Environmental Science: Nano Blog

Graphene oxide (GO) is a precursor material in the preparation of graphene. Despite its name, on the surface of this material there are different types of functional groups including epoxy, hydroxyl and carbonyl groups. As a result, GO is hydrophilic and easily dispersed in water. This has led to a variety of investigations relating to GO as a potential pollutant, as well as a possible treatment to cancer.

The disrupted π-bond structure in GO enables the absorption of significant amounts of light from solar radiation. Therefore, environmental processing of GO can be expected to include photochemical processes. One important outcome of such processing is the generation of reactive oxygen species (ROS). These ROS can include singlet oxygen (¹O₂), superoxide anions (O₂^.–) and hydroxyl radicals (^.OH). Generation of ROS has a significant impact on ecological risks associated with GO and is critical in understanding the transformation pathways of carbon in the GO structure.

Therefore, Yingcan Zhao and Chad T. Jafvert at Purdue University (West Lafayette, USA) has investigated the ability of aqueous dispersions of single layered GO to generate ROS upon exposure to light within the solar spectrum (λ=300-410 nm). The generated ROS was detected using specific chemical probes, UV-vis spectroscopy and Raman spectroscopy.

The findings of this research highlighted that upon exposure to solar radiation there is electron transfer reactions occurring from GO to dissolved O₂, forming O₂^.– and significant quantities of H₂O₂.

Given the fact that these are reduction reactions, this resulted in an overall oxidation of GO. Some of the generated ROS reacted directly with the GO surface and therefore, the oxidation of GO was found to be non-stoichiometric.

The exposure to light also increased the chromophores content or the absorptivity of existing chromophores, as suggested by the increased darker colour of the GO suspensions. However, Raman spectroscopic analysis also indicated an increase in non-aromatic defects.

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

Environmental photochemistry of single layered graphene oxide in water
Yingcan Zhao and   Chad T. Jafvert
Environ. Sci.: Nano, 2015, 2, 136-142
DOI: 10.1039/C4EN00209a

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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 until the 21/06/2015 through a registered RSC account

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