Fueling the chemical industry's future

November 29, 2003-- Nanotechnology, as a whole, is still an emerging area with the need to make progress in both scientific and technological terms before enormous commercialization of products may occur. Nevertheless, commercial products are out there - more in some application areas than in others.

Over the past year, it seems as though "nanotechnology" has become a household term. Fueled by the launching of the National Nanotechnology Initiative in early 2000 (see p. 48S), an awareness of the promise of nanoscale science and engineering is flourishing beyond the academic and industrial research community.

Nanotechnology is the ability to synthesize, manipulate and characterize matter at the sub-100-nm level. This broad and multidisciplinary field encompasses several major areas of development and commercialization, including nanomaterials, nanobiotechnology, nanoelectronics and nanosystems, such as nanoelectromechanical systems (NEMS) and molecular machines. This article highlights the commercial applications of nanotechnology in the chemical industry, including the companies working on new catalysts, coatings, lubricants, filtration technologies and other end products, as well as the materials upon which these products are based, such as nanoporous structures and dendrimers. A snapshot of companies that currently manufacture or use nanotechnology-based products in the chemicals sector is presented in tabular form on p. 46S.

Applications for nanotechnology-improved catalysts are prevalent in the chemical and related industries, especially in areas where chemical reactions are pivotal. Nanoporous materials (see sidebar, p. 37S), such as zeolites, have long been used to refine crude oil, an industry that will readily adopt catalysts that have been improved through control of structures on the nanoscale. However, for the large incumbents, the development of novel catalyst structures (e.g., nanoporous materials) are likely to be off the radar, offering great opportunities for any company that might devise a scalable approach to an industrially viable chemical synthesis process that is either new or significantly cheaper (i.e., uses milder reaction conditions) than existing processes. An example of this would be an efficient method for converting methane into a liquid fuel, such as a diesel substitute. Current methods for doing this are expensive and involve a large physical, rather than chemical, component.

The catalytic qualities of nanoparticles are attributed to their high surface-to-volume ratio. In addition, the substrate that holds the catalyst in place has a large influence on the catalyst efficacy, and can further boost the effectiveness of the catalyst if comprised of a nanostructerd material. To illustrate, catalytic nanoparticles of silica substrate can increase in the efficiency of the catalyst by a factor of ten. In some cases, the use of silica nanoparticles as a catalyst support has been inhibited by the brittleness of the silica material. This problem has been overcome by cross-linking the silica nanoparticles through polymerization. The crosslinked nanoparticles can also be used as catalyst supports.

In the energy industry, nanocatalysts may benefit a $2 billion coal liquefaction project in China involving Shenhua Group Corp. (http://ns.coalinfo.net.cn/shenhua/e1.htm), Hydrocarbon Technologies Inc. (HTI; htinj.com), and the U.S. Dept. of Energy (DOE; doe.gov). The process produces extremely clean diesel fuel and is economical enough for many regions in China to compete with imported oil or diesel at average global prices. Catalysis is also important in the promising area of fuel cells. The platinum catalysts used in current commercial prototypes are about 2 nm across.

In the filtration industry, nanofiltration generally refers to the use of membranes with pore sizes larger than those in reverse osmosis membranes. The process is broadly applicable in water and air purification and many industrial processes, including purification of pharmaceuticals and enzymes, oil/water separation and waste removal. Slightly farther away is the goal of separating oxygen from nitrogen molecules, which only differ in size by two hundredths of a nanometer. The main application of such a process would be to cost-effectively produce pure oxygen without cryogenic methods.

In particular, nanofiltration technologies offer the potential to remove many contaminants from water. The world's first nanofiltration facility for drinking water, built by Generale des Eaux, went into operation in 2000 in France, using polymer membranes with pores of slightly less than 1 nm. Although power consumption is higher than for traditional purification technologies, there are offsetting benefits, such as avoiding the need to add chlorine.

