Environmental Science: Nano Blog

Everyone loves and hates nanoparticle aggregation. Why? Because it is a fascinating phenomenon but it complicates all of our experiments, ranging from in vitro / in vivo studies, all the way to the environmental models. For ease of study, it can be broken down into homoaggregation and heteroaggregation. Investigating the former is relatively easier than the latter (relatively!), but in the real world we are forced to deal with the latter. Simply, heteroaggregation in the environment refers to attachment of ENPs to naturally occurring solids (e.g. soil particles, suspended sediments). This plays a key role in determining ENPs bioavailability and mobility in the environment.

Large-scale fate and transport models have been adapted for modelling of ENPs. Earlier models use mass balance as a framework with partition coefficients (K_d) to describe the soil-water distribution of ENPs, but recent studies argue that particle number-based kinetic models using attachment efficiency (α) are better at this, given that colloidal suspensions never reach an equilibrium state as well as ignore the size dependent properties. Yet no agreement has been established on the best way to treat heteroaggregation in these models.

Therefore, to shed light on this matter, Amy L. Dale (Engineering and Public Policy, Carnegie Mellon University, PA), Gregory V. Lowry (Civil and Environmental Engineering, Carnegie Mellon University, PA), and Elizabeth A. Casman (CEINT, Duke University, NC) discuss in detail the ongoing practical challenges in model formulation, parameterization, and calibration for ENPs in their perspective.

A couple of highlights in this article are:

– Particle balance models are more complex, making it challenging to parameterize ENPs in the environment. Therefore, many assumptions are needed that have been discussed in detail in the perspective.

– Attachment efficiency is agreed to be the most appropriate fate descriptor for small-scale models, but at large-scale these models it is claimed to be relative insensitive to the particulate nature of ENPs.

Given the lack of scientific understanding on ENP heteroaggregation it was suggested that balance models to be the better choice, at least in the short term. Overall rates of sorption and desorption has been suggested to be used in the place of equilibrium partition coefficients to overcome concerns arising from using the equilibrium K_d.

To access the full article, download a copy for free* by clicking the link below.

Much ado about α: reframing the debate over appropriate fate descriptors in nanoparticle environmental risk modeling
Amy L. Dale, Gregory V. Lowry, Elizabeth A. Casman
Environ. Sci.: Nano, 2015, Perspective
DOI: 10.1039/C4EN00170B

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free through a registered RSC account

Of all nanomaterials that I know and have studied in these past seven years working with environmental nanoscience, Quantum Dots (QDs) have by far been my favorites. They just sound so sci-fi. I mean, just listen to their name: Quantum dots [imagine a low, cinema narrator voice]. Also, they glow in neon multi-colors when exposed to UV light.

This interesting optical property of quantum dots is due to quantum confinement, a phenomenon that takes place when some semiconductor particles are so small that the trajectory of their electrons becomes confined. The level of confinement depends on the size of the particles, which is why QDs of different sizes emit different colors.

QDs present the potential for a wide variety of applications, such as solar cells, lasers, LEDs, medical imaging, and even quantum computing. They are just so cool!

One more thing I have learned in these few years working with environmental nanoscience is that anything with so many potential applications is bound to, somehow, end up in the environment.

Quantum dot dispersions hanging out and emitting their neon quantum confinement glow, no big deal.

A common type of QD is a nanohybrid made of a cadmium selenide (CdSe) core and a zinc sulfide (ZnS) shell (CdSe/ZnS), which has been shown to be toxic to organisms and is a known carcinogen to humans. So, it is important to understand the way in which these QDs will be transported through the environment.

QDs and other nanomaterials are often coated with surfactants or polymers to improve stability—to prevent nanoparticles from sticking to each other, which they love to do. The presence of coatings may deeply affect their interactions with the environment.

M. D. Becker and colleagues recently published a study to improve existing models for the transport of coated QDs through porous media, which is an idealized template for groundwater and soil.

They observed that QDs became increasingly stuck to the porous media as they were transported. Both the coating and the presence of other constituents in the environment (such as natural organic matter) may help QDs “slide” more easily through the porous media. But as these coatings are stripped off over time, particles end up getting stuck.

This behavior could not be explained by traditional nanoparticle transport models, so they developed a new transport model to account for the influence that coatings and other constituents may have in the transport of nanomaterials through porous media.


To access the full article, download a copy for free* by clicking the link below:

A multi-constituent site blocking model for nanoparticle and stabilizing agent transport in porous media
Matthew D. Becker, Yonggang Wang, Kurt D. Pennell and Linda M. Abriola
Environ. Sci.: Nano, 2015, Advance Article
DOI: 10.1039/C4EN00176A

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About the webwriter

Marina is a PhD research scientist at Virginia Tech and Assoc. Director of @VTSuN. She is interested in air quality, nanotechnology and human health. You can find more information about her in her website mevance.com.

