Environmental Science: Nano Blog

Having recently read several papers regarding the toxicity of nanoparticles to the aquatic environment, I was starting to view nanoparticles as an environmental bad guy. However, this study conducted by Anthony B. Dichiara and colleagues from Rochester Institute of Technology has stopped me in my tracks. It appears that nanoparticles could provide a sustainable solution for future aqueous purification systems – in the form of carbon nanocomposite papers – and we like sustainable solutions!

Activated carbon is currently the most commonly used material for water purification, but carbon nanotubes have higher adsorption capacities. For an adsorption material to be used for large-scale removal of pollutants from water, the regeneration property and reusability must also be taken into consideration.

In this study, the recycling efficiency of Graphene nanoplatelet-single-walled nanontube hybrid papers (graphene cylinders) when saturated with 2,4-dichlorophenoxyacetic acid was investigated.  Figure 1 shows that every time the papers were recycled the uptake of 2,4-dichlorophenoxyacetic acid always exceeded that of the original adsorbents.

Figure 1

Carbon nanocomposite papers are therefore potential adsorbents for future aqueous purification systems due to their larger adsorption capacity and enhanced recovery ability. So perhaps nanoparticles are not too bad after all!

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

Enhanced adsorption of carbon nanocomposites exhausted with 2,4-dichlorophenoxyacetic acid after regeneration by thermal oxidation and microwave irradiation, Antony Dichiara, Jordan Benton-Smith and Reginald Rogers

DOI: 10.1039/C3EN00093A

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Cellulose-derived structural supports can improve the performance and the environmental credentials of gold nanoparticle catalysts. This study from the Polymer Research Institute of Sichuan University in China demonstrates the potential of this approach.

Achieving the optimum performance and stability of catalysts is of paramount importance to the development of a wide range of industrial processes and the manufacture of new products and devices. Gold nanoparticles (Au NPs) are widely used as catalysts in many chemical processes. However, these often suffer from instability owing to their large active surface area which can lead to self-aggregation. They therefore require a supporting matrix, commonly using polymeric encapsulation or support on graphene oxide or silica surfaces.

However, greener, more sustainable approaches are now being sought to improve the environmental credentials of these processes. Cellulose is the most common and abundant natural polymer.  Cellulose nanocrystals (CNs) can therefore provide a possible solution as these posses the desired properties (mechanical strength, self-assembly, high specific surface area, nanometirc dispersity and high stability) to allow them to act as an effective catalyst carrier.

However the use of these have previously involved use of toxic reducing agents such as sodium borohydride or hydrazine hydride. A cleaner synthesis is required. In this study Xiaodong Wu and co workers report the first instance of a one-step, environmentally-friendly synthesis of gold NPs (Au NPs) deposited on cellulose nanocrystals and demonstrate the technical and environmental advantages of this approach.

CNs were derived from bulk cellulose using controlled acid hydrolysis of waste cotton fabric. The Au NPs were synthesised and deposited on to CNs by hydrothermal reduction of HAuCl₄. Both Au NP-CN hybrids and unsupported Au NPs were prepared and their performance in the reduction of 4-nitrophenol was compared using UV-Vis spectroscopic analysis. The structure and properties of the resulting particles were characterized using transmission electron microscopy (TEM), X-Ray Diffraction (XRD) and X-Ray photoelectron spectrometric (XPS) techniques.

It was shown that the electron-rich –OH groups, abundant on their surface allow the CNs to provide the dual role of reductant and stabilizer in this process. The larger specific surface area and better dispersity of Au NPs supported on CNs meant these nano-hybrid catalysts displayed enhanced stability and superior catalytic activity than an unsupported Au NP catalyst for the reduction of 4-NP.

This approach offers a number of important advantages over previous traditional techniques. It has a lower overall cost and avoids the use of toxic or dangerous reducing, capping or dispersing agents. Furthermore this process utilises a renewable and biodegradable natural resource since the CNs can be obtained from various plant materials.

This investigation could therefore potentially pave the way to green production of bio-supported organic/inorganic nano-hybrid catalysts with possible further applications in the production of sensors, antibacterial materials and electronic devices.