The ability to control pore sizes more accurately will lead to near-term niche applications. Pacific Northwest National Labs (pnl.gov) has already created a class of structures called self- assembled monolayers on mesoporous supports (SAMMS) that contain uniform cylindrical pores with sizes from 1-50 nm, depending on the application. The pores are coated with self-assembled monolayers to which active groups, such as enzymes, are attached. SAMMS have been successfully demonstrated to extract a variety of metals and organics from both aqueous and non-aqueous media.

The adsorbent and absorbent properties of nanoporous materials also offer potential in environmental remediation, for example by mopping up heavy metals, such as arsenic or mercury. But, filtration technologies not based on nanoporous materials are also advancing. A prime example is the technology developed by Argonide Nanomaterials (argonide.com), which uses 2-nm dia. fibers to create high- throughput systems that can filter out viruses, arsenic and other contaminants.

Some new polymer-inorganic composites also promise higher- throughput rates for gas filtration systems. A membrane made of aligned carbon nanotubes should offer very high-throughputs for gases, due to the lack of interaction between the nanotubes and gas molecules. One of the great promises of such materials is the inexpensive separation of gases in power stations, mainly because the high flowrate translates into lower pressure requirements. Such membranes could be used to remove carbon dioxide from a gas stream, or separate hydrogen from carbon monoxide, which would find applications in new-generation power stations, coal-to-liquid plants and gas-to-liquid plants. Membranes containing precisely sized nanotubules also hold great potential for separating biochemicals.

Using nanoparticles in composite materials can: enhance material strength and/or reduce weight; increase chemical, heat and abrasion resistance; add new properties such as electrical conductivity; and change the interaction with light and other radiation.

The market for clay-based nanocomposites looks set to expand significantly in the near future. The prospect of new structural materials based on nanotube composites is just a few years away, with the major obstacles being the cost and availability of the best fillers (i.e., single-walled nanotubes) and the ability to leverage their properties in composites. Significant applications using the larger and less-perfect carbon nanofibers can be expected to start around 2004. These developments could put a dent in structural applications for nanoclay composites.

The potential for nanoclays is reflected in the planned expansion of production by companies such as Nanocor, Inc. (a subsidiary of AMCOL International Corp.; nanocor.com), which is gearing up to produce 20,000 ton/yr of nanoclays, in light of two important facts: nanoclay makes up about 5% of the composite product and Nanocor is not the only company successfully selling nanoclays into the composites market.

Most major polymer companies are also exploring nanocomposite technologies. Plastics compounder RTP (rtpcompany.com) has commercialized organoclay nylon nanocomposites for film and sheet applications, and Triton Systems (tritonsys.com) uses a silica nanocomposite in a polymer matrix nanocomposite, which it developed into a coating material. Other firms, such as Honeywell (honeywell.com), Ube Industries (ube-ind.co.jp) and Unitika (unikita.co.jp) commercially produce nylon nanocomposites as high- barrier plastics (HBPs) for packaging applications. Nanocor and Mitsubishi Gas Chemical Co. (mgc.co.jp) recently formed a strategic alliance to manufacture and sell HBP packaging for the food and beverage segments. In addition, Bayer (bayer.com) is looking at nylon 6 nanocomposites for use in multilayer packaging and protective films. In tests using Nanocor's clay, Bayer halved oxygen transmission through the packaging, while increasing the material's clarity and stiffness.

Another material showing near-term promise as a filler in nanocomposites is the class of complex molecules known as polyhedral oligomeric silsesquioxanes (POSS). Hybrid Plastics (hybridplastics.com) says it can manufacture POSS in bulk quantities, and, to this end, is collaborating with plastics producers and users, including the U.S. Air Force. There is also significant interest in producing nanocrystalline versions of metals and alloys. A \new steel produced by NKK (nkk.co.jp), and now included in Toyota vehicles, incorporates nanoparticulate carbon during the rolling process, allowing weight savings without compromising structural integrity.