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* Access is free through a registered RSC account

Graphene and graphene oxide are among the recent attractions in novel nanomaterials for electronic and composite applications. Structure of graphene can simply be viewed as taking a single walled carbon nanotubes and unrolling it to give a sheet.

History of graphene runs all the way back to the 19th century but the very first single layer graphene was synthesized in 2004, by Andre Geim and Kostya Novoselov at The University of Manchester, UK. Graphene can be synthesized to contain a single layer or multiple layers. Nanoscience and nanotechnology community has always been very excited about the remarkable electrical and heat conductivity of these materials and a significant influx of graphene into the composite and electronic markets are being anticipated.

There are raising concerns about environmental and health risks of these materials with this increasing usage as there are no established methods for their extraction from complex matrices and quantification. Therefore, Kyle Doudrick and co-workers from the University of Notre Dame and Arizona State University have successfully developed an extraction and quantification method for graphene and graphene oxide from biomass using in situ reduction method followed by detection with programmed thermal analysis (PTA).

PTA is known to determine the carbon mass based on the thermal stability. In this study, the separation was achieved by subjecting the samples to a time dependent temperature ramp program where the less thermally stable carbon compounds evolved early in the program and the high thermally stable compounds were evolved later. Graphene, which has a high thermal stability was therefore easily separated from rest of the components in the biomass. In order to obtain similar separation for graphene oxide that has a higher oxygen content, which limits the separation, an in situ reduction was conducted using sodium borohydride.

Since this makes the graphene oxides more hydrophobic forcing aggregation an efficient separation and extraction was expected. The results of the study has proved that this technique is capable of recovering 52 ± 8% and 80 ± 6% of few layer graphene (FLG) and graphene oxide (GO) from dried biomass, respectively. Therefore, this technique can be applied to the extraction of graphene from complex organic matrices used in nanotoxicological studies.

To access the full article, download a copy for free* by clicking the link below:

Quantification of graphene and graphene oxide in complex organic matrices
Kyle Doudrick, Takayuki Nosaka, Pierre Herckes, Paul Westerhoff
Environ. Sci.: Nano, 2015,2, 60-67
DOI: 10.1039/C4EN00134F

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free through a registered RSC account

When friends and family ask me questions about the safety of nanotechnology, what follows is a conversation more or less like this:

Family member: “Are nanomaterials toxic by nature?”

Me: “It depends, nanomaterials can behave very differently from one another.”

Family member: “So, should I avoid products that have nanoparticles?”

Me: “Maybe. It depends on the type of nanomaterial, and how you will use the product.”

Family member: “But, will or will they not hurt me?”

Me: “Maybe. We don’t have a final answer to that yet, because there might be long-term effects that vary tremendously according to the nanomaterial’s composition, size, shape, and other attributes; like comparing apples and oranges.”

Did you sense a theme in this conversation? Yes, there is a lot of unhelpful uncertainty. But that is why researchers continue to work on understanding the possible effects of nanomaterials to human health and the environment, while concurrently developing novel applications for this great technology.

In a recently published ESN paper, Dr. Navid Saleh and his colleagues explore the topic of nanohybrids and their relevance to environmental health and safety (EHS).

A nanohybrid is commonly defined as a coupling of two or more types of nanomaterials that (1) integrate the unique properties of each nanomaterial to (2) create novel or enhanced properties, usually caused by the interaction between these nanomaterials. Moreover, combining two or more nanomaterials may result in (3) a novel material that has different physical dimensions in terms of their nano-ness (for example, from being “nano-thin” and “nano-long” to being “nano-structured”).

A good example of a nanohybrid is a combination of titanium dioxide (TiO₂) nanoparticles and carbon nanotubes, which allow the TiO₂ to be activated as a photocatalyst by visible light. Usually, the photocatalytic properties of TiO₂ can only be activated by UV light.

If nanohybrids have distinct properties from the nanomaterials that originated them, it is fair to wonder about their potential impacts to environmental health and safety (EHS). Can we safely add the known risks of these nano apples and oranges, when we know that the combination of both may generate novel properties?

This perspective paper by Saleh and colleagues proposes a strategy for tackling this complex issue. Hopefuly the nano-EHS community can use this information as a tool to narrow down the plethora of nanohybrid scenarios to focus on those most likely to pose a risk to health and the environment.

To access the full article, download a copy for free* by clicking the link below:

Research strategy to determine when novel nanohybrids pose unique environmental risks
Navid B. Saleh, Nirupam Aich, Jaime Plazas-Tuttle, Jamie R. Lead and Gregory V. Lowry
Environ. Sci.: Nano, 2015, Advance Article
DOI: 10.1039/c4en00104d

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About the webwriter

Marina is a PhD research scientist at Virginia Tech and Assoc. Director of @VTSuN. She is interested in air quality, nanotechnology and human health. You can find more information about her in her website mevance.com.

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* Access is free through a registered RSC account