ACS Chemistry for Life

Artificial leaf could debut new era of “fast-food energy”
Chemical & Engineering News

Technology for making an “artificial leaf” holds the potential for opening an era of “fast-food energy,” in which people generate their own electricity at home with low-cost equipment perfect for the 3 billion people living in developing countries and even home-owners in the United States. C&EN Senior Correspondent Stephen K. Ritter describes research on electrofuels, made by using energy from the sun and renewable ingredients like water and carbon dioxide, reported at a gathering of experts sponsored by the U.S. Department of Energy’s Advanced Research Projects Agency (ARPA-E). Created in 2009 by the American Recovery & Reinvestment Act, ARPA-E is funding electrofuels research, with the goal of developing technologies that improve on nature’s approach – photosynthesis. The artificial leaf, made of inexpensive materials, is one of the electrofuels technologies, which breaks down ordinary water into the oxygen and hydrogen that can power an electricity-producing fuel cell. Just drop the credit-card-sized device into a bucket of water and expose it to sunlight. With the cost-conscious technology, one door-sized solar cell and three gallons of water could produce a day’s worth of electricity for a typical American home.

Cotton fabric cleans itself when exposed to ordinary sunlight
ACS Applied Materials & Interfaces

Scientists are reporting development of a new cotton fabric that does clean itself of stains and bacteria when exposed to ordinary sunlight. Mingce Long and Deyong Wu say their fabric uses a coating made from a compound of titanium dioxide, the white material used in everything from white paint to foods to sunscreen lotions, and nitrogen. Titanium dioxide breaks down dirt and kills microbes when exposed to some types of light. It already has found uses in self-cleaning windows, kitchen and bathroom tiles, odor-free socks and other products. Self-cleaning cotton fabrics have been made in the past, the authors note, but they self-clean thoroughly only when exposed to ultraviolet rays. They show that fabric coated with the material removes an orange dye stain when exposed to sunlight.

Controversy over reopening the “Sistine Chapel” of Stone Age art
Chemical & Engineering News

Carmen Drahl, C&EN associate editor notes that Spanish officials closed Spain’s Altamira caves to the public in 2002 after scientists realized that visitors were fostering growth of bacteria that damage the paintings. Moisture and carbon dioxide from tourists’ breath, body heat and footsteps (which kick up bacterial spores) foster growth of bacteria on the cave walls. Those bacteria damage the precious wall paintings, which supposedly influenced great modern artists like Picasso. Now, however, they plan to reopen the caves. Declared a World Heritage Site by the United Nations’ Educational, Scientific and Cultural Organization (UNESCO), Altamira’s rock paintings of animals and human hands made scientists realize that Stone Age people had intellectual capabilities far greater than previously believed. Drahl discusses the scientific controversy over limited reopening of the caves to tourism and measures that could minimize further damage to the painting.

At long last, new plastics for baby bottles, shopping bags, and much more
Chemical & Engineering News

With most of the plastics that define modern life dating to the1930s-1960s, a new breed of these ubiquitous materials are starting to gain a foothold in products ranging from teapots to potato chip bags to plastic plant pots that biodegrade right in the soil. C&EN Senior Editor Alexander H. Tullo explains that a “golden age of polymers,” spanning the late 1930s through the mid-1960s, engendered nylon, polyethylene, polypropylene, polycarbonate, polyester, and other plastics that have replaced everything from silk to steel in everyday products. With that success, manufacturers were reluctant to switch to new and untested plastics, and companies that tried to introduce innovative polymers faced an Everest-like-landscape of hurdles. Now a new genre of plastics is overcoming those barriers. Among them is a new plastic with the crystal-clear clarity, toughness, resistance to heat, and other advantages needed to compete with polycarbonate. Made without the worrisome bisphenol A (BPA), it is replacing polycarbonate in baby bottles and beverage bottles. Another new plastic has potential for fighting global warming, consisting of 40 per cent carbon dioxide, the main greenhouse gas.

