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Posted: Jul 12th, 2007
The potential for nanotechnology to replace hazardous substances
(Nanowerk Spotlight) Our modern lifestyle exposes us to hundreds of chemical substances every day, quite a number of them are known to be hazardous, if not outright toxic. The long, long list ranges from toxic chemicals and heavy metals included in electronic waste to insecticides and herbicides that find their way into the food chain, to flame retardant chemicals in buildings and furniture. A European project has set out to give an overview of already used and conceivable applications of nanotechnology in order to replace hazardous chemicals. The overall idea behind this project is to identify new nanotechnology applications which could help to reduce the risks related to hazardous substances and chemical processes. Currently, nanotechnologies are not contributing exceptionally to an increase in the substitution of hazardous substances for safer ones. However, experts believe that this could well change in the future. These are two of the messages coming out of a study by STOA, the European Parliament's Scientific Technology Options Assessment committee, on the role of nanotechnology in chemical substitution.
Many articles on environmental benefits of nanotechnologies deal with the potential for cleaning up pollution or preventing pollution through better filtration methods. In contrast, the European projects looks at ways how nanotechnology could prevent the polluting agents in the first place.
One of the first findings of STOA was that their study ("The role of Nanotechnology in Chemical Substitution"; pdf download, 5 MB) was unique, and there is in fact very little research into the potential of nanotechnologies to replace hazardous chemicals. This is very surprising given the hoopla over "green nanotechnology".
The interesting assumption behind the study is that "substitution" is not restricted to the replacement of a hazardous substance by a less or non-hazardous substance. In this project a broader meaning of substitution is applied as it is in the chemical context.
The report states that "due to the fact that nanotechnology is neither a group of substances nor a group of products but an enabling technology the way nanotechnology can provide solutions is more fundamental than just replacing the function of the substitute. It is assumed that nanotechnology provides new effects which are not based on chemical properties of the related material but on the physical properties caused by its size and shape. It can be used to develop completely different processes or different products which serve the same purpose but in a completely different way."
One area where nanotechnology is already making inroads as a substitute for hazardous chemicals is coatings. Coatings can create anti-adhesive surfaces which resist things sticking to them, such as dirt, or have biocidal properties to prevent living organisms from sticking to them. One example for this is biofouling and protective coatings for ship hulls: To avoid the growth of organisms of different types on surfaces in a marine or freshwater environment usually coatings incorporating biocides (chemicals that kill organisms) are used. Instead of these biocide containing coatings there exist several approaches of nanostructuring the surfaces which prevents biofilm formation and bacterial adhesion as well as the attachment of larger organisms.
Apart from coatings, the report identified five other categories where nanotechnology could substitute hazardous chemical substances:
There are several approaches to replace bromine flame retardants with products using nanotechnology. Bromine is used as a reaction inhibitant by absorbing oxygen. A similar effect could be realized by nanoparticles. If TiO2, SiO2, MgO, or ZnO nanoparticles are added to substances oxygen is accumulated and builds up an oxide layer.
Flexibilizer leads to elastic bindings between the polymer chains. It is known from tires that the addition of nanoparticles can enhance the flexibility of the rubber mixture. A similar effect is conceivable with plastics.
Substitution or reduction of solvents
Organic solvents or volatile organic compounds (VOC) in general are one group of chemicals which are often toxic, bio-accumulative and, due to their volatility, difficult to control. Solvents can not be directly substituted by nanotechnology. But in the literature it is often mentioned that nanotechnology may change processes in a way that in some cases solvents can be reduced or will even become dispensable in future.
Research on catalysts is an old and vast research field. In this field, the distinction between 'pure' chemistry and nanotechnology is especially difficult. Research in this field was already in the dimension of nanometers, therefore it is not clear to which extent further developments may be attributed to nanotechnology. The development of new catalysts is seldom directly aimed at substituting hazardous substances. Instead, in the development of new catalysts several objectives are pursued at the same time. Therefore, substitution of hazardous substances in this field is often very indirect. The effect of catalysts on human health and the environment, if they are released, could be detrimental. Their benefits and risks have to be balanced in
A very well investigated example of a case of substitution is styrol synthesis where it was possible to reduce the by-production of heavy metals due to nanotechnology catalysts.
Within nanotechnology there exist several attempts to improve the efficiency of pharmaceuticals by bringing them directly to the cells where they are needed. Of course, the main goal is to reduce the side effects of the therapy, hence making the therapy more tolerable and effective. But especially chemotherapeutics are detrimental for the environment and the release of antibiotics causes severe problems due to resistance of bacteria.
The report lists some other interesting areas where nanotechnologies could substitute or at least reduce toxic materials, for example:
Soldering: Solder includes lead, tin, and indium. Especially lead is known to be toxic. An approach to substitute solder is to generate conductive plastics by carbon nanoparticles as conducting filler, hence to glue instead of soldering.
Insecticides: There exist some attempts to alter the application of insecticides by nanotechnology. The idea is to immobilize the chemical agents of plant protectants by nanotechnology and to delay their release. It is perceived that this could be realized by nanocapsules releasing the insecticide continuously.
The big challenge, of course, is how to find a connection in a systematic way between a hazardous substance and a particular nanotechnology application which could facilitate the substitution of this substance. The report suggests that a first step in this direction is the systematization of the functions nanotechnology can provide.
These functionalities could be compared with the functionalities hazardous chemical substances provide. Thus the question of which hazardous substances could be substituted by which nanotechnology is reduced to the question of which functionality of the hazardous substance could be provided by which nanotechnology.
Of course, nanotechnology can also pose a risk by itself because the toxicity of nanoparticles is considered as a potential threat. Nanotoxicology as a research field is in its very early stages and the question if and to what degree certain engineered nanomaterials pose a threat can not be answered yet. Here the report recommends:
"Inherent in the process of substitution, balancing of positive versus negative effects has to be performed. If no data and no experience on the effects of the NT under consideration is available, the substitution process should be carefully performed and should be accompanied by systematic scientific research. This is especially true for nanoparticle-based catalysts, which are not attached to a carrier system or could be released by the use as it happens with platinum particles used in catalysts for automobiles."
Overall, the report concludes: "At present, nanotechnologies and nanotechnological concepts deliver a variety of mostly incremental improvements of existing bulk materials, coatings or products. These improvements point in several directions and often are aimed at improving several properties at the
same time. With respect to substitution this means that nanotechnological approaches often cannot lead to direct substitution of a hazardous substance, but may lead in general to a more environmentally friendly product or process."