Safe, efficient and compact hydrogen storage is a major challenge in order to realize hydrogen powered transport. According to the U.S. Department of Energy's Freedom CAR program roadmap, the on-board hydrogen storage system should provide a gravimetric density of 6 wt% at room temperature to be considered for technological implementation. Currently, the storage of hydrogen in the absorbed form is considered as the most appropriate way to solve this problem. Research groups worldwide are seeking and experimenting with materials capable of absorbing and releasing large quantities of hydrogen easily, reliably, and safely. One candidate material that is being considered as a candidate for hydrogen storage media is single-walled carbon nanotubes. So far, carbon nanotubes have been unable to meet the DOE's hydrogen storage target. New theoretical work from China suggests that silicon nanotubes can store hydrogen more efficiently than their carbon nanotube counterparts. This raises the possibility that, after powering the micro-electronics revolution, silicon could also become a key material for the future hydrogen economy.
The greenhouse effect is primarily a function of the concentration of water vapor, carbon dioxide, and other trace gases in the Earth's atmosphere that absorb the terrestrial radiation leaving the surface of the Earth. Changes in the atmospheric concentrations of these greenhouse gases can alter the balance of energy transfers between the atmosphere, space, land, and the oceans. The capture and storage of greenhouse gases could play a significant role in reducing the release of greenhouse gases into the atmosphere (read more about capture and storage of carbon dioxide here). Carbon dioxide (CO2) is the most important greenhouse gas and captures the limelight in most reports on global warming. While other greenhouse gases make up less of the atmosphere, they account for about 40 percent of the greenhouse gas radiation sent back to Earth. They can also be much more efficient at absorbing and re-emitting radiation than carbon dioxide, so they are small but important elements in the equation. In fact, molecule-for-molecule some gases containing lots of fluorine are 10,000 times stronger at absorbing radiation than carbon dioxide. A new systematic computational study shows an interesting approach of how nanotechnology, in this case the use of carbon nanotubes and other nanomaterials, could lead to effective filters for the capture and storage of greenhouse gases.
You probably have seen quite a number of research reports on the amazing climbing abilities of geckos. Here at Nanowerk, we ran several Spotlights on this topic, for instance on mimicking gecko toe structures to fabricate super-strong dry adhesives. One demonstration of so-called 'gecko tape' has already been used in building Stickybot, a quadruped robot capable of climbing smooth vertical surfaces, such as glass, acrylic and whiteboard. In addition to the animal kingdom, scientists have started looking at plants to identify biological climbing mechanisms that could be exploited for engineering applications. One obvious candidate is ivy, a climbing woody plant. Researchers now have found that ivy secretes nanoparticles which allow the plant to affix to a surface and play an important role in the plant's climbing capability. This ivy secretion mechanism may inspire new, 'green' methods for synthesizing nanoparticles biologically or new approaches to adhesion mechanisms for mechanical devices.
Years of engineering research and design, together with uncounted billions of dollars from government and industry, went into the development of the modern petroleum industry. It would be unreasonable to expect that we can replace this industry with greener alternatives without a similarly expansive and sustained effort. Point in case is a recently published roadmap to 'Next Generation Hydrocarbon Biorefineries' that outlines a number of novel process pathways for biofuels production based on scientific and engineering proofs of concept demonstrated in laboratories around the world. The key conclusion from this (U.S.-centric) report is that 'while the U.S. has made a significant investment in technologies focusing on breaking the biological barriers to biofuels, principally ethanol, there has not been a commensurate investment in the research needed to break the chemical and engineering barriers to hydrocarbon fuels such as gasoline, diesel, and jet fuel.' This statement of course holds true not only for biofuels but for any kind of green energy technology. The production of ethanol from corn has come under intense scrutiny and discussion for its potential environmental and economic side effects. Advances in agriculture and biotechnology have made it possible to inexpensively produce lignocellulosic biomass (plant biomass that is composed of cellulose and lignin) at costs that are significantly lower (about $15 per barrel of oil energy equivalent) than crude oil. The key bottleneck for lignocellulosic-derived biofuels is the lack of technology for the efficient conversion of biomass into liquid fuels. Advances in nanotechnology have given us an unprecedented ability to understand and control chemistry at the molecular scale, which promises to accelerate the development of biomass-to-fuels production technologies.