Nanotechnology makes big inroads into construction industry
Chemical & Engineering News

Some experts believe that nanotechnology will revolutionize the construction industry, which builds, renovates, and repairs society’s infrastructure. C&EN senior editor Bethany Halford describes nanotechnology’s surprising and largely unrecognized contributions to some of humanity’s biggest and most visible projects. Nano-sized particles of the white pigment titanium dioxide, for instance, are giving the surfaces of buildings, windows, and other objects self-cleaning surfaces that stay bright white or crystal clear for years, shrugging off airborne soot, dust and grime. When titanium dioxide absorbs ultraviolet light from the sun, it breaks down pollutants that come in contact with concrete or glass. Hollow cylinders of carbon called carbon nanotubes, so small that they can’t even been seen under a regular microscope, are boosting the strength of reinforced concrete, one of the most ubiquitous construction materials. Nanotechnology also is helping to make concrete more sustainable, allowing the recycling of more fly ash, a waste product of coal-fired electric power plants, into fresh concrete used in new construction.

Bionic microrobot mimics the “water strider” and walks on water
ACS Applied Materials & Interfaces

Scientists are reporting development of a new aquatic microrobot with a body about the size of a quarter; ten water-repellent, wire legs; and two movable, oar-like legs – propelled by two miniature motors that mimic the amazing water-walking abilities of the water strider – the long-legged insect that scoots across the surface of ponds, lakes and other waterways. The bionic microrobot incorporates improvements over previous devices of this kind positioning it as a prime candidate for military spy missions, water pollution monitoring, and other applications, the scientists say. “Walking on the water surface is a dream of humans, but it is exactly the way of life for some aquatic insects,” Qinmin Pan and colleagues note, citing water striders, mosquitoes, and water spiders. This is due largely to their highly water-repellent (superhydrophobic) legs. Other scientists have made tiny aquatic devices based on the water strider with the hope of developing bionic robots that can monitor water supplies, conduct military spy missions when equipped with a camera, and perform other tasks. But until now, no one has found a way to make water-walking robots that are practical, agile, and inexpensive.

An advance toward ultra-portable electronic devices
Journal of the American Chemical Society

Yuji Okawa and colleagues are reporting a key advance toward the long-awaited era of “single-molecule electronics,” when common electronic circuits in computers, smart phones, audio players, and other devices may shrink to the size of a grain of sand. The “key to single-molecule electronics is connecting functional molecules to each other using conductive nanowires. This involves two issues: how to create conductive nanowires at designated positions, and how to ensure chemical bonding between the nanowires and functional molecules.” Okawa, et al. demonstrated a method that uses the tip of a scanning tunneling microscope to jump-start the formation of a molecule chain. The chain or “wire” spontaneously chemically bonds with other molecular components in the circuit under construction, a process that Okawa and colleagues dub “chemical soldering.” The wiring method can be used to connect molecular switches, memory bits, and transistors.

New invisibility cloak hides objects from human view
Nano Letters

For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. Xiang Zhang and colleagues note that invisibility cloaks, which route electromagnetic waves around an object to make it undetectable, “are still in their infancy.” Most cloaks are made of materials that can only hide things using microwave or infrared waves, which are just below the threshold of human vision. To remedy this, the researchers built a reflective “carpet cloak” out of layers of silicon oxide and silicon nitride etched in a special pattern. The carpet cloak works by concealing an object under the layers, and bending light waves away from the bump that the object makes, so that the cloak appears flat and smooth like a normal mirror. Although the study cloaked a microscopic object roughly the diameter of a red blood cell, the device demonstrates that it may be “capable of cloaking any object underneath a reflective carpet layer.”

Trash to treasure: Turning steel-mill waste into bricks
Industrial & Engineering Chemistry Research

In the report, Ana Andrés and colleagues note that steel mills around the world produce vast quantities of waste dust each year – 8 million – 12 million tons in the United States, for instance, and 700,000 tons in the European Union countries. The dust often is converted into a rock-like material known as Waelz slag, which is usually disposed of in landfills and contains iron, calcium, silicon oxide and other minor oxides as manganese, lead or zinc oxide. Scientists have been searching for practical and safe uses for Waelz slag. In earlier research, scientists showed that Waelz slag had potential as an ingredient in bricks, roof tiles and other ceramic products. The new research moves large-scale recycling of Waelz slag closer to reality, establishing at two real-world brick factories that the material can successfully be incorporated into commercial-size bricks. The findings also eased concerns about large amounts of potentially toxic metals leaching out of such bricks.