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

Green synthesis and formation mechanism of cellulose nanocrystal-supported gold nanoparticles with enhanced catalytic performance

Xiaodong Wu, Canhui Lu, Zehang Zhou, Guiping Yuan, Rui Xiong and Xinxing Zhang Environ. Sci.: Nano, 2014, 1, 71-79 DOI: 10.1039/C3EN00066D

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Virtually all environmental surfaces have microbial biofilms, which are an essential component of natural systems.  Nanoparticles are abundant in nature, but how much do we know about nanoparticle-biofilm interactions?

Kaoru Ikuma and colleagues from the University of Massachusetts Amherst have completed a study highlighting the importance of assessing small-scale biofilm surface characteristics in future nanoparticle-biofilm interaction studies. They hypothesized that the contribution of electrostatic forces in relation to other forces would be dominant in governing the deposition of bare nanoparticles onto polysaccharide-coated surfaces. The also expected biofilm surface charge to impact nanoparticle deposition.

Polysaccharides are a major extracellular component of biofilms. They are ubiquitous in the environment and occur in pure forms as well as in complexes. As polysaccharides are extracellular they are an initial point of contact for nanoparticles and play an important role in early nanoparticle-biofilm interactions. Typical characterization of biofilms often treat all polysaccharides as one entity.  This study suggests that the small-scale chemical and electrochemical identities of the polysaccharides present in the biofilms may play an important role in the initial surface attachment of nanoparticles; therefore effecting their deposition.

The significance of polysaccharide coatings on the deposition of nanoparticles was examined using in-depth characterization of surface properties. It would appear that surface charge density and distribution of the biofilms both contribute to different nanoparticle deposition behaviours.

Kelvin probe force microscopy was used as a probe for spatial variations of surface potential across two different polysaccharides (alginate and dextran sulphate). Patches of lower surface potential are observed as the areas of darker colour on the images below.

alginate (a) and dextran sulfate (b)

The results showed that even though the interactions between nanoparticles and surfaces coated with pure polysaccharides may be governed by electrostatic forces, these interactions can be altered by microscale and nanoscale differences in surface charge. Therefore, instead of treating polysaccharides as one entity, spatial characterization of biofilm surface properties is necessary to improve our understanding of nanoparticle-biofilm interactions.

To find out more, download your free* copy by following the link below.

Deposition of nanoparticles onto polysaccharide-coated surfaces: Implications for nanoparticle-biofilm interactions. Kaoru Ikuma, Andrew Madden, Alan Decho and Boris L. T. Lau 10.1039/C3EN00075C

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One of our recent Environmental Science: Nano papers looks into the effect of natural organic matter on the disagglomeration of manufactured TiO₂ nanoparticles.

This research, conducted by Frédéric Loosli and colleagues from the University of Geneva, studied the stability of TiO₂ nanoparticles at various pH values.

TiO₂ nanoparticles (the most produced nanoparticles to date) are used in consumer goods such as cosmetics, paints and as a UV protection agent. These consumer goods are then released into our environment, but there is a lack of data on nanomaterial transformations under relevant environmental conditions.

It is generally assumed that agglomerated nanoparticles are less toxic to aquatic organisms than single nanoparticles. As a given amount of nanoparticles will enter aquatic environments in an agglomerated, potentially less toxic form, the potential risk comes from natural processes which may considerably alter the stability of such agglomerated nanoparticles. Such processes have the possibility to disperse them, increasing diffusion and potential toxicity of the nanoparticles.

This study looked at the effects of two types of natural organic matter, at typical environmental concentrations, to determine if their presence induced significant disagglomeration of large submicron nanoparticle agglomerates. The natural organic matter used for this research were: Suwannee River humic acid, which can act as a pH regulator, and Alginate, which is found in the cell walls of seaweed and is commonly used in the food industry as a stabilizer and a thickening agent.

Figure 1

It was shown that the addition of natural organic material significantly modifies the stability of TiO₂ nanoparticles by inducing disagglomeration. Figure 1, taken from the paper, demonstrates how alginate and Suwannee River humic acid effect the disagglomeration of agglomerated nanoparticles differently.

To find out more about this research, download your free* copy by following the link below:

Effect of natural organic matter on the disagglomeration of manufactured TiO₂ nanoparticles by Frédéric Loosli, Philippe Le Coustumer and Serge Stoll DOI: 10.1039/C3EN00061C

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