Nanoparticles have had a significant impact on the coatings sector, but approaches such as sol-gel monolayers, which are already producing scratch-resistant and non-stick coatings, and self- assembled monolayers are making inroads, too. Dendrimers complement these latter technologies and may even be combined with nanoparticle- based technologies.

Coatings based on nanoparticles offer a variety of properties, such as strength, abrasion resistance and transparency and conductivity. Bayer, in collaboration with Nanogate (nanogate.com) is working on conductive and transparent coatings for plastics.

However, creating nanoparticle-based coatings is not without difficulties. Nanopowders can be hard to handle. An approach used by the U.S. Navy is to work with microscale agglomerates, which are delivered as a plasma (a hot, ionized gas), and break up upon application. In other thermal spraying techniques, the powders are partially melted, so that they fuse when they form the coating.

Bayer and Hansa Metallwerke (hansametall.com) are working on water- and dirt-repelling coatings using nanoparticles. In 2002, BASF introduced a spray-on coating based on nanoparticles and polymers that self-assemble upon drying into a nanostructured surface exhibiting the lotus effect - water landing on the surface can find so little cohesion with the surface that beads form that simply roll off, taking dirt with them (Figure 2).

Figure 2. BASF AG's new nanotechnology-based coatings have a water-repellant effect.

Along similar lines, nanoparticle coatings, such as those of Inframat (inframat.com) are being used to combat fouling on ship hulls. Hard but not brittle, Inframat's alumina-titania ceramic coatings have won the firm a $4 million contract with the U.S. Navy (http://nanoscience.nrl.navy.mil), which will use the material to coat all of its submarine periscopes. Nanophase Technologies also supplies alumina nanoparticles, which are used in scratch-resistant coatings for floor tiling. Nanogate provides nanoparticle-based coatings for a Spanish tile manufacturer that makes tiles easier to clean, and also produces scratch-resistant coatings for eyeglasses.

Nanoparticle-enhanced coatings also show promise in biological applications. The inclusion of nanoparticles such as copper has been shown to reduce cell growth on surfaces, which can be a major problem for implants.

In the composites space, nanoparticulate clay and POSS are already making headway. In the near future, carbon nanotubes may also have an impact. However, the variety of forms of dendrimer structures and the ease with which they can be functionalized will enable the creation of composites based on a particular structure and a wider variety of properties, which would be conferred by a dendrimer filler.

The potential of dendrimers as hosts or containers for small molecules was demonstrated in the mid-1990s by Bert Meijer, chemistry professor at Eindhoven Univ. of Technology (tue.nl). A "dendritic box" (similar to a hard shell) was built around the softcore dendrimer, once a small molecule was encapsulated within the dendrimer (Figure 3). Since then, dendrimers have been shown to encapsulate dye molecules in their cavities. Through chemical modification of their end groups, using total or partial alkylation, dendrimers can be made chemically compatible with linear polymers, to improve mixing. The role of the dendrimers would, in this case, be the creation of molecular microenvironments, or "nanoscopic pockets" in the plastic bulk material to host the dye molecules.

Figure 3. This structure, dubbed a "dendritic box," is a nanoscale container for molecules. Courtesy of Eindhoven Univ. of Technology in the Netherlands.

By acting as morphological, structural or interfacial modifiers, dendrimers also add toughness to a material without altering its processability. In blends and composites, they act as compatibilizers and bonding agents between the phases. Such findings have led Perstorp Specialty Chemicals (perstorp.se) to use dendrimers as additives for engineering plastics. Dendritic hyperbranched polymers have also been used as tougheners for epoxy resins. An addition of only 5% by weight content of dendritic polymer provokes a significant increase of the toughness of the materials. The dendritic particles are finely dispersed in the resin through a controlled phase-separation process. Dendrimer-resin interaction is strengthened by the chemical bonding of reactive epoxy groups that are grafted with functional dendritic structures.