New molecular robot can be programmed to follow instructions
Nano Letters

Andrew Turberfield and colleagues have developed a programmable “molecular robot” – a sub-microscopic molecular machine made of synthetic DNA that moves between track locations separated by 6nm. The robot, a short strand of DNA, follows instructions programmed into a set of fuel molecules determining its destination, for example, to turn left or right at a junction in the track. They point out that other scientists have developed similar DNA-based robots, which move autonomously. Tuberfield describes a robot that can be programmed to choose among different branches of a molecular track, rather than just move in a straight line to harness their potential as cargo-carrying molecular machines. The key to this specialized movement is a so-called “fuel hairpin,” a molecule that serves as both a chemical energy source for propelling the robot along the track and as a routing instruction. The instructions tell the robot which point it should move to next, allowing the selection between the left or right branches of a junction in the track, precisely controlling the route of the robot – which could potentially allow the transport of pharmaceuticals or other materials.

Archaeological whodunit from the hometown of Romeo & Juliet
Chemical & Engineering News

C&EN Associate Editor Carmen Drahl notes three new bright blue pigments – Romeo Blue, Juliet Blue, and Flint Blue – with origins in the hometown of Shakespeare’s star-crossed lovers Romeo and Juliet, have become stars in a drama that is unsettling experts on conservation of archaeological treasures around the world. The drama began last year when prehistoric flint tools began showing visible signs of contamination – a bright blue tinge. The tainted relics came from a museum in Verona, Italy, the setting for Shakespeare’s great tragedy. Archaeologists were fascinated, having never encountered such a color change in their careers, especially one involving a hard stone like flint. Scientists traced the possible origins of the pigments to an ingredient in synthetic rubber mats, which held the tools, and contaminated them. The incident is creating a new awareness among museum conservation experts about the possibility of other, previously unknown interactions occurring between ancient treasures and the environments in which they are stored.

No longer just a spectator, silicon oxide gets into the electronics action on computer chips
Journal of the American Chemical Society

Jun Yao, Douglas Natelson, Lin Zhong, and James Tour are documenting that one fundamental component of computer chips, long regarded as a passive bystander, can actually be made to act like a switch. That potentially allows it to take part in the electronic processes that power cell phones, iPads, computers, and thousands of other products. They document the multiple ways in which silicon dioxide, long regarded simply as an electric insulator, gets involved in the action. They explain that manufacturers have long used silicon oxide, normally a very poor conductor of electricity, as both a supportive and insulating material in electronics. The scientists recently showed, however, that the oxide material can be converted to a switchable conductor by an electrical process. This phenomenon may hold the key to developing a new generation of smaller, more powerful computer chips, but the mechanism behind this switching was unclear, until now.

Advance could speed use of genetic material RNA in nanotechnology
ACS Nano

Peixuan Guo and colleagues describe development of a highly stable RNA nanoparticle overcoming a major barrier to the use of the genetic material RNA in nanotechnology – the field that involves building machines thousands of times smaller than the width of a human hair and now is dominated by its cousin, DNA. They point out that DNA, the double-stranded genetic blueprint of life, and RNA, its single-stranded cousin, share common chemical features that can serve as building blocks for making nanostructures and nanodevices. In some ways, RNA even has advantages over DNA. However, the chemical instability of RNA and its tendency to breakdown in the presence of enzymes have slowed progress in the field. They tested its ability to power the nano-sized biological motor of a certain bacteriophage – a virus that infects bacteria – that operates using molecules of RNA. The modified RNA showed excellent biological activity similar, even in the presence of high concentrations of enzymes that normally breakdown RNA activity similar to DNA.

