A lot of buzz has been created by the term "green nanotechnology". In a broad sense, this term includes a wide range of possible applications, from nanotechnology-enabled, environmentally friendly manufacturing processes that reduce waste products (ultimately leading to atomically precise molecular manufacturing with zero waste); the use of nanomaterials as catalysts for greater efficiency in current manufacturing processes by minimizing or eliminating the use of toxic materials (green chemistry principles); the use of nanomaterials and nanodevices to reduce pollution (e.g. water and air filters); and the use of nanomaterials for more efficient alternative energy production (e.g. solar and fuel cells). Unfortunately, there is a flip side to these benefits. As scientists experiment with the development of new chemical or physical methods to produce nanomaterials, the concern for a negative impact on the environment is also heightened: some of the chemical procedures involved in the synthesis of nanomaterials use toxic solvents, could potentially generate hazardous byproducts, and often involve high energy consumption (not to mention the unsolved issue of the potential toxicity of certain nanomaterials). This is leading to a growing awareness of the need to develop clean, nontoxic and environmentally friendly procedures for synthesis and assembly of nanoparticles. Scientists are now exploring the use of biological organisms to literally grow nanomaterials.
Ethanol is all the rage these days. Although we have been drinking ethanol, an alcohol, for thousands of years (fermented beverages such as beer and wine may contain up to 15-25% ethanol by volume), the recent interest has been sparked by its use as a renewable fuel alternative to gasoline. Indeed, the largest single use of ethanol is as a motor fuel and fuel additive. Ethanol is produced by fermentation when certain species of yeast metabolize sugar. The process works with all biological feedstocks that contain appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. The primary feedstock for ethanol production in the U.S. is corn. In Brazil, the world's leading ethanol producer, it's mostly derived from sugar cane. While there is a heated controversy over the economic and ecological benefits of using biomass for producing ethanol fuel, it seems that nanotechnology's jack-of-all-trades, the carbon nanotube (CNT), might provide a solution here as well. CNTs are increasingly recognized as promising materials for catalysis, either as catalysts themselves, as catalyst additives or as catalyst supports. Researchers in China now have used CNTs loaded with rhodium (Rh) nanoparticles as reactors to convert a gas mixture of carbon monoxide and hydrogen into ethanol. This appears to be the first example where the activity and selectivity of a metal-catalyzed gas-phase reaction benefits significantly from proceeding inside a nanosized CNT reaction vessel.
Diesel-burning engines are a major contributor to environmental pollution. They emit a mixture of gases and fine particles that contain some 40, mostly toxic chemicals, including benzene, butadiene, dioxin and mercury compounds. Diesel exhaust is listed as a known or probable human carcinogen by several state and federal agencies in the United States. Wouldn't it be nice if we could render diesel soot harmless before it gets released into the environment? Wouldn't it even be nicer if we could use this soot to manufacture something useful? Japanese scientists have come up not only with a unique technique for effectively collecting diesel soot but also a method for using this soot as a precursor for the production of single-walled carbon nanotubes. How is that as a practical example for green nanotechnology?
Polystyrene (PS), also known under its trademark name styrofoam, is found in your home, office, local grocery, fast food outlet and in the cafeteria. It comes in many shapes and forms, from foam egg cartons and meat trays, plates and salad boxes, from coffee cups and utensils to CD jewel boxes, and from produce trays to those foam peanuts used in packing and the lightweight foam pieces that cushion new appliances and electronics. According to the U.S. Environmental Protection Agency's Municipal Solid Waste statistics (the things we read at Nanowerk to bring you interesting stories...), solid waste in the U.S. in 2005 contained almost 2.6 million tons of PS - a material that takes hundreds of years to break down and which is not recovered in recycling. PS is also a principle component of marine debris. Motivated by this problem of 'white pollution', a group of researchers in China developed a nanocomposite material that not only has superabsorbent capabilities but also utilizes waste PS foam. If commercially successful, this and similar methods of recycling waste PS into new products could go along way in reducing the worldwide harmful effects of white pollution.
While the first reported fullerenes and nanotube structures were composed of carbon, it was soon recognized that a plethora of comparable inorganic candidates should also exist. A rich assortment of IF (inorganic fullerene-like structures, or IF for short) nanostructures have been synthesized, and are finding practical uses in tribology, photonics, batteries, and catalysis. On such inorganic molecule that can achieve fullerene-like nanostructures, cesium oxide, is particularly useful for a multitude of applications in photoemissive systems. Unfortunately, it is extremely reactive in the ambient atmosphere, so its production and handling require high vacuum and very pure inert conditions; which translates into problematic and expensive manufacturing and handling, which in turn limits its technological scope and device lifetime. In their quest for a relatively uncomplicated high-yield synthesis method for chemically stable cesium oxide IFs, scientists succeeded in exploiting highly concentrated solar radiation (ultrabright incoherent light) toward that end. This resulted in a simple, inexpensive, and reproducible photothermal procedure for synthesizing IF nanoparticles.
The use of renewable resources (biomass) as an alternate source for fuel and the production of valuable chemicals is becoming a topic of great interest and a driving force behind research into biorefinery concepts. In the early parts of the 20th century, most nonfuel industrial products such as medicines, paints, chemicals, dyes, and fibers were made from vegetables, plant and crops. During the 1970s, petroleum based organic chemicals had largely replaced those derived from plant materials, capturing more than 95% of the markets previously held by products from biological sources. By then, petroleum accounted for more than 70% of our fuel. However, recent developments in biobased materials research show prospects that many petrochemical derived products can be replaced with industrial materials processed from renewable resources. Researchers continue to make progress in research and development of new technologies that bring down the cost of processing plant matter into value-added products. Rising environmental concerns are also suggesting the use of agriculture and forestry resources as alternative feedstock. Being able to develop soft nanomaterials and fuel from biomass will have a direct impact on industrial applications and economically viable alternatives. Researchers already have used plant-derived resources to make a variety of soft nanomaterials, which are useful for a wide range of applications.
The ability to generate functional nanoswitches might ultimately allow the integration of nano-components into electronic components. Single molecule switches using scanning tunneling microscope (STM) manipulation have been demonstrated before. Mostly these switches are based on single atoms or small molecules and operate between two distinct states. Researchers now realized the first multi-step switching process by STM manipulation on a single molecule. Instead of small organic molecules they used a large plant molecule which is environmentally friendly and abundant in nature.
Conventionally, the fabrication of thin film nanostructures is primarily done by using selective etching or templating growth on a prepatterned resist and then performing lift-off. The solvents used in developing resist are typically toxic and add to the cost of lithographic processing. Recently, many environmentally friendly lithographic processes have been designed using either a water-based solution or supercritical carbon dioxide to develop the resist. A novel pure water developable spin-coatable lanthanum strontium manganese oxide (LSMO) resist has been developed by scientists in Taiwan. The use of pure water instead of organic or alkaline solvents would undoubtedly be not only environmentally desirable but also could greatly simplify the imaging process.