DuPont also manufactures and uses hyperbranched structures as additives in polymer blends to improve processing. The result is a polymer that combines the physical properties of glass with the flexibility of organic materials. And, DSM has commercialized hyperbranched-polypropylene-imine (PPI) dendrimers, which it markets as Astramol technology. These dendrimers are mainly used as additives in the manufacture of low-cost plastics and rubbers, for viscosity reduction, and have similar applications in the production of coatings, inks and adhesives. Meanwhile, the National Aeronautics and Space Administration (NASA; nasa.gov) is funding a project in which Dow Corning (dowcorning.com) and the Materials Electrochemical Research Corp. (mercorp.com) are exploring plasma-deposited dendrimer coatings and dendrimerfullerene nanocomposites for lubrication of micron- and submicron surfaces.

Decontamination is one application where dendrimers seem particularly suited, compared with other approaches, which tend to be based on size alone (e.g., nanofiltration) or require functionalization. Dendrimers act as scavengers of metal ions, offering potential for environmental clean-up. Changing the acidity of a medium causes the dendrimers to release the metal ions. The dendrimers can be recovered via ultrafiltration and reused. In the same way, dendrimer-encapsulated catalysts can be separated from reaction products and recycled. The Center for Biologic Nanotechnology at Michigan Univ. (http://nano.med.umich.edu) is planning to develop and evaluate dendrimer-enhanced ultrafiltration as a novel water treatment process for removing metal ions from water.

Moreover, the ability of dendrimers to capture small molecules in their cavities or on their modified end groups makes them suitable for the absorption or adsorption of biological and chemical contaminants. The U.S. Army (army.mil) is evaluating the potential of dendrimers for these applications.

Dendrimers are also effective as reactive components in topical skin-protection creams. This application may be extended to protective clothing, by stabilizing the dendritic layer against washing and weather conditions. Amphiphilic dendrimers with a half- dendrimer, half "tail" structure are used to fix the active dendrimers in the protective film.

In addition, over the last few years, much activity has centered around the use of nanoparticles to detect and/or protect against chemical warfare agents. Nanosphere, Inc. (nanosphere.com) will soon release a system that eventually could be used to detect biological warfare agents, such as anthrax. The system uses gold nanoparticle sensors developed at Northwestern Univ. (northwestern.edu). Meanwhile, Altair Nanotechnologies (altairnano.com) and Western Michigan Univ. (wmu.edu) are jointly developing sensors for the detection of biological and/or chemical weapons based on titanium dioxide nanoparticles. Magnesium-oxide nanoparticles that destroy bacteria (including anthrax) have been developed by NanoScale Materials, for placement in filtration masks.

Silver, which is touted for its antibacterial qualities, is being produced in the nanoparticle form by Shenzhen Tsinghua-Yuanxing Nanomaterial Co. and Nucryst (nucryst.com), the latter of which is using its product in antibacterial dressings. NanoBio (nanobio.com) has released an antibacterial liquid, NanoProtect, which contains nanoscopic droplets of oil that destroy bacterial spores, virus particles and even funguses via an explosive release of surface tension. Surprisingly, the product is not harmful to human tissue. The U.S. military is now NanoBio's primary customer.

The increasing demand for power of portable electronics, combined with the desire to reduce their weight and size, has created a new market for nanoparticles, which, because of their high surface area, can improve reaction rates in fuel cells and batteries.

Nanopowder manufacturer AP Materials (apmaterials.com) and its partner Millennium Cell (millenniumcell.com), a developer of hydrogen fuel systems, have recently been awarded a Phase I Small Business Innovation Research (SBIR) contract from the U.S. Missile Defense Agency for development of nanoscale titanium diboride for use in advanced batteries and other energy-storage systems.

Altair recently announced a successful series of its advanced solid-oxide fuel-cell test demonstrations. The entire fuel cell, including connectors, electrolyte, anode and cathode, was constructed of micro- and nanoscale materials. Additionally, Altair has developed nanoparticle lithium-based battery electrode materials that have exhibited charge and discharge rates up to 10 times faster than those of current lithium ion battery materials.