“Nanodragster” races toward the future of molecular machines
Langmuir

James Tour, Kevin Kelly and colleagues are reporting the development of a “nanodragster” that may speed the course toward development of a new generation of futuristic molecular machines. The vehicle – only 1/50,000th the width of a human hair – resembles a hot-rod in shape and can outperform previous nano-sized vehicles. They note that the ability to control the motion of small molecules is essential for building much-anticipated molecular machines, which may find use in manufacturing computer circuits and other electronic components in the future. The new vehicle addresses some of the problems related to the control of its movement. The front end has a smaller axle and wheels made of special materials that roll easier. The rear wheels sport a longer axle but are still made of buckyballs, which provide strong surface grip. These changes result in a “nanodragster” that can operate at lower temperatures than a regular nanocar and possibly has better agility, paving the way for better molecular machines, the scientists say.

New “frozen smoke” material: One ounce could carpet three football fields
ACS Nano

Lei Zhai and colleagues are reporting the development of a new, ultra-light form of aerogel, “frozen smoke” – renowned as the world’s lightest solid material – with amazing strength and an incredibly large surface area. The new so-called “multiwalled carbon nanotube (MCNT) aerogel” could be used in sensors to detect pollutants and toxic substances, chemical reactors, and electronics components. The report describes a process for making MCNT aerogels and tests to determine their properties. Only a few scientists have succeeded in making aerogels from carbon nanotubes, wisps of carbon so small that almost 50,000 would fit across the width of a human hair. The MCNT aerogels also are excellent conductors of electricity, making them ideal for sensing applications, such as sensing as little as 0.003527 ounce of a material resting in the palm of one hand.

Small particles show big promise in beating unpleasant odors
Langmuir

Brij Moudgil and colleagues report development of a new approach for dealing with offensive household and other odors – one that doesn’t simply mask odors like today’s room fresheners, but eliminates them at the source. The scientists describe development of a new material consisting of nanoparticles of silica (the main ingredient in beach sand) – each 1/50,000th the width of a human hair – coated with copper. That metal has well-established antibacterial and anti-odor properties, and the nanoparticles gave copper a greater surface area to exert its effects. Tests of the particles against ethyl mercaptan, the stuff that gives natural gas its unpleasant odor, showed that nanoparticles were up to twice as effective as the gold standard – activated carbon – at removing the material’s foul-smelling odor. In addition to fighting odors, the particles also show promise for removing sulfur contaminants found in crude oil and for fighting harmful bacteria, they add.

An electrifying discovery: New material to harvest electricity from body movements
Nano Letters

Michael McAlpine and colleagues describe development of flexible, biocompatible rubber films for use in implantable or wearable energy harvesting systems. So-called “piezoelectric” materials are obvious candidates for harvesting energy from body movements, since they generate electricity when flexed or subjected to pressure. However, manufacturing piezoelectric materials requires temperatures of more than 1,000 degrees F., making it difficult to combine them with rubber. The scientists describe a new manufacturing method that applies nano-sized ribbons of lead zirconate titanate (PZT) – each strand about 1/50,000th the width of a human hair – to ribbons of flexible silicone rubber. PZT is one of the most efficient piezoelectric materials developed to date and can convert 80 percent of mechanical energy into electricity. The material could be used, for instance, to harvest energy from the motion of the lungs during breathing and use it to run pacemakers without the need for batteries that must be surgically replaced every few years.

New method for recovering pricey nanoparticles
Langmuir

Julian Eastoe and colleagues are reporting first use of a new method that may make it easier for manufacturers to recover, recycle, and reuse nanoparticles, some of which ounce for ounce can be more precious than gold. Recovering and recycling nanoparticles is especially difficult because they tend to form complex, hard-to-separate mixtures with other substances. They describe the development of a special type of microemulsion from cadmium and zinc nanoparticles, which separated into two layers when heated. One layer contained nanoparticles that could be recovered and the other contained none. The separation process is reversible and the recovered particles retain their shape and chemical properties, which is crucial for their reuse. The method, which offers a solution to a nagging problem, could speed application of nanotechnology in new generations of solar cells, flexible electronic displays, and other products.

