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

Halloysite nanotubes (HNT) are products of nature. In chemical composition they are similar to kaolin and can be considered as rolled kaolin sheets with inner diameter of 10-20 nm, outer diameter of 40-70 nm and a length of 500-1500 nm. The internal side of halloysite is composed of Al₂O₃ while the external is mainly SiO₂.

These clay tubes are excavated from mines as stone minerals and processed by milling to form fine power of tubes, which is then used to dope a variety of polymers. The polymer doping has been observed to enhance various properties of these polymers including strength, adhesivity and flame retardancy. In addition, the large surface area and oppositely charged inner and out diameter facilitate loading a variety of biomolecules useful in medical applications. Given this wide range of applications there is an inevitable release of these materials back to the environment in this refined forms.

Despite the many reports on in vitro toxicity of HNTs, there is only limited information available with regard to its in vivo toxicity. Therefore, to shed light on this matter., Professor Fakhrullin and colleagues at Kazan Federal University investigated for the first time the in vivo toxicity of HNT using Caenorhabditis elegans nematode as a model organism. The C. elegans are an important tool in molecular biology because its fully sequenced genome is closely homologous to the human genome.

The findings of this research has shown that the primary pathway of the HNT entry into the organism is the intestinal uptake. The toxic effects of HNT uptake was then investigated by comparing the body size, fertility (or the number of eggs laid in other words) and longevity of the nematodes.

These comparisons did not give statistically significant differences between the controls, which suggests that these are potentially environmentally safe materials to work with. This is in fact is in contrast to the toxicities observed with other nanomaterials such as single walled carbon nanotubes (SWCNTS), graphene oxides, TiO₂ nanoparticles and platinum nanoparticles.

Even coating the nematode eggs with the HNT did not result in any significant deviations from the control nematodes. At extremely high doses of HNT did inflict some mechanical stress on the alimentary systems but these levels are highly unlikely to be encountered under environmentally relevant conditions.

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

Toxicity of halloysite clay nanotubes in vivo: A Caenorhabditis elegans study
Gölnur I. Fakhrullina, Farida S. Akhatova, Yuri M. Lvov and Rawil F. Fakhrullin
Environ. Sci.: Nano, 2015, 2, 54-59
DOI: 10.1039/C4EN00135D

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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.

People in modern societies produce a lot of waste. I propose that you think about it next time you buy something. How much of it is comprised of packaging? How much of that packaging is recyclable? How much of it will become waste after a short while?

With the fast advancement of nanotechnological applications to enhance consumer products, we can expect nanomaterials to become ubiquitous in our domestic waste. So what happens when we burn nanotechnology-enhanced waste (or nanowaste)? Unlike that great Jerry Lee Lewis song that everybody knows, the answer to this question is a little bit more complex.

Most modern incinerator facilities are equipped to minimize the emission of air pollutants from the incineration process, especially particulate matter (also known as fly ash).

But what if some nanomaterials lead to the production of different pollutants during the incineration process? As we know from this blog, nanomaterials are multi-talented. Some have the ability to catalyze reactions, which can lead to the production of potentially toxic combustion by-products.

There are many locations around the world that perform open burning to dispose of waste. Therefore, it is possible that air pollutants generated may be slightly different if the waste contains nanomaterials.

In their most recent work—and ES Nano cover article—Vejerano and colleagues evaluated the toxic response of fly ash from waste that contained a wide variety of nanomaterials, such as nanosilver, titania, ceria, fullerenes, quantum dots, and more.

They found that waste that contained nanosilver, titania, and C₆₀ fullerenes led to a toxic response in human lung epithelial cells, which is signalled by an increase in the production of reactive oxygen species (ROS). But, in addition to that, this study also shows that the presence of nanomaterials in waste is not expected to significantly alter the environmental and health risk of the fly ash emitted from combustion processes.

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

Toxicity of particulate matter from incineration of nanowaste
Eric P. Vejerano, Yanjun Ma, Amara L. Holder, Amy Pruden, Subbiah Elankumaran and Linsey C. Marr
Environ. Sci.: Nano, 2014, 2, 143-154
DOI: 10.1039/C4EN00182F

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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 health. You can find more information about her in her website mevance.com.

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