A number of companies are planning to commercialize methanol- based fuel cells for portable electronics applications in 2004 or soon thereafter. In these cells, hydrogen produced from methanol is stripped of its electrons, which become the source of electricity. Protons (hydrogen ions) pass through a membrane and combine with oxygen to produce water. The catalyst used \in this process is nanoparticulate platinum applied in a slurry.

Targeting battery applications, Brookhaven National Laboratory (bnl.gov) has made a lithium-tin nanocrystalline alloy that was used as a high-performance electrode. Created by reacting lithium hydride with tin oxide, but with more of the former than was needed to react fully, it produced a lithium tin alloy with lithium oxide left over. The repeated addition and removal of hydrogen resulted in a nanocomposite with grain sizes of 20-30 nm. Other elements that form stable metal hydrides could be used to make nanocomposite materials with this method, with potential applications not just in batteries, but also in catalysis.

Nanotubes and nanohorns are also being investigated for their potential to hold hydrogen and hydrocarbons for use in fuel cells. According to the DOE, hydrogen-based fuel cells will be practical for use in vehicles when the hydrogen content is 6.5% by weight. To date, claims of figures above 1.5% have been contested. Predictions of significant commercial use of hydrogen-based fuel cells in cars also vary widely from 2005 to 2015. Nanomix (nanomix.com), which has fuel cells as a long-term target, using hydrogen as a fuel, believes it will be able to produce systems holding 5-6 kg of hydrogen for under $1,000/vehicle.

Another storage medium for hydrogen is BASF's "nanocubes" (which are not actually nanoscale). For this technology, scalability and production economics look promising, but it's still too soon to be certain. The first target market is personal electronics.

Many of the direct applications of nanotechnology pertain to the removal of some element or compound from the environment through, for example, the use of nanofiltration, nanoporous adsorbents and catalysts. However, most effects are likely to be indirect. For instance, in environmental affairs, nanotechnology opens new doors to companies that want to enhance their "green" credentials without hurting their balance sheets.

Nevertheless, like any new technology, nanotechnology can have positive or negative effects on the environment and society. Clearly, improving the efficiency of energy production and supply has both commercial and environmental advantages. In this area, we are likely to see the biggest impact in savings through lighter composite materials, growth of the use of alternative energy (through improved economic viability of solar and wind energy generation, for example) and the advent of commercially viable fuel cells in a number of applications.

Slightly more contested, however, are the widely-pursued applications of nanoparticles in medicine, notably drug delivery, where the effect of nanoparticles on human health is inconclusive. Any new compound or product must and will be fully characterized before approval, and the long-term implications must be studied before any product is commercialized. The normal procedures used to evaluate of such products will likely face numerous challenges.

RECENT IMPROVEMENTS IN OUR ABILITY to see and manipulate on the nanoscale are transforming our use of nanoporous materials from the merely opportunistic to directed design. This is most strikingly the case in the creation of a wide variety of membranes where control over pore size is increasing dramatically, often to atomic levels of perfection, as is the ability to modify physical and chemical characteristics of the materials that make up the pores.

Nanoporous solids have been made out of a wide variety of substances, including carbon, silicon, silicates, various polymers, ceramics, various metallic minerals and compounds of organic materials and metals or organic materials and silicon such as methylsilsesquioxane (one of the polyhedral oligomeric silsesquioxanes, or POSS, family used in nanocomposites and other applications).

* Aerogels are highly porous materials that contain pores of a variety of sizes. For nanoporous silica aerogels, the pore-size distribution peaks around 5 nm in radius. Although traditional aerogels are robust enough to be used in catalysis and filtering, the low strength and brittleness of their nanoporous siblings has resulted in limited applications.

One way to make aerogels is via the sol-gel method. A gas is dispersed in a gel, producing a very light solid (only four times as dense as air). Unlike earlier methods for making aerogels, which required high temperatures, the sol-gel approach works at room temperature.