An electrifying advance toward tomorrow’s power suits
Nano Letters

Yi Cui and colleagues are reporting an easier way of changing ordinary cotton and polyester into “conductive energy textiles” — e-Textiles that double as a rechargeable battery. They note, “Wearable electronics represent a developing new class of materials with an array of novel functionalities, such as flexibility, stretchability, and lightweight, which allow for many applications and designs previously impossible with traditional electronics technology. High-performance sportswear, wearable displays, new classes of portable power, and embedded health monitoring systems are examples of these novel applications.” The report describes a new process for making E-textiles that uses “ink” made from single-walled carbon nanotubes — electrically conductive carbon fibers barely 1/50,000 the width of a human hair. When applied to cotton and polyester fabrics, the ink produced e-Textiles with an excellent ability to store electricity, retained the flexibility and stretchability of regular cotton and polyester, and kept their new e-properties under conditions that simulated repeated laundering.

Toward safer plastics that lock in potentially harmful plasticizers
Macromolecules

Helmut Reinecke and colleagues report on a new way of preventing potentially harmful plasticizers — the source of long-standing human health concerns — from migrating from one of the most widely used groups of plastics. The advance could lead to a new generation of polyvinyl chloride (PVC) plastics that are safer than those now used in packaging, medical tubing, toys, and other products, they say. Manufacturers add large amounts of plasticizers to PVC to make it flexible and durable. Unfortunately, they migrate to the surface of the plastic over time and escape into the environment. People who come into contact with the plastics face possible health risks. The scientists describe development of a way to make phthalate permanently bond, or chemically attach to, the internal structure of PVC so that it will not migrate. Laboratory tests showed that the method completely suppressed the migration of plasticizer to the surface of the plastic.

Alternative chemicals ease safety concerns about nonstick, repellent coatings
Chemical & Engineering News

C&EN Senior Editor Stephen K. Ritter cites indications that long-chain compounds like perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) used in nonstick cookware, water-repellent clothing, and other consumer products can cause developmental problems, liver toxicity, and cancer in animals. Uncertainty exists over their health effects in people. Nevertheless, chemical companies are working with the U.S. Environmental Protection Agency (EPA) to phase out PFOS and are in the process of phasing out PFOA, and replacing these chemicals with shorter chain fluorochemicals that perform just as well but appear to be safer. Although these new ingredients are considered sound replacements, they may only be a temporary fix, pending development of a new generation of less toxic substitutes. After being surprised by the unexpected environmental persistence of PFOA and PFOS, EPA is taking extra caution with the replacements to avoid a similar problem in the future.

Carbon nanotubes twice as strong as once thought
ACS Nano

New studies by Stephen Cronin and colleagues on the strength of carbon nanotubes indicate that on an ounce-for-ounce basis they are at least 117 times stronger than steel and 30 times stronger than Kevlar, the material used in bulletproof vests and other products. The nanotubes could also be stretched up to 14 percent of their normal length without breaking, or more than twice that of previous reports by others. This establishes “a new lower limit for the ultimate strength of carbon nanotubes,” which could expand the commercial and industrial applications of nanotube materials.

Behind-the-scenes advances underpin new super-strong plastics
Chemical & Engineering News

C&EN Senior Editor Alexander Tullo notes that certain catalysts, called “metallocenes,” engendered excitement years ago because they allowed production of stronger forms of polyethylene plastics. These upgraded forms of polyethylene have led to availability of stronger, more durable consumer products ranging from garbage bags to camping cookware. However, hopes that metallocene plastics would replace conventional polyethylene plastics faded because of the high costs of these catalysts. A revival in the use of metallocenes and expanded marketing of super-strong polyethylene plastics has resulted from technological advances that have cut the catalysts’ cost and fostered production of millions of tons of the new plastics.

Small particles show big promise in beating unpleasant odors
Langmuir

A deodorant made from nanoparticles — hundreds of times smaller than peach fuzz — eliminates odors up to twice as effectively as today’s gold standard. Brij Moudgil and colleagues note that consumers use a wide range of materials to battle undesirable odors in clothing, on pets, in rooms, and elsewhere. Tests of the particles against ethyl mercaptan, the stuff that gives natural gas its unpleasant odor, showed that nanoparticles were up to twice as effective as the gold standard — activated carbon — at removing the material’s foul-smelling odor. In addition to fighting odors, the particles also show promise for removing sulfur contaminants found in crude oil and for fighting harmful bacteria.