Only 30% of all freshwater on the planet is not locked up in ice caps or glaciers (not for much longer, though). Of that, some 20% is in areas too remote for humans to access and of the remaining 80% about three-quarters comes at the wrong time and place - in monsoons and floods - and is not always captured for use by people. The remainder is less than 0.08 of 1% of the total water on the planet. Expressed another way, if all the earth's freshwater were stored in a 5-liter container, available fresh water would not quite fill a teaspoon. The problem is that we don't manage this teaspoon very well. Currently, 600 million people face water scarcity. Depending on future rates of population growth, between 2.7 billion and 3.2 billion people may be living in either water-scarce or water-stressed conditions by 2025. Freshwater looks like it will become the oil of the 21st century - scarce, expensive and the reason for armed conflicts. While in our previous article we have only talked about nanotechnology and water in general terms, a new paper gives us the opportunity to look in more detail at the role that nanotechnology could play in resolving issues relating to water shortage and water quality. This review highlights the uses of nanotechnology in areas relevant to water purification, including separation and reactive media for water filtration, as well as nanomaterials and nanoparticles for use in water bioremediation and disinfection.
Diatoms are a major group of hard-shelled algae and one of the most common types of phytoplankton. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica. Silicate materials are very important in nature and they are closely related to the evolution of living organisms. Diatom walls show a wide diversity in form, some quite beautiful and ornate, but usually consist of two symmetrical sides with a split between them, hence the group name. There is great potential for the use of diatoms in nanotechnology. This potential lies in the pores and channels which give rise to a greatly increased surface area, and the silica structure which lends itself to chemical modification. In addition there is a huge variety in the sizes and shapes of diatoms available, providing scope for the selection of a particular species of diatom tailored to a particular requirement. Researchers in the UK have demonstrated that the silica walls of diatoms can be used for the attachment of active biomolecules, such as antibodies, using either primary amine groups or the carbohydrate moiety. These modified structures can, therefore, be used for antibody arrays or for use in techniques such as immunoprecipitation.
One statement of the second law of thermodynamics is that the efficiency of any heat engine or other thermodynamic process is always less that 100%. There will always be some type of friction or other inefficiency that will generate waste heat. The useful work that a heat engine can perform will therefore always be less than the energy put into the system. Engines must be cooled, as a radiator cools a car engine, because they generate waste heat. While there is no way around the second law of thermodynamics, the performance of today's power generation technology is quite appalling. The average efficiency today for fossil-fired power generation, 35% for coal, 45% for natural gas and 38% for oil-fired power generation. By the way, be skeptical when people tell you that nuclear power is good in the fight against global warming - nuclear power plants have a worse thermal efficiency (30-33%) than fossil-fired plants. Approximately 90% of the world's power is generated in such a highly inefficient way. In other words: every year some 15 billion kilowatts of heat is dumped into the atmosphere during power generation (talk about fueling global warming...). This is roughly the same amount as the total power consumption of the world in 2004. Reducing these inefficiencies would go a long way in solving the coming energy and climate problems. Thermoelectric materials - which can directly convert heat into electricity - could potentially convert part of this low-grade waste heat. Problem is that good thermoelectric materials are scarce and so far solid-state heat pumps have proven too inefficient to be practical. Two papers in this week's Nature describe how silicon devices could in principle be adapted and possibly scaled up for this purpose.
Just because hydrogen is a clean fuel doesn't mean that hydrogen production is a clean process. As more and more companies and investors jump onto the 'cleantech' bandwagon, hydrogen occupies an important place in this vision of a sustainable, carbon-free, and non-polluting energy future. If you look closer though, you'll find that you are not always told the full story about "clean" hydrogen. The U.S. department of Energy's Hydrogen Energy Roadmap foresees up to 90% of hydrogen production coming from fossil fuels - coal, gas, oil. In other words, a clean fuel is produced by the same dirty fuel that is causing all the problems we are facing today (read more in our recent Spotlight: Nanotechnology could clean up the hydrogen car's dirty little secret). Hydrogen can be produced in a clean way, of course, but the greatest challenge to clean hydrogen production is cost - so far, the cheapest way today to produce hydrogen is from fossil fuels. And as long as the political will and the resulting large-scale funding isn't there, this won't change. Unfortunately, large-scale deployment of artificial water-splitting technologies looks unlikely given the need for large amounts of expensive precious metals - such as platinum, which currently cost about $45,000 per kilogram, and which will become scarce at some point in the future - required to catalyze the multi electron water-splitting reactions. Intriguingly, there are mechanism of biological hydrogen activation found in nature and researchers have identified several microbes that can activate the dihydrogen bond through the catalytic activity of hydrogenases (enzymes that play a vital role in anaerobic metabolism). Scientists hope that these proteins could one day serve as catalysts for hydrogen production and oxidation in fuel cells. So far, their efforts have been hampered by the difficulty of incorporating these enzymes into electrical devices because the enzymes do not form good electrical connections with fuel cell components. New research now demonstrates the first successful electrical connection between a carbon nanotube and hydrogenase.