* Nanoporous silicon, which is created by etching silicon with acid, is capable of stimulated light emission, as in lasers, and also holds promise as a biocompatible material. One issue with such silicon for optical applications is its instability. However, scientists at Purdue Univ. have managed to apply a stabilizing coating using a reaction initiated by light.

* Zeolites are naturally nanoporous materials that have been in use for decades and never cease to fascinate researchers. In late 2002, a modified zeolite was shown to be the first of an interesting class of materials called electrides that are inorganic and stable at room temperature. Electrides have a positively-charged structure in which the charge is balanced in the form of an electron "gas" in the pores. Apart from the obvious catalytic applications, the materials have interesting electrical, magnetic, and optical properties.

* Activated carbon, like zeolites, has been in use for a long time. Taking a fresh approach to fabrication, researchers in Korea have developed a templating technique using silica nanoparticles that can create activated carbon with uniform 8-nm and 12-nm pores. The resulting material was 10 times more adsorbent than commercial activated carbon. Removing metal ions from a crystalline matrix containing both metal and carbon allows the creation of a variety of novel nanoporous carbon materials depending on process conditions. This approach is being commercialized by Skeleton Technologies (skeleton.com).

* Nanoporous carbon with new geometries has been created by other methods. A multinational group of researchers created, in early 2002, a form of highly nanoporous carbon with a fractal internal geometry (fractals are patterns that show similar structures at different scales, such as coastlines or the branches of trees). The group believes the material has potential for methane storage for vehicles.

There are many ways to make nanoporous materials. Substances can be selectively leached out of a solid, leaving pores in their place, or combinations of polymers can be formed into nanoporous solids by heating, so that one polymer degrades and escapes.

A promising recent development (early 2002) in organic/inorganic hybrid approaches comes from researchers in Japan who created a self- assembled structure out of silica and benzene with pores 3-5 nanometers in dia. The insides of these pores are perfectly ordered structures. In addition, the benzene can be functionalized without this regularity being lost.

1. Harper, T., et al., "The Nanotechnology Opportunity Report," Cientifica, London, U.K. (Apr. 2002).

2. Harper,T., et al., "The Nanotechnology Opportunity Report," 2nd Ed., Cientifica, London, U.K. (June 2003).

TIM HARPER is the founder and president of CMP Cientifica (Officina 19-20, Edificio BurgoSol, C/ Comunidad de Madrid 35 bis, 28230 Las Rozas, Spain; Phone: +34 91 640 71 85; Fax: +34 91 640 71 86; Phone/Fax from U.S.: (877) 295-4480; E-mail: tim.harper@cientifica.com) and the CEO of Cientifica Ltd. (London, U.K.), the business research and consulting arm of CMP Cientifica. Harper was formerly an engineer at the European Space Agency's R&D center in the Netherlands, where he managed a microscale and nanoscale characterization facility. He has a BSc in physics from Lanchester Polytechnic (now the Univ. of Coventry).

PAUL HOLISTER (E-mail: paul.holister@cientifica.com) is the editor-in-chief of X Report and TNT Weekly, the latter of which has a readership spanning the nanotechnology community from academics to investors. After early training in biochemistry, Hollister worked in scientific publishing and in the information technology industry as a consultant, business analyst and system designer.

CRISTINA ROMAN VAS is senior scientific consultant and managing director at Cientifica in Madrid, Spain (Phone: +34 91 636 06 26; Fax: +34 91 640 71 86; E-mail: cristina.roman@cientifica.com). Prior to joining Cientifica, she worked at Johnson & Johnson to develop pharmaceutical processes based on supercritical fluid technology and studied the use of nanodevices as drug carriers. Roman Vas obtained an MS in chemistry from the Univ. of Alcala de Henares (Madrid, Spain) and a PhD in macromolecular and organic chemistry at the Eindhoven Univ. of Technology.

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