Our ancestors, hundreds of years ago, paved the way for our current fascination with the minuscule. Their exploratory adventures of the past - the building of telescopes, the uncovering of basic anatomical details - provided a foundation for the current sophistication of space probes and genetic medicine. Our awareness of the invisible world emerged, indeed was fuelled, by our technological prowess, our scientific derring-do on the microscopic and molecular scale. We have built microscopes capable of imaging the tiniest cellular, molecular, and even atomic structures, such as atomic force, scanning electron, and X-ray photoelectron. We are now capable of viewing and manipulating matter at the nanoscale, actually creating products with new functionalities at the macro-scale (e.g. Stark, 2007). Ironically, this new nanotechnology, literally the smallest scale science (i.e. a billionth of a meter), has the potential to help solve some of the world's biggest environmental and energy challenges.
Investment in nanotechnology is projected to exceed more than USD20 billion in the next 2 decades, with current investment in the sector totaling close to USD8 billion worldwide (Cientifica, 2007). Nanotechnology has evolved from first generation passive nanostructures found in coatings, nanoparticles polymers and ceramics (~2000) to the current second generation of so-called active nanostructures found in products such as 3D transistors, amplifiers and targeted drugs. In the near future (~2010-2020), we will see the advent of nanostructure systems that will incorporate externally guided assembly (i.e. bio-assembly) and molecular nanosystems that will mimic simple biological systems (Roco, 2004).
Let's take a look at some of the most important nanotechnologies (mainly passive) currently available that will enable us to meet the ambitious greenhouse gas and energy reduction targets set by the world's governments. These technologies find application in four energy categories: conservation, generation, storage, and conversion.
Nanostructures, such as aero-gels, help to conserve energy and have been in use since 2003. Originally discovered in 1931, these ultra lightweight super insulators are 2-8 times more effective than fiberglass or polymer foams. They are made when silica fibers are tangled such that nanoscale air pockets trap up to 99.5% air. These tough nanostructures are ideal for use in architectural glass and roofing applications as they trap heat and reduce heating and artificial lighting costs. The super insulating aero-gels are also used in reducing transportation costs for Liquefied Natural Gas (Cientifica, 2007). Nanostructures based on silica nanoparticle binders are also being developed for use in architectural paints. Not only will these paints be solvent free but their low dirt pick-up will mean less energy wasted on cleaning and maintenance, less repainting and energy use during manufacturing (Iden, 2007).
Nanocomposites are conventional polymers to which nanoparticles are added in order to significantly alter the bulk material properties. The main goal is to produce stronger, but lighter, materials than conventional steel, thereby enabling significant fuel savings, particularly in the transportation sector. Many new generation aircraft (i.e. Boeing 787) will have outer skins made entirely from nanocomposites. Carbon nanotubes and nanofiber additives may also impart additional functionality to non-metal composites - previously unlikely candidates in fuel storage applications due to their static electricity and fire hazard concerns. These technologies are currently in use in Turkey and in the Philippines and are awaiting EPA approval (Cientifica, 2007).
Organic solar cells, most likely available from 2009 onwards, are thin film, flexible cells, based on inexpensive nanoparticles and polymers that will replace expensive old generation silicon-based brittle solar cells. These are easily manufactured on a continuous roll process, and their flexibility means increased application in the automotive industry as, for example, sun-roofs. Increased flexibility means, of course, increased usage, at increased efficiencies, which in turn translates into increased sustainable energy generation.
Nanoparticle fuel additives, such as cerium oxide (8-25 nm), increase fuel economy and lower emissions, particularly for diesel engines. Increased surface to volume ratios mean that more of the active catalyst particles are attached to the nanoparticle surface where they remain reactive, not buried inside larger particles. A leading UK fuel additive company, Oxonica, through a deal with Turkey's largest fuel distributor, Petrol Ofisi A.S., is expected to reduce CO2 emissions by as much as 200,000 tons per year. The same technology if used in the USA could reduce emissions by as much as 30 million tons (Cientifica, 2007).
Fuel cell (FC) vehicles are currently undergoing worldwide industrial trials and may be launched as early as 2009. One of the largest hurdles in fuel cell technology is the low cost and weight storage of sufficient quantities of on-board hydrogen. Enter Metal-Organic Framework nanocubes that act as extremely efficient gas adsorbents, thus increasing the amount of stored gas per system volume by up to three times (e.g. BASF BASOCUBE). FCs can be used in buildings, homes and laptop computers without emitting greenhouse gases.
Conventional capacitors store energy on the surfaces of metallized plastic film or metal electrodes. Super capacitors are basically electrical storage devices, with up to 100 times more storage density than conventional capacitors and 10 times higher power density than conventional batteries, as they incorporate high surface area nanoparticles. These devices are currently in trials in mobile phones and hybrid electric vehicles and may be used on portable electronics or in electric vehicles. In addition, they may play a role of super efficient devices for storing renewable energy from wind and solar systems.
Large payoffs, however, do not come without potential dangers and risks. By alleviating some of our most serious global energy problems, we may inadvertently be creating a number of dangerous problems with the use of nanotechnology. The laws of Newtonian physics break down at molecular and sub atomic scales, and similarly, the properties and behavior of nanostructures may not mimic those of more familiar macrostructures. Because of unknown quantum effects, the increased chemical reactivity of nanoparticles, and their unpredictable electronic, optical, and mechanical properties (Iden, 2007), the potential toxicity, transport, transformation and bioaccumulation of nanostructures in the environment remain unknown.
Additionally, because of the high surface to volume ratios of these structures there may be many hidden dangers to human health. Nanostructures have active large surface areas that enable their interaction with a large number of targets in the body. These structures may be poorly recognized by our immune systems and may exacerbate allergenic and inflammatory responses. Research has shown that nanoparticles derived from diesel combustion and air pollution may trigger asthma, arthrosclerosis and heart disease. Furthermore, nanoparticles have been shown to pass barriers normally effective at protecting highly vulnerable organs (e.g. blood-brain barrier) as well as the placenta, potentially causing detrimental effects during fetal development (e.g. Borm, 2006).
So, while our ethical and moral responsibility to ensure the integrity and health of natural systems is certainly worthwhile, in reality, the need for immediate action to control the planetary energy situation may be rather complicated. Hippocrates wrote some 2500 years ago: "Declare the past, diagnose the present, foretell the future; practice these acts. As to diseases, make a habit of two things — to help, or at least to do no harm" (Hippocrates, Epidemics, Bk. I, Sect. XI.). As we embark on restoring balance to this world, let us try to remember those words of wisdom.
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Wilma Pretorius, Ph.D.. Nanotech-cleantech: bridging the gap to real sustainability. EnvironmentalChemistry.com. Aug 15, 2007. Accessed on-line: 10/20/2021