persist regarding the hazards of both novel nanomaterials and traditional chemicals. Historically, problematic chemicals undergoing restriction have been substituted with another chemical providing, at best, marginally reduced hazard, a problem that AA was, in part, developed to solve. Its successful implementation will depend on our ability to reduce hazard during the design stage, which is currently precluded by the “commercially available and economically viable” emphasis of AA. Methods are needed to bridge AA with sustainable chemical design to prevent it from becoming a tool of only incremental improvement

Toward safer multi-walled carbon nanotube design: Establishing a statistical model that relates surface charge and embryonic zebrafish mortality

<p>Given the increased utility and lack of consensus regarding carbon nanotube (CNT) environmental and human health hazards, there is a growing demand for guidelines that inform safer CNT design. In this study, the zebrafish (<i>Danio rerio</i>) model is utilized as a stable, sensitive biological system to evaluate the bioactivity of systematically modified and comprehensively characterized multi-walled carbon nanotubes (MWNTs). MWNTs were treated with strong acid to introduce oxygen functional groups, which were then systematically thermally reduced and removed using an inert temperature treatment. While 25 phenotypic endpoints were evaluated at 24 and 120 hours post-fertilization (hpf), high mortality at 24 hpf prevented further resolution of the mode of toxicity leading to mortality. Advanced multivariate statistical methods are employed to establish a model that identifies those MWNT physicochemical properties that best estimate the probability of observing an adverse outcome. The physicochemical properties considered in this study include surface charge, percent surface oxygen, dispersed aggregate size and morphology and electrochemical activity. Of the five physicochemical properties, surface charge, quantified as the point of zero charge (PZC), was determined as the best predictor of mortality at 24 hpf. From a design perspective, the identification of this property–hazard relationship establishes a foundation for the development of design guidelines for MWNTs with reduced hazard.</p

Highly Conductive Single-Walled Carbon Nanotube Thin Film Preparation by Direct Alignment on Substrates from Water Dispersions

A safe, scalable method for producing highly conductive aligned films of single-walled carbon nanotubes (SWNTs) from water suspensions is presented. While microfluidic assembly of SWNTs has received significant attention, achieving desirable SWNT dispersion and morphology in fluids without an insulating surfactant or toxic superacid is challenging. We present a method that uniquely produces a noncorrosive ink that can be directly applied to a device <i>in situ</i>, which is different from previous fabrication techniques. Functionalized SWNTs (f-SWNTs) are dispersed in an aqueous urea solution to leverage binding between the amine group of urea and the carboxylic acid group of f-SWNTs and obtain urea-SWNT. Compared with SWNTs dispersed using conventional methods (e.g., superacid and surfactants), the dispersed urea-SWNT aggregates have a higher aspect ratio with a rodlike morphology as measured by light scattering. The Mayer rod technique is used to prepare urea-SWNT, highly aligned films (two-dimensional nematic order parameter of 0.6, 5 μm spot size, via polarized Raman) with resistance values as low as 15–1700 Ω/sq in a transmittance range of 2–80% at 550 nm. These values compete with the best literature values for conductivity of SWNT-enabled thin films. The findings offer promising opportunities for industrial applications relying on highly conductive thin SWNT films

Shape-Dependent Surface Reactivity and Antimicrobial Activity of Nano-Cupric Oxide

Shape of engineered nanomaterials (ENMs) can be used as a design handle to achieve controlled manipulation of physicochemical properties. This tailored material property approach necessitates the establishment of relationships between specific ENM properties that result from such manipulations (e.g., surface area, reactivity, or charge) and the observed trend in behavior, from both a functional performance and hazard perspective. In this study, these structure–property-function (SPF) and structure–property-hazard (SPH) relationships are established for nano-cupric oxide (n-CuO) as a function of shape, including nanospheres and nanosheets. In addition to comparing these shapes at the nanoscale, bulk CuO is studied to compare across length scales. The results from comprehensive material characterization revealed correlations between CuO surface reactivity and bacterial toxicity with CuO nanosheets having the highest surface reactivity, electrochemical activity, and antimicrobial activity. While less active than the nanosheets, CuO nanoparticles (sphere-like shape) demonstrated enhanced reactivity compared to the bulk CuO. This is in agreement with previous studies investigating differences across length-scales. To elucidate the underlying mechanisms of action to further explain the shape-dependent behavior, kinetic models applied to the toxicity data. In addition to revealing different CuO material kinetics, trends in observed response cannot be explained by surface area alone. The compiled results contribute to further elucidate pathways toward controlled design